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At least 487 records · Page 27Linked to original sources
PubMed1993

Comparison of interactions of [3H]muscimol, t-butylbicyclophosphoro[35S]thionate, and [3H]flunitrazepam with cloned gamma-aminobutyric acidA receptors of the alpha 1 beta 2 and alpha 1 beta 2 gamma 2 subtypes.

The alpha 1 beta 2 and alpha 1 beta 2 gamma 2 subtypes, common subtypes of gamma-aminobutyric acid (GABA)A receptors in the brain, are known to share many ligands, but only the latter interacts with benzodiazepines. In this study, we attempted to examine whether the presence of the gamma 2 subunit in the cloned receptors alters the binding properties of GABA and t-butylbicyclophosphorothionate (TBPS) (a highly sensitive probe for conformational changes in the chloride ionophore of GABAA receptors) and their interactions. Using a high-level expression system of SF-9 cells infected with baculovirus, we produced a group of cloned GABAA receptors with variations in the ratio (0 to 3) of the virion carrying the cDNA for the gamma 2 subunit to those carrying the cDNAs for the alpha 1 and beta 2 subunits. The number of benzodiazepine binding sites increased as the level of the gamma 2 virion was raised and reached that of GABA high affinity sites at a gamma 2 to alpha 1 beta 2 ratio of 0.5 or more. It appears that the conversion of the alpha 1 beta 2 to the alpha 1 beta 2 gamma 2 subtype is favorable and complete in the presence of a sufficient level of the gamma 2 subunit, assuming the number of the GABA sites to be equal to the total number of the cloned GABAA receptors. In all preparations, the dissociation constants for flunitrazepam, muscimol, and TBPS were fairly constant, and the maximal number of binding sites for TBPS appeared to be equal to that for muscimol, with no dependence on the gamma 2 virion levels. The effect of GABA on TBPS binding, however, were markedly altered by the gamma 2 subunit. With the alpha 1 beta 2 subtype GABA at concentrations occupying its high affinity sites markedly stimulated but at higher concentrations (micromolar ranges) inhibited TBPS binding, whereas with the alpha 1 beta 2 gamma 2 subtype GABA inhibited TBPS binding without the early stimulatory phase. We also confirmed the selective interaction of Zn2+ (50 microM) with the alpha 1 beta 2 subtype, as probed with TBPS binding, and observed a progressive disappearance of Zn2+ sensitivity as the gamma 2 virion level increased.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1976

Regional changes in the rate of turnover of acetylcholine in rat brain following diazepam or muscimol.

Muscimol (8.8 mumol/kg i.v.) and diazepam (7.04 mumol/kg i.p.) decreased the rate of turnover of acetylcholine in midbrain and cortex of rat brain but failed to change acetylcholine turnover in striatum and hippocampus. The similarity in the profile of the action of diazepam and muscimol on acetylcholine turnover in various brain structures adds support to the view that GABA participates in mediating the actions of diazepam. Since the striatum contains an abundance of GABA neurones and intrinsic cholinergic neurones, it is inferred that the metabolism of acetylcholine, and presumably the activity of striatal cholinergic neurones are not regulated by the activation of GABA receptors. Similar considerations apply to the cholinergic pathway projecting from the septum to the hippocampus.

Acetylcholine↗
PubMed1995

Effects of strongly anisosmotic and NaCl deficient solutions on muscimol- and glutamate evoked whole-cell currents in freshly dissociated hippocampal neurons.

Sudden exposure of dissociated hippocampal neurons to strongly hypo- or hyperosmotic solutions suppresses voltage gated Na+, K+ and Ca2+ currents. We investigated whether ligand gated ion currents were similarly shut down by exposure to anisosmotic solutions. The effect of hypo-osmotic, NaCl deficient (mannitol-substituted), or hyper-osmotic test solutions delivered from a flow pipette was tested on voltage gated Ca2+ currents and on currents and conductance changes evoked by brief administration of either the GABAA-agonist muscimol or glutamate. Hyper-osmotic solution caused cells to shrink, but cell membrane capacitance did not change. Muscimol-induced conductance increases were depressed by hypo-osmotic and by NaCl deficient solutions and often by hyper-osmotic solution. Voltage gated Ca2+ currents were depressed by anisosmotic, but not by NaCl deficient isosmotic solution. NMDA- and non-NMDA evoked conductance increases were depressed by hyperosmotic solution; hypo-osmotic and NaCl deficient solutions were not tested on glutamate induced currents. Ligand gated currents are suppressed by anisosmotic solutions more slowly than are voltage gated channels. The changes caused by anisosmotic and NaCl deficient solutions were much greater then expected from calculated electrochemical effects and are probably the result of change in receptor controlled channels.

Animals↗
PubMed1978

Muscimol antagonizes morphine hypermotility without potentiation of analgesia.

Muscimol, a very potent and specific GABA agonist, strongly depressed characteristic morphine-induced locomotor activity. Muscimol induced only a very weak increase in the morphine analgesia measured in the hot plate test which perhaps could be a result of a freezing reaction. No effect on morphine analgesia was observed in the wire grid test. These results indicate that GABA differentially influences morphine stimulation and analgesia.

Analgesia↗
PubMed1983

Benzodiazepines stimulate muscimol receptor binding in an Ro 15-1788 reversible manner.

Diazepam and other benzodiazepines caused a concentration-dependent increase of [3H]muscimol (15 nM) specific binding. The maximal increase was 23.6 +/- 5% at the diazepam concentration of 10 microM. Concentrations of half-maximal stimulation for diazepam and clonazepam were 43 +/- 17 and 12.6 +/- 6 nM respectively. Ro 15-1788 was found to inhibit the stimulation of muscimol specific binding induced by other benzodiazepines. The IC50 for diazepam (1000 nM)-induced stimulation was 280 +/- 60 nM. Intensive treatment of membranes with Triton X-100 decreased the stimulatory effect of benzodiazepines.

Animals↗
PubMed1992

NMDA-receptor-dependent, muscimol-sensitive role of the entorhinal cortex in post-training memory processing.

The bilateral infusion into the entorhinal cortex of the NMDA receptor antagonist, AP5 (5.0µg) or of the GABA(A) agonist, muscimol (0.03µg) 90min after training but not 30min before training, 0min after training or 10min before testing, hindered retention test performance 24h after inhibitory avoidance in rats. Glutamate (5.0µg) or picrotoxin (0.08µg) infused 90min after training had no effect. In animals trained with a low level footshock a second training session, 120min after the first, was needed in order to obtain a good retention test performance. This was taken to reflect summation of the consecutive memory traces left by the two training sessions. In these animals, the infusion of AP5 or muscimol into the entorhinal cortex between the two training sessions impeded their summation. The present results suggest that the entorhinal cortex plays a late role in memory processing, that this role does not need a hyperactivation of the entorhinal cortex, and that it is important for the interaction between consecutive memory traces.

Journal Article↗
PubMed1979

Improvement in tardive dyskinesia after muscimol therapy.

Muscimol, thought to be a agonist of gamma-aminobutyric acid (GABA), was administered to eight neuroleptic-free subjects with tardive dyskinesia. At oral dose levels from 5 to 9 mg, involuntary movements were consistently attenuated, usually in the absence of sedation. These results support the view that pharmacologic attempts to stimulate GABA-mediated synaptic transmission may afford symptomatic relief to patients with tardive dyskinesia.

Adult↗
PubMed1992

Muscimol and N,N-dimethylmuscimol: from a GABA agonist to a glycine antagonist.

By using molecular modeling methods, a molecular mechanism was identified which can explain how the incorporation of two methyl groups in place of two hydrogen atoms on the terminal nitrogen atom of muscimol can not only convert this potent agonist at GABAnergic receptors to an inactive molecule at these receptors, but also can convert this new derivative to an antagonist of glycine at glycinergic receptors. This insight into the molecular mechanism operative in the conversion of physiological function provides a basis for understanding how a single molecule may be able to act at both the GABA- and glycine-inhibitory receptors.

Chemical Phenomena↗
PubMed1995

Muscimol induces retrograde amnesia for changes in reward magnitude.

These experiments examined the effect of the GABAA agonist, muscimol (MUS), on memory for changes in reward magnitude. In Experiment 1 rats were trained to run a straight alley for either a large or small food reward. After reaching asymptotic performance rats in the high reward group were shifted to the small food reward. Half the animals received 1.0 or 3.0 mg/kg (ip) of MUS or the equivalent volume of saline immediately after training. Shifted training continued for 3 more days and no further injections were given. Shifted saline animals displayed an increase in response latencies compared to unshifted controls with a sharp peak on the day after the shift. Shifted MUS receiving 1.0 mg/kg performed comparably to shifted saline animals. In contrast, Shifted MUS animals receiving 3.0 mg/kg displayed performance comparable to shifted saline animals on the day of the shift but displayed a sharp increase in response latencies on the second day after the shift. These findings indicate that post-training systemic MUS injections delay the peak increase in response latencies and suggest that MUS induces retrograde amnesia for reward reduction. Experiment 2 examined the effect of MUS on the memory of a reward increase. Rats were first trained as in Experiment 1 and rats under the high reward condition were then shifted to the small reward. On the next training session, the large food reward was reinstated.(ABSTRACT TRUNCATED AT 250 WORDS)

Amnesia, Retrograde↗
PubMed1982

Antagonism of gamma-aminobutyric acid and muscimol by picrotoxin, bicuculline, strychnine, bemegride, leptazol, D-tubocurarine and theophylline in the isolated olfactory cortex.

gamma-Aminobutyric acid (GABA) applied to neurones in the olfactory cortex slice in vitro, increases input conductance and produces a small depolarization, which mimics the action of the inhibitory transmitter. In previous experiments it was shown that this inhibition could be blocked by picrotoxin, bicuculline, strychnine, leptazol, bemegride, theophylline and d-tubocurarine. In the present study the effects of the above blockers on the action of bath-applied GABA were assessed. These blockers all antagonised the action of GABA at concentrations similar to those required to block synaptic inhibition. However, the amount of antagonism of GABA action was variable and this variability was attributed to the cellular uptake of GABA. The variability was circumvented by using muscimol, a GABA agonist not subjected to uptake. This GABA antagonism explains the convulsant action of many of the agents studied and reinforces the idea that GABA mediated inhibitory transmission in the olfactory cortex.

Animals↗
PubMed1998

Role of the retrorubral nucleus in striatally elicited orofacial dyskinesia in cats: effects of muscimol and bicuculline.

Orofacial dyskinesia (OFD) is a disorder characterized by involuntary movements of the oral and facial muscles. OFD attacks can be elicited acutely in cats by local injections of dopaminergic agents into the anterodorsal part (r-CRM) of the caudate nucleus. Because the dopaminergic A8 cell group, being embedded in the retrorubral nucleus (RRN), gives rise to fibres which terminate in the r-CRM, two questions arose: (1) whether the A8 cell group forms part of the circuitry that directs and/or modulates OFD, and (2) whether GABA-ergic compounds in the RRN play a role in OFD, and if so, whether a pharmacological GABA-ergic intervention of the activity in the RRN modulates or mediates OFD. For this purpose, the activity of the RRN was manipulated with local injections of the GABA(A) agonist muscimol and antagonist bicuculline. These local injections into the RRN were subsequently combined with manipulations of dopamine transmission in the r-CRM with local injections of the selective DAi receptor agonist (3,4-dihydroxyphenylimino)-2-imidazoline. The present study shows that local injections of GABA-ergic compounds into the RRN do not elicit OFD attacks in cats, but can modulate oral behaviour elicited from the r-CRM. The latter effect is dose dependent and GABA-ergic specific.

Animals↗
PubMed1998

Deficits in vertical and torsional eye movements after uni- and bilateral muscimol inactivation of the interstitial nucleus of Cajal of the alert monkey.

The mesencephalic interstitial nucleus of Cajal (iC) is considered the neural integrator for vertical and torsional eye movements and has also been proposed to be involved in saccade generation. The aim of this study was to elucidate the function of iC in neural integration of different types of eye movements and to distinguish eye movement deficits due to iC impairment from that of the immediately adjacent rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). We addressed the following questions: (1) According to the neural integrator hypothesis, all eye movements including the saccadic system and the vestibulo-ocular reflex (VOR) share a common neural integrator. Do iC lesions impair gaze-holding function for vertical and torsional eye positions and the torsional and vertical VOR gain to a similar degree? (2) What are the dynamic properties of vertical and torsional eye movements deficits after iC lesions, e.g., the specificity of torsional and vertical nystagmus? (3) Is iC involved in saccade generation? We performed 13 uni- and three bilateral iC inactivations by muscimol microinjections in four alert monkeys. Three-dimensional eye movements were studied under head-stationary conditions during vertical and torsional VOR. Under static conditions, unilateral iC injections evoked a shift of Listing's plane to the contralesional side (up to 20 degrees), which increased (ipsilesional ear down) or decreased (ipsilesional ear up) by additional static vestibular stimulation in the roll plane, i.e., ocular counterroll was preserved. The monkeys showed a spontaneous torsional nystagmus with a profound downbeat component. The fast phases of torsional nystagmus always beat toward the lesion side (ipsilesional). Pronounced gaze-holding deficit for torsional and vertical eye positions (neural integrator failure) was reflected by the reduction of time constants of the exponential decay of the slow phase to 330-370 ms. Whereas the vertical oculomotor range was profoundly decreased (up to 50%) and vertical saccades were reduced in amplitude, saccade velocity remained normal and horizontal eye movements were not affected. Bilateral iC injections reduced the shift of Listing's plane caused by unilateral injections, i.e., back toward the plane of zero torsion. Torsional nystagmus reversed its direction and ceased, whereas vertical nystagmus persisted. In contrast to unilateral injection, there was additional upbeating nystagmus. Time constants of the position integrator of the gaze-holding system did not differ between unilateral and bilateral injections. The range of stable vertical eye positions and saccade amplitude was smaller when compared with unilateral injections, but the main sequence remained normal. Dynamic vestibular stimulation after unilateral iC injections had virtually no effect on torsional and vertical VOR gain and phase at the same time when time constants already indicated severe integrator failure. Torsional VOR elicited a constant slow-phase velocity offset up to 30 degrees toward the contralesional side, i.e., in the opposite direction to spontaneous torsional nystagmus. Likewise, vertical VOR showed a velocity offset in an upward direction, i.e., opposite to the spontaneous downbeat nystagmus. Contralesional torsional and upward vertical quick phases were missing or severely reduced in amplitude but showed normal velocity. In contrast, bilateral iC injections reduced the gain of the torsional and vertical VOR by 50% and caused a phase lead of 10-20 degrees (eye compared with head velocity). We propose that the slow-phase velocity offset during torsional and vertical VOR reflects a vestibular imbalance. It therefore appears likely that the vertical and torsional nystagmus after iC lesions is not only caused by a neural integrator failure but also by a vestibular imbalance. Unilateral iC injections have clearly differential effects on the VOR and the gaze-holding function. (ABSTRACT TRUNCATED)

Animals↗
PubMed1988

Melatonin enhancement of [3H]-gamma-aminobutyric acid and [3H]muscimol binding in rat brain.

The pineal hormone, melatonin, enhanced the sodium-independent binding of [3H]-gamma-aminobutyric acid ([3H]GABA) and [3H]muscimol in the rat cerebral cortex in vitro. This effect was augmented by preincubation of synaptic membranes with melatonin but was abolished by preincubation with Triton X-100. Saturation binding studies using [3H]GABA (2.5 to 1000 nM) indicated that the melatonin-induced enhancement of binding is due to an increase in low-affinity GABAA binding sites. These findings suggest that the central effects of melatonin involve modulation of GABAergic function.

Animals↗
PubMed1984

Intranigral muscimol suppresses ethanol withdrawal seizures.

Intranigral administration of muscimol produced a dose-related suppression of audiogenic motor convulsions which accompanied withdrawal from chronic ethanol administration. Similar administration of saline did not alter withdrawal seizures. These results are interpreted as supporting the hypothesis that GABA-receptive neurons in the vicinity of the substantia nigra are important in the mediation of seizures induced by ethanol withdrawal.

Acoustic Stimulation↗
PubMed1985

Deficits in manipulative behaviors induced by local injections of muscimol in the first somatosensory cortex of the conscious monkey.

Injection of muscimol (GABA agonist) in the finger region of area 2 of the alert monkey led to the striking yet reversible loss of finger coordination, thus disabling the monkey from picking up a small piece of food from a small hole or a funnel. Symptoms varied depending on sites of injection within the finger region. Neither weakness of hand or finger movements nor deficit in hand reach was observed.

Animals↗