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Muscimol
Kinds of Muscimol Selected AbstractsGlutamate AMPA/kainate receptors, not GABAA receptors, mediate estradiol-induced sex differences in the hypothalamusDEVELOPMENTAL NEUROBIOLOGY, Issue 3 2007Brigitte J. Todd Abstract Sex differences in brain morphology underlie physiological and behavioral differences between males and females. During the critical perinatal period for sexual differentiation in the rat, gonadal steroids act in a regionally specific manner to alter neuronal morphology. Using Golgi-Cox impregnation, we examined several parameters of neuronal morphology in postnatal day 2 (PN2) rats. We found that in the ventromedial nucleus of the hypothalamus (VMN) and in areas just dorsal and just lateral to the VMN that there was a sex difference in total dendritic spine number (males greater) that was abolished by treating female neonates with exogenous testosterone. Dendritic branching was similarly sexually differentiated and hormonally modulated in the VMN and dorsal to the VMN. We then used spinophilin, a protein that positively correlates with the amount of dendritic spines, to investigate the mechanisms underlying these sex differences. Estradiol, which mediates most aspects of masculinization and is the aromatized product of testosterone, increased spinophilin levels in female PN2 rats to that of males. Muscimol, an agonist at GABAA receptors, did not affect spinophilin protein levels in either male or female neonates. Kainic acid, an agonist at glutamatergic AMPA/kainate receptors, mimicked the effect of estradiol in females. Antagonizing AMPA/kainate receptors with NBQX prevented the estradiol-induced increase in spinophilin in females but did not affect spinophilin level in males. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007 [source] Cortical inhibitory circuits in eye-movement generationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2003Peter H. Schiller Abstract The role inhibitory circuits play in target selection with saccadic eye movements was examined in area V1, the frontal eye fields (FEF) and the lateral intraparietal sulcus (LIP) of the Rhesus Macaque monkey by making local infusions of the GABA agonist muscimol and antagonist bicuculline. In V1, both agents greatly interfered with target selection and visual discrimination of stimuli placed into the receptive field of the affected neurons. In the FEF, bicuculline facilitated target selection without affecting visual discrimination and generated many spontaneous saccades. Muscimol in the FEF interfered with saccadic eye-movement generation. In the LIP, bicuculline was ineffective and muscimol had only a small effect. These findings suggest that in the FEF GABAergic inhibitory circuits play a central role in eye-movement generation whereas in V1 these circuits are essential for visual analysis. Inhibitory circuits in the LIP do not appear to play a central role in target selection and in visual discrimination. [source] Selective lesion of retrotrapezoid Phox2b-expressing neurons raises the apnoeic threshold in ratsTHE JOURNAL OF PHYSIOLOGY, Issue 12 2008Ana C. Takakura Injection of the neurotoxin saporin,substance P (SSP-SAP) into the retrotrapezoid nucleus (RTN) attenuates the central chemoreflex in rats. Here we ask whether these deficits are caused by the destruction of a specific type of interneuron that expresses the transcription factor Phox2b and is non-catecholaminergic (Phox2b+TH,). We show that RTN contains around 2100 Phox2b+TH, cells. Injections of SSP-SAP into RTN destroyed Phox2b+TH, neurons but spared facial motoneurons, catecholaminergic and serotonergic neurons and the ventral respiratory column caudal to the facial motor nucleus. Two weeks after SSP-SAP, the apnoeic threshold measured under anaesthesia was unchanged when fewer than 57% of the Phox2b+TH, neurons were destroyed. However, destruction of 70 ± 3.5% of these cells was associated with a dramatic rise of the apnoeic threshold (from 5.6 to 7.9% end-expiratory P). In anaesthetized rats with unilateral lesions of around 70% of the Phox2b+TH, neurons, acute inhibition of the contralateral intact RTN with muscimol instantly eliminated phrenic nerve discharge (PND) but normal PND could usually be elicited by strong peripheral chemoreceptor stimulation (8/12 rats). Muscimol had no effect in rats with an intact contralateral RTN. In conclusion, the destruction of the Phox2b+TH, neurons is a plausible cause of the respiratory deficits caused by injection of SSP-SAP into RTN. Two weeks after toxin injection, 70% of these cells must be killed to cause a severe attenuation of the central chemoreflex under anaesthesia. The loss of an even greater percentage of these cells would presumably be required to produce significant breathing deficits in the awake state. [source] GABAergic modulation of primary gustatory afferent synaptic efficacyDEVELOPMENTAL NEUROBIOLOGY, Issue 2 2002Andrew A. Sharp Abstract Modulation of synaptic transmission at the primary sensory afferent synapse is well documented for the somatosensory and olfactory systems. The present study was undertaken to test whether GABA impacts on transmission of gustatory information at the primary afferent synapse. In goldfish, the vagal gustatory input terminates in a laminated structure, the vagal lobes, whose sensory layers are homologous to the mammalian nucleus of the solitary tract. We relied on immunoreactivity for the GABA-transporter, GAT-1, to determine the distribution of GABAergic synapses in the vagal lobe. Immunocytochemistry showed dense, punctate GAT-1 immunoreactivity coincident with the layers of termination of primary afferent fibers. The laminar nature and polarized dendritic structure of the vagal lobe make it amenable to an in vitro slice preparation to study early synaptic events in the transmission of gustatory input. Electrical stimulation of the gustatory nerves in vitro produces synaptic field potentials (fEPSPs) predominantly mediated by ionotropic glutamate receptors. Bath application of either the GABAA receptor agonist muscimol or the GABAB receptor agonist baclofen caused a nearly complete suppression of the primary fEPSP. Coapplication of the appropriate GABAA or GABAB receptor antagonist bicuculline or CGP-55845 significantly reversed the effects of the agonists. These data indicate that GABAergic terminals situated in proximity to primary gustatory afferent terminals can modulate primary afferent input via both GABAA and GABAB receptors. The mechanism of action of GABAB receptors suggests a presynaptic locus of action for that receptor. © 2002 Wiley Periodicals, Inc. J Neurobiol 52: 133,143, 2002 [source] Localized transmeningeal muscimol prevents neocortical seizures in rats and nonhuman primates: Therapeutic implicationsEPILEPSIA, Issue 4 2009Nandor Ludvig Summary Purpose:, To determine whether muscimol delivered epidurally or into the subarachnoid space can prevent and/or terminate acetylcholine (Ach),induced focal neocortical seizures at concentrations not affecting behavior and background electroencephalography (EEG) activity. Methods:, Rats (n = 12) and squirrel monkeys (n = 3) were chronically implanted with an epidural or subarachnoid drug delivery device, respectively, over the right frontal/parietal cortex, with adjacent EEG electrodes. Recordings were performed in behaving rats and chaired monkeys. Via the implants, either a control solution (artificial cerebrospinal fluid, ACSF) or muscimol (0.25,12.5 mm) was delivered locally as a "pretreatment," followed by the similar delivery of a seizure-inducing concentration of Ach. In five additional rats, the quantities of food-pellets consumed during epidural ACSF and muscimol (2.5 mm) exposures were measured. In a last group of four rats, muscimol (0.8,2.5 mm) was delivered epidurally during the ongoing, Ach-induced EEG seizure. Results:, In contrast to ACSF pretreatments, epidural muscimol pretreatment in rats completely prevented the seizures at and above 2.5 mm. In the monkeys, subarachnoid muscimol pretreatments at 2.5 mm completely prevented the focal-seizure,inducing effect of Ach, whereas similar deliveries of ACSF did not affect the seizures. Furthermore, 2.5 mm epidural muscimol left the eating behavior of rats intact and caused only slight changes in the EEG power spectra. Finally, muscimol delivery during Ach-induced EEG seizures terminated the seizure activity within 1,3 min. Conclusions:, The results of this study suggest that muscimol is a viable candidate for the transmeningeal pharmacotherapy of intractable focal epilepsy. [source] Neuronal activity in the subthalamic nucleus modulates the release of dopamine in the monkey striatumEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2009Yasushi Shimo Abstract The primate subthalamic nucleus (STN) is commonly seen as a relay nucleus between the external and internal pallidal segments, and as an input station for cortical and thalamic information into the basal ganglia. In rodents, STN activity is also known to influence neuronal activity in the dopaminergic substantia nigra pars compacta (SNc) through inhibitory and excitatory mono- and polysynaptic pathways. Although the anatomical connections between STN and SNc are not entirely the same in primates as in rodents, the electrophysiologic and microdialysis experiments presented here show directly that this functional interaction can also be demonstrated in primates. In three Rhesus monkeys, extracellular recordings from SNc during microinjections into the STN revealed that transient pharmacologic activation of the STN by the acetylcholine receptor agonist carbachol substantially increased burst firing of single nigral neurons. Transient inactivation of the STN with microinjections of the GABA-A receptor agonist muscimol had the opposite effect. While the firing rates of individual SNc neurons changed in response to the activation or inactivation of the STN, these changes were not consistent across the entire population of SNc cells. Permanent lesions of the STN, produced in two animals with the fiber-sparing neurotoxin ibotenic acid, reduced burst firing and firing rates of SNc neurons, and substantially decreased dopamine levels in the primary recipient area of SNc projections, the striatum, as measured with microdialysis. These results suggest that activity in the primate SNc is prominently influenced by neuronal discharge in the STN, which may thus alter dopamine release in the striatum. [source] Cholinergic modulation of visuospatial responding in central thalamusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2007Lori A. Newman Abstract Central thalamus has extensive connections with basal ganglia and frontal cortex that are thought to play a critical role in sensory-guided goal-directed behavior. Central thalamic activity is influenced by cholinergic projections from mesopontine nuclei. To elucidate this function we trained rats to respond to lights in a reaction time (RT) task and compared effects of muscarinic (2.4, 7.3, 22 nmol scopolamine) and nicotinic (5.4, 16, 49, 98 nmol mecamylamine) antagonists with the GABAA agonist muscimol (0.1, 0.3, 1.0 nmol) in central thalamus. We compared this with subcutaneous (systemic) effects of mecamylamine (3.2, 9.7, 29 µmol/kg) and scopolamine (0.03, 0.09, 0.26 µmol/kg). Subcutaneous scopolamine increased omissions (failure to respond within a 3-s response window) at the highest dose tested. Subcutaneous mecamylamine increased omissions at the highest dose tested while impairing RT and per cent correct at lower doses. Intrathalamic injections of muscimol and mecamylamine decreased per cent correct at doses that did not affect omissions or RT. Intrathalamic scopolamine increased omissions and RT at doses that had little effect on per cent correct. Anatomical controls indicated that the effects of mecamylamine were localized in central thalamus and those of scopolamine were not. Drug effects did not interact with attention-demanding manipulations of stimulus duration, proximity of stimulus and response locations, or stimulus array size. These results are consistent with the hypothesis that central thalamus mediates decisional processes linking sensory stimuli with actions, downstream from systems that detect sensory signals. They also provide evidence that this function is specifically influenced by nicotinic cholinergic receptors. [source] Basolateral amygdala inactivation by muscimol, but not ERK/MAPK inhibition, impairs the use of reward expectancies during working memoryEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2007Lisa M. Savage Abstract Rats were trained on a delayed matching to position (DMTP) task that embedded either a differential outcomes procedure (DOP) or a non-differential outcomes procedure (NOP). The DOP, via Pavlovian conditioning (stimulus,outcome associations), results in the use of unique reward expectancies that facilitate learning and memory performance above subjects trained with a NOP that requires subjects to retain cue information for accurate choice behavior (stimulus,response associations). This enhancement in learning and/or memory produced by the DOP is called the differential outcomes effect (DOE). After being trained on the DMTP task, rats were implanted with two cannulae aimed at the basolateral amygdala (BLA) nuclei. Rats trained with the DOP, relative to those trained with the NOP, displayed enhanced short-term memory (STM) performance under vehicle conditions (i.e. the DOE). However, injections of the ,-aminobutyric acid (GABA)A agonist muscimol into the BLA dose-dependently (0.0625 and 0.125 µg) impaired STM performance only in DOP-trained rats. These results support the role of the BLA in the use of established reward expectancies during a short-term working memory task. Despite the fact that extracellular signal-regulated kinase/mitogen-activated protein kinases (ERK/MAPK) have been shown to be necessary for amygdala-dependent long-term potentiation and some forms of long-term and STM, inhibition of the ERK/MAPK signaling cascade by U0126 (2.0 or 4.0 µg) in the BLA was not critical for updating the STM of either spatial information or reward expectation. [source] Cocaine-induced locomotor activity and Fos expression in nucleus accumbens are sensitized for 6 months after repeated cocaine administration outside the home cageEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2006Bruce T. Hope Abstract Induction of the immediate early gene protein product Fos has been used extensively to assess neural activation in the striatum after repeated cocaine administration to rats in their home cages but rarely after repeated administration outside the home cage, which produces more robust locomotor sensitization. In the present study, we found cocaine-induced Fos expression in nucleus accumbens, but not caudate-putamen, was enhanced 1 and 6 months after repeated drug administration in locomotor activity chambers. Double-labelling of Fos protein and enkephalin mRNA indicated that Fos expression in nucleus accumbens was enhanced in enkephalin-positive, but not enkephalin-negative, medium spiny neurons. In contrast, cocaine-induced Fos expression was absent altogether in nucleus accumbens and unaltered in caudate-putamen 1 month after repeated cocaine administration in the home cage. As cocaine-induced locomotor activity was also enhanced 1 and 6 months after repeated cocaine administration in locomotor activity chambers, we wanted to confirm that neuronal activity in nucleus accumbens mediates cocaine-induced locomotor activity using our particular treatment regimen. Bilateral infusions of the GABA agonists baclofen and muscimol (1 µg/side) into nucleus accumbens of sensitized rats blocked cocaine-induced Fos expression and locomotor activity. Thus, while neuronal activity in both D1- and D2-type neurons in nucleus accumbens can mediate acute cocaine-induced locomotor activity, the enhanced activation of enkephalinergic D2-type neurons suggests that these latter neurons mediate the enhancement of cocaine-induced locomotor activity for up to 6 months after repeated drug administration outside the home cage. [source] The role of the dorsomedial striatum in instrumental conditioningEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2005Henry H. Yin Abstract Considerable evidence suggests that, in instrumental conditioning, rats learn the relationship between actions and their specific consequences or outcomes. The present study examined the role of the dorsomedial striatum (DMS) in this type of learning after excitotoxic lesions and reversible, muscimol-induced inactivation. In three experiments, rats were first trained to press two levers for distinct outcomes, and then tested after training using a variety of behavioural assays that have been established to detect action-outcome learning. In Experiment 1, pre-training lesions of the posterior DMS abolished the sensitivity of rats' instrumental performance to both outcome devaluation and contingency degradation when tested in extinction, whereas lesions of the anterior DMS had no effect. In Experiment 2, both pre-training and post-training lesions of the posterior DMS were equally effective in reducing the sensitivity of performance both to devaluation and degradation treatments. In Experiment 3, the infusion of muscimol into the posterior DMS selectively abolished sensitivity of performance to devaluation and contingency degradation without impairing the ability of rats to discriminate either the instrumental actions performed or the identity of the earned outcomes. Taken together, these results suggest that the posterior region of the DMS is a crucial neural substrate for the acquisition and expression of action,outcome associations in instrumental conditioning. [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] Pro-VGF-derived peptides induce penile erection in male rats: possible involvement of oxytocinEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2004Salvatora Succu Abstract The effect of five peptides derived from the C-terminal portion of rat pro-VGF (VGF577-617, VGF588-617, VGF599-617, VGF556-576 and VGF588-597) on penile erection was studied after injection into the hypothalamic paraventricular nucleus of male rats. VGF577-617, VGF588-617, VGF599-617 and, to a lower extent, VGF588-597 (0.1,2 µg) induced penile erection episodes in a dose-dependent manner when injected into the paraventricular nucleus, while VGF556-576 was ineffective. VGF588-617 -induced penile erection was reduced by nitro, - l -arginine methylester (L-NAME; 20 µg), by morphine (5 µg) and by muscimol (1 µg), but not by dizocilpine [(+)MK-801; 1 µg], nor by cis -flupenthixol (10 µg) given into the paraventricular nucleus 10 min before the VGF peptide. d(CH2)5Tyr(Me)-Orn8 -vasotocin (1 µg) effectively reduced VGF588-617 -induced penile erection when given into the lateral ventricles but not when injected into the paraventricular nucleus. Immunocytochemistry with antibodies specific for the C-terminal nonapeptide sequence of pro-VGF (VGF609-617) revealed numerous neuronal fibres and terminals within the paraventricular nucleus, including its parvocellular components. Here, many immunostained neuronal terminals impinged on parvocellular oxytocinergic neurons. The present results show for the first time that certain pro-VGF C-terminus-derived peptides promote penile erection when injected into the paraventricular nucleus and suggest that, within this nucleus, these or closely related pro-VGF-derived peptides may be released to influence sexual function by activating paraventricular oxytocinergic neurons mediating penile erection. [source] Temporary inactivation of the perirhinal cortex by muscimol injections block acquisition and expression of fear-potentiated startleEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2004Brigitte Schulz Abstract The present study examined the role of the perirhinal cortex (PRh) in aversive information processing and emotional learning. Specifically, we studied the effects of temporary inactivation of the PRh on acquisition and expression of conditioned fear as measured by fear-potentiated startle in rats, as well as on shock sensitization of startle. Temporary inactivation of the PRh was induced by local injections of the GABAA agonist muscimol (0.0, 1.1, 2.2, 4.4 nmol/0.5 µL). Muscimol injections into the PRh blocked both the expression and acquisition of fear-potentiated startle, as well as shock sensitization of startle. Shock sensitivity was not affected by muscimol injections, indicating that the observed blockade of acquisition and shock sensitization was not caused by a disruption in the perception of shock. Taken together, the present data show that the PRh is critical for the processing of aversive information and is necessary for the expression of emotional learning. [source] Cortical inhibitory circuits in eye-movement generationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2003Peter H. Schiller Abstract The role inhibitory circuits play in target selection with saccadic eye movements was examined in area V1, the frontal eye fields (FEF) and the lateral intraparietal sulcus (LIP) of the Rhesus Macaque monkey by making local infusions of the GABA agonist muscimol and antagonist bicuculline. In V1, both agents greatly interfered with target selection and visual discrimination of stimuli placed into the receptive field of the affected neurons. In the FEF, bicuculline facilitated target selection without affecting visual discrimination and generated many spontaneous saccades. Muscimol in the FEF interfered with saccadic eye-movement generation. In the LIP, bicuculline was ineffective and muscimol had only a small effect. These findings suggest that in the FEF GABAergic inhibitory circuits play a central role in eye-movement generation whereas in V1 these circuits are essential for visual analysis. Inhibitory circuits in the LIP do not appear to play a central role in target selection and in visual discrimination. [source] SHORT COMMUNICATION Inhibition of GABAergic neurotransmission in the ventral tegmental area by cannabinoidsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2002Bela Szabo Abstract It was shown recently that ,9-tetrahydrocannabinol, like several other drugs eliciting euphoria, stimulates dopaminergic neurons projecting from the ventral tegmental area (VTA) to the nucleus accumbens. The aim of the present work was to clarify the mechanism of this stimulatory effect. Our hypothesis was that cannabinoids depress the GABAergic inhibition of dopaminergic neurons in the VTA. Electrophysiological properties of VTA neurons in rat coronal midbrain slices were studied with the patch-clamp technique. GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs) were evoked by electrical stimulation in the vicinity of the recorded neurons. The amplitude of IPSCs was depressed by the synthetic mixed CB1/CB2 cannabinoid receptor agonist WIN55212-2 (10,6 and 10,5 m). The CB1 cannabinoid receptor antagonist SR141716A (10,6 m) prevented the inhibition produced by WIN55212-2 (10,5 m). Two observations showed that IPSCs were depressed with a presynaptic mechanism. WIN55212-2 (10,5 m) did not change the amplitude of miniature IPSCs recorded in the presence of tetrodotoxin. Currents evoked by pressure ejection of muscimol from a pipette were also not changed by WIN55212-2 (10,5 m). The results indicate that activation of CB1 cannabinoid receptors inhibits GABAergic neurotransmission in the VTA with a presynaptic mechanism. Depression of the GABAergic inhibitory input of dopaminergic neurons would increase their firing rate in vivo. Accordingly, dopamine release in the projection region of VTA neurons, the nucleus accumbens, would also increase. [source] Postnatal maturation of GABAA and GABAC receptor function in the mammalian superior colliculusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2001Mathias Boller Abstract In the stratum griseum superficiale (SGS) of the mammalian superior colliculus, GABAC receptors seem to control the excitability of projection neurons by selective inactivation of local GABAergic interneurons. As the onset of visual responses to SC begins well after birth in the rat, it is possible to study developmental changes in GABAergic mechanisms that are linked to the onset of visual information processing. In order to analyse postnatal changes in inhibitory mechanisms that involve GABA receptor function, we used extracellular field potential (FP) recordings and single cell patch-clamp techniques in slices from postnatal day 4 (P4) to P32 and examined the effects of GABA and muscimol on electrically evoked SGS cell activity. While GABAA receptor activation affected FP amplitudes throughout postnatal development, GABAC receptor activation did not significantly change FP amplitudes until the third postnatal week. Results from patch-clamping single cells, however, clearly demonstrate that GABAC receptors are already functional at P4 , similar to GABAA receptors. Throughout postnatal development, activation of GABAC receptors leads to a strong inhibition of inhibitory postsynaptic activity, indicating that GABAC receptors are expressed by inhibitory interneurons. Furthermore, the proportion of neurons that show decreased excitatory postsynaptic activity during GABAC receptor activation correlates with the proportion of GABAergic interneurons in SGS. Our patch-clamp results indicate that the functional expression of GABAC receptors by GABAergic interneurons does not change significantly during postnatal development. However, our measurements of FP amplitudes indicate that the maturation of the efferent connections of these GABAergic neurons within SGS during the third postnatal week strongly changes GABAC receptor function. [source] GABAA -receptor expression in glioma cells is triggered by contact with neuronal cellsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2001Michael Synowitz Abstract The expression of functional GABAA -receptors in glioma cells correlates with low malignancy of tumours and cell lines from glioma lack these receptors. Here we show that contact with neurons induces the expression of functional GABAA -receptors. C6 and F98 glioma cell lines were labelled by recombinant expression of enhanced green fluorescent protein injected into rat brain and studied in acute slices after two to three weeks of tumour growth. The cells responded to GABA or the specific agonist, muscimol with a current typical for GABAA -receptors, as studied with the patch-clamp technique. To get insight into the mechanism of GABAA receptor induction, the C6 or F98 cells were co-cultured with neurons, astrocytes, oligodendrocytes and microglia. Glioma cells expressed functional GABAA receptors within 24 h only in cultures where physical contact to neurons occurred. Activation of GABAA -receptors in the co-cultures attenuated glioma cell metabolism while blockade of the receptors increased metabolism. We conclude that with this form of interaction, neurons can influence tumour behaviour in the brain. [source] Differential c-fos expression in the rhinencephalon and striatum after enhanced sleep,wake states in the catEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2000J. P. Sastre Abstract In order to delimit the supra-brainstem structures that are activated during the sleep,waking cycle, we have examined c-fos immunoreactivity in four groups of polygraphically recorded cats killed after 3 h of prolonged waking (W), slow-wave sleep (SWS), or paradoxical sleep (PS), following microinjection of muscimol (a ,-aminobutyric acid, GABA agonist) into the periaqueductal grey matter and adjacent areas [Sastre et al. (1996) , Neuroscience, 74, 415,426]. Our results demonstrate that there was a direct relationship between a significant increase in c-fos labelling and the amount of PS in the laterodorsalis tegmenti in the pons, supramamillary nucleus, septum, hippocampus, gyrus cingulate, amygdala, stria terminalis and the accumbens nuclei. Moreover, in all these structures, the number of Fos-like immunoreactive neurons in the PS group was significantly higher (three to 30-fold) than in the SWS and W groups. We suggest that the dense expression of the immediate-early gene c-fos in the rhinencephalon and striatum may be considered as a tonic component of PS at the molecular level and that, during PS, the rhinencephalon and striatum are the main targets of an excitatory system originating in the pons. [source] Possible involvement of GABAergic modulation in the protective effect of gabapentin against immobilization stress-induced behavior alterations and oxidative damage in miceFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 6 2007Anil Kumar Abstract Introduction Acute stress may be experienced in response to an immediate physical, emotional or psychological stimulus. Stress has been known to affect several brain activities and promote long-term changes in multiple neural systems. In the present study, we investigated the possible involvement of GABAergic modulation in the protective effect of gabapentin in acute immobilization-induced behavioral alterations and oxidative damage in mice. Materials and methods Mice were immobilized for periods of 6 h. Animals were divided into different groups, consisting of six in each. Various GABAergic modulators were administered either alone or in their combinations, 30 min before subjecting the animals for immobilization stress. Various behavioral tests (mirror chamber, actophotometer) followed by oxidative parameters (malondialdehyde level, glutathione, catalase, nitrite and protein) were assessed in animals. Results Six hours acute immobilization stress caused significant locomotor impairment, anxiety-like behavior in mice. Biochemical analyses also revealed an increase malondialdehyde, nitrite level and depletion of glutathione and catalase activity in 6 h stressed brains. Pretreatment with gabapentin (50 and 100 mg/kg, i.p.) significantly improved ambulatory movements, anti-anxiety effect (decreased time latency to enter in mirror chamber, increased number of entries and duration in mirror chamber) and antioxidative activity in stressed mice (P < 0.05). Further, picrotoxin (1.0 mg/kg) blocked and muscimol (0.05 mg/kg) potentiated the protective action of gabapentin (50 mg/kg). Results of both behavior as well as biochemical alterations in combination studies were significant as compared to their effect per se (P < 0.05). Conclusion Results of present study suggest GABAergic modulation might be involved in the protective effect of gabapentin against immobilization-induced behavior alteration and oxidative damage in mice. [source] Cooperation and competition between the dorsal hippocampus and lateral amygdala in spatial discrimination learningHIPPOCAMPUS, Issue 7 2006Stephane Gaskin Abstract The conditioned cue preference (CCP) was used to study how rats discriminate between adjacent arms on a radial maze. Chai and White (Behav Neurosci 2004, 118:770,784) showed that an intact dorsal hippocampus is required to learn this discrimination and that an amygdala-based conditioned approach response that produces an equal tendency to enter both arms is simultaneously acquired. In the present experiments, rats were preexposed to the maze with no food and trained by alternately confining them at the ends of two adjacent arms, one that contained food and one that did not. When given a choice between these arms with no food present, the rats spent more time on their food-paired arms, suggesting they had learned to discriminate their locations. Temporary inactivation of the dorsal hippocampus with muscimol during confinement on the food-paired arm had no effect on the discrimination, but inactivation while on the no-food arm impaired it. This pattern of effects was reversed in rats with amygdala lesions (inactivation on the food-paired arm impaired, but inactivation on the no-food arm had no effect on the discrimination), showing that hippocampus-based and amygdala-based learning interact to influence the behavior of normal rats in this situation. The dorsal hippocampus learns about locations that contain food and about locations that do not contain food. The amygdala-based tendency to enter the food-paired arm cooperates with hippocampus-based foraging for food on the food-paired, but the amygdala-based tendency to enter the no-food arm competes with hippocampus-based learning about the absence of food on that arm. © 2006 Wiley-Liss, Inc. [source] Confirmation of the anxiolytic-like effect of dihydrohonokiol following behavioural and biochemical assessmentsJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 5 2001Yuji Maruyama Previous studies in this laboratory revealed that dihydrohonokiol-B (DHH-B; 3,-(2 propenyl)-5-propyl-(1,1,-biphenyl)-2,4,-diol), a partially reduced derivative of honokiol, was an effective anxiolytic-like agent in mice at an oral dose of 0.04 mg kg,1, and at higher doses, when evaluated by the elevated plus-maze test. The aim of this study was to further confirm the anxiolytic-like effect of DHH-B using an additional behavioural procedure (Vogel's conflict test in mice) and a biochemical assessment (in-vitro determination of muscimol-stimulated 36Cl, uptake into mouse cortical synaptoneurosomes). As in earlier experiments, DHH-B (0.04,1 mg kg,1, p.o.) was shown to prolong the time spent in the open-sided arms of the elevated plus-maze in a dose-dependent manner. Moreover, in the Vogel's conflict test, DHH-B (5 mg kg,1, p.o.) significantly increased punished water intake. In tests with mouse cerebral cortical synaptoneurosomes, 10 and 30 ,m of DHH-B significantly increased 36Cl, influx in the absence of muscimol. In the presence of 25 ,m muscimol, the addition of 1 ,m DHH-B led to significant enhancement of 36Cl, uptake, while 30 ,m DHH-B was required to further stimulate the 36Cl, uptake induced by 250 ,m muscimol. The results of these studies confirm that DHH-B is a potent anxiolytic-like agent and that GABAA receptor-gated Cl, -channel complex is involved in the anxiolytic-like efficacy of DHH-B. [source] Attenuation of the Stimulant Response to Ethanol is Associated with Enhanced Ataxia for a GABAA, but not a GABAB, Receptor AgonistALCOHOLISM, Issue 1 2009Sarah E. Holstein Background:, The ,-aminobutyric acid (GABA) system is implicated in the neurobiological actions of ethanol, and pharmacological agents that increase the activity of this system have been proposed as potential treatments for alcohol use disorders. As ethanol has its own GABA mimetic properties, it is critical to determine the mechanism by which GABAergic drugs may reduce the response to ethanol (i.e., via an inhibition or an accentuation of the neurobiological effects of ethanol). Methods:, In this study, we examined the ability of 3 different types of GABAergic compounds, the GABA reuptake inhibitor NO-711, the GABAA receptor agonist muscimol, and the GABAB receptor agonist baclofen, to attenuate the locomotor stimulant response to ethanol in FAST mice, which were selectively bred for extreme sensitivity to ethanol-induced locomotor stimulation. To determine whether these compounds produced a specific reduction in stimulation, their effects on ethanol-induced motor incoordination were also examined. Results:, NO-711, muscimol, and baclofen were all found to potently attenuate the locomotor stimulant response to ethanol in FAST mice. However, both NO-711 and muscimol markedly increased ethanol-induced ataxia, whereas baclofen did not accentuate this response. Conclusions:, These results suggest that pharmacological agents that increase extracellular concentrations of GABA and GABAA receptor activity may attenuate the stimulant effects of ethanol by accentuating its intoxicating and sedative properties. However, selective activation of the GABAB receptor appears to produce a specific attenuation of ethanol-induced stimulation, suggesting that GABAB receptor agonists may hold greater promise as potential pharmacotherapies for alcohol use disorders. [source] Coregulation of Ethanol Discrimination by the Nucleus Accumbens and AmygdalaALCOHOLISM, Issue 3 2003Joyce Besheer Background: Activation of GABAA receptors in the amygdala or nucleus accumbens produces discriminative stimulus effects that substitute fully for those of systemically administered ethanol. This study was conducted to determine if GABAA receptors in the amygdala and nucleus accumbens interactively modulate ethanol discrimination. Methods: Male Long-Evans rats were trained to discriminate between intraperitoneal injections of ethanol (1 g/kg) and saline on a 2-lever drug discrimination task. The rats were then surgically implanted with bilateral injection cannulae aimed at the nucleus accumbens and the amygdala. Results: Infusion of the GABAA agonist muscimol in the nucleus accumbens resulted in full substitution for systemically administered ethanol. Concurrent infusion of the GABAA antagonist bicuculline in the amygdala shifted the muscimol substitution curve in the nucleus accumbens 10-fold to the right. Conclusions: These results indicate that blockade of GABAA receptors in the amygdala significantly reduces the potency of the GABAA agonist in the nucleus accumbens. This suggests that the ethanol-like stimulus effects of GABAA receptor activation in the nucleus accumbens are modulated by GABAA receptor activity in the amygdala. These data support the hypothesis that the addictive stimulus properties of alcohol are mediated by GABAergic transmission in a neural circuit involving the amygdala and nucleus accumbens. [source] Dysfunction of the subthalamic nucleus induces behavioral and movement disorders in monkeys,MOVEMENT DISORDERS, Issue 8 2009Carine Karachi MD Abstract High-frequency stimulation of the subthalamic nucleus (STN) in parkinsonian patients is reported to induce psychiatric effects. The likely explanation for these effects is the partitioning of the STN into sensorimotor, associative, and limbic anatomo-functional territories. Thus, a specific neuronal dysfunction of the STN sensorimotor territory could lead to abnormal movements, whereas a dysfunction of the associative or limbic territory could lead to behavioral disturbances. To test this hypothesis, neuronal dysfunction of the STN was induced by microinjections of the GABA agonist muscimol, or antagonist bicucculline, in various parts of the nucleus in three monkeys. Stereotyped behaviors (licking and biting fingers) and/or violent hyperactivity were obtained with bicuculline injected into the anteromedial, associative, and limbic territories, whereas injections of muscimol induced no major effects. Abnormal limb movements (contralateral ballism) were obtained after muscimol or bicuculline injections into the posterolateral, sensorimotor territory. Control injections localized around the STN induced other effects (mainly torticollis), which underlines the specificity of STN injection effects. Our study supports the hypothesis that the anteromedial part of the STN is involved in behavioral control. © 2009 Movement Disorder Society [source] High-level expression and purification of Cys-loop ligand-gated ion channels in a tetracycline-inducible stable mammalian cell line: GABAA and serotonin receptorsPROTEIN SCIENCE, Issue 9 2010Zuzana Dostalova Abstract The human neuronal Cys-loop ligand-gated ion channel superfamily of ion channels are important determinants of human behavior and the target of many drugs. It is essential for their structural characterization to achieve high-level expression in a functional state. The aim of this work was to establish stable mammalian cell lines that enable high-level heterologous production of pure receptors in a state that supports agonist-induced allosteric conformational changes. In a tetracycline-inducible stable human embryonic kidney cells (HEK293S) cell line, GABAA receptors containing ,1 and ,3 subunits could be expressed with specific activities of 29,34 pmol/mg corresponding to 140,170 pmol/plate, the highest expression level reported so far. Comparable figures for serotonin (5-HT3A) receptors were 49,63 pmol/mg and 245,315 pmol/plate. The expression of 10 nmol of either receptor in suspension in a bioreactor required 0.3,3.0 L. Both receptor constructs had a FLAG epitope inserted at the N-terminus and could be purified in one step after solubilization using ANTI-FLAG affinity chromatography with yields of 30,40%. Purified receptors were functional. Binding of the agonist [3H]muscimol to the purified GABAAR was enhanced allosterically by the general anesthetic etomidate, and purified 5-hydroxytryptamine-3A receptor supported serotonin-stimulated cation flux when reconstituted into lipid vesicles. [source] , -Amino Butyric Acid Control of Arginine Vasopressin Release from the Ewe Hypothalamus In Vitro: Sensitivity to OestradiolREPRODUCTION IN DOMESTIC ANIMALS, Issue 5 2007SPS Ghuman Contents The present study aims to ascertain the influence of , -amino butyric acid (GABA)A or B receptors on arginine vasopressin (AVP) release in vitro and determine whether E2 modulates GABA,AVP interaction. Within 10 min of ewe killing, saggital midline hypothalamic slices (from the anterior preoptic area to the mediobasal hypothalamus along with the median eminence, 2-mm thick, two per ewe) were dissected, placed in oxygenated minimum essential media (MEM)- , at 4°C and within 2 h were singly perifused at 37°C with oxygenated MEM- , (pH 7.4; flow rate 0.15 ml/min), either with or without E2 (24 pg/ml). After 4-h equilibration, 10-min fractions were collected for 4 h interposed with a 10-min exposure at 60 min to a specific GABAA or B receptor agonist or antagonist at various doses (0.1,10 mm). GABAA (muscimol; no E2, n = 7 perifusion chambers, with E2, n = 11) or GABAB (baclofen; no E2, n = 8, with E2, n = 15) agonists (10 mm) did not influence AVP concentrations. However, AVP release increased (p < 0.05) 20,30 min after exposure to 10 mm GABAA or B antagonists (bicuculline, no E2, n = 7: from 4.6 ± 0.7 to 33.0 ± 0.4, with E2, n = 17: from 11.9 ± 1.4 to 32.8 ± 6.0; CGP52432, with E2, n = 14: from 14.0 ± 2.6 to 28.8 ± 3.9 pg/ml). At the end of the collection period, hypothalamic slices responded to KCl (100 mm) with AVP efflux (p < 0.05). GABAB but not GABAA antagonist-stimulated AVP release was enhanced in the presence of E2. In summary, AVP release is under the inhibitory influence of GABA input with further potentiation by E2 through GABAB receptors in vitro. [source] Specific GABAA agonists and partial agonistsTHE CHEMICAL RECORD, Issue 6 2002Povl Krogsgaard-Larsen Abstract The GABAA receptor system is implicated in a number of neurological and psychiatric diseases, making GABAA receptor ligands interesting as potential therapeutic agents. Only a few different classes of structures are currently known as ligands for the GABA recognition site on the hetero-pentameric GABAA receptor complex, reflecting the very strict structural requirements for GABAA receptor recognition and activation. Within the series of compounds showing agonist activity at the GABAA receptor site that have been developed, most of the ligands are structurally derived from the GABAA agonists muscimol, THIP, or isoguvacine, which we developed in the initial stages of the project. Using recombinant GABAA receptors, functional selectivity was demonstrated for a number of compounds, including THIP, showing highly subunit-dependent potency and maximal response. In light of the interest in partial GABAA receptor agonists as potential therapeutics, structure,activity studies of a number of analogs of 4-PIOL, a low-efficacy partial GABAA agonist derived from THIP, have been performed. In this connection, a series of GABAA ligands has been developed that exhibit pharmacological profiles from moderately potent low-efficacy partial GABAA agonist activity to potent and selective antagonist effects. Very little information is available on direct-acting GABAA receptor agonists in clinical studies. However, the results of clinical studies on the effect of the partial GABAA agonist THIP on human sleep patterns show that the functional consequences of a direct-acting agonist are different from those seen after the administration of GABAA receptor modulators, such as benzodiazepines and barbiturates. © 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc., Chem Rec 2: 419,430; 2002: Published online in Wiley Interscience (www.interscience.wiley.com) DOI 10.1002/tcr.10040 [source] Distinct activities of GABA agonists at synaptic- and extrasynaptic-type GABAA receptorsTHE JOURNAL OF PHYSIOLOGY, Issue 8 2010Martin Mortensen The activation characteristics of synaptic and extrasynaptic GABAA receptors are important for shaping the profile of phasic and tonic inhibition in the central nervous system, which will critically impact on the activity of neuronal networks. Here, we study in isolation the activity of three agonists, GABA, muscimol and 4,5,6,7-tetrahydoisoxazolo[5,4-c]pyridin-3(2H)-one (THIP), to further understand the activation profiles of ,1,3,2, ,4,3,2 and ,4,3, receptors that typify synaptic- and extrasynaptic-type receptors expressed in the hippocampus and thalamus. The agonists display an order of potency that is invariant between the three receptors, which is reliant mostly on the agonist dissociation constant. At , subunit-containing extrasynaptic-type GABAA receptors, both THIP and muscimol additionally exhibited, to different degrees, superagonist behaviour. By comparing whole-cell and single channel currents induced by the agonists, we provide a molecular explanation for their different activation profiles. For THIP at high concentrations, the unusual superagonist behaviour on ,4,3, receptors is a consequence of its ability to increase the duration of longer channel openings and their frequency, resulting in longer burst durations. By contrast, for muscimol, moderate superagonist behaviour was caused by reduced desensitisation of the extrasynaptic-type receptors. The ability to specifically increase the efficacy of receptor activation, by selected exogenous agonists over that obtained with the natural transmitter, may prove to be of therapeutic benefit under circumstances when synaptic inhibition is compromised or dysfunctional. [source] Cardiovascular and thermal responses evoked from the periaqueductal grey require neuronal activity in the hypothalamusTHE JOURNAL OF PHYSIOLOGY, Issue 6 2009Rodrigo C. A. De Menezes Stimulation of neurons in the lateral/dorsolateral periaqueductal grey (l/dlPAG) produces increases in heart rate (HR) and mean arterial pressure (MAP) that are, according to traditional views, mediated through projections to medullary autonomic centres and independent of forebrain mechanisms. Recent studies in rats suggest that neurons in the l/dlPAG are downstream effectors responsible for responses evoked from the dorsomedial hypothalamus (DMH) from which similar cardiovascular changes and increase in core body temperature (Tco) can be elicited. We hypothesized that, instead, autonomic effects evoked from the l/dlPAG depend on neuronal activity in the DMH. Thus, we examined the effect of microinjection of the neuronal inhibitor muscimol into the DMH on increases in HR, MAP and Tco produced by microinjection of N -methyl- d -aspartate (NMDA) into the l/dlPAG in conscious rats. Microinjection of muscimol alone modestly decreased baseline HR and MAP but failed to alter Tco. Microinjection of NMDA into the l/dlPAG caused marked increases in all three variables, and these were virtually abolished by prior injection of muscimol into the DMH. Similar microinjection of glutamate receptor antagonists into the DMH also suppressed increases in HR and abolished increases in Tco evoked from the PAG. In contrast, microinjection of muscimol into the hypothalamic paraventricular nucleus failed to reduce changes evoked from the PAG and actually enhanced the increase in Tco. Thus, our data suggest that increases in HR, MAP and Tco evoked from the l/dlPAG require neuronal activity in the DMH, challenging traditional views of the place of the PAG in central autonomic neural circuitry. [source] Selective lesion of retrotrapezoid Phox2b-expressing neurons raises the apnoeic threshold in ratsTHE JOURNAL OF PHYSIOLOGY, Issue 12 2008Ana C. Takakura Injection of the neurotoxin saporin,substance P (SSP-SAP) into the retrotrapezoid nucleus (RTN) attenuates the central chemoreflex in rats. Here we ask whether these deficits are caused by the destruction of a specific type of interneuron that expresses the transcription factor Phox2b and is non-catecholaminergic (Phox2b+TH,). We show that RTN contains around 2100 Phox2b+TH, cells. Injections of SSP-SAP into RTN destroyed Phox2b+TH, neurons but spared facial motoneurons, catecholaminergic and serotonergic neurons and the ventral respiratory column caudal to the facial motor nucleus. Two weeks after SSP-SAP, the apnoeic threshold measured under anaesthesia was unchanged when fewer than 57% of the Phox2b+TH, neurons were destroyed. However, destruction of 70 ± 3.5% of these cells was associated with a dramatic rise of the apnoeic threshold (from 5.6 to 7.9% end-expiratory P). In anaesthetized rats with unilateral lesions of around 70% of the Phox2b+TH, neurons, acute inhibition of the contralateral intact RTN with muscimol instantly eliminated phrenic nerve discharge (PND) but normal PND could usually be elicited by strong peripheral chemoreceptor stimulation (8/12 rats). Muscimol had no effect in rats with an intact contralateral RTN. In conclusion, the destruction of the Phox2b+TH, neurons is a plausible cause of the respiratory deficits caused by injection of SSP-SAP into RTN. Two weeks after toxin injection, 70% of these cells must be killed to cause a severe attenuation of the central chemoreflex under anaesthesia. The loss of an even greater percentage of these cells would presumably be required to produce significant breathing deficits in the awake state. [source] | ||||||||||||||||