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PubMed1985

Colocalization of [3H]muscimol and antisera to GABA and glutamic acid decarboxylase within the same neurons in monkey retina.

Two procedures have been used to test for the colocalization of different neuroanatomical gamma-aminobutyric acid (GABA)ergic markers within the same neurons in primate retina. First, sequential immunocytochemical processing of sections was done using antisera to glutamic acid decarboxylase and to GABA, and these antisera were visualized by peroxidase-antiperoxidase and fluorescein isothiocyanate techniques respectively. Colocalization of both antisera was found within the same neuron cell bodies. In the second experiment, immunocytochemical staining using GABA antiserum was performed on retinal tissue that had been previously incubated in vitro for neuronal uptake of [3H]muscimol. Both markers colocalized in 70% of the labeled cell body population.

Animals↗
PubMed1989

Anticonvulsant effect of muscimol injected into the thalamus of spontaneously epileptic Mongolian gerbils.

Injections of muscimol (12.5 or 25 ng bilaterally), a GABAA agonist, into the posterior nuclei of the thalamus suppressed generalized convulsive seizures in the spontaneously epileptic Mongolian gerbil. This anticonvulsant effect was dose-dependent and was reversed by picrotoxin (10 ng bilaterally), a GABAA antagonist. Bilateral intrathalamic injections of 1-baclofen (50 ng), an agonist of the GABAB receptor, were ineffective in suppressing seizures in this model. These results suggest that GABAergic transmission within the thalamus is involved in the control or the genesis of some generalized convulsive seizures.

Animals↗
PubMed1994

Injection of bicuculline elicits firing of luteinizing hormone releasing hormone pulse generator in muscimol-treated ovariectomized rats.

We have already demonstrated that, although exogenous gamma-aminobutyric acidA (GABAA) receptor agonist is capable of inhibiting the activity of luteinizing hormone releasing hormone (LHRH) pulse generator, the reduction in the endogenous GABAA receptor activity does not have a significant effect in ovariectomized rats, suggesting a minor role of inhibitory GABA neurons in the control of pulsatile release of LHRH. In this study, we further analyzed the role of the GABAA receptor system in the regulation of LHRH pulse generator activity observed by recording the multiunit activity (MUA) in the hypothalamus of ovariectomized rats. An abrupt increase (volley) in the MUA in the arcuate nucleus (ARC)-median eminence region (ME) was accompanied by the initiation of a luteinizing hormone (LH) pulse, determined by measuring LH concentrations in blood sampled simultaneously. The injection of 1-3 mg/kg muscimol (MUS), a GABAA receptor agonist, decreased the basal MUA and delayed the occurrence of the next MUA volley, but it did not change the LH pulse amplitude. I.v. injection of 5 mg/kg bicuculline (BIC), a GABAA receptor antagonist, during continuous infusion of MUS (5 mg/kg/h) which decreased the basal MUA and prevented the MUA volley from occurring, evoked MUA volleys and LH pulses whose amplitudes were similar to those found before the MUS infusion. Injection of the same dose of BIC during the infusion of saline increased the MUA transiently, but this increase was not accompanied by an LH pulse and afterwards there occurred MUA volleys at ordinary intervals accompanied by LH pulses with unchanged pulse amplitudes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Fos-like immunoreactivity in the mamillary body and thalamus following injections of muscimol into the ventral tegmental nucleus of Gudden in the rat.

In many neurons, increased rates of firing are accompanied by expression of the proto-oncoprotein Fos. The current study examined Fos-like immunoreactivity in the mamillary body and the anterior thalamus following unilateral injections of the inhibitory GABA-A agonist muscimol into the ventral tegmental nucleus of Gudden (VTN). These injections resulted in a marked increase in Fos-like immunoreactivity ipsilaterally in both the medial mamillary nucleus and in its principle thalamic projection targets, the anteroventral and anteromedial thalamic nuclei. Since the projection from the VTN to the mamillary body has been shown to contain a substantial GABAergic component, these results are likely to reflect a disinhibition of mamillothalamic circuitry resulting from suppression of tonic inhibitory inputs arising in the VTN.

Animals↗
PubMed1984

Effects of intrathecally administered THIP, baclofen and muscimol on nociceptive threshold.

This study examined whether the antinociceptive activity of THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol), a GABA agonist, is mediated through an action exerted at the level of the spinal cord. Intrathecal injection of doses of THIP devoid of motor effects (1-2 micrograms) did not increase tail flick or hot plate latencies in the rat. Although hot plate latency was transiently increased by intrathecal injection of 5 micrograms THIP, slight motor impairment was observed at this dose. Higher doses of THIP (15-50 micrograms) produced flaccidity of the hindlimbs. Intrathecal injection of low doses of muscimol (0.25 microgram) that did not produce motor impairment increased tail flick, but not hot plate, latencies. Baclofen produced motor incoordination following intrathecal injection of 10 micrograms; however, intrathecal injection of 1 microgram significantly increased both tail flick and hot plate latencies without attendant motor effects. Thus, baclofen was the only compound in which the antinociceptive effect was clearly distinguished from the motor effect. These results additionally indicate that the spinal cord does not mediate the antinociceptive activity of THIP.

Animals↗
PubMed1984

Investigation of the effects of muscimol on different components of [3H]propyl beta-carboline-3-carboxylate binding to rat hippocampal and cerebellar membranes.

The binding of [3H]propyl beta-carboline-3-carboxylate [( 3H]PCC) to rat hippocampal and cerebellar membranes was investigated together with the displacement by PCC of [3H]flunitrazepam [( 3H]FNM). Results were consistent with the presence of a single recognition site in cerebellum and two sites in hippocampys, but the affinity of neither of the hippocampal sites correlated with that in the cerebellum. Muscimol did not alter the affinity or capacity of any of these sites under the conditions used, indicating that PCC does not show the benzodiazepine-like property of GABAergic modulation, at any of the subpopulations of its binding sites.

Animals↗
PubMed1986

Diazepam and muscimol blockade of the gastrointestinal motor disturbances induced by acoustic stress in dogs.

The influence of various drugs on the gastric motor inhibition induced by acoustic stress (AS) was investigated in fasted dogs fitted with strain-gauge transducers implanted on the antrum and proximal jejunum at 10 and 80 cm from the pylorus respectively. Started 40-50 min after the last gastric migrating motor complex (MMC), a 1 h acoustic stress delayed by 75% the occurrence of the next gastric but not jejunal MMC and was associated with a 4-fold increase in plasma cortisol. This AS-induced inhibition of the gastric MMC cycle was abolished after previous administration of diazepam (0.2 and 0.5 mg/kg i.m.) or muscimol (10 micrograms/kg i.v.) and partially reduced by a lower dose of diazepam (0.1 mg/kg i.m.); in contrast, it was still present after either naloxone (0.1 mg/kg i.m.), phentolamine (0.2 mg/kg i.v.) or propranolol (0.1 mg/kg i.v.) treatment. This selective benzodiazepine or GABA agonist blockade of noise-induced gastric motor alteration supports the hypothesis that release of CRF may be responsible for the gastrointestinal motor effects induced by acoustic stress.

Animals↗
PubMed1986

Anticonvulsant action of 2-amino-7-phosphonoheptanoic acid and muscimol in the deep prepiriform cortex.

Microinjection of 2-amino-phosphonoheptanoic acid (2APH, 1 nmol), and antagonist for n-methyl-d-aspartate-sensitive receptors, into the deep prepiriform cortex (DPC) of the rat, prevented seizures induced by the intravenous administration of bicuculline. The GABA agonist, muscimol (39 pmol), injected into DPC produced a similar anticonvulsant effect. The DPC may therefore represent an important site of action for the anticonvulsant effects of GABA agonists and excitatory amino acid antagonists. Moreover, our data support the hypothesis that seizures induced by a deficiency in GABA transmission result, at least in part, from a relative overactivity of excitatory amino acid transmission in the DPC.

2-Amino-5-phosphonovalerate↗
PubMed1990

Autoradiographic localization of [3H]muscimol binding sites in rat stomach: evidence for mucosal GABAA receptors.

The distribution in the rat stomach of specific [3H]muscimol binding sites, which show characteristics of GABAA receptors, was examined by light microscopic autoradiography. Silver grains representing specific binding were present both in the antrum and body, with highest densities in the muscle layers. A small fraction of the binding was confined to gland cells of the mucosa in the gastric body, rather than in the antrum. The label was not specifically concentrated at the myenteric ganglia. These findings, along with earlier data, suggests that the local GABA content may regulate not only the contractility, but also the secretory functions of the stomach via gastric GABAA receptors.

Animals↗
PubMed1986

Antistereotype effects of ceruletide and some neuroleptics differentiated by interactions with clonazepam, muscimol, scopolamine and clonidine.

Compulsive gnawing was produced in mice by administration of either methylphenidate or (after sensitizing pretreatment with the neuroleptic, tetflutixol) apomorphine. Drugs which antagonise stereotypy, such as ceruletide (CER, a sulphated decapeptide related to cholecystokinin octapeptide), haloperidol, zuclopenthixol and fluphenazine were applied in equipotent doses (reducing stereotypy by 80%). Clonazepam, muscimol, clonidine and scopolamine (but not methylscopolamine) antagonized to a different extent the antistereotype effect of ceruletide and the neuroleptics. The ED50s for clonazepam and other drugs, were determined; clonazepam had the greatest potency. Regarding the antagonism of the antistereotype effect, ceruletide was similar to but by no means congruent with haloperidol. The antagonism of the antistereotype effect was specific because other effects of ceruletide and cholecystokinin octapeptide (inhibition of exploratory rearing activity, ptosis, antinociception, hypothermia) were not antagonized by clonazepam and only weakly modified by scopolamine. Methylscopolamine was ineffective throughout, indicating a central site for the mechanism of the actions studied of scopolamine. In conclusion, the antistereotype effect of ceruletide is different from that of conventional neuroleptic drugs and functionally independent of other behavioural effects of the cholecystokinin-like peptides.

Animals↗
PubMed1984

Zinc deficiency and anorexia in rats: the effect of central administration of norepinephrine, muscimol and bromerogocryptine.

Anorexia is a major manifestation of zinc deficiency, but the mechanism(s) for this anorexia are not well defined. In this study we investigated the effects of three modulators of feeding response on the food consumption of zinc deficient rats. Zinc deficient rats showed partial resistance to norepinephrine, eating significantly less at the 20 micrograms dose than the zinc sufficient ad lib controls, and food ingestion could not be induced at the 10 micrograms dose. Similarly, higher doses of the GABA agonist, muscimol, were required to induce feeding in the zinc deficient animals compared to the zinc sufficient controls. The dopamine agonist, bromergocryptine, failed to induce feeding in the zinc deficient animals. These findings are compatible with the concept that zinc deficiency produces a generalized decrease in receptor responsibility, possibly secondary to alterations in membrane fluidity.

Animals↗
PubMed1982

Chlordiazepoxide-induced ataxia, muscle relaxation and sedation in the rat: effects of muscimol, picrotoxin and naloxone.

Chlordiazepoxide-induced ataxia was potentiated by muscimol (0.5 mg/kg) and antagonised by picrotoxin (2 and 4 mg/kg) and by naloxone (2 and 4 mg/kg). The muscle-relaxant effects of chlordiazepoxide were not significantly altered by any of these three drugs and nor was the chlordiazepoxide-induced decrease in exploratory head-dipping. However, the sedative effects of chlordiazepoxide, measured by a reduction in spontaneous motor activity, were antagonised by picrotoxin.

Animals↗
PubMed1989

Diazepam sensitizes mice to FG 7142 and reduces muscimol-stimulated 36Cl- flux.

Chronic treatment with benzodiazepine receptor agonists increases sensitivity to the convulsant action of FG 7142, an inverse agonist. We investigated whether or not changes in the number and function of GABA-gated chloride channels accompanies this increased sensitivity. Diazepam, 5 mg.kg-1, was administered to mice daily for five days, and mice were then tested with a single injection of FG 7142, 40 mg.kg-1, at several intervals thereafter. At 24 hours after the last diazepam dose, 10 of 15 mice had clonic seizures following FG 7142 and four of the remaining five had myoclonic jerks. At 48 hours, only one of six mice developed a clonic seizure, and none were observed in mice tested at 96 or 144 hours. Muscimol-stimulated chloride flux was reduced in cortical synaptosomes from diazepam-treated mice at 24 hours but not at 48 or 96 hours. However, the binding of [35S]TBPS, a ligand closely associated with the chloride channel, was unchanged at 24 hours. These results suggest that a transient diminution in GABA-gated chloride channel function; unaccompanied by a reduction in channel number, may underlie the sensitization to the convulsant action of FG 7142 observed after withdrawal from chronic diazepam treatment.

Animals↗
PubMed1994

Perispinal progestins enhance the antinociceptive effects of muscimol in the rat.

The intrathecal (IT) injection of progesterone (PROG) or three of its ring A-reduced metabolites (5 beta,3 alpha-pregnanolone, 5 alpha,3 alpha-pregnanolone, or 5 beta,3 beta-pregnanolone) did not significantly alter any of two pain thresholds (vocalization threshold to tail shock, VTTS, or tail flick latency, TFL) in ovariectomized rats when tested in a wide range of doses (2.5-250 micrograms). When combined with a subanalgesic dose of muscimol (MUSC; 1 microgram IT), PROG and its two 3 alpha-hydroxy derivatives, but not the 3 beta, caused significant analgesia in the VTTS but not in the TFL test. No clear dose-response relationships were noted in the analgesic response to the combination of the progestins and MUSC. The present results indicate that PROG, either directly or through its ring A-reduction, can modulate nociceptive information by enhancing the action of GABA agonists on GABAA receptors.

Analgesics↗
PubMed1984

Nigral muscimol infusions facilitate the development of seizures in immature rats.

Since recent data utilizing GABAergic stimulation of the substantia nigra (SN) suggest that the SN is a crucial site in a circuitry involved in the modification of seizures in adult rats, the role of the SN was investigated in seizures of rat pups. Bilateral nigral infusions of the GABA agonist muscimol partially protected adult rats against flurothyl-induced seizures, while similar infusions actually facilitated the development of flurothyl seizures in 15-day-old rat pups. These results suggest that age-related differences in the nigral GABA sensitive system may account for the increased susceptibility to generalized seizures of the developing brain.

Age Factors↗
PubMed1993

Responses of floccular Purkinje cells to sinusoidal vertical rotation and effects of muscimol infusion into the flocculus in alert cats.

To understand how the flocculus is involved in the integration process in the vertical VOR, we examined the responses of floccular Purkinje cells during whole-body rotation in many vertical and horizontal planes in alert cats. The great majority of cells that responded to pitch rotation received excitation from the contralateral posterior canal, whereas the minority received excitation from the anterior canal, either on the ipsilateral or contralateral side; 35% of these vertical canal responding cells received convergent inputs, either from the ipsilateral or contralateral horizontal canal. After infusion of a GABA agonist (muscimol) into the area where many posterior canal responding Purkinje cells were recorded, the downward VOR induced by nose-up pitch was selectively impaired at low stimulus frequencies, together with an impairment of gaze holding after downward saccades. These results indicate a crucial role for posterior canal responding floccular Purkinje cells in generating downward eye position signals. Since the flocculus inhibits VOR interneurons related to the anterior and horizontal canals but not the posterior canal (Ito, 1984), our results suggest the possibility that posterior canal responding floccular Purkinje cells may form a transfloccular inhibitory pathway to anterior canal related VOR interneurons. This pathway may facilitate the positive feedback effect in the vestibular commissural inhibitory pathway between the co-planar vertical canals for the posterior canal signal, and may thereby be specifically involved in integration in the vertical VOR.

Animals↗
PubMed1979

High-affinity binding of [3H]muscimol to subcellular particles of a neurone-enriched culture of embryonic rat brain.

High-affinity, Na+-independent binding of [3H]muscimol (KB approximately equal to 1.6 x 10(-8) M; Bmax approximately equal to 0.14 nmol/g pellet) occurred to a frozen-thawed particulate fraction of 74-h-old neurone-enriched cultures prepared from the cerebra of 12-13-day-old rat embryos. This finding provides evidence that GABA-receptors exist on cultured neurones which contain only a few synaptic connections.

Animals↗