Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Muscimol”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources
PubMed1984

Enhanced GABA function in the angular complex (lateral periaqueductal grey matter and adjacent reticular formation) alters the postural component of striatal- or nigral-derived circling.

Unilateral injection of muscimol into the angular complex (lateral periaqueductal grey matter and adjacent reticular formation) caused ipsiversive rotation. Focal injection of picrotoxin into the same site produced contraversive rotation. Administration of apomorphine to animals with a unilateral 6-OHDA lesion of the left medial forebrain bundle caused contraversive rotation. Focal injection of muscimol into the angular complex reversed the direction of rotation such that apomorphine administration now produced ipsiversive circling. Unilateral injection of muscimol into substantia nigra zona reticulata caused contraversive rotation. Focal injection of picrotoxin into the same site produced ipsiversive rotation. The prior injection of muscimol into the ipsilateral angular complex prevented the contraversive rotation induced by intranigral administration of muscimol such that animals now showed ipsiversive circling. In both 6-OHDA-lesioned animals and animals receiving intranigral muscimol, focal injection of muscimol into the angular complex caused a reversal in the direction of circling through loss of the postural component with no obvious change in locomotor activity. Bilateral electrolytic lesions of the angular complex overall had no effect on amphetamine-induced locomotion. Manipulation of GABA function in the angular complex alters circling behaviour initiated from the striatum or substantia nigra by altering the postural component without affecting the locomotor response of the animals. The data suggest a critical role for the angular complex as an outflow station from basal ganglia.

Animals↗
PubMed2000

Ethanol modulation of gamma-aminobutyric acid (GABA)-mediated inhibition of cerebellar Purkinje neurons: relationship to GABAb receptor input.

BACKGROUND: Electrophysiological recording reveals that only a portion of cerebellar Purkinje neurons are sensitive to ethanol enhancement of gamma-aminobutyric acid (GABA) responses. Although activation of beta-adrenergic receptors permits ethanol enhancement of GABA function from some cerebellar Purkinje neurons, other neurons remain insensitive to ethanol. These findings are consistent with the finding that other external neural inputs are required to allow ethanol enhancement of GABA responses from Purkinje neurons. Because of a high expression of GABA(B) receptors on Purkinje cells, we tested whether activation of GABA(B) receptors might modulate the action of ethanol on GABA responsiveness. METHODS: Extracellular single-unit electrophysiological recording was used to investigate the effects of ethanol on responses to GABA and muscimol (a GABA(A) agonist) from cerebellar Purkinje neurons. Drugs tested were baclophen (a GABA(B) agonist) and CGP35348 (a GABA(B) antagonist). RESULTS: Ethanol did not enhance responses to GABA and muscimol from all Purkinje neurons. Systemic administration of the GABA(B) agonist, baclophen (3 mg/kg intravenously), permitted ethanol to enhance GABA inhibition from approximately 75% of cerebellar Purkinje neurons not initially enhanced by ethanol. Local iontophoretic application of baclophen to Purkinje neurons also allowed ethanol to enhance GABA and muscimol responsiveness from a portion of neurons in which ethanol initially did not affect their actions. An inhibitory action of ethanol on responses to GABA and muscimol, which was also influenced by baclophen, was observed from some Purkinje neurons. From Purkinje neurons initially sensitive to ethanol enhancement of GABA and muscimol function, administration of CGP35348, a GABA(B) antagonist, diminished the effect of ethanol on the responsiveness of these agonists from the majority (9/15) of neurons. CONCLUSIONS: The present findings demonstrated that baclophen allows ethanol enhancement of GABA and muscimol responsiveness from some, but not all, cerebellar Purkinje neurons initially not sensitive to ethanol. Likewise, a GABA(B) antagonist can diminish ethanol enhancement of GABA and muscimol responses from some ethanol-sensitive neurons. Thus, these results emphasize that GABA(B) receptors on a portion of Purkinje neurons act as an auxiliary neural input that allows ethanol enhancement of GABA responses. Consequently, receptor structure alone does not account for the action of ethanol on GABA(A) receptor function on this cell type.

Animals↗
PubMed1983

Involvement of preoptic-anterior hypothalamic GABA neurons in the regulation of pituitary LH and prolactin release.

The effects of intraventricular injections of the highly specific gamma-amino-butyric acid (GABA) agonist muscimol (5 nmol/animal) on blood LH and prolactin levels were measured in ovariectomized (ovx) and in ovx estrogen-progesterone (OEP) primed rats. While the drug stimulated pituitary prolactin release in both experimental groups, pituitary LH release was significantly inhibited in the ovx animals. Muscimol was without any effect on LH levels in ovx-OEP primed rats. Bilateral implantation of tubes containing a muscimol-mannitol mixture into the medial preoptic/anterior hypothalamic (MPO/AH) area abolished pulsatile LH release whereas blood prolactin values were elevated. The intraventricular injection of GABA (8 mumol) also reduced LH and increased prolactin levels in the blood. Measurements of catecholamine turnover rates in the MPO/AH and in the mediobasal hypothalamus (MBH) yielded reduced preoptic but unchanged hypothalamic norepinephrine (NE) and stimulated hypothalamic dopamine (DA) turnover. In view of the well known stimulatory involvement of the NE system in the mechanism of pulsatile LH release and the inhibitory effect of GABA and its agonist muscimol on pulsatile LH release, it is suggested that GABA inhibits NE release in the MPO/AH by the mechanism of presynaptic inhibition. The observation that muscimol is unable to suppress LH release in vox OEP-primed rats may indicate that those estrogen receptive neurons in the MPO/AH which mediate the negative feedback action of the steroid may use GABA as neurotransmitter and that they are the neurons which inhibit NE release. The inhibitory effect of locally implanted muscimol into the MPO/AH also supports this hypothesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

The effects of compounds related to gamma-aminobutyrate and benzodiazepine receptors on behavioural responses to anxiogenic stimuli in the rat: choice behaviour in the T-maze.

Two methods were used to test rats' responses to novelty in the T-maze: (1) a test of spontaneous alternation allowing separate measurement of place and body turn alternation; and (2) a test of entry into an arm of changed brightness ("response to stimulus change"). Chlordiazepoxide reduced spontaneous alternation by specifically weakening body turn alternation and eliminated the response to stimulus change. These findings are similar to those previously reported for the barbiturate sodium amylobarbitone. The same pattern of change in the two tests was seen after a low dose of the GABAA agonist muscimol (0.00125 mg/kg); when the dose of muscimol was raised (0.01 and 0.25 mg/kg), place alternation was also reduced. Picrotoxin but not bicuculline (both GABAA blockers) reversed the effects of muscimol and partially those of chlordiazepoxide on the response to stimulus change; in the spontaneous alternation test picrotoxin only marginally affected the response to 0.25 mg/kg muscimol and actually enhanced the effect of 0.000125 mg/kg. The GABAB agonist baclofen (1 mg/kg) acted in the test of response to stimulus change like chlordiazepoxide and muscimol; however, when baclofen was combined with muscimol, the two drugs tended to show mutual blocking. These results are generally consistent with the hypothesis that GABAergic mechanisms play a role in anxiolytic behavioural activity, but many details are difficult to explain.

Animals↗
PubMed1981

GABA-ergic mechanisms in central respiratory control in the anesthetized rat.

Rats lightly anesthetized with halothane were injected intracerebroventricularly (i.c.v.) with gamma aminobutyric acid (GABA) and the GABA-like drugs muscimol, baclofen, and gamma-hydroxybutyric acid (GHBA). Respiratory frequency (f) was reduced after GABA (1 mg) but increased after baclofen (0.5 microgram), while muscimol (0.5 microgram) or GHBA (1 mg) did no affect f. However, GHBA administered repeatedly caused a dose-dependent increase in f. Tidal volume (VT) decreased in a dose-dependent fashion after i.c.v. administration of all the drugs used. Taken together, these changes in f and VT resulted mainly in a dose dependent decrease in minute volume (VE) after GABA and muscimol while after baclofen and GHBA VE was increased due to the marked stimulation of f after repeated administration. Mean arterial pressure (MAP) decreased after GABA and muscimol while no effect or a slight increase was seen after baclofen and GHBA. Heart rate (HR) was unaltered after muscimol, decreased after gaba but slightly increased after GHBA and baclofen. No alterations were seen in blood gases except after administration of GABA which induced a slight hypoxia, hypercapnia and acidosis. The data indicate that an activation of GABA-ergic mechanisms results in a respiratory depression. Moreover, the effects of GABA and muscimol are probably due to a direct GABA-ergic receptor activation while the effects elicited by baclofen and GHBA are due to other mechanisms than direct GABA receptor activation or indirect effects via other system on respiratory regulating centers.

Animals↗
PubMed1996

Thiopentone induced enhancement of somatic motor responses to noxious stimulation: influence of GABAA receptor modulation.

PURPOSE: This study was conducted to determine whether hyperalgesic effects of subanaesthetic concentrations of thiopentone could be attributed to GABAA receptor effects. METHODS: All studies were performed on 50 rats in a prospective, randomized, blinded fashion using saline-injected animals as controls. Using a modified Randall-Selitto technique, the motor behavior stimulated by noxious stimulation was quantified by determining the lowest tail pressure required to provoke a withdrawal response (somatic motor response threshold, SMRT). In the first protocol (21 rats), we studied the effects of 0.5, 1.5 and 5 mg.kg-1 i.v. of the GABAA agonist, muscimol, on SMRT. In the second protocol (20 rats), the effects of administration of saline, muscimol 0.5 mg.kg-1, or the competitive GABAA antagonist, bicuculline 0.25 mg.kg-1, upon the SMRT-reducing effects of a standardized thiopentone infusion were observed. RESULTS: No dose of muscimol produced hyperalgesia. The highest dose of muscimol used (5 mg.kg-1) produced pronounced analgesic effects, raising the SMRT above 750 g. No change in SMRT was detected with the smaller doses of muscimol. Given in combination with muscimol (0.5 mg.kg-1), thiopentone produced analgesia, as shown by an increase in SMRT (P = 0.009). In the bicuculline treated animals, SMRT decreased linearly with increasing plasma thiopentone concentrations (P < 0.001). The slope of the relationship in the bicuculine group was not significantly different from that observed in the saline-treated group, indicating that bicuculline did not block the hyperalgesic effects of thiopentone. CONCLUSION: The results of these studies suggest that hyperalgesia associated with thiopentone is not mediated primarily by GABAA receptors.

Animals↗
PubMed1981

The role of GABA in the regulation of the dopamine/tyrosine hydroxylase-containing neurons of the rat retina.

Dopamine (DA) and gamma-aminobutyric acid (GABA) are putative neurotransmitters in two separate populations of amacrine neurons in the mammalian retina. Pharmacological studies have been conducted to determine if GABA neurons regulate the neuronal activity of the neurons that secrete DA. Tyrosine hydroxylase (TH) activity, a biochemical indicator of changes in activity of DA/TH-containing neurons, was low in dark-adapted retinas and high in light-exposed retinas. Muscimol (a GABA receptor agonist) produced a dose-related, biphasic effect on the light-evoked activation of TH, when the drug was injected into the vitreous (intravitreal injection) of dark-adapted rats. At low doses, (35 and 60 pmol) muscimol enhanced the light-evoked activation of TH, but at higher doses (greater than or equal to 120 pmol) it inhibited the light-evoked increase in enzyme activity. Muscimol had no significant effect on the TH activity of dark-adapted retinas. GABA antagonists, bicuculline and picrotoxin, produced effects on TH activity that were dependent on both dose and light-exposure. At low doses (0.4-0.5 nmol), bicuculline and picrotoxin both inhibited the light-evoked activation of TH, but had no effect on TH activity of the dark-adapted retinas. At a higher dose (2.0 nmol), both antagonists increased TH activity in the dark-adapted retina and attenuated the further activation of the enzyme by light. Rat retinas were dissociated into suspensions of viable cells in order to investigate the direct effects of muscimol and picrotoxin on the DA/TH-containing cells. The process of dissociating dark-adapted retinas resulted in an apparent activation of TH. Incubation of the cells with muscimol resulted in a decrease of TH activity in a concentration-dependent manner. Picrotoxin antagonized the inhibitory effect of muscimol, but had no effect when incubated alone. The biphasic effects of GABA agonists and antagonists in vivo suggest that a certain subpopulation of GABA neurons are involved in the activation of the DA/TH-containing neurons by photic stimulation, while another subpopulation of GABA neurons produce a tonic inhibition of the DA/TH-containing neurons in darkness. The experiments with retinal cell suspensions indicate that the tonic inhibition is probably mediated by synapses of GABA neurons directly onto the DA/TH-containing cells.

Animals↗
PubMed1985

Glucocorticoids are modulators of GABAA receptors in brain.

Modulation of binding of [3H]muscimol, a GABAA receptor agonist, by natural and synthetic glucocorticoids was investigated in crude synaptosomal membranes and in brain sections of rat. In adrenalectomized (Adx) rats, muscimol binding was reduced by 30-50% in cerebral cortex, cerebellum, thalamus and hippocampus, as compared to sham-operated controls. This decrease was due to reduced binding affinities of GABA receptors for muscimol. In contrast muscimol binding was increased by 38% in the hypothalamus and did not change in the pons-medulla after Adx. Nanomolar concentrations of corticosterone and pregnenolone-sulfate, but not dexamethasone, enhanced muscimol binding in brain regions that were characterized by reduced binding following Adx. This steroid-induced increase in muscimol binding was due to enhanced affinities of GABA receptors.

Adrenalectomy↗
PubMed1994

Interaction between adenosine and GABAA receptors on hippocampal neurones.

Extracellular recordings were made from the CA1 pyramidal cell layer of hippocampal slices in response to stimulation of Schaffer collateral fibres in stratum radiatum. Adenosine and muscimol induced concentration-dependent reductions in the amplitude of orthodromically induced population potentials. In order to eliminate effects of these agents on potassium channels, experiments were performed in the presence of barium, 1 mM. This concentration increased potential size, and reduced the inhibitory effect of adenosine on population spike size, but not synaptic potential size. This profile is consistent with the blockade of potassium channels associated only with the postsynaptic effects of adenosine. Muscimol responses were unaffected. Adenosine potentiated the ability of muscimol to inhibit evoked potentials in the absence or presence of barium. The potentiation was prevented by the A1 selective antagonist 8-cyclopentyltheophylline. The effects of adenosine as well as muscimol were reduced by the chloride channel blockers DIDS, which also prevented the adenosine potentiation of muscimol. The results indicate the ability of adenosine to operate chloride channels in hippocampal neurones, and suggest a potentiative interaction between adenosine and muscimol which may also involve chloride channels.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1993

Interaction between benzodiazepine and GABA-A receptors in state-dependent learning.

State-dependent learning (SDL) induced by benzodiazepine (BDZ) and GABA-A agonists was investigated in the step-through passive avoidance task in rats. Pre-training injection of diazepam or muscimol dose-dependently reduced step-through latency in the test session conducted 24 hr after the training. Injection of either drug before both the training and test sessions, however, failed to reduce the latency. The results show that passive avoidance failures induced by pre-training injections of diazepam and muscimol are due to SDL. In contrast to diazepam and muscimol, baclofen induced no SDL. Diazepam and muscimol were found to substitute for each other in producing SDL. The failure of learning performance in SDL (dissociation in SDL) induced by diazepam was blocked by flumazenil and picrotoxin but not by bicuculline injected before the training session, whereas dissociation in SDL induced by muscimol was blocked by flumazenil, bicuculline and picrotoxin. On the other hand, the success of learning performance in SDL (non-dissociation in SDL) induced by diazepam was blocked by flumazenil, bicuculline and picrotoxin injected before the test session, whereas non-dissociation in SDL induced by muscimol was blocked by bicuculline and picrotoxin but not by flumazenil. These results demonstrate that 1) BDZ and GABA-A agonists produce a common drug state, but, 2) roles of each receptor in SDL might be different, i.e., BDZ receptors for dissociation in SDL and GABA-A receptors for non-dissociation in SDL, and 3) chloride ion channels are essential for the induction of SDL by BDZ and GABA-A agonists.

Animals↗
PubMedDate not supplied

Anticonvulsant actions and interaction of GABA agonists and a benzodiazepine in pars reticulata of substantia nigra.

In a previous study, infusion of flurazepam and midazolam, but not GABA or muscimol into the pars reticulata of substantia nigra (SNpr), blocked the tonus induced by a high dose of pentylenetetrazol (PTZ). It was hypothesized that the divergence of GABAA agonist and benzodiazepine (BZ) actions might be due to a complex action of the GABAA agonists in SNpr that is not shared by the BZs, and which is specific for certain experimental seizures. This was tested in the present study in which GABA, muscimol, midazolam, and combinations of midazolam with GABA and with muscimol were tested against seizures induced by PTZ (40 or 100 mg/kg, i.p.), bicuculline (0.5 mg/kg, i.v.) and maximal electroshock (MES). Intranigral midazolam was effective against PTZ, bicuculline and MES seizures. Intranigral GABA or muscimol, infused together with midazolam, prevented midazolam from blocking tonus induced by the high dose of PTZ. For bicuculline seizures, midazolam alone had a better overall anticonvulsant effect than did the combination of midazolam plus muscimol. Intranigral muscimol, midazolam and a combination of two were equally effective against the low dose PTZ (40 mg/kg, i.p.) and MES seizures. Since the effect of intranigral drugs was model-specific, it was suggested that different populations of nigral output neurons were involved in regulating the generalization of these seizures.

Animals↗
PubMed1995

Characterisation of delta-subunit containing GABAA receptors from rat brain.

Polyclonal antibodies have been raised in rabbits against the predicted cytoplasmic loop region of the delta-subunit of the GABAA receptor. These specifically identify the expressed fragment by Western blot but do not cross react with analogous polypeptides from the gamma 1, gamma 2 or gamma 3-subunits. Polyclonal antisera immunoprecipitated [3H]muscimol binding sites from several brain regions consistent with the reported distribution of delta-subunit mRNA and also detected the delta-subunit by Western blot, identifying a polypeptide of 55KDa. Receptors immunoprecipitated from rat brain with the delta-antisera exhibited an atypical profile with respect to their radioligand binding properties. Receptors immunoprecipitated from all regions tested bound [3H]muscimol, but did not bind benzodiazepine site ligands [3H]Ro 15,1788 or [3H]flunitrazepam with high affinity. Receptors containing a delta-subunit accounted for 10.7 +/- 2% of all GABAA receptors ([3H]muscimol binding sites) in the rat central nervous system as deduced from quantitative immunoprecipitation experiments, the largest population being in the cerebellum where approximately 27% of all receptors contained a delta-subunit. The pharmacology of the GABA (gamma-aminobutyric acid) binding site on receptors immunoprecipitated from cerebellum with gamma 2 and delta-antisera was compared. The rank order of potency of a series of 6 compounds to compete for [3H]muscimol binding sites was similar in these two populations, but muscimol had a significantly higher affinity for receptors containing the delta-subunit. These receptors therefore comprise a novel population of GABAA receptors which do not bind benzodiazepines but have a 5-fold higher affinity for muscimol.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Disconnection of the hippocampal-prefrontal cortical circuits impairs spatial working memory performance in rats.

There is a unidirectional, ipsilateral and monosynaptic projection from the hippocampus to the prefrontal cortex. The cognitive function of hippocampal-prefrontal cortical circuit is not well established. In this paper, we use muscimol treated rats to investigate the roles of the hippocampal-prefrontal cortical circuits in spatial working memory, as assessed with a delayed spatial alternation task. First of all, the effect of muscimol on EEG power of infusion area was observed for confirmation of the dosage of muscimol to inhibit the function of infusion area. The results show that the EEG power of the ventral hippocampus and the prelimbic area of the prefrontal cortex were inhibited by local infusion of muscimol (0.5 microg in 0.25 microl PBS) into the above areas, respectively. Delayed alternation performance was significantly impaired when muscimol at this dosage was infused (1) bilaterally into the ventral hippocampus, (2) bilaterally into the prelimbic area, (3) unilaterally into the ventral hippocampus and simultaneously contralaterally into the prelimbic area. Infusion of muscimol either unilaterally into the ventral hippocampus or unilaterally into the prelimbic area did not impair delayed alternation performance. The present results suggest that any structures in this circuit is damaged or inhibited bilaterally, the spatial working memory will be disrupted. It means the hippocampal-prefrontal cortical circuit plays an important role in spatial working memory.

Animals↗
PubMed2005

Activation of membrane receptors by a neurotransmitter conjugate designed for surface attachment.

The derivatization of surfaces with bioactive molecules is a research area of growing importance for cell and tissue engineering. Tetherable molecules used in such applications must contain an anchoring moiety as well as the biofunctional group, typically along with a spacer to prevent steric clashes between the target molecule and the tethering surface. Post-synaptic membrane receptors at chemical synapses in neural tissue mediate signaling to the post-synaptic neuron and are activated by the binding of diffusible neurotransmitter molecules released by the pre-synaptic neuron. However, little attention has been directed at developing neurotransmitter analogs that might retain functionality when tethered to a surface that could be interfaced with post-synaptic receptor proteins. Muscimol (5-aminomethyl-3-hydroxyisoxazole), an analog of GABA (gamma-aminobutryic acid), is a known potent agonist of GABA(A) and GABA(C) post-synaptic receptors found in retina and other central nervous system tissue. The present paper reports experiments testing the electrophysiological activity of "muscimol-biotin" on cloned GABA receptors expressed in Xenopus oocytes. This compound, which is potentially suitable for tethering at avidin-coated surfaces, consists of muscimol conjugated through an N-acyl linkage to a 6-aminohexanoyl chain that is distally terminated by biotin. We find that muscimol-biotin, as well as a structurally similar compound (muscimol-BODIPY) containing a bulky fluorophore at the distal end of the aminohexanoyl chain, exhibits substantial agonist activity at GABA(A) and GABA(C) receptors. Muscimol-biotin and other similarly biotinylated neurotransmitter analogs, in combination with surface functionalization using avidin-biotin technology, may be useful in applications involving the controlled activation of neuronal post-synaptic receptors by surface-attached molecules.

Animals↗
PubMed2004

Defense reaction mediated by NMDA mechanisms in the inferior colliculus is modulated by GABAergic nigro-collicular pathways.

Electrical stimulation of the inferior colliculus (IC) causes a behavioral activation together with autonomic responses similar to fear reactions to threatening situations. GABAergic mechanisms exert a tonic inhibitory control on the neural substrates of aversion in the IC insofar as local injections of GABA agonists or antagonists inhibit or mimic these defensive behaviors, respectively. Recently, we have shown that systemic injections of the GABA-A receptor agonist muscimol unexpectedly enhanced the freezing and escape responses provoked by gradual increases in the intensity of the electrical stimulation of the IC. Taking into account that the neural circuits mediated by excitatory amino acids (EAA) in the IC may be responsible for the integration of fear states, in the present study we examined whether the defensive behavior induced by local injections of NMDA into the IC is influenced by prior treatment with systemic muscimol and also whether this GABAergic control could be exerted by GABAergic fibers that project to the inferior colliculus from the substantia nigra pars reticulata (SNpr). Rats were implanted with two guide-cannulae aimed at the IC and SNpr through which drug microinfusions with glass micropipette could be made with reduced brain damage. One week after surgery, the animals received either NMDA (7 nmol/0.2 microl) or saline into the IC and were placed into the middle of an enclosure where behavioral responses such as freezing, crossings, jumping, rearing, and turnings could be measured as an indirect index of unconditioned fear. These animals were pretreated either with saline or muscimol (0.5 mg/kg, IP) or with brain injections of saline or muscimol (1 nmol/0.2 ìl into SNpr). NMDA applied into the IC produced a behavioral activation with significant increases in all behavioral measures. IP injections of muscimol or into the SNpr enhanced the defense reaction caused by microinjections of NMDA into the IC. These findings give support to the idea that unconditioned defensive responses generated in the IC may be mediated by NMDA mechanisms. Additionally, a reduction of the inhibitory control exerted by nigrocollicular GABAergic neurons seems to be responsible for the unexpected pro-aversive action of systemic injections of muscimol on the neural substrates of aversion mediated by NMDA in the IC.

Animals↗
PubMed1999

Fluorescence imaging of GABAA receptor-mediated intracellular [Cl-] in P19-N cells reveals unique pharmacological properties.

This study describes the pharmacological properties of GABAA receptors expressed in P19-N cells using fluorescence imaging of intracellular chloride with 6-methoxy-N-ethylquinolinium iodide (MEQ). We show that application of the GABA agonist, muscimol (10-200 microM), produces time- and concentration-dependent increases in intracellular [Cl-] that are blocked by bicuculline. Diazepam (10 microM) and pentobarbital (1 mM) potentiate muscimol-stimulation. These receptors exhibit novel pharmacological properties. The neurosteroid, 3alpha-hydroxy-5alpha-pregnane-20-one (1-10 microM) exhibited weak potency in enhancement of muscimol-stimulation. Ethanol (50 and 100 mM) exhibited high efficacy on muscimol responses, a 4- to 5-fold potentiation, respectively, of muscimol (10 microM) alone. GABA and muscimol allosterically modulated specific binding of [3H]flunitrazepam to differentiated P19 cells. Modulation of GABAA receptor mediated increases in intracellular [Cl-] demonstrated stability in response magnitude from 7 to 15 days following removal of retinoic acid. In concert, GABAA receptor subunit mRNA and protein expression patterns in these neuron-like cells were stable over the same period. Using RT-PCR we determined that differentiated P19 cells lack gamma1, gamma2L, alpha6 and delta subunit mRNAs while expressing alpha1, alpha2, alpha3, alpha4, alpha5, beta1, beta2, beta3, gamma2S and gamma3. Furthermore, subunit specific antibody immunocytochemical labeling of cells with a neuronal morphology indicated the presence of alpha1, alpha2, alpha4, and gamma2 subunits (the only subunits tested). Therefore, P19-N cells should prove useful to researchers in need of a model cell culture system in which to study function and regulation of neuronal GABAA receptors.

Animals↗
PubMed2002

Dopaminergic and cholinergic stimulation of the ventrolateral striatum elicit rat jaw movements that are funnelled via distinct efferents.

It has been reported that two distinct types of jaw movements can be elicited by bilateral injections of drugs into the ventrolateral striatum: (1) dopamine receptor-mediated jaw movements that are elicited by a mixture of (+/-)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 82958; 5 microg) and quinpirole (10 microg), and (2) acetylcholine receptor-mediated jaw movements that are elicited by carbachol (2.5 microg). In the present study, electromyographic analysis was used to characterise these movements: the dopamine receptor-mediated jaw movements were marked by a dominant digastric activity during jaw opening and a dominant masseter activity during jaw closing (digastric/masseter type), whereas the acetylcholine receptor-mediated jaw movements were marked by a dominant digastric activity during jaw opening without any significant change in masseter activity during jaw closing (digastric type). The main goal was to (in)validate the hypothesis that these two types of jaw movements are funnelled via distinct gamma-aminobutyric acid (GABA)ergic output channels. Bilateral injections of both muscimol (25 and 50 ng/0.2 microl per side) and bicuculline (50 and 150 ng/0.2 microl per side) into the ventral pallidum, entopeduncular nucleus or dorsolateral part of the substantia nigra pars reticulata essentially inhibited dopamine receptor-mediated jaw movements to various degrees. In contrast, acetylcholine receptor-mediated jaw movements were inhibited by muscimol given into the entopeduncular nucleus and dorsolateral part of the substantia nigra pars reticulata, whereas these movements were enhanced by bicuculline. The acetylcholine receptor-mediated jaw movements were not affected by muscimol injections into the ventral pallidum, but were inhibited by bicuculline injections. Studies on such injections into the ventral pallidum, entopeduncular nucleus or dorsolateral part of the substantia nigra pars reticulata of naive rats revealed that jaw movements of the digastric/masseter type were elicited either by muscimol injections into the dorsolateral part of the substantia nigra pars reticulata or by combined injections of muscimol and bicuculline into the entopeduncular nucleus, and that jaw movements of the digastric type were elicited only by combined injections of muscimol and bicuculline into the entopeduncular nucleus. Together, the data allow the conclusion that dopamine receptor-mediated and acetylcholine receptor-mediated jaw movements are two distinct types of jaw movements that are funnelled via separate GABAergic output channels. It is suggested that the three different profiles of responses to GABAergic drugs in animals showing either dopamine receptor-mediated or acetylcholine receptor-mediated jaw movements reflect the involvement of three distinct types of output neurons of the striatum, namely: type I neurons with collateralised axons to the ventral pallidum, entopeduncular nucleus and dorsolateral part of the substantia nigra pars reticulata, mediating the dopamine receptor-mediated jaw movements; type II neurons with collateralised axons to the globus pallidus that, in turn, project to the entopeduncular nucleus and the dorsolateral part of the substantia nigra pars reticulata, mediating directly the acetylcholine receptor-mediated jaw movements; and type III neurons with a single axon to the ventral pallidum, mediating indirectly the acetylcholine receptor-mediated movements. It is evident that future studies are required to provide direct evidence in favour of the latter hypothesis.

Animals↗
PubMed1993

Effects of GABA-receptor stimulation and blockade on micturition in normal rats and rats with bladder outflow obstruction.

The effects on micturition of the GABA receptor agonists muscimol (selective for GABAA-receptors) and baclofen (selective for GABAB-receptors), given intrathecally and intra-arterially to unanesthetized rats with and without bladder hypertrophy secondary to outflow obstruction, were studied by continuous cystometry. When given intrathecally in increasing doses, both muscimol (1 to 10 micrograms) and baclofen (0.1 to 5 micrograms) produced a dose-dependent inhibition of micturition with progressive increases in bladder capacity and residual volume, and a decrease in micturition pressure ending with urinary retention and dribbling incontinence. Generally, the effects were similar in normal rats and rats with bladder hypertrophy. In normal rats, bicuculline (blocking GABAA-receptors) decreased bladder capacity and micturition volume, and increased micturition pressure. In both types of rat, the effects of muscimol and baclofen were partly counteracted by bicuculline and baclofen, respectively. In rats with bladder hypertrophy, the amplitude of the spontaneous bladder contractions during filling was significantly increased after administration of muscimol and baclofen. When given intra-arterially in high doses, muscimol (2 to 16 mg./kg.) and baclofen (8 to 16 mg./kg.) produced effects on cystometric parameters and spontaneous bladder contractions similar to those obtained with intrathecal administration. These results suggest that muscimol and baclofen have insignificant peripheral effects on the lower urinary tract, but depress micturition by an effect on the central nervous system. They also suggest that the inhibitory GABA-ergic system does not play a role in the genesis of bladder hyperactivity in rats with outflow obstruction.

Animals↗