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Pyramidal Cells (pyramidal + cell)
Kinds of Pyramidal Cells Terms modified by Pyramidal Cells Selected AbstractsDifferential responses to NMDA receptor activation in rat hippocampal interneurons and pyramidal cells may underlie enhanced pyramidal cell vulnerabilityEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2005E. Avignone Abstract Hippocampal interneurons are generally more resistant than pyramidal cells to excitotoxic insults. Because NMDA receptors play a crucial role in neurodegeneration, we have compared the response to exogenous NMDA in CA1 pyramidal cells and interneurons of the stratum oriens using combined whole-cell patch-clamp recording and ratiometric Ca2+ imaging. In voltage-clamp, current-clamp or in nominally Mg2+ -free medium, NMDA (10 µm; 3,5 min exposure in the presence of tetrodotoxin) induced a markedly larger inward current and Ca2+ rise in pyramidal cells than in interneurons. Pyramidal cells also showed a more pronounced voltage dependence in their response to NMDA. We hypothesized that this enhanced response to NMDA receptor activation in pyramidal cells could underlie their increased vulnerability to excitotoxicity. Using loss of dye as an indicator of degenerative membrane disruption, interneurons tolerated continuous exposure to a high concentration of NMDA (30 µm) for longer periods than pyramidal cells. This acute neurodegeneration in pyramidal cells was independent of intracellular Ca2+, because high intracellular BAPTA (20 mm) did not prolong survival time. Thus, a plausible explanation for the enhanced sensitivity of pyramidal neurons to excitotoxic insults associated with cerebral ischemia is their greater response to NMDA receptor activation, which may reflect differences in NMDA receptor expression and/or subunit composition. [source] A comparison of different models of stroke on behaviour and brain morphologyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2003C.L.R. Gonzalez Abstract We compared the effects of three models of permanent ischemia, as well as cortical aspiration, on behaviour and brain morphology. Rats received a stroke either by devascularization or by two different procedures of medial cerebral artery occlusion (MCAO; small vs. large). Animals were trained in a reaching task, forepaw asymmetry, forepaw inhibition, sunflower seed task and tongue extension. Behaviour was assessed 1 week after the lesion and at 2-week intervals for a total of 9 weeks. One week after the surgery all animals were severely impaired on all tasks and although they improved over time they only reached preoperative base lines on tongue extension. Animals with small MCAOs performed better in reaching and sunflower tasks; no other behavioural differences were detected among the groups. Pyramidal cells in forelimb and cingulate areas as well as spiny neurons of the striatum were examined for dendritic branching and spine density using a Golgi,Cox procedure. Each lesion type had a different impact on cell morphology. Overall, different changes (atrophy or hypertrophy) were observed with each kind of lesion and these changes were specific for the region (forelimb, cingulate, striatum) and the condition (intact vs. damaged hemisphere). These results suggest that: (i) different lesions to the motor cortex produce subtle differences in behaviour, and (ii) the method used to induce the lesion produces striking differences in cortical and subcortical plasticity. [source] Disabled-1 mRNA and protein expression in developing human cortexEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2003Gundela Meyer Abstract Disabled-1 (Dab1) forms part of the Reelin,Dab1 signalling pathway that controls neuronal positioning during brain development; Dab1 deficiency gives rise to a reeler-like inversion of cortical layers. To establish a timetable of Dab1 expression in developing human brain, Dab1 mRNA and protein expression were studied in prenatal human cortex. The earliest Dab1 signal was detected at 7 gestational weeks (GW), the stage of transition from preplate to cortical plate, suggesting a role of the Reelin,Dab1 signalling pathway in preplate partition. From 12 to 20 GW, the period of maximum cortical migration, Dab1 expression was prominent in the upper tiers of the cortical plate, to decline after midgestation. Radially orientated apical dendrites of Dab1-expressing neurons indicated a predominant pyramidal phenotype. Pyramidal cells in hippocampus and entorhinal cortex displayed a more protracted time of Dab1 expression compared to neocortex. In addition, at later stages (18,25 GW), Dab1 was also expressed in large neurons scattered throughout intermediate zone and subplate. From 14 to 22 GW, particularly high levels of Dab1 mRNA and protein were observed in cells of the ventricular/subventricular zone displaying the morphology of radial glia. The partial colocalization of vimentin and Dab1 in cells of the ventricular zone supported a radial glia phenotype. The concentration of Dab1 protein in ventricular endfeet and initial portions of radial processes of ventricular-zone cells points to a possible involvement of Dab1 in neurogenesis. Furthermore, a subset of Cajal,Retzius cells in the marginal zone colocalized Dab1 and Reelin, and may thus represent a novel target of the Reelin,Dab1 signalling pathway. [source] Abnormal Excitability of Hippocampal CA3 Neurons in Noda Epileptic Rat (NER): Alteration of Seizure with AgingEPILEPSIA, Issue 2000Ryosuke Hanaya Purpose: Noda epileptic rat (NER), a mutant found in thc colony of Crj:Wistar rats, spontaneously shows tonic-clonic convulsions approximately once every 30 hours from 8,16 weeks of age. A long-lasting dcpolarization shift accompanied by repetitivc firings are observed in hippocampal CA3 pyramidal neurons of NER with seizures. Using hippocampal slice preparations of NER, the present electrophysiologi- cal study was performed to elucidate whether this abnormal firing in CA3 neurons developed with age and if abnormality of Ca2+ channel was involved. Methods: Hippocampal slices (40Opm) werc prepared from NER and normal Wistar rats (age; 4,29 weeks). A single rectangular pulse stimulus composed of 0.1-ms duration was delivered to the mossy fibers every 5 seconds though a bipolar electrode placed in the granular cell layer of the dentate gyrus. Intracellular recording was made from the CA3 pyramidal cell using a microelectrode containing 3M KCI intracellular recordings. A Ca2+ spike was elicited by applying a depolarizing pulse (InA, 120ms) in the cell through the recording electrode under a blockadc of Na+ and K+ channels using 1 pM tetrodotoxin and I 0mM tctraethylammonium added to the artificial CSF, respectivcly. Nicardipine (I-IOOnM), a Ca2+ channel blocker, was applicd to the bath. Results: Thirty-seven slices from I9 NER and 6 slices from 4 normal Wishe rats were used. There were no obvious changes in the resting membrane potentials of CA3 neurons between NER and Wistar rats tested. When a single stimulus was delivered to the mossy fibers, a long-lasting depolarization shift accompanied by repetitive firings followed by after-hyperpolarization werc also obtained i n hippocampal CA3 neurons of young NER (4,5 weeks of age) before occurrence of any seizurcs, although the depolarization shift in younger NER was shorter than that in NER aged more than 6 weeks. These abnormal firings werc evokcd in 58% and 30% of all CA3 neurons tested in the younger and mature NER (6,1 5 weeks of age), respectively. Furthermore, abnormal firing was not elicited in NER aged after I6 weeks. Agc-matched Wistar rats showed only single action potentials without any depolarization shift with single mossy fiber stimulation. Bath application of nicardipine (IOnM) inhibited this long-lasting depolarization shift and the accompanying repetitive firing followed by afterhypcrpolarization without affecting the first spike induced by mossy fiber stimulations. Furthermore, nicai-dipine (IOnM) inhibited the Ca2+ spikes elicited by applying a depolarizing pulse in the neurons of NER with seizures, although a higher dose (100nM) did not affect those in Wistar rats. Conclusions: These findings indicate that abnormal excitability of the NER CA3 pyramidal neurons is probably due to abnormality in the Ca2+ channcls. The abnorinal excitability was observed in NER at an age when tonic-clonic convulsions were not detected, suggesting that thc hippocampus may probably scrve as an epileptogenic focus in younger NER and the seizure impulses originating i n this area are transinittcd to the new other seizurc foci in mature NER. [source] The anterior olfactory nucleus: Quantitative study of dendritic morphologyTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 9 2010Peter C. Brunjes Abstract The anterior olfactory nucleus (AON) occupies a crucial position within the olfactory circuit, as it is able to influence function in nearly every major synaptic processing stage of both the ipsilateral and the contralateral pathways. Nevertheless, very little is known about the region's internal organization and circuitry. The present study provides basic quantitative and qualitative data on the morphology of several cell types within the two major regions of the AON, pars externa and pars principalis. In pars externa two types of cells are analyzed, the "classical" cell (type I), containing only apically directed dendrites with large spines, and a previously unreported cell with basilar dendrites and complex, spiny apical processes (type II). In pars principalis the characteristic pyramidal cell is described both on the basis of the depth of the cell bodies in the cell layer comprising the structure and on the basis of their radial location. Several other nonpyramidal neurons are also described. The findings provide useful basic information necessary for understanding and modeling the circuitry of the AON. J. Comp. Neurol. 518:1603,1616, 2010. © 2009 Wiley-Liss, Inc. [source] A novel pharmacological concept in an animal model of psychosis,ACTA PSYCHIATRICA SCANDINAVICA, Issue 2001R. R. Dawirs Objective:,We have analysed pharmacologically induced perturbation of functional and structural neurogenesis in the prefrontal cortex (PFC) and hippocampus. Method:,Juvenile gerbils received a single dose of methamphetamine (METH, 50 mg/kg, i.p.). In adults the following parameters were quantitatively investigated: prefrontal dopaminergic and GABAergic innervation densities (immunocytochemistry), morphogenesis of pyramidal cells (Golgi), dentate granule cell proliferation (BrdU-labelling), working memory and behavioural inhibition (delayed response, open-field). Results:,A single challenge of METH continuously suppresses granule cell proliferation in adult gerbils and initiates rewiring of neuronal networks in the PFC which run concurrently with the development of severe deficits in PFC-related behaviours. Conclusion:,It appears that a continuous remodelling of neuronal circuits is an inherent property of the brain, the biological significance of which seems to be to ascertain adaptive interaction between brain and environment. Learning more about drug-induced neuronal reorganization might be basic for understanding the genesis of psychotic conditions in the brain. This presentation is based both on own research and on a review of the literature. [source] Area-Specific Resonance of Excitatory Networks in Neocortex: Control by Outward CurrentsEPILEPSIA, Issue 8 2007Manuel A. Castro-Alamancos Summary:, During disinhibition or low [Mg++]o buffer, 7,14 Hz (,10 Hz) oscillations are generated by excitatory networks of interconnected pyramidal cells in motor (agranular) cortex but are absent in barrel (granular) cortex. Here we studied if the inability of barrel cortex to produce ,10 Hz oscillations during these conditions is because barrel cortex networks lack the necessary cellular mechanisms or, alternatively, because those mechanisms are inhibited by outward currents. The results show that blockers of slowly inactivating voltage-dependent K+ currents unmask ,10 Hz oscillations in barrel cortex, and this occurs in unison with the unmasking of intrinsic inward Ca++ currents that are kept suppressed by the outward currents. Moreover, the ,10 Hz oscillations unmasked in barrel cortex occur independently in upper and lower layers indicating that the ,10 Hz oscillation mechanisms are kept suppressed in multiple networks. The results reveal that the propensity of distinct excitatory networks of neocortex to generate epileptiform oscillatory activities is controlled by outward currents. [source] Characterization of Neuronal Migration Disorders in Neocortical Structures: Loss or Preservation of Inhibitory Interneurons?EPILEPSIA, Issue 7 2000Petra Schwarz Summary: Purpose: Neuronal migration disorders (NMD) are often associated with therapy-resistant epilepsy. In human cerebral cortex, this hyperexcitability has been correlated with a loss of inhibitory interneurons. We used a rat model of focal cortical NMD (microgyria) to determine whether the expression of epileptiform activity in this model coincides with a decrease in inhibitory interneurons. Methods: In 2- to 4-month-old rats, the density of interneurons immunoreactive for ,-aminobutyric acid (GABA), cal-bindin, and parvalbumin was determined in fronto-parietal cortex in nine 200-,m-wide sectors located up to 2.5 mm lateral and 2.0 mm medial from the lesion center in primary parietal cortex (Par 1). Quantitative measurements in homotopic areas of age-matched sham-operated rats served as controls. Results: The freeze lesion performed in newborn rat cortex resulted in adult rats with a microgyrus extending in a rostro-caudal direction from frontal to occipital cortex. The density of GABA- and parvalbumin-positive neurons in fronto-parietal cortex was not significantly different between lesioned and control animals. Only the density of calbindin-immunoreactive neurons located 1.0 mm lateral and 0.5 mm medial from the lesion was significantly (Student t test, p > 0.05) larger in freeze-lesioned rats (5.817 ± 562 and 6,400 ± 795 cells per mm3, respectively; n = 12) compared with measurements in homotopic regions in Parl cortex of controls (4,507 ± 281 and 4,061 ± 319 cells per mm3, respectively; n = 5). Conclusions: The previously reported widespread functional changes in this model of cortical NMD are not related to a general loss of inhibitory interneurons. Other factors, such as a decrease in GABA receptor density, modifications in GABAA receptor subunit composition, or alterations in the excitatory network, e.g., an increase in the density of calbindin-immunoreactive pyramidal cells, more likely contribute to the global disinhibition and widespread expression of pathophysiological activity in this model of cortical NMD. [source] N -methyl- d -aspartate, hyperpolarization-activated cation current (Ih) and ,-aminobutyric acid conductances govern the risk of epileptogenesis following febrile seizures in rat hippocampusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2010Mohamed Ouardouz Abstract Febrile seizures are the most common types of seizure in children, and are generally considered to be benign. However, febrile seizures in children with dysgenesis have been associated with the development of temporal lobe epilepsy. We have previously shown in a rat model of dysgenesis (cortical freeze lesion) and hyperthermia-induced seizures that 86% of these animals developed recurrent seizures in adulthood. The cellular changes underlying the increased risk of epileptogenesis in this model are not known. Using whole cell patch-clamp recordings from CA1 hippocampal pyramidal cells, we found a more pronounced increase in excitability in rats with both hyperthermic seizures and dysgenesis than in rats with hyperthermic seizures alone or dysgenesis alone. The change was found to be secondary to an increase in N -methyl- d -aspartate (NMDA) receptor-mediated excitatory postsynaptic currents (EPSCs). Inversely, hyperpolarization-activated cation current was more pronounced in naïve rats with hyperthermic seizures than in rats with dysgenesis and hyperthermic seizures or with dysgenesis alone. The increase in GABAA -mediated inhibition observed was comparable in rats with or without dysgenesis after hyperthermic seizures, whereas no changes were observed in rats with dysgenesis alone. Our work indicates that in this two-hit model, changes in NMDA receptor-mediated EPSCs may facilitate epileptogenesis following febrile seizures. Changes in the hyperpolarization-activated cation currents may represent a protective reaction and act by damping the NMDA receptor-mediated hyperexcitability, rather than converting inhibition into excitation. These findings provide a new hypothesis of cellular changes following hyperthermic seizures in predisposed individuals, and may help in the design of therapeutic strategies to prevent epileptogenesis following prolonged febrile seizures. [source] Metabotropic glutamate receptor 1 activity generates persistent, N -methyl- d -aspartate receptor-dependent depression of hippocampal pyramidal cell excitabilityEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2009J. P. Clement Abstract Metabotropic glutamate receptors (mGluRs) are involved in many forms of neuronal plasticity. In the hippocampus, they have well-defined roles in long-lasting forms of both synaptic and intrinsic plasticity. Here, we describe a novel form of long-lasting intrinsic plasticity that we call (S)-3,5-dihydroxyphenylglycine (DHPG)-mediated long-term depression of excitability (DHPG-LDE), and which is generated following transient pharmacological activation of group I mGluRs. In extracellular recordings from hippocampal slices, DHPG-LDE was expressed as a long-lasting depression of antidromic compound action potentials (cAPs) in CA1 or CA3 cells following a 4-min exposure to the group I mGluR agonist (S)-DHPG. A similar phenomenon was also seen for orthodromic fibre volleys evoked in CA3 axons. In single-cell recordings from CA1 pyramids, DHPG-LDE was manifest as persistent failures in antidromic action potential generation. DHPG-LDE was blocked by (S)-(+)- a -amino-4-carboxy-2-methylbenzeneacetic acid (LY367385), an antagonist of mGluR1, but not 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP), an mGluR5 inhibitor. Although insensitive to antagonists of ,-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate/kainate and ,-aminobutyric acidA receptors, DHPG-LDE was blocked by antagonists of N -methyl- d -aspartate (NMDA) receptors. Similarly, in single-cell recordings, DHPG-mediated antidromic spike failures were eliminated by NMDA receptor antagonism. Long after (S)-DHPG washout, DHPG-LDE was reversed by mGluR1 antagonism. A 4-min application of (S)-DHPG also produced an NMDA receptor-dependent persistent depolarization of CA1 pyramidal cells. This depolarization was not solely responsible for DHPG-LDE, because a similar level of depolarization elicited by raising extracellular K+ increased the amplitude of the cAP. DHPG-LDE did not involve HCN channels or protein synthesis, but was eliminated by blockers of protein kinase C or tyrosine phosphatases. [source] Dynamics of action potential backpropagation in basal dendrites of prefrontal cortical pyramidal neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2008Wen-Liang Zhou Abstract Basal dendrites of neocortical pyramidal neurons are relatively short and directly attached to the cell body. This allows electrical signals arising in basal dendrites to strongly influence the neuronal output. Likewise, somatic action potentials (APs) should readily propagate back into the basilar dendritic tree to influence synaptic plasticity. Two recent studies, however, determined that sodium APs are severely attenuated in basal dendrites of cortical pyramidal cells, so that they completely fail in distal dendritic segments. Here we used the latest improvements in the voltage-sensitive dye imaging technique (Zhou et al., 2007) to study AP backpropagation in basal dendrites of layer 5 pyramidal neurons of the rat prefrontal cortex. With a signal-to-noise ratio of >,15 and minimal temporal averaging (only four sweeps) we were able to sample AP waveforms from the very last segments of individual dendritic branches (dendritic tips). We found that in short- (< 150 µm) and medium (150,200 µm in length)-range basal dendrites APs backpropagated with modest changes in AP half-width or AP rise-time. The lack of substantial changes in AP shape and dynamics of rise is inconsistent with the AP-failure model. The lack of substantial amplitude boosting of the third AP in the high-frequency burst also suggests that in short- and medium-range basal dendrites backpropagating APs were not severely attenuated. Our results show that the AP-failure concept does not apply in all basal dendrites of the rat prefrontal cortex. The majority of synaptic contacts in the basilar dendritic tree actually received significant AP-associated electrical and calcium transients. [source] Dendritic nicotinic receptors modulate backpropagating action potentials and long-term plasticity of interneuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2008Balázs Rózsa Abstract Stratum radiatum interneurons, unlike pyramidal cells, are rich in nicotinic acetylcholine receptors (nAChRs); however, the role of these receptors in plasticity has remained elusive. As opposed to previous physiological studies, we found that functional ,7-subunit-containing nAChRs (,7-nAChRs) are abundant on interneuron dendrites of rats. Moreover, dendritic Ca2+ transients induced by activation of ,7-nAChRs increase as a function of distance from soma. The activation of these extrasynaptic ,7-nAChRs by cholinergic agonists either facilitated or depressed backpropagating action potentials, depending on the timing of ,7-nAChR activation. We have previously shown that dendritic ,7-nAChRs are involved in the regulation of synaptic transmission, suggesting that ,7-nAChRs may play an important role in the regulation of the spike timing-dependent plasticity. Here we provide evidence that long-term potentiation is indeed boosted by stimulation of dendritic ,7-nAChRs. Our results suggest a new mechanism for a cholinergic switch in memory encoding and retrieval. [source] Secreted factors from ventral telencephalon induce the differentiation of GABAergic neurons in cortical culturesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2006H.-h. Trinh Abstract It is widely believed that the pyramidal cells and interneurons of the cerebral cortex are distinct in their origin, lineage and genetic make up. In view of these findings, the current thesis is that the phenotype determination of cortical neurons is primarily directed by genetic mechanisms. Using in vitro assays, the present study demonstrates that secreted factors from ganglionic eminence (GE) of the ventral telencephalon have the potency to induce the differentiation of a subset of cortical neurons towards ,-aminobutyric acid (GABA)ergic lineage. Characterization of cortical cultures that were exposed to medium derived from GE illustrated a significant increase in the number of GABA-, calretinin- and calbindin-positive neurons. Calcium imaging together with pharmacological studies showed that the application of exogenous medium significantly elevated the intracellular calcium transients in cortical neurons through the activation of ionotropic glutamate receptors. The increase in GABA+ neurons appeared to be associated with the elevated calcium activity; treatment with blockers specific for glutamate receptors abolished both the synchronized transients and reduced the differentiation of GABAergic neurons. Such studies demonstrate that although intrinsic mechanisms determine the fate of cortical interneurons, extrinsic factors have the potency to influence their neurochemical differentiation and contribute towards their molecular diversity. [source] Nicotine withdrawal suppresses nicotinic modulation of long-term potentiation induction in the hippocampal CA1 regionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2006Yoshihiko Yamazaki Abstract We have previously reported that acute and chronic nicotine exposure lower the threshold for long-term potentiation (LTP) induction in the rat hippocampal CA1 region, and acute application of nicotine in the chronic-nicotine-treated hippocampus further reduces the threshold. However, it is unknown how withdrawal from chronic nicotine exposure affects the induction of LTP. Here, we show that, following nicotine withdrawal, the threshold for LTP induction fluctuates before returning to the basal level and acute nicotine is no longer effective in lowering the threshold at 4 days after withdrawal. Chronic nicotine-induced enhancement of N -methyl- d -aspartate receptor responses slowly diminishes and returns to the control level by 8 days of withdrawal. In 4-day-withdrawn hippocampi, there is functional up-regulation of postsynaptic ,7 nicotinic acetylcholine receptors (nAChRs) on interneurons in the stratum radiatum, whereas the release of ,-aminobutyric acid from their terminals is reduced. In both control and chronic nicotine-exposed hippocampi, acute nicotine depresses monosynaptic inhibitory postsynaptic currents recorded in pyramidal cells but has almost no effect at 4 days of withdrawal. The lack of effect is due, at least in part, to the loss of a presynaptic nicotine effect. These withdrawal-induced changes are accompanied by decreases in normal nicotine-induced enhancement of N -methyl- d -aspartate receptor responses, which may be responsible for the lack of acute nicotine-mediated facilitation of LTP induction in 4-day-withdrawn hippocampi. These withdrawal-induced changes may contribute to the cellular basis of unpleasant withdrawal symptoms and, thus, nicotine dependence. [source] Immunolocalization of BK channels in hippocampal pyramidal neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2006Claudia A. Sailer Abstract Neurons are highly specialized cells in which the integration and processing of electrical signals critically depends on the precise localization of ion channels. For large-conductance Ca2+ - activated K+ (BK) channels, targeting to presynaptic membranes in hippocampal pyramidal cells was reported; however, functional evidence also suggests a somatodendritic localization. Therefore we re-examined the subcellular distribution of BK channels in mouse hippocampus using a panel of independent antibodies in a combined approach of conventional immunocytochemistry on cultured neurons, pre- and postembedding electron microscopy and immunoprecipitation. In cultured murine hippocampal neurons, the colocalization of BK channels with both pre- and postsynaptic marker proteins was observed. Electron microscopy confirmed targeting of BK channels to axonal as well as dendritic membranes of glutamatergic synapses in hippocampus. A postsynaptic localization of BK channels was also supported by the finding that the channel coimmunoprecipitated with PSD95, a protein solely expressed in the postsynaptic compartment. These results thus demonstrate that BK channels reside in both post- and presynaptic compartments of hippocampal pyramidal neurons. [source] Regulated expression of HCN channels and cAMP levels shape the properties of the h current in developing rat hippocampusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2006Rainer Surges Abstract The hyperpolarization-activated current (Ih) contributes to intrinsic properties and network responses of neurons. Its biophysical properties depend on the expression profiles of the underlying hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels and the presence of cyclic AMP (cAMP) that potently and differentially modulates Ih conducted by HCN1, HCN2 and/or HCN4. Here, we studied the properties of Ih in hippocampal CA1 pyramidal cells, the developmental evolution of the HCN-subunit isoforms that contribute to this current, and their interplay with age-dependent free cAMP concentrations, using electrophysiological, molecular and biochemical methods. Ih amplitude increased progressively during the first four postnatal weeks, consistent with the observed overall increased expression of HCN channels. Activation kinetics of the current accelerated during this period, consonant with the quantitative reduction of mRNA and protein expression of the slow-kinetics HCN4 isoform and increased levels of HCN1. The sensitivity of Ih to cAMP, and the contribution of the slow component to the overall Ih, decreased with age. These are likely a result of the developmentally regulated transition of the complement of HCN channel isoforms from cAMP sensitive to relatively cAMP insensitive. Thus, although hippocampal cAMP concentrations increased over twofold during the developmental period studied, the coordinated changes in expression of three HCN channel isoforms resulted in reduced effects of this signalling molecule on neuronal h currents. [source] Relation of apical dendritic spikes to output decision in CA1 pyramidal cells during synchronous activation: a computational studyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2006José M. Ibarz Abstract Recent studies on the initiation and propagation of dendritic spikes have modified the classical view of postsynaptic integration. Earlier we reported that subthreshold currents and spikes recruited by synaptic currents play a critical role in defining outputs following synchronous activation. Experimental factors strongly condition these currents due to their nonlinear behaviour. Hence, we have performed a detailed parametric study in a CA1 pyramidal cell model to explore how different variables interact and initiate dendritic spiking, and how they influence cell output. The input pattern, the relative excitability of axon and dendrites, the presence/modulation of voltage-dependent channels, and inhibition were cross analysed. Subthreshold currents and spikes on synaptically excited branches fired spikes in other branches to jointly produce different modalities of apical shaft spiking with a variable impact on cell output. Synchronous activation initiated a varying number and temporal scatter of firing branches that produced in the apical shaft-soma axis nonpropagating spikes, pseudosaltatory or continuous forward conduction, or backpropagation. As few as 6,10 local spikes within a time window of 2 ms ensure cell output. However, the activation mode varied extremely when two or more variables were cross-analysed, becoming rather unpredictable when all the variables were considered. Spatially clustered inputs and upper modulation of dendritic Na+ or Ca2+ electrogenesis favour apical decision. In contrast, inhibition biased the output decision toward the axon and switched between dendritic firing modes. We propose that dendrites can discriminate input patterns and decide immediate cell output depending on the particular state of a variety of endogenous parameters. [source] Differential responses to NMDA receptor activation in rat hippocampal interneurons and pyramidal cells may underlie enhanced pyramidal cell vulnerabilityEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2005E. Avignone Abstract Hippocampal interneurons are generally more resistant than pyramidal cells to excitotoxic insults. Because NMDA receptors play a crucial role in neurodegeneration, we have compared the response to exogenous NMDA in CA1 pyramidal cells and interneurons of the stratum oriens using combined whole-cell patch-clamp recording and ratiometric Ca2+ imaging. In voltage-clamp, current-clamp or in nominally Mg2+ -free medium, NMDA (10 µm; 3,5 min exposure in the presence of tetrodotoxin) induced a markedly larger inward current and Ca2+ rise in pyramidal cells than in interneurons. Pyramidal cells also showed a more pronounced voltage dependence in their response to NMDA. We hypothesized that this enhanced response to NMDA receptor activation in pyramidal cells could underlie their increased vulnerability to excitotoxicity. Using loss of dye as an indicator of degenerative membrane disruption, interneurons tolerated continuous exposure to a high concentration of NMDA (30 µm) for longer periods than pyramidal cells. This acute neurodegeneration in pyramidal cells was independent of intracellular Ca2+, because high intracellular BAPTA (20 mm) did not prolong survival time. Thus, a plausible explanation for the enhanced sensitivity of pyramidal neurons to excitotoxic insults associated with cerebral ischemia is their greater response to NMDA receptor activation, which may reflect differences in NMDA receptor expression and/or subunit composition. [source] Projections from the hippocampal region to the mammillary bodies in macaque monkeysEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2005John P. Aggleton Abstract A combination of anterograde and retrograde tracers mapped the direct hippocampal and parahippocampal inputs to the mammillary bodies in two species of macaque monkey. Dense projections arose from pyramidal cells in layer III of the subiculum and prosubiculum, and terminated in the medial mammillary nucleus. While there was no evidence of an input from the dentate gyrus or fields CA1,3, a small contribution arose from the presubiculum and entorhinal cortices. All of the hippocampal and parahippocampal projections to the mammillary bodies appeared to use the fornix as a route. The caudal portions of the subiculum and prosubiculum contained the greatest numbers of cells projecting to the mammillary bodies. A light contralateral projection to the medial mammillary nucleus was also observed, although this appeared to arise primarily from the more rostral portions of the subiculum and prosubiculum. There was a crude topography within the medial mammillary nucleus, with the caudal subicular projections terminating in the mid and dorsal portions of the nucleus while the rostral subicular and entorhinal projections terminated in the ventral and lateral portions of the medial nucleus. Light ipsilateral projections throughout the lateral mammillary nucleus were sometimes observed. Comparisons with related studies of the macaque brain showed that the dense hippocampal projections to the mammillary bodies arise from a population of subicular cells separate from those that project to the anterior thalamic nuclei, even though the major output from the mammillary bodies is to the anterior thalamic nuclei. Other comparisons revealed underlying similarities with the corresponding projections in the rat brain. [source] Spontaneous recurrent network activity in organotypic rat hippocampal slicesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2005Majid H. Mohajerani Abstract Organotypic hippocampal slices were prepared from postnatal day 4 rats and maintained in culture for >6 weeks. Cultured slices exhibited from 12 days in vitro spontaneous events which closely resembled giant depolarizing potentials (GDPs) recorded in neonatal hippocampal slices. GDP-like events occurred over the entire hippocampus with a delay of 30,60 ms between two adjacent regions as demonstrated by pair recordings from CA3,CA3, CA3,CA1 and interneurone,CA3 pyramidal cells. As in acute slices, spontaneous recurrent events were generated by the interplay of GABA and glutamate acting on AMPA receptors as they were reversibly blocked by bicuculline and 6,7-dinitroquinoxaline-2,3-dione but not by dl -2-amino-5-phosphonopentaoic acid. The equilibrium potentials for GABA measured in whole cell and gramicidin-perforated patch from interconnected interneurones,CA3 pyramidal cells were ,70 and ,56 mV, respectively. The resting membrane potential estimated from the reversal of N -methyl- d -aspartate-induced single-channel currents in cell-attach experiments was ,75 mV. In spite of its depolarizing action, in the majority of cases GABA was still inhibitory as it blocked the firing of principal cells. The increased level of glutamatergic connectivity certainly contributed to network synchronization and to the development of interictal discharges after prolonged exposure to bicuculline. In spite of its inhibitory action, in a minority of cells GABA was still depolarizing and excitatory as it was able to bring principal cells to fire, suggesting that a certain degree of immaturity is still present in cultured slices. This was in line with the transient bicuculline-induced block of GDPs and with the isoguvacine-induced increase of GDP frequency. [source] Role of the GLT-1 subtype of glutamate transporter in glutamate homeostasis: the GLT-1-preferring inhibitor WAY-855 produces marginal neurotoxicity in the rat hippocampusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2005Julie V. Selkirk Abstract Glutamate is the major excitatory neurotransmitter in the central nervous system and is tightly regulated by cell surface transporters to avoid increases in concentration and associated neurotoxicity. Selective blockers of glutamate transporter subtypes are sparse and so knock-out animals and antisense techniques have been used to study their specific roles. Here we used WAY-855, a GLT-1-preferring blocker, to assess the role of GLT-1 in rat hippocampus. GLT-1 was the most abundant transporter in the hippocampus at the mRNA level. According to [3H]- l -glutamate uptake data, GLT-1 was responsible for approximately 80% of the GLAST-, GLT-1-, and EAAC1-mediated uptake that occurs within dissociated hippocampal tissue, yet when this transporter was preferentially blocked for 120 h with WAY-855 (100 µm), no significant neurotoxicity was observed in hippocampal slices. This is in stark contrast to results obtained with TBOA, a broad-spectrum transport blocker, which, at concentrations that caused a similar inhibition of glutamate uptake (10 and 30 µm), caused substantial neuronal death when exposed to the slices for 24 h or longer. Likewise, WAY-855, did not significantly exacerbate neurotoxicity associated with simulated ischemia, whereas TBOA did. Finally, intrahippocampal microinjection of WAY-855 (200 and 300 nmol) in vivo resulted in marginal damage compared with TBOA (20 and 200 nmol), which killed the majority of both CA1,4 pyramidal cells and dentate gyrus granule cells. These results indicate that selective inhibition of GLT-1 is insufficient to provoke glutamate build-up, leading to NMDA receptor-mediated neurotoxic effects, and suggest a prominent role of GLAST and/or EAAC1 in extracellular glutamate maintenance. [source] Loss of zolpidem efficacy in the hippocampus of mice with the GABAA receptor ,2 F77I point mutationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2005D. W. Cope Abstract Zolpidem is a hypnotic benzodiazepine site agonist with some ,-aminobutyric acid (GABA)A receptor subtype selectivity. Here, we have tested the effects of zolpidem on the hippocampus of ,2 subunit (,2F77I) point mutant mice. Analysis of forebrain GABAA receptor expression with immunocytochemistry, quantitative [3H]muscimol and [35S] t-butylbicyclophosphorothionate (TBPS) autoradiography, membrane binding with [3H]flunitrazepam and [3H]muscimol, and comparison of miniature inhibitory postsynaptic current (mIPSC) parameters did not reveal any differences between homozygous ,2I77/I77 and ,2F77/F77 mice. However, quantitative immunoblot analysis of ,2I77/I77 hippocampi showed some increased levels of ,2, ,1, ,4 and , subunits, suggesting that differences between strains may exist in unassembled subunit levels, but not in assembled receptors. Zolpidem (1 µm) enhanced the decay of mIPSCs in CA1 pyramidal cells of control (C57BL/6J, ,2F77/F77) mice by ,,60%, and peak amplitude by ,,20% at 33,34 °C in vitro. The actions of zolpidem (100 nm or 1 µm) were substantially reduced in ,2I77/I77 mice, although residual effects included a 9% increase in decay and 5% decrease in peak amplitude. Similar results were observed in CA1 stratum oriens/alveus interneurons. At network level, the effect of zolpidem (10 µm) on carbachol-induced oscillations in the CA3 area of ,2I77/I77 mice was significantly different compared with controls. Thus, the ,2F77I point mutation virtually abolished the actions of zolpidem on GABAA receptors in the hippocampus. However, some residual effects of zolpidem may involve receptors that do not contain the ,2 subunit. [source] Segregation of two endocannabinoid-hydrolyzing enzymes into pre- and postsynaptic compartments in the rat hippocampus, cerebellum and amygdalaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2004A. I. Gulyas Abstract Fatty acid amide hydrolase (FAAH) and monoglyceride lipase (MGL) catalyse the hydrolysis of the endocannabinoids anandamide and 2-arachidonoyl glycerol. We investigated their ultrastructural distribution in brain areas where the localization and effects of cannabinoid receptor activation are known. In the hippocampus, FAAH was present in somata and dendrites of principal cells, but not in interneurons. It was located mostly on the membrane surface of intracellular organelles known to store Ca2+ (e.g. mitochondria, smooth endoplasmic reticulum), less frequently on the somatic or dendritic plasma membrane. MGL immunoreactivity was found in axon terminals of granule cells, CA3 pyramidal cells and some interneurons. In the cerebellum, Purkinje cells and their dendrites are intensively immunoreactive for FAAH, together with a sparse axon plexus at the border of the Purkinje cell/granule cell layers. Immunostaining for MGL was complementary, the axons in the molecular layer were intensively labelled leaving the Purkinje cell dendrites blank. FAAH distribution in the amygdala was similar to that of the CB1 cannabinoid receptor: evident signal in neuronal somata and proximal dendrites in the basolateral nucleus, and hardly any labelling in the central nucleus. MGL staining was restricted to axons in the neuropil, with similar relative signal intensities seen for FAAH in different nuclei. Thus, FAAH is primarily a postsynaptic enzyme, whereas MGL is presynaptic. FAAH is associated with membranes of cytoplasmic organelles. The differential compartmentalization of the two enzymes suggests that anandamide and 2-AG signalling may subserve functional roles that are spatially segregated at least at the stage of metabolism. [source] Cell type-dependent expression of HCN1 in the main olfactory bulbEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2003Noémi B. Holderith Abstract In many brain regions, hyperpolarization-activated cationic currents (Ih) are involved in the generation of rhythmic activities, but the role of Ih in olfactory oscillations remains unclear. Knowledge of the cellular and subcellular distributions of hyperpolarization-activated and cyclic nucleotide-gated channel (HCN) subunits is necessary for understanding the role of Ih in olfactory network activities. Using light microscopic immunocytochemistry, we demonstrate strong HCN1 labelling of the glomerular layer and moderate staining of granule cell, internal and external plexiform layers of the rat main olfactory bulb. In the glomerular layer, among many unlabelled neurons, two distinct subpopulations of juxtaglomerular cells are labelled. Approximately 10% of the juxtaglomerular cells strongly express HCN1. These small diameter cells are immunoreactive for GABA and comprise a subpopulation of periglomerular cells. An additional subset of juxtaglomerular cells (, 1%) expresses low levels of HCN1. They are large in diameter, GABA immunonegative but immunopositive for vesicular glutamate transporter 2, characterizing them as external tufted cells. Quantitative immunogold localization revealed that the somatic plasma membranes of periglomerular cells contain approximately four times more HCN1 labelling than those of external tufted cells. Unlike in cortical pyramidal cells, immunogold density for HCN1 does not significantly differ in somatic and dendritic plasma membranes of external tufted cells, indicating that post-synaptic potentials arriving at proximal and distal dendrites are modulated by the same density of Ih. Our results demonstrate a cell type-dependent expression of HCN1 in the olfactory bulb and predict a differential contribution of distinct juxtaglomerular cell types to network oscillations. [source] High level of mGluR7 in the presynaptic active zones of select populations of GABAergic terminals innervating interneurons in the rat hippocampusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2003Peter Somogyi Abstract The release of neurotransmitters is modulated by presynaptic metabotropic glutamate receptors (mGluRs), which show a highly selective expression and subcellular location in glutamatergic terminals in the hippocampus. Using immunocytochemistry, we investigated whether one of the receptors, mGluR7, whose level of expression is governed by the postsynaptic target, was present in GABAergic terminals and whether such terminals targeted particular cells. A total of 165 interneuron dendritic profiles receiving 466 synapses (82% mGluR7a-positive) were analysed. The presynaptic active zones of most GAD-(77%) or GABA-positive (94%) synaptic boutons on interneurons innervated by mGluR7a-enriched glutamatergic terminals (mGluR7a-decorated) were immunopositive for mGluR7a. GABAergic terminals on pyramidal cells and most other interneurons in str. oriens were mGluR7a-immunonegative. The mGluR7a-decorated cells were mostly somatostatin- and mGluR1,-immunopositive neurons in str. oriens and the alveus. Their GABAergic input mainly originated from VIP-positive terminals, 90% of which expressed high levels of mGluR7a in the presynaptic active zone. Parvalbumin-positive synaptic terminals were rare on mGluR7a-decorated cells, but on these neurons 73% of them were mGluR7a-immunopositive. Some type II synapses innervating interneurons were immunopositive for mGluR7b, as were some type I synapses. Because not all target cells of VIP-positive neurons are known it has not been possible to determine whether mGluR7 is expressed in a target-cell-specific manner in the terminals of single GABAergic cells. The activation of mGluR7 may decrease GABA release to mGluR7-decorated cells at times of high pyramidal cell activity, which elevates extracellular glutamate levels. Alternatively, the presynaptic receptor may be activated by as yet unidentified endogenous ligands released by the GABAergic terminals or the postsynaptic dendrites. [source] Involvement of post-synaptic kainate receptors during synaptic transmission between unitary connections in rat neocortexEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2003Afia B. Ali Abstract The properties of functional kainate receptor-mediated EPSCs were studied in acute slices from 19,35-day-old rats. EPSCs elicited in pyramidal and fast-spiking cells in layers 2/3 and 5 of the rat motor cortex by extracellular single shock stimulus in the presence of GYKI 53655 and D-2-amino-5-phosphopentanoic resulted in a residual current. This current was not enhanced by cyclothiazide but was blocked by 6-cyano-7-nitroquinoxalin-2,3-dione and is thought to be mediated by kainate receptors. These kainate receptor-mediated currents displayed a wide range of time courses depending on which pre-synaptic fibres were activated. With paired recordings, unitary EPSCs elicited in pyramidal cells were almost totally blocked by GYKI 53655 and D-2-amino-5-phosphopentanoic. However, when L-transpyrrolidine-2,4-dicarboxylate (PDC), a glutamate uptake blocker, was introduced in the bath, the amplitude of kainate receptor-mediated currents, which is resistant to GYKI 53655 and D-2-amino-5-phosphopentanoic, was revealed. The rise and decay time constants of the kainate receptor-mediated currents were identical to control EPSCs. PDC was not required to reveal the kainate receptor-mediated currents elicited in fast-spiking cells which also displayed similar rise and decay time constants to the control EPSCs. Excitatory input onto pyramidal and fast-spiking cells in the neocortex mediated by kainate receptors contributed between 14 and 40% of the total control unitary EPSCs which displayed identical time courses to the AMPA receptor-mediated component of the EPSCs. Post-synaptic kainate receptors at connected pyramidal cell synapses may be located extra-synaptically. [source] In vivo blockade of neural activity alters dendritic development of neonatal CA1 pyramidal cellsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2002Laurent Groc Abstract During development, neural activity has been proposed to promote neuronal growth. During the first postnatal week, the hippocampus is characterized by an oscillating neural network activity and a rapid neuronal growth. In the present study we tested in vivo, by injecting tetanus toxin into the hippocampus of P1 rats, whether this neural activity indeed promotes growth of pyramidal cells. We have previously shown that tetanus toxin injection leads to a strong reduction in the frequency of spontaneous GABA and glutamatergic synaptic currents, and to a complete blockade of the early neural network activity during the first postnatal week. Morphology of neurobiotin-filled CA1 pyramidal cells was analyzed at the end of the first postnatal week (P6,10). In activity-reduced neurons, the total length of basal dendritic tree was three times less than control. The number, but not the length, of basal dendritic branches was affected. The growth impairment was restricted to the basal dendrites. The apical dendrite, the axons, or the soma grew normally during activity deprivation. Thus, the in vivo neural activity in the neonate hippocampus seems to promote neuronal growth by initiating novel branches. [source] Innervation of interneurons immunoreactive for VIP by intrinsically bursting pyramidal cells and fast-spiking interneurons in infragranular layers of juvenile rat neocortexEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2002Jochen F. Staiger Abstract Cortical columns contain specific neuronal populations with characteristic sets of connections. This wiring forms the structural basis of dynamic information processing. However, at the single-cell level little is known about specific connectivity patterns. We performed experiments in infragranular layers (V and VI) of rat somatosensory cortex, to clarify further the input patterns of inhibitory interneurons immunoreactive (ir) for vasoactive intestinal polypeptide (VIP). Neurons in acute slices were electrophysiologically characterized using whole-cell recordings and filled with biocytin. This allowed us to determine their firing pattern as regular-spiking, intrinsically bursting and fast-spiking, respectively. Biocytin was revealed histochemically and VIP immunohistochemically. Sections were examined for contacts between the axons of the filled neurons and the VIP-ir targets. Twenty pyramidal cells and five nonpyramidal (inter)neurons were recovered and sufficiently stained for further analysis. Regular-spiking pyramidal cells displayed no axonal boutons in contact with VIP-ir targets. In contrast, intrinsically bursting layer V pyramidal cells showed four putative single contacts with a proximal dendrite of VIP neurons. Fast-spiking interneurons formed contacts with two to six VIP neurons, preferentially at their somata. Single as well as multiple contacts on individual target cells were found. Electron microscopic examinations showed that light-microscopically determined contacts represent sites of synaptic interactions. Our results suggest that, within infragranular local cortical circuits, (i) fast-spiking interneurons are more likely to influence VIP cells than are pyramidal cells and (ii) pyramidal cell input probably needs to be highly convergent to fire VIP target cells. [source] Postnatal maturation of Na+, K+, 2Cl, cotransporter expression and inhibitory synaptogenesis in the rat hippocampus: an immunocytochemical analysisEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2002Serge Marty Abstract GABA, a major inhibitory neurotransmitter, depolarizes hippocampal pyramidal neurons during the first postnatal week. These depolarizations result from an efflux of Cl, through GABAA -gated anion channels. The outward Cl, gradient that provides the driving force for Cl, efflux might be generated and maintained by the Na+, K+, 2Cl, cotransporter (NKCC) that keeps intracellular Cl, concentration above electrochemical equilibrium. The developmental pattern of expression of the cotransporter in the hippocampus is not known. We studied the postnatal distribution pattern of NKCC in the hippocampus using a monoclonal antibody (T4) against a conserved epitope in the C-terminus of the cotransporter molecule. We also examined the temporal relationships between the developmental pattern of NKCC expression and the formation of perisomatic GABAergic synapses. This study was aimed at determining, with antivesicular inhibitory amino acid transporter (VIAAT) antibodies, whether perisomatic GABAergic synapses are formed preferentially at the time when GABA is depolarizing. During the first postnatal week, NKCC immunolabelling was restricted to cell bodies in the pyramidal cell layer and in the strata oriens and radiatum. In contrast, at postnatal day 21 (P21) and in adult animals little or no labelling occurred in cell bodies; instead, a prominent dendritic labelling appeared in both pyramidal and nonpyramidal neurons. The ultrastructural immunogold study in P21 rat hippocampi corroborated the light-microscopy results. In addition, this study revealed that a portion of the silver-intensified colloidal gold particles were located on neuronal plasmalemma, as expected for a functional cotransporter. The formation of inhibitory synapses on perikarya of the pyramidal cell layer was a late process. The density of VIAAT-immunoreactive puncta in the stratum pyramidale at P21 reached four times the P7 value in CA3, and six times the P7 value in CA1. Electron microscopy revealed that the number of synapses per neuronal perikaryal profile in the stratum pyramidale of the CA3 area at P21 was three times higher than at P7, even if a concomitant 20% increase in the area of these neuronal perikaryal profiles occurred. It is concluded that, in hippocampal pyramidal cells, there is a developmental shift in the NKCC localization from a predominantly somatic to a predominantly dendritic location. The presence of NKCC during the first postnatal week is consistent with the hypothesis that this transporter might be involved in the depolarizing effects of GABA. The depolarizing effects of GABA may not be required for the establishment of the majority of GABAergic synapses in the stratum pyramidale, because their number increases after the first postnatal week, when GABA action becomes hyperpolarizing. [source] The KCl cotransporter, KCC2, is highly expressed in the vicinity of excitatory synapses in the rat hippocampusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2001A. I. Gulyás Abstract Immunocytochemical visualization of the neuron-specific K+/Cl, cotransporter, KCC2, at the cellular and subcellular level revealed an area- and layer-specific diffuse labelling, and a discrete staining outlining the somata and dendrites of some interneurons in all areas of the rat hippocampus. KCC2 was highly expressed in parvalbumin-containing interneurons, as well as in subsets of calbindin, calretinin and metabotropic glutamate receptor 1a-immunoreactive interneurons. During the first 2 postnatal weeks, an increase of KCC2 staining was observed in the molecular layer of the dentate gyrus, correlating temporally with the arrival of entorhinal cortical inputs. Subcellular localization demonstrated KCC2 in the plasma membranes. Immunoreactivity in principal cells was responsible for the diffuse staining found in the neuropil. In these cells, KCC2 was detected primarily in dendritic spine heads, at the origin of spines and, at a much lower level on the somata and dendritic shafts. KCC2 expression was considerably higher in the somata and dendrites of interneurons, most notably of parvalbumin-containing cells, as well as in the thorny excrescences of CA3 pyramidal cells and in the spines of spiny hilar and stratum lucidum interneurons. The data indicate that KCC2 is highly expressed in the vicinity of excitatory inputs in the hippocampus, perhaps in close association with extrasynaptic GABAA receptors. A high level of excitation is known to lead to a simultaneous net influx of Na+ and Cl,, as evidenced by dendritic swelling. KCC2 located in the same microenvironment may provide a Cl, extrusion mechanism to deal with both ion and water homeostasis in addition to its role in setting the driving force of Cl, currents involved in fast postsynaptic inhibition. [source] | |||||||||||||||||||||||||