EUROPEAN JOURNAL OF NEUROLOGY, Issue 9 2010
H. T. Hendricks
Background:, Dysautonomia after traumatic brain injury (TBI) is characterized by episodes of increased heart rate, respiratory rate, temperature, blood pressure, muscle tone, decorticate or decerebrate posturing, and profuse sweating. This study addresses the incidence of dysautonomia after severe TBI, the clinical variables that are associated with dysautonomia, and the functional outcome of patients with dysautonomia. Methods:, A historic cohort study in patients with severe TBI [Glasgow Coma Scale (GCS) , 8 on admission]. Results:, Seventy-six of 119 patients survived and were eligible for follow-up. The incidence of dysautonomia was 11.8%. Episodes of dysautonomia were prevalent during a mean period of 20.1 days (range 3,68) and were often initiated by discomfort. Patients with dysautonomia showed significant longer periods of coma (24.78 vs. 7.99 days) and mechanical ventilation (22.67 vs. 7.21 days). Dysautonomia was associated with diffuse axonal injury (DAI) [relative risk (RR) 20.83, CI 4.92,83.33] and the development of spasticity (RR 16.94, CI 3.96,71.42). Patients with dysautonomia experienced more secondary complications. They tended to have poorer outcome. Conclusions:, Dysautonomia occurs in approximately 10% of patients surviving severe TBI and is associated with DAI and the development of spasticity at follow-up. The initiation of dysautonomia by discomfort supports the Excitatory: Inhibitory Ratio model as pathophysiological mechanism. [source]

In vivo optical recordings of synaptic transmission and intracellular Ca2+ and Cl, in the superior colliculus of fetal rats

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2006
Yoshiyuki Sakata
Abstract Although the N -methyl- d -aspartate (NMDA) receptor is known to play a crucial role in activity-dependent remodeling of synaptic connections in the fetal superior colliculus (SC), its contribution to the electrical activity of fetal SC neurons has not been determined. Furthermore, whether ,-aminobutyric acid (GABA)-mediated inhibition occurs either as early as prenatal periods or only after eye opening has been controversial. We therefore performed optical recordings using voltage-, Ca2+ - and Cl, -sensitive fluorescent dyes to analyse synaptic transmission and changes in intracellular Ca2+ and Cl, in the SC of fetal rats that were still connected with the dams by the umbilical cord. Excitatory and inhibitory responses were evoked by focal SC stimulation. The excitatory synaptic responses are composed of early and late components. The early component was mediated by both non-NMDA and NMDA receptors, whereas the late component occurred mainly via NMDA receptors. Train pulse stimulation at higher currents was required for induction of the inhibition, which was antagonized by bicuculline, and blocking of the GABA-mediated inhibition by bicuculline uncovered masked excitatory synaptic responses. Focal SC stimulation induced increases in [Cl,]i and [Ca2+]i that were mediated by GABA-A receptors and mainly by NMDA receptors, respectively. GABA antagonists augmented SC-induced increases in [Ca2+]i. These results indicate that, in the fetal SC, excitatory and inhibitory synaptic transmissions occur before birth, that the NMDA receptor is a major contributor to excitatory synaptic transmission and increased [Ca2+]i, and that the GABA-A receptor is already functioning to inhibit excitatory neurotransmission. [source]

Dual Excitatory and Inhibitory Effects of Stimulation of Intrinsic Innervation of the Anterior Pituitary on Adrenocorticotropic Hormone Release in the Rat

JOURNAL OF NEUROENDOCRINOLOGY, Issue 1 2004
L.-Z. Gao
Abstract The gland cells of the mammalian anterior pituitary are innervated by substantial amounts of nerve fibres, and there is evidence that the nerve fibres are functionally active. In the rat, the nerve fibres make typical excitatory synapses with corticotropes. The physiological significance of this synaptic relationship was investigated in the present study. The anterior pituitary of the rat was sliced and stimulated with electrical field in a chamber. The perfusate was continuously collected and immunoradioassayed for adrenocorticotropic hormone (ACTH). When the gland slices were stimulated at a high frequency of 10 Hz, there was a significant inhibition of ACTH secretion. Stimulation at a low frequency of 2 Hz resulted in a quick and transient excitation of ACTH release. The results indicate that stimulation of the nerve fibres in the anterior pituitary has dual excitatory and inhibitory effects on ACTH secretion. [source]

Vasopressin Preferentially Depresses Excitatory Over Inhibitory Synaptic Transmission in the Rat Supraoptic Nucleus In Vitro

JOURNAL OF NEUROENDOCRINOLOGY, Issue 4 2000
Kombian1
Endogenous arginine-vasopressin (AVP) in the supraoptic nucleus is known to decrease the firing rate of some supraoptic nucleus neurones. To determine a possible mechanism by which this locally released AVP produces this change in neuronal excitability, we investigated the effects of AVP on evoked excitatory (e.p.s.c.) and inhibitory post-synaptic (i.p.s.c.) responses recorded in magnocellular neurones in a hypothalamic slice preparation, using the perforated-patch recording technique. Our data show that AVP produces a dose-dependent decrease in the evoked e.p.s.c. in about 80% of magnocellular neurones tested with an estimated EC50 of about 0.9 ,M. The maximum decrease in e.p.s.c. amplitude was about 31% of control and was obtained with an AVP concentration of 2 ,M. The AVP-induced synaptic depression was blocked by Manning Compound (MC), a non-selective antagonist of oxytocin (OXT) and vasopressin (AVP) receptors, but not by a selective OXT receptor antagonist. It was not mimicked by desmopressin (ddAVP), a V2-receptor subtype agonist. By contrast, AVP used at the same concentration (2 ,M), had no global effect on pharmacologically isolated i.p.s.c.s in the majority of magnocellular neurones tested. These results show that AVP acts in the supraoptic nucleus to reduce excitatory synaptic transmission to magnocellular neurones by activating a non-OXT receptor, presumably the V1 receptor subtype. [source]

Effects of Ethanol on Persistent Activity and Up-States in Excitatory and Inhibitory Neurons in Prefrontal Cortex

ALCOHOLISM, Issue 12 2009
John J. Woodward
Background:, Elucidating mechanisms that underlie the neural actions of ethanol is critical for understanding how this drug affects behavior. Increasing evidence suggests that, in addition to mid-brain dopaminergic regions, higher cortical structures play an important role in the pathophysiology associated with alcohol abuse. Previous studies from this laboratory used a novel slice co-culture system to demonstrate that ethanol reduces network-dependent patterns of activity in excitatory pyramidal neurons of the prefrontal cortex (PFC). In the present study, we examine the effect of ethanol on the activity of fast-spiking (FS) interneurons, a sub-population of neurons critically involved in shaping cortical activity. Methods:, Slices containing the dorsolateral PFC were prepared from neonatal C57 mice and maintained in culture. After 2 to 3 weeks in vitro, whole-cell patch-clamp electrophysiology was used to monitor spontaneous episodes of persistent activity in prelimbic PFC neurons. In some experiments, the use-dependent NMDA receptor blocker, MK801, was included in the pipette recording solution to assess the contribution of NMDA receptors to up-states. Results:, MK801 reduced up-state amplitude and revealed underlying fast EPSPs in excitatory pyramidal neurons while having little effect on these parameters in FS interneurons. Despite this difference, ethanol (44 mM), significantly reduced up-state duration and up-state area in both pyramidal and FS interneurons. Conclusions:, These results suggest that ethanol reduces the activity of FS interneurons due to disruption of network-dependent activity. This would be expected to further impair the ability of PFC networks to carry out their normal function and may contribute to the adverse effects of ethanol on PFC-dependent behaviors. [source]

Developmental shift in bidirectional functions of taurine-sensitive chloride channels during cortical circuit formation in postnatal mouse brain

DEVELOPMENTAL NEUROBIOLOGY, Issue 2 2004
Mika Yoshida
Abstract Taurine (2-aminoethanesulfonic acid) is the most abundant free amino acid in the developing mammalian cerebral cortex, however, few studies have reported its neurobiological functions during development. In this study, by means of whole-cell patch-clamp recordings, we examined the effects of taurine on chloride channel receptors in neocortical neurons from early to late postnatal stages, which cover a critical period in cortical circuit formation. We show here that taurine activates chloride channels in cortical neurons throughout the postnatal stages examined (from postnatal day 2 to day 36). The physiological effects of taurine changed from excitatory to inhibitory due to variations in the intracellular Cl, concentration during development. An antagonist blocking analysis also demonstrated a developmental shift in the receptor target of taurine, from glycine receptors to GABAA receptors. Taken together, these results may reflect genetically programmed, bidirectional functions of taurine. At the early developmental stage, taurine acting on glycine receptors would serve to promote cortical circuit formation. As cortical circuit has to be regulated in the later stages, taurine would serve as a safeguard against hyperexcitable circuit. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 166,175, 2004 [source]

Epileptiform synchronization in the cingulate cortex

EPILEPSIA, Issue 3 2009
Gabriella Panuccio
Summary Purpose:, The anterior cingulate cortex (ACC),which plays a role in pain, emotions and behavior,can generate epileptic seizures. To date, little is known on the neuronal mechanisms leading to epileptiform synchronization in this structure. Therefore, we investigated the role of excitatory and inhibitory synaptic transmission in epileptiform activity in this cortical area. In addition, since the ACC presents with a high density of opioid receptors, we studied the effect of opioid agonism on epileptiform synchronization in this brain region. Methods:, We used field and intracellular recordings in conjunction with pharmacological manipulations to characterize the epileptiform activity generated by the rat ACC in a brain slice preparation. Results:, Bath-application of the convulsant 4-aminopyridine (4AP, 50 ,M) induced both brief and prolonged periods of epileptiform synchronization resembling interictal- and ictal-like discharges, respectively. Interictal events could occur more frequently before the onset of ictal activity that was contributed by N -methyl- d -aspartate (NMDA) receptors. Mu-opioid receptor activation abolished 4AP-induced ictal events and markedly reduced the occurrence of the pharmacologically isolated GABAergic synchronous potentials. Ictal discharges were replaced by interictal events during GABAergic antagonism; this GABA-independent activity was influenced by subsequent mu-opioid agonist application. Conclusions:, Our results indicate that both glutamatergic and GABAergic signaling contribute to epileptiform synchronization leading to the generation of electrographic ictal events in the ACC. In addition, mu-opioid receptors appear to modulate both excitatory and inhibitory mechanisms, thus influencing epileptiform synchronization in the ACC. [source]

In Vivo Modulation of Hippocampal Epileptiform Activity with Radial Electric Fields

EPILEPSIA, Issue 6 2003
Kristen A. Richardson
Summary: Purpose: Electric field stimulation can interact with brain activity in a subthreshold manner. Electric fields have been previously adaptively applied to control seizures in vitro. We report the first results from establishing suitable electrode geometries and trajectories, as well as stimulation and recording electronics, to apply this technology in vivo. Methods: Electric field stimulation was performed in a rat kainic acid injection seizure model. Radial electric fields were generated unilaterally in hippocampus from an axial depth electrode. Both sinusoidal and multiphasic stimuli were applied. Hippocampal activity was recorded bilaterally from tungsten microelectrode pairs. Histologic examination was performed to establish electrode trajectory and characterize lesioning. Results: Electric field modulation of epileptiform neural activity in phase with the stimulus was observed in five of six sinusoidal and six of six multiphasic waveform experiments. Both excitatory and suppressive modulation were observed in the two experiments with stimulation electrodes most centrally placed within the hippocampus. Distinctive modulation was observed in the period preceding seizure-onset detection in two of six experiments. Short-term histologic tissue damage was observed in one of six experiments associated with high unbalanced charge delivery. Conclusions: We demonstrated in vivo electric field modulation of epileptiform hippocampal activity, suggesting that electric field control of in vivo seizures may be technically feasible. The response to stimulation before seizure could be useful for triggering control systems, and may be a novel approach to define a preseizure state. [source]

Simultaneous Kindling of the Bilateral Hippocampi: An Advanced Model for Epilepsy Research

EPILEPSIA, Issue 8 2000
Shinichi Kogure
Summary: Purpose: To examine whether simultaneous kindling of bilateral hippocampi [bilateral kindling (BK)] could accelerate the achievement of seizures by the breakdown of kindling antagonism or decelerate the achievement of seizures by its enhancement. Methods: The hippocampi of 17 adult rabbits were simultaneously kindled bilaterally according to Goddard's method. Results: All animals developed stage 5 convulsions after a mean of 28 stimulations. Six animals showed spontaneous seizure discharges. Afterdischarge duration increased abruptly during the early period of kindling, but thereafter it gradually progressed. Chronological analyses of interictal discharges (HDs) demonstrated that simple as well as complex types of IIDs increased their frequencies during BK. Conclusions: Compared with unilaterally kindled animals, the BK procedure significantly increased the percentage of animals that successfully kindled (100% vs. 59%; p < 0.01), whereas it significantly decelerated the kindling progression (28 days vs. 19 days; p < 0.02). We conclude that the BK procedure represents potentiation of both excitatory and inhibitory mechanisms. Although the reason why such an antagonistic relationship between them breaks down is still unknown, the BK provides an advanced animal model to study the pathogenic mechanisms of kindling and to screen anticonvulsants. [source]

Characterization of Neuronal Migration Disorders in Neocortical Structures: Loss or Preservation of Inhibitory Interneurons?

EPILEPSIA, Issue 7 2000
Petra 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]

Functional subdivision of feline spinal interneurons in reflex pathways from group Ib and II muscle afferents; an update

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2010
Elzbieta Jankowska
Abstract A first step towards understanding the operation of a neural network is identification of the populations of neurons that contribute to it. Our aim here is to reassess the basis for subdivision of adult mammalian spinal interneurons that mediate reflex actions from tendon organs (group Ib afferents) and muscle spindle secondary endings (group II afferents) into separate populations. Re-examining the existing experimental data, we find no compelling reasons to consider intermediate zone interneurons with input from group Ib afferents to be distinct from those co-excited by group II afferents. Similar patterns of distributed input have been found in subpopulations that project ipsilaterally, contralaterally or bilaterally, and in both excitatory and inhibitory interneurons; differences in input from group I and II afferents to individual interneurons showed intra- rather than inter-population variation. Patterns of reflex actions evoked from group Ib and II afferents and task-dependent changes in these actions, e.g. during locomotion, may likewise be compatible with mediation by premotor interneurons integrating information from both group I and II afferents. Pathological changes after injuries of the central nervous system in humans and the lineage of different subclasses of embryonic interneurons may therefore be analyzed without need to consider subdivision of adult intermediate zone interneurons into subpopulations with group Ib or group II input. We propose renaming these neurons ,group I/II interneurons'. [source]

Mu opioid receptor modulation of somatodendritic dopamine overflow: GABAergic and glutamatergic mechanisms

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2009
V. I. Chefer
Abstract Mu opioid receptor (MOR) regulation of somatodendritic dopamine neurotransmission in the ventral tegmental area (VTA) was investigated using conventional microdialysis in freely moving rats and mice. Reverse dialysis of the MOR agonist DAMGO (50 and 100 ,m) into the VTA of rats produced a concentration-dependent increase in dialysate dopamine concentrations. Basal dopamine overflow in the VTA was unaltered in mice lacking the MOR gene. However, basal ,-aminobutyric acid (GABA) overflow in these animals was significantly increased, whereas glutamate overflow was decreased. Intra-VTA perfusion of DAMGO into wild-type (WT) mice increased dopamine overflow. GABA concentrations were decreased, whereas glutamate concentrations in the VTA were unaltered. Consistent with the loss of MOR, no effect of DAMGO was observed in MOR knockout (KO) mice. These data provide the first direct demonstration of tonically active MOR systems in the VTA that regulate basal glutamatergic and GABAergic neurotransmission in this region. We hypothesize that increased GABAergic neurotransmission following constitutive deletion of MOR is due to the elimination of a tonic inhibitory influence of MOR on GABAergic neurons in the VTA, whereas decreased glutamatergic neurotransmission in MOR KO mice is a consequence of intensified GABA tone on glutamatergic neurons and/or terminals. As a consequence, somatodendritic dopamine release is unaltered. Furthermore, MOR KO mice do not exhibit the positive correlation between basal dopamine levels and the glutamate/GABA ratio observed in WT mice. Together, our findings indicate a critical role of VTA MOR in maintaining an intricate balance between excitatory and inhibitory inputs to dopaminergic neurons. [source]

Developmental changes in the BDNF-induced modulation of inhibitory synaptic transmission in the Kölliker,Fuse nucleus of rat

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2007
Miriam Kron
Abstract The Kölliker,Fuse nucleus (KF), part of the pontine respiratory group, is involved in the control of respiratory phase duration, and receives both excitatory and inhibitory afferent input from various other brain regions. There is evidence for developmental changes in the modulation of excitatory inputs to the KF by the neurotrophin brain-derived neurotrophic factor (BDNF). In the present study we investigated if BDNF exerts developmental effects on inhibitory synaptic transmission in the KF. Recordings of inhibitory postsynaptic currents (IPSCs) in KF neurons in a pontine slice preparation revealed general developmental changes. Recording of spontaneous and evoked IPSCs (sIPSCs, eIPSCS) revealed that neonatally the ,-aminobutyric acid (GABA)ergic fraction of IPSCs was predominant, while in later developmental stages glycinergic neurotransmission significantly increased. Bath-application of BDNF significantly reduced sIPSC frequency in all developmental stages, while BDNF-mediated modulation on eIPSCs showed developmental differences. The eIPSCs mean amplitude was uniformly and significantly reduced following BDNF application only in neurons from rats younger than postnatal day 10. At later postnatal stages the response pattern became heterogeneous, and both augmentations and reductions of eIPSC amplitudes occurred. All BDNF effects on eIPSCs and sIPSCs were reversed with the tyrosine kinase receptor-B inhibitor K252a. We conclude that developmental changes in inhibitory neurotransmission, including the BDNF-mediated modulation of eIPSCs, relate to the postnatal maturation of the KF. The changes in BDNF-mediated modulation of IPSCs in the KF may have strong implications for developmental changes in synaptic plasticity and the adaptation of the breathing pattern to afferent inputs. [source]

Heterogeneity of V2-derived interneurons in the adult mouse spinal cord

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2007
A. Al-Mosawie
Abstract Spinal neurons and networks that generate rhythmic locomotor activity remain incompletely defined, prompting the use of molecular biological strategies to label populations of neurons in the postnatal mouse. During spinal cord development, expression of Lhx3 in the absence of Isl1 specifies a V2 interneuronal fate. In this study, postnatal V2-derived interneurons were identified by yellow fluorescent protein (YFP) expression in the double-transgenic offspring of Lhx3Cre/+ × thy1-loxP-stop-loxP-YFP mice. While some motoneurons were labelled, several populations of interneurons predominantly located in lamina VII could also be distinguished. Small interneurons were located throughout the spinal cord whereas larger interneurons were concentrated in the lumbar enlargement. Some V2-derived interneurons were propriospinal, with axons that bifurcated in the lateral funiculus. V2-derived interneurons gave rise to populations of both excitatory and inhibitory interneurons in approximately equal proportions, as demonstrated by in situ hybridization with VGLUT2 mRNA. Immunohistochemical studies revealed YFP+ boutons throughout the spinal cord. Both glutamatergic and glycinergic YFP+ boutons were observed in lamina IX where many apposed motoneuron somata. GABAergic YFP+ boutons were also observed in lamina IX, and they did not form P-boutons. At P0, more than half of the YFP+ interneurons expressed Chx10 and thus were derived from the V2a subclass. In adult mice, there was an increase in Fos expression in V2-derived interneurons following locomotion, indicating that these neurons are active during this behaviour. The heterogeneity of V2-derived interneurons in adult mice indicates that physiologically distinct subpopulations, including last-order interneurons, arise from these embryonically defined neurons. [source]

Selective 5-HT1B receptor inhibition of glutamatergic and GABAergic synaptic activity in the rat dorsal and median raphe

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2006
Julia C. Lemos
Abstract The dorsal (DR) and median (MR) raphe nuclei contain 5-hydroxytryptamine (5-HT) cell bodies that give rise to the majority of the ascending 5-HT projections to the forebrain. The DR and MR have differential roles in mediating stress, anxiety and depression. Glutamate and GABA activity sculpt putative 5-HT neuronal firing and 5-HT release in a seemingly differential manner in the MR and DR, yet isolated glutamate and GABA activity within the DR and MR has not been systematically characterized. Visualized whole-cell voltage-clamp techniques were used to record excitatory and inhibitory postsynaptic currents (EPSC and IPSC) in 5-HT-containing neurons. There was a regional variation in action potential-dependent (spontaneous) and basal [miniature (m)] glutamate and GABAergic activity. mEPSC activity was greater than mIPSC activity in the DR, whereas in the MR the mIPSC activity was greater. These differences in EPSC and IPSC frequency indicate that glutamatergic and GABAergic input have distinct cytoarchitectures in the DR and MR. 5-HT1B receptor activation decreased mEPSC frequency in the DR and the MR, but selectively inhibited mIPSC activity only in the MR. This finding, in concert with its previously described function as an autoreceptor, suggests that 5-HT1B receptors influence the ascending 5-HT system through multiple mechanisms. The disparity in organization and integration of glutamatergic and GABAergic input to DR and MR neurons and their regulation by 5-HT1B receptors may contribute to the distinction in MR and DR regulation of forebrain regions and their differential function in the aetiology and pharmacological treatment of psychiatric disease states. [source]

In vivo optical recordings of synaptic transmission and intracellular Ca2+ and Cl, in the superior colliculus of fetal rats

Ret deficiency in mice impairs the development of A5 and A6 neurons and the functional maturation of the respiratory rhythm

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2005
J. C. Viemari
Abstract Although a normal respiratory rhythm is vital at birth, little is known about the genetic factors controlling the prenatal maturation of the respiratory network in mammals. In Phox2a mutant mice, which do not express A6 neurons, we previously hypothesized that the release of endogenous norepinephrine by A6 neurons is required for a normal respiratory rhythm to occur at birth. Here we investigated the role of the Ret gene, which encodes a transmembrane tyrosine kinase receptor, in the maturation of norepinephrine and respiratory systems. As Ret -null mutants (Ret,/,) did not survive after birth, our experiments were performed in wild-type (wt) and Ret,/, fetuses exteriorized from pregnant heterozygous mice at gestational day 18. First, in wt fetuses, quantitative in situ hybridization revealed high levels of Ret transcripts in the pontine A5 and A6 areas. Second, in Ret,/, fetuses, high-pressure liquid chromatography showed significantly reduced norepinephrine contents in the pons but not the medulla. Third, tyrosine hydroxylase immunocytochemistry revealed a significantly reduced number of pontine A5 and A6 neurons but not medullary norepinephrine neurons in Ret,/, fetuses. Finally, electrophysiological and pharmacological experiments performed on brainstem ,en bloc' preparations demonstrated impaired resting respiratory activity and abnormal responses to central hypoxia and norepinephrine application in Ret,/, fetuses. To conclude, our results show that Ret gene contributes to the prenatal maturation of A6 and A5 neurons and respiratory system. They support the hypothesis that the normal maturation of the respiratory network requires afferent activity corresponding to the A6 excitatory and A5 inhibitory input balance. [source]

Spontaneous recurrent network activity in organotypic rat hippocampal slices

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2005
Majid 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]

Electrical and neurotransmitter activity of mature neurons derived from mouse embryonic stem cells by Sox-1 lineage selection and directed differentiation

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2004
R. J. Lang
Abstract Sx1TV2/16C is a mouse embryonic stem (ES) cell line in which one copy of the Sox1 gene, an early neuroectodermal marker, has been targeted with a neomycin (G418) selection cassette. A combination of directed differentiation with retinoic acid and G418 selection results in an enriched neural stem cell population that can be further differentiated into neurons. After 6,7 days post-plating (D6,7PP) most neurons readily fired tetrodotoxin (TTX)-sensitive action potentials due to the expression of TTX-sensitive Na+ and tetraethylammonium (TEA)-sensitive K+ channels. Neurons reached their maximal cell capacitance after D6,7PP; however, ion channel expression continued until at least D21PP. The percentage of cells receiving spontaneous synaptic currents (s.s.c.) increased with days in culture until 100% of cells received a synaptic input by D20PP. Spontaneous synaptic currents were reduced in amplitude and frequency by TTX, or upon exposure to a Ca2+ -free, 2.5 mm Mg2+ saline. S.s.c. of rapid decay time constants were preferentially blocked by the nonNMDA glutamatergic receptor antagonists CNQX or NBQX. Ca2+ levels within ES cell-derived neurons increased in response to glutamate receptor agonists l -glutamate, AMPA, N -methyl- d -aspartate (NMDA) and kainic acid and to acetylcholine, ATP and dopamine. ES cell-derived neurons also generated cationic and Cl, -selective currents in response to NMDA and glycine or GABA, respectively. It was concluded that ES-derived neurons fire action potentials, receive excitatory and inhibitory synaptic input and respond to various neurotransmitters in a manner akin to primary central neurons. [source]

Amygdala amino acid and monoamine levels in genetically Fast and Slow kindling rat strains during massed amygdala kindling: a microdialysis study

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2004
Rick S. Shin
Abstract We investigated the neurochemistry of epileptic seizures in rats selectively bred to be seizure-prone (Fast) vs. seizure-resistant (Slow) to amygdala kindling. Microdialysis was used to measure levels of amino acids [glutamate, aspartate and gamma-aminobutyric acid (GABA)] and monoamines (noradrenaline, dopamine and serotonin) during ,massed' stimulation (MS) (every 6 min) of the ipsilateral amygdala for a total of 40 stimulation trials. Behavioral seizure profiles together with their afterdischarge thresholds (ADTs) and associated durations were assessed during the procedure, and subsequently were redetermined 1, 7 and 14 days later. Then normal ,daily' kindling commenced and continued until the animal reached the fully kindled state. During MS, several generalized seizures were triggered in Fast rats that were associated with long afterdischarge (AD) durations and intermittent periods of elevated thresholds, but in Slow rats, most stimulations were associated with stable ADTs and short ADs. Progressively increasing extracellular glutamate and decreasing GABA was observed in Fast rats during the MS, whereas Slow rats showed levels similar to baseline values. Levels of noradrenaline and dopamine, but not of serotonin, were also increased in both strains throughout the MS treatment. In Fast rats, a dramatic lengthening of AD durations occurred 7 and 14 days following MS, as well as subsequent strong positive transfer to daily kindling, all of which were not seen in Slow rats. Together, these results show that repeated, closely spaced stimulations of the amygdala can differentially alter excitatory and/or inhibitory transmitter levels in a seizure network, and that sensitivity to this manipulation is genetically determined. [source]

Convergence of excitatory and inhibitory inputs onto CCK-containing basket cells in the CA1 area of the rat hippocampus

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2004
Ferenc Mátyás
Abstract The number and distribution of excitatory and inhibitory inputs affect the integrative properties of neurons. These parameters have been studied recently for several hippocampal neuron populations. Besides parvalbumin- (PV) containing cells that include basket and axo-axonic cells, cholecystokinin (CCK)-containing interneurons also form a basket cell population with several properties distinct from PV cells. Here, at the light microscopic level, we reconstructed the entire dendritic tree of CCK-immunoreactive (IR) basket cells to describe their geometry, the total length and laminar distribution of their dendrites. This was followed by an electron microscopic analysis of serial ultrathin sections immunostained against ,-aminobutyric acid, to estimate the density of excitatory and inhibitory synapses on their somata, axon initial segments and different subclasses of dendrites. The dendritic tree of CCK-IR basket cells has an average length of 6300 µm and penetrates all layers. At the electron microscopic level, CCK basket cells receive dendritic inputs with a density of 80,230 per 100 µm. The ratio of inhibitory inputs is relatively high (35%) and increases towards the soma (83%). The total numbers of excitatory and inhibitory synapses converging onto CCK-IR cells are ,,8200. Comparison of the two, neurochemically distinct basket cells reveals that CCK-containing basket cells receive much less synaptic input than PV cells; however, the relative weight of inhibition is higher on CCK cells. Additional differences in their anatomical and physiological properties predict that CCK basket cells are under a more diverse, elaborate control than PV basket cells, and thus the function of the two populations must be different. [source]

Hormonal enhancement of neuronal firing is linked to structural remodelling of excitatory and inhibitory synapses

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2002
A. Parducz
Abstract The ovarian hormone estradiol induces morphological changes in the number of synaptic inputs in specific neuronal populations. However, the functional significance of these changes is still unclear. In this study, the effect of estradiol on the number of anatomically identified synaptic inputs has been assessed in the hypothalamic arcuate nucleus. The number of axo-somatic, axodendritic and spine synapses was evaluted using unbiased stereological methods and a parallel electrophysiological study was performed to assess whether synaptic anatomical remodelling has a functional consequence on the activity of the affected neurons. Estradiol administration to ovariectomized rats induced a decrease in the number of inhibitory synaptic inputs, an increase in the number of excitatory synapses and an enhancement of the frequency of neuronal firing. These results indicate that oestrogen modifications in firing frequency in arcuate neurons are temporally linked to anatomical modifications in the numerical balance of inhibitory and excitatory synaptic inputs. [source]

A new class of neurotoxin from wasp venom slows inactivation of sodium current

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2000
Yoshinori Sahara
Abstract The effects of ,-pompilidotoxin (,-PMTX), a new neurotoxin isolated from the venom of a solitary wasp, were studied on the neuromuscular synapses in lobster walking leg and the rat trigeminal ganglion (TG) neurons. Paired intracellular recordings from the presynaptic axon terminals and the innervating lobster leg muscles revealed that ,-PMTX induced long bursts of action potentials in the presynaptic axon, which resulted in facilitated excitatory and inhibitory synaptic transmission. The action of ,-PMTX was distinct from that of other known facilitatory presynaptic toxins, including sea anemone toxins and ,-scorpion toxins, which modify the fast inactivation of Na+ current. We further characterized the action of ,-PMTX on Na+ channels by whole-cell recordings from rat trigeminal neurons. We found that ,-PMTX slowed the Na+ channels inactivation process without changing the peak current,voltage relationship or the activation time course of tetrodotoxin (TTX)-sensitive Na+ currents, and that ,-PMTX had voltage-dependent effects on the rate of recovery from Na+ current inactivation and deactivating tail currents. The results suggest that ,-PMTX slows or blocks conformational changes required for fast inactivation of the Na+ channels on the extracellular surface. The simple structure of ,-PMTX, consisting of 13 amino acids, would be advantageous for understanding the functional architecture of Na+ channel protein. [source]

Localization of the A kinase anchoring protein AKAP79 in the human hippocampus

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2000
Attila Sík
Abstract The phosphorylation state of the proteins, regulated by phosphatases and kinases, plays an important role in signal transduction and long-term changes in neuronal excitability. In neurons, cAMP-dependent protein kinase (PKA), protein kinase C (PKC) and calcineurin (CN) are attached to a scaffold protein, A kinase anchoring protein (AKAP), thought to anchor these three enzymes to specific sites of action. However, the localization of AKAP, and the predicted sites of linked phosphatase and kinase activities, are still unknown at the fine structural level. In the present study, we investigated the distribution of AKAP79 in the hippocampus from postmortem human brains and lobectomy samples from patients with intractable epilepsy, using preembedding immunoperoxidase and immunogold histochemical methods. AKAP79 was found in the CA1, presubicular and subicular regions, mostly in pyramidal cell dendrites, whereas pyramidal cells in the CA3, CA2 regions and dentate granule cells were negative both in postmortem and in surgical samples. In some epileptic cases, the dentate molecular layer and hilar interneurons also became immunoreactive. At the subcellular level, AKAP79 immunoreactivity was present in postsynaptic profiles near, but not attached to, the postsynaptic density of asymmetrical (presumed excitatory) synapses. We conclude that the spatial selectivity for the action of certain kinases and phosphatases regulating various ligand- and voltage-gated channels may be ensured by the selective presence of their anchoring protein, AKAP79, at the majority of glutamatergic synapses in the CA1, but not in the CA2/CA3 regions, suggesting profound differences in signal transduction and long-term synaptic plasticity between these regions of the human hippocampus. [source]

Chronic neuropathic pain: mechanisms, drug targets and measurement

FUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 2 2007
Nanna B. Finnerup
Abstract Neuropathic pain is common in many diseases or injuries of the peripheral or central nervous system, and has a substantial impact on quality of life and mood. Lesions of the nervous system may lead to potentially irreversible changes and imbalance between excitatory and inhibitory systems. Preclinical research provides several promising targets for treatment such as sodium and calcium channels, glutamate receptors, monoamines and neurotrophic factors; however, treatment is often insufficient. A mechanism-based treatment approach is suggested to improve treatment. Valid and reliable tools to assess various symptoms and signs in neuropathic pain and knowledge of drug mechanisms are prerequisites for pursuing this approach. The present review summarizes mechanisms of neuropathic pain, targets of currently used drugs, and measures used in neuropathic pain trials. [source]

Evidence against ,2 -adrenoceptors mediating relaxation in rat thoracic aortae: ,2 -agonists relaxation depends on interaction with ,1 -adrenoceptors

FUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 4 2006
Enrique F. Castillo
Abstract In rat aorta, the presence of functional ,2 -adrenoceptors (,2 -AR) was investigated in ring preparations preconstricted with ,1 -adrenergic and non- ,1 -adrenergic agonists. Particularly, the hypothetical interference of ,2 -AR agonists with ,1 -AR-mediated vasoconstriction was evaluated. Relaxant and contractile responses to ,2 -AR agonists were obtained. In endothelium-intact and endothelium-denuded aortic rings preconstricted with phenylephrine (1 × 10,6 m), the imidazoline derivatives, clonidine and UK14304, induced relaxations with similar order of potencies (,log EC50) and maxima relaxant effects respectively. Pretreatment with the NO synthase inhibitor, NG -nitro- l -arginine methyl ester (l -NAME) had no effect on the relaxant responses to clonidine and UK14304. In phenylephrine-constricted rings with endothelium, relaxations to clonidine and UK 14304 were not antagonized by the selective ,2 -AR antagonist, rauwolscine (,1 × 10,6 m). Clonidine and UK 14304 induced only contractions on endothelium-intact and endothelium-denuded aortic rings contracted with prostaglandin F2, (3 × 10,7 m). Moreover, clonidine and UK 14304-induced relaxation of endothelium-denuded arteries precontracted with methoxamine but not with serotonin. Finally, the concentration,contraction curves to clonidine and UK 14304 in endothelium-denuded aortic rings were significantly shifted to the right by the ,1D -AR selective antagonist, BMY 7378, and rauwolscine. The pA2 and pKB values for BMY 7378 and rauwolscine, respectively, against endothelium-independent actions of clonidine and UK 14304 were characteristic of an effect on the ,1D -AR. The other selective ,2 -AR agonist tested BHT 933 (an azepine derivative), lacks considerable relaxant and contractile effects in rat aorta. The results provide no evidence for the presence of functional ,2 -AR in rat aorta. Respectively, the relaxant and contractile effects of the imidazoline derivatives, clonidine and UK 14304, may be due to an adjustable (in relation to the agonist-dependent active state of the ,1 -AR), inhibitory and excitatory, interaction with ,1 -ARs. [source]

Glial cells promote dendrite formation and the reception of synaptic input in Purkinje cells from postnatal mice

GLIA, Issue 5 2010
Isabelle Buard
Abstract Previous studies suggest that glial cells contribute to synaptogenesis in specific neurons from the postnatal CNS. Here, we studied whether this is true for Purkinje cells (PCs), which represent a unique neuronal cell type due to their large size, massive synaptic input, and high vulnerability. Using new glia-free cultures enriched in PCs from postnatal mice we show that these neurons survived and grew, but displayed only low levels of excitatory and inhibitory synaptic activity. Coculture with glial cells strongly enhanced the frequency and size of spontaneous and miniature excitatory synaptic currents as well as neurite growth and branching. Immunocytochemical staining for microtubule-associated protein 2- (MAP2-) positive neurites revealed impaired dendrite formation in PCs under glia-free conditions, which can explain the absence of synaptic activity. Glial signals strongly enhanced dendritogenesis in PCs and thus their ability to receive excitatory synaptic input from granule cells (GCs). The enhancement of dendrite formation was mimicked by glia-conditioned medium (GCM), whereas the increase in synaptic activity required physical presence of glia. This indicated that dendrite development is necessary but not sufficient for PCs to receive excitatory synaptic input and that synaptogenesis requires additional signals. The level of inhibitory synaptic activity was low even in cocultures due to a low incidence of inhibitory interneurons. Taken together, our results reinforce the idea that glial cells promote synaptogenesis in specific neuronal cell types. © 2009 Wiley-Liss, Inc. [source]

Glutamate spillover augments GABA synthesis and release from axodendritic synapses in rat hippocampus

HIPPOCAMPUS, Issue 1 2010
Misty M. Stafford
Abstract Tight coupling between gamma-aminobutyric acid (GABA) synthesis and vesicle filling suggests that the presynaptic supply of precursor glutamate could dynamically regulate inhibitory synapses. Although the neuronal glutamate transporter excitatory amino acid transporter 3 (EAAT3) has been proposed to mediate such a metabolic role, highly efficient astrocytic uptake of synaptically released glutamate normally maintains low-extracellular glutamate levels. We examined whether axodendritic inhibitory synapses in stratum radiatum of hippocampal area CA1, which are closely positioned among excitatory glutamatergic synapses, are regulated by synaptic glutamate release via presynaptic uptake. Under conditions of spatially and temporally coordinated release of glutamate and GABA within pyramidal cell dendrites, blocking glial glutamate uptake enhanced quantal release of GABA in a transporter-dependent manner. These physiological findings correlated with immunohistochemical studies revealing expression of EAAT3 by interneurons and uptake of D-asparate into putative axodendritic inhibitory terminals only when glial uptake was blocked. These results indicate that spillover of glutamate between adjacent excitatory and inhibitory synapses can occur under conditions when glial uptake incompletely clears synaptically released glutamate. Our anatomical studies also suggest that perisomatic inhibitory synapses, unlike synapses within dendritic layers of hippocampus, are not capable of glutamate uptake and therefore transporter-mediated dynamic regulation of inhibition is a unique feature of axodendritic synapses that may play a role in maintaining a homeostatic balance of inhibition and excitation. © 2009 Wiley-Liss, Inc. [source]

Electrical activation of common bile duct nerves modulates sphincter of Oddi motility in the Australian possum

HPB, Issue 4 2005
Y. Sonoda
Abstract Background: Sphincter of Oddi (SO) motility is regulated by extrinsic and intrinsic nerves. The existence of neural circuits between the SO and the proximal extrahepatic biliary tree has been reported, but they are poorly understood. Using electrical field stimulation (EFS), we determined if a neural circuit exists between the common bile duct (CBD) and the SO in anaesthetized Australian brush-tailed possums. Methods: The gallbladder, cystic duct or CBD were subjected to EFS with a stimulating electrode. Spontaneous SO phasic waves were measured by manometry. Results: EFS at sites on the distal CBD (12,20 mm proximal to the SO), but less commonly at more proximal CBD, evoked a variety of responses consisting of an excitatory and/or inhibitory phase. Bi-phasic responses consisting of an excitation followed by inhibition were the most common. Tri-phasic responses were also observed as well as excitation or inhibition only. These evoked responses were blocked by topical application of local anaesthetic to the distal CBD or transection of the CBD. EFS at sites on the gallbladder body, neck or cystic duct did not consistently evoke an SO response. Pretreatment with atropine or guanethidine reduced the magnitude of the evoked response by about 50% (p<0.05), pretreatment with hexamethonium had no consistent effect and pretreatment with a nitric oxide synthase inhibitor increased the response. Discussion: A neural circuit(s) between the SO and the distal CBD modulates SO motility. Damage to this area of the CBD during bile duct exploration surgery could adversely affect SO motility. [source]

Secondary neurogenesis and telencephalic organization in zebrafish and mice: a brief review

INTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 1 2009
Mario F. WULLIMANN
Abstract Most zebrafish neurodevelopmental studies have focused on the embryo, which is characterized by primary neurogenesis of mostly transient neurons. Secondary neurogenesis becomes dominant in the hatching larva, when major brain parts are established and begin to differentiate. This developmental period allows for a comparative analysis of zebrafish brain organization with amniotes at equivalent stages of neurogenesis. Within a particular time window, the early forebrains of mice (Embyronic stage [E] 12.5/13.5 days [d]) and zebrafish (3 d) reveal highly comparable expression patterns of genes involved in neurogenesis, for example proneural and other transcription factors (Neurogenin1, NeuroD, Mash1/Zashla and Pax6). Further topological correspondences are seen in the expression of LIM and homeobox genes, such as Lhx6/7, Tbr2 and Dlx2a. When this analysis is extended to gamma-aminobutyric acid/glutamic acid decarboxylase (GABA/GAD) cell patterns during this critical time window, an astonishing degree of similarity between the two species is again seen, for example regarding the presence of GABA/GAD cells in the subpallium, with the pallium only starting to be invaded by such cells from the subpallium. Furthermore, the expression of proneural and other genes correlates with GABA cell patterns (e.g. Mash1/Zash1a gene expression in GABA-positive and Neurogenin1/NeuroD in GABA-negative telencephalic regions) in mice and zebrafish. Data from additional vertebrates, such as Xenopus, are also highly consistent with this analysis. Therefore, the vertebrate forebrain appears to undergo a phylotypic stage of secondary neurogenesis, characterized by regionally separated GABAergic (inhibitory) versus glutamatergic (excitatory) cell production sites, which are obscured later in development by tangential migration. This period is highly advantageous for molecular neuroanatomical cross-species comparisons. [source]