Muscimol Research Articles

A Mechanism for Vocal-Respiratory Coupling in the Mammalian Parabrachial Nucleus

Mammalian vocalizations require the precise coordination of separate laryngeal and respiratory motor pathways. Precisely how and where in the brain vocal motor patterns interact with respiratory rhythm control is unknown. The parabrachial nucleus (PB) is known to mediate key respiratory reflexes and is also considered a principle component of the mammalian vocal motor pathway, making it a likely site for vocal-respiratory interactions, yet a specific role for the PB in vocalizing has yet to be demonstrated. To investigate the role of the PB in vocal-respiratory coordination, we pharmacologically manipulated synaptic activity in the PB while spontaneously vocalizing horseshoe bats were provoked to emit either short, single syllable or long, multisyllabic vocal motor patterns. Iontophoresis of the GABAA agonist muscimol (MUS) into the lateral PB extended expiratory durations surrounding all vocalizations and increased mean call durations. Alternatively, application of the GABAA antagonist bicuculline methiodide (BIC) shortened expirations and call durations. In addition, BIC eliminated the occurrence of multisyllabic vocalizations. BIC caused a mild increase in quiet breathing rates, whereas MUS tended to slow quiet breathing. The results indicate that GABAA receptor-mediated inhibition in the lateral PB modulates the time course of respiratory phase switching during vocalizing, and is needed for proper coordination of calling and breathing in mammals. We hypothesize that vocal-respiratory rhythm entrainment is achieved at least in part via mechanisms similar to other forms of locomotor-respiratory coupling, namely somatosensory feedback influences on respiratory phase-switching in the lateral PB.

Analysis of hallucinogenic constituents in Amanita mushrooms circulated in Japan

The constituents of seven mushrooms sold as Amanita muscaria or Amanita pantherina (five A. muscaria and two A. pantherina) and four “extracts purported to contain A. muscaria” products that are currently circulated in Japan were determined. All mushroom samples were identified as A. muscaria or A. pantherina by macroscopic and microscopic observation. The dissociative constituents, ibotenic acid (IBO) and muscimol (MUS), were extracted with 70% methanol twice and determined by gas chromatography/mass spectrometry. The IBO (as the hydrate)/MUS contents were in the range of <10–2845 ppm/46–1052 ppm in the cap of A. muscaria and 188–269 ppm/1554–1880 ppm in the cap of A. pantherina. In the caps, these compounds had a tendency to be more concentrated in the flesh than in the cuticle. On the other hand, the IBO/MUS contents in the stem were far lower than in the caps. In the “extracts purported to contain A. muscaria” products, IBO/MUS were detected below the lower limit of calibration curve (<10 ppm/<25 ppm) or not detected. However, these samples contained other psychoactive compounds, such as psychoactive tryptamines (5-methoxy- N,N-diisopropyltryptamine and 5-methoxy- N,N-dimethyltryptamine), reversible monoamine oxidase inhibitors (harmine and harmaline) and tropane alkaloids (atropine and scopolamine), which were not quantified. This is the first report of the chemical analysis of Amanita mushrooms that are circulated in the drug market.

Analysis of gamma-aminobutyric acid-mediated responses in the pulmonary vascular bed of the cat.

In this investigation, we sought to identify the role of gamma-aminobutyric acid (GABA)(A) and GABA(B) receptors in the feline pulmonary vascular bed. Using adult mongrel cats and in separate experiments, we investigated the effects of l-N(5)-(1-iminoethyl) ornithine hydrochloride (l-NIO) (a nitric oxide synthase inhibitor), glibenclamide (an adenosine triphosphate (ATP)-sensitive K(+) channel blocker), meclofenamate (a nonselective cyclooxygenase inhibitor), bicuculline (a GABA(A) receptor antagonist), and saclofen (a GABA(B) receptor antagonist) on pulmonary arterial responses to pinacidil (an ATP-sensitive K(+) channel activator), bradykinin (a nitric oxide synthase inducer), muscimol (a GABA(A) receptor agonist), and 3-aminopropyl(methyl)phosphinic acid, hydrochloride (SKF-97541; a GABA(B) receptor agonist). Under increased tone conditions in the isolated left lower lobe vascular bed of the cat, muscimol induced a dose-dependent vasodepressor response that was not significantly altered after the administration of l-NIO, glibenclamide, meclofenamate, and saclofen. SKF-97541-induced vasodepression was not significantly attenuated after the administration of l-NIO, meclofenamate, and bicuculline. Responses to SKF-97541 were significantly attenuated after the administration of glibenclamide and saclofen. Responses to muscimol were significantly reduced after the administration of bicuculline. The results suggest that muscimol and SKF-97541 have potent vasodepressor activity in the feline pulmonary vascular bed and that these responses are modulated by, respectively, GABA(A) and GABA(B) receptor-sensitive pathways. Further, SKF-97541-induced vasodepression is mediated or modulated by an ATP-sensitive K(+) channel.

GABAergic regulation of REM sleep in reticularis pontis oralis and caudalis in rats.

The nucleus reticularis pontis oralis (RPO) and nucleus reticularis pontis caudalis (RPC) are implicated in the generation of rapid eye movement sleep (REM). Work in cats has indicated that GABA in RPO plays a role in the regulation of REM. We assessed REM after local microinjections into RPO and RPC of the gamma-aminobutyric acid-A (GABA(A)) agonist, muscimol (MUS), and the GABA(A) antagonist, bicuculline (BIC). Rats (90-day-old male Sprague-Dawley) were implanted with electrodes for recording electroencephalographs (EEG) and electromyographs (EMG). Guide cannulae were aimed into RPO (n = 9) and RPC (n = 8) for microinjecting MUS (200, 1,000.0 microM) and BIC (0.056, 0.333, 1.0, 1,000.0, and 10,000.0 microM). Animals received bilateral microinjections of saline, MUS, and BIC (0.2 microl microinjected at 0.1 microl/min) into each region followed by 6-h sleep recordings. In RPO, MUS (1,000.0 microM) suppressed REM and BIC (1,000.0 microM) enhanced REM. In RPC, MUS (200, 1,000.0 microM) suppressed REM, but BIC (1,000.0 microM and less) did not significantly affect REM. Higher concentrations of BIC (10,000.0 microM) injected into RPO (n = 9) and RPC (n = 4) produced wakefulness and escape behavior. The results indicate that GABA in RPO/RPC is involved in the regulation of REM and suggest site-specific differences in this regulation.

Effects of three neurochemical stimuli on delayed feeding and energy metabolism

Infusions of norepinephrine (NE), the gamma-aminobutyric acid agonist, muscimol (MUS), or neuropeptide Y (NPY) into the paraventricular nucleus (PVN) of the hypothalamus all increase food intake. Such feeding may be due to direct activation of behavioral processes driving ingestion and/or to alterations in nutrient metabolism that feeding serves to normalize. To examine these possibilities, male Sprague–Dawley rats received PVN infusions of vehicle, 20 nmol NE, 1 nmol MUS or 100 pmol NPY at dark onset, then food intake was measured under three feeding conditions: (1) 1 and 2 h immediately after injections, (2) 1 h after a 1 h delay between injections and access to food, and (3) 1 h after a 1 h feeding delay, but with injections occurring just before presenting food. Measures of energy expenditure (EE) and respiratory quotients (RQs) in the absence of food were made over 2 h in parallel experiments. Results confirmed that NE, MUS and NPY all increased dark-onset feeding, but only NPY increased intake above control levels after a 1 h feeding delay. No neurochemically-induced changes in EE were observed, nor were there changes in RQs after NE or MUS. However, NPY reliably enhanced RQs from 30 to 120 min of testing. Our findings imply that NE and MUS initiate relatively immediate, short-term feeding that is not associated with changes in nutrient metabolism and does not summate with cues stimulated by delayed access to food. NPY initiates more protracted feeding temporally linked to enhanced carbohydrate metabolism. This may indicate that part of NPY’s feeding stimulatory effects are secondary to physiological processes driving ingestion.

Interactions between Neuropeptide Y and -Aminobutyric Acid in Stimulation of Feeding: A Morphological and Pharmacological Analysis

Neuropeptide Y (NPY) produced in neurons in the arcuate nucleus and brain stem and released in the paraventricular nucleus (PVN) and surrounding areas is involved in stimulation of feeding in rats. We recently reported that γ-aminobutyric acid (GABA) is coexpressed in a subpopulation of NPY neurons in the arcuate nucleus. To determine whether GABA is colocalized in NPY terminals in the PVN, the site of NPY action, light and electron microscopic double staining for NPY and GABA using pre- and postembedding immunolabeling was performed on rat brain sections. GABA was detected in NPY-immunopositive axons and axon terminals within both the parvocellular and magnocellular divisions of the PVN. These morphological findings suggested a NPY-GABA interaction in the hypothalamic control of feeding. Therefore, the effects of muscimol (MUS), a GABAA receptor agonist, on NPY-induced food intake were examined in sated rats. When injected intracerebroventricularly, both NPY and MUS elicited dose-dependent feeding responses that were blocked by the administration of 1229U91 (a putative Y1 receptor antagonist) or bicuculline (a GABAA receptor antagonist), respectively. Coadministration of NPY and MUS intracerebroventricularly amplified the feeding response over that evoked by NPY or MUS alone. Similarly, microinjection of either NPY or MUS into the PVN stimulated food intake in a dose-related fashion, and coinjection elicited a significantly higher response than that evoked by either individual treatment. These results suggest that GABA and NPY may coact through distinct receptors and second messenger systems in the PVN to augment food intake.

Interactions between neuropeptide Y and gamma-aminobutyric acid in stimulation of feeding: a morphological and pharmacological analysis.

Neuropeptide Y (NPY) produced in neurons in the arcuate nucleus and brain stem and released in the paraventricular nucleus (PVN) and surrounding areas is involved in stimulation of feeding in rats. We recently reported that gamma-aminobutyric acid (GABA) is coexpressed in a subpopulation of NPY neurons in the arcuate nucleus. To determine whether GABA is colocalized in NPY terminals in the PVN, the site of NPY action, light and electron microscopic double staining for NPY and GABA using pre- and postembedding immunolabeling was performed on rat brain sections. GABA was detected in NPY-immunopositive axons and axon terminals within both the parvocellular and magnocellular divisions of the PVN. These morphological findings suggested a NPY-GABA interaction in the hypothalamic control of feeding. Therefore, the effects of muscimol (MUS), a GABA(A) receptor agonist, on NPY-induced food intake were examined in sated rats. When injected intracerebroventricularly, both NPY and MUS elicited dose-dependent feeding responses that were blocked by the administration of 1229U91 (a putative Y1 receptor antagonist) or bicuculline (a GABA(A) receptor antagonist), respectively. Coadministration of NPY and MUS intracerebroventricularly amplified the feeding response over that evoked by NPY or MUS alone. Similarly, microinjection of either NPY or MUS into the PVN stimulated food intake in a dose-related fashion, and coinjection elicited a significantly higher response than that evoked by either individual treatment. These results suggest that GABA and NPY may coact through distinct receptors and second messenger systems in the PVN to augment food intake.

Honokiol and magnolol increase the number of [3H] muscimol binding sites three-fold in rat forebrain membranes in vitro using a filtration assay, by allosterically increasing the affinities of low-affinity sites.

1. The bark of the root and stem of various Magnolia species has been used in Traditional Chinese Medicine to treat a variety of disorders including anxiety and nervous disturbances. The biphenolic compounds honokiol (H) and magnolol (M), the main components of the Chinese medicinal plant Magnolia officinalis, interact with GABA(A) receptors in rat brain in vitro. We compared the effects of H and M on [3H]muscimol (MUS) and [3H]flunitrazepam (FNM) binding using EDTA/water dialyzed rat brain membranes in a buffer containing 150 mM NaCl plus 5 mM Tris-HCl, pH 7.5 as well as [35S]t-butylbicyclophosphorothionate (TBPS) in 200 mM KBr plus 5 mM Tris-HCl, pH 7.5. H and M had similar enhancing effects on [3H]MUS as well as on [3H]FNM binding to rat brain membrane preparations, but H was 2.5 to 5.2 times more potent than M. 2. [3H]FNM binding. GABA alone almost doubled [3H]FNM binding with EC50 = 450 nM and 200 nM using forebrain and cerebellar membranes, respectively. In the presence of 5 microM H or M the EC50 values for GABA were decreased to 79 and 89 nM, respectively, using forebrain, and 39 and 78 nM, using cerebellar membranes. H and M potently enhanced the potentiating effect of 200 nM GABA on [3H]FNM binding with EC50 values of 0.61 microM and 1.6 microM using forebrain membranes, with maximal enhancements of 33 and 47%, respectively. Using cerebellar membranes, the corresponding values were 0.25 and 1.1 microM, and 22 and 34%. 3. [3H]MUS binding. H and M increased [3H]MUS binding to whole forebrain membranes about 3-fold with EC50 values of 6.0 and 15 microM. Using cerebellar membranes, H and M increased [3H]MUS binding approximately 68% with EC50 values of 2.3 and 12 microM, respectively. Scatchard analysis revealed that the enhancements of [3H]MUS binding were due primarily to increases in the number of binding sites (Bmax values) with no effect on the high affinity binding constants (Kd values). The enhancing effect of H and M were not additive. 4. [35S]TBPS binding. H and M displaced [35S]TBPS binding from sites on whole rat forebrain membranes with IC50 values of 7.8 and 6.0 microM, respectively. Using cerebellar membranes, the corresponding IC50 values were 5.3 and 4.8 microM. These inhibitory effects were reversed by the potent GABA(A) receptor blocker R5135 (10 nM), suggesting that H and M allosterically increase the affinity of GABA(A) receptors for GABA and MUS by binding to sites in GABA(A) receptor complexes. 5. Two monophenols, the anesthetic propofol (2,6-diisopropylphenol, P) and the anti-inflammatory diflunisal (2',4'-difluoro-4-hydroxy-3-biphenyl carboxylic acid, D) also enhanced [3H]MUS binding, decreased the EC50 values for GABA in enhancing [3H]FNM binding and potentiated the enhancing effect of 200 nM GABA on [3H]FNM binding, although enhancements of [3H]MUS binding for these monophenols were smaller than those for H and M, using forebrain and cerebellar membranes. The enhancing effect of P and D on [3H]MUS binding were almost completely additive. 2,2'-biphenol was inactive on [3H]MUS and [3H]FNM binding. These, and other preliminary experiments, suggest that appropriate ortho (C2) and para (C4) substitution increases the GABA-potentiating activity of phenols. 6. The potentiation of GABAergic neurotransmission by H and M is probably involved in their previously reported anxiolytic and central depressant effects.

Tris(2-chloroethyl)phosphate Increases Ambulatory Activity in Mice: Pharmacological Analyses of Its Neurochemical Mechanism

The present study was conducted to clarify the acute effect of tris(2-chloroethyl)phosphate (TRCP), an organophosphate flame-retardant, on spontaneous ambulatory activity (AA) in male ICR mice and to examine the neurochemical mechanism of this effect. Single dose administration of 200 mg/kg ip of TRCP increased AA in ICR mice. Neither the nicotinic cholinergic antagonist mecamylamine (MA) nor the muscarinic cholinergic antagonist scopolamine (SCP) affected the AA response to TRCP. On the other hand, the benzodiazepine agonist diazepam (DZ), the GABAAagonist muscimol (MUS) and the GABABagonistbaclofen (BAC) all attenuated the effect of TRCP. DZ and MUS blocked the increase of AA within the first 10 min after administration of TRCP. These drugs did not attenuate the AA-increasing effect of SCP, suggesting that the mechanism of TRCP action is distinct from that of SCP. MUS and BAC did, but DZ did not, inhibit the AA increasing effect of the dopaminergic agonist apomorphine (APO), suggesting that dopamine is involved in the control of AA, and that GABA can affect AA through interaction with dopaminergic neurons. These results suggest that TRCP acts as a GABA antagonist and not as a cholinergic agonist, and that TRCP increases AA in ICR mice through a GABAergic mechanism.

The amygdala modulates memory for changes in reward magnitude: involvement of the amygdaloid GABAergic system

Rats with bilateral amygdala cannulae were trained to run a straight alley for a large or small food reward. Muscimol (MUS), a GABA A agonist, or bicuculline methiodide (BMI), a GABA A antagonist, were infused into the amygdala immediately after a reward shift. In Experiment 1, rats in the large-reward group were shifted to the small reward and immediately after received an infusion of vehicle or MUS bilaterally into the amygdala. The runway latencies of the shifted vehicle animals were increased in comparison with those of the unshifted controls. In contrast, the shifted MUS (0.001 nM, but not 0.01 nM) animals displayed latencies that were comparable to those of unshifted animals by the second postshift day. These findings suggest that muscimol dose-dependently attenuated the memory of the reward reduction. In Experiment 2 rats were trained as before except they received bilateral infusions of BMI into the amygdala immediately after reward reduction. The shifted BMI (0.1 nM, but not 0.3 nM) animals displayed increased runway latencies, in comparison with those of shifted vehicle animals, by the second postshift day. These findings suggest that BMI dose-dependently enhanced memory of the reward reduction. In Experiment 3, animals were trained as before except they first experienced a reward increase before receiving post-training injections of vehicle, MUS (0.001 nM) or BMI (0.1 nM). On the next day the reward was reduced. Despite reward reduction, shifted BMI animals persisted displaying low latencies for more trials than did shifted MUS animals. These findings suggest that BMI enhanced memory for the reward increase. More generally, the findings suggest that the amygdala and its GABAergic system is involved in memory consolidation for both positive and negative affective experiences.

Regulation of anxiety by GABA A receptors in the rat amygdala

Blockade of GABAergic inhibition in the region of the anterior basolateral amygdala (BLA) of rats elicits physiologic changes associated with a defense reaction. The present study was undertaken to determine whether GABA receptors in the BLA might be involved in regulating experimental anxiety using the social interaction (SI) and conflict test. Guide cannulae were stereotaxically implanted bilaterally in the BLA of rats for intracerebral microinjections. In the BLA, injection of the GABA A receptor antagonists bicuculline methiodide (BMI) and picrotoxin (PIC) produced anxiogenic-like effects in the SI paradigm, as did BMI injection using the conflict paradigm. Injection of the GABA A agonist muscimol (MUS) into the central nucleus of the amygdala (Ce) produced anxiolytic-like effects in the SI test. Microinjection of MUS, baclofen (GABA B agonist), 2OH-saclofen (GABA B antagonist) or strychnine (glycine antagonist) into the BLA or BMI into the Ce elicited no change in experimental anxiety as measured by the SI test. These results suggest that endogenous GABA acts tonically at GABA A receptors in the BLA to inhibit anxiety responses.

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. Immediately after the session all animals were injected with saline or 3.0 mg/kg of MUS. The large food reward was continued for the remainder of training and no further injections were given. On the following session, the performance of the shifted saline animals was comparable to that of the unshifted controls while shifted MUS animals displayed significantly higher response latencies. The findings that MUS prevented the reduction in response latencies seen in saline-injected animals suggest that MUS also induces retrograde amnesia for reward increases.

Muscimol (MUS), a specific GABA A receptor agonist, reverses disruption of the migrating myoelectric complex (MMC) induced by progesterone (PROG) in female rats : [formula omitted], E. Gurpinar, M.H. Clench, J.R. Mathias. Div. Gastro., Dept. Int. Med., The Univ. TX Medical Branch, Galveston, TX

Muscimol (MUS), a specific GABA A receptor agonist, reverses disruption of the migrating myoelectric complex (MMC) induced by progesterone (PROG) in female rats : [formula omitted], E. Gurpinar, M.H. Clench, J.R. Mathias. Div. Gastro., Dept. Int. Med., The Univ. TX Medical Branch, Galveston, TX

Microinjections of GABAergic agents in the locus coeruleus modify the gain of vestibulospinal reflexes in decerebrate cats.

1. Precollicular decerebrate cats show a good postural activity in the four limbs and a small-amplitude vestibulospinal (VS) reflex, as revealed by recording the EMG response of the triceps brachii to sinusoidal roll tilt of the animal at 0.15 Hz, +/- 10 degrees. This preparation was used to study whether inactivation of the locus coeruleus (LC) elicited by local administration either of the GABA-A agonist muscimol or of the GABA-B baclofen produced changes in posture as well as in gain of the VS reflexes. 2. Microinjection into the LC of one side of 0.13-0.25 microliter of a muscimol or baclofen solution (at 2.5 or 1 microgram/microliter saline, respectively) stained with 5% pontamine, usually decreased the extensor tonus in the ipsilateral limbs and to a lesser extent also in the contralateral limbs. However, the amplitude of modulation and thus the gain of the first harmonic component of the multiunit EMG responses of the ipsilateral and to a lesser extent also of the contralateral triceps brachii to the same parameters of labyrinth stimulation increased. The phase angle of the responses remained nearly unchanged by this treatment. The effects appeared 5-10 min after the injection of muscimol, fully developed in 30 min and progressively declined within the following 2-2.5 hours. 3. The increased gain of the VS reflexes acting on the triceps brachii did not depend on the decreased postural activity following the injection of the GABA-A or GABA-B agonist, since it was still observed if the reduced EMG activity following the injection was compensated by an increased static stretch of the muscle. Moreover, the postural and reflex changes described above were not due to irritative events following the injection, since they were not observed in control experiments following injection of 0.25 microliter saline within the LC-complex. On the other hand, postural and reflex changes opposite in sign to those elicited by muscimol or baclofen were obtained by local injection into the LC-complex of a GABA-A or GABA-B antagonist (0.25 microliter of bicuculline or faclofen at 8 micrograms/microliters saline). 4. In some experiments, the decrease in postural activity of the forelimbs after injection of muscimol into the LC complex was followed by transient episodes of postural atonia, which affected not only the ipsilateral but also the contralateral triceps muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of central GABAA-but not of GABAB-receptors rapidly reduces pituitary LH release and GnRH gene expression in the preoptic/anterior hypothalamic area of ovariectomized rats.

gamma-Aminobutyric acid (GABA) exerts an inhibitory action on gonadotropin-releasing hormone (GnRH) release from the hypothalamus. In vivo, this inhibitory action appears to be mediated via the GABAA receptor since in ovariectomized (ovx) rats and sheep direct application of muscimol (MUS), a GABAA agonist, into the preoptic area (POA), the site were the GnRH cell bodies are located, caused an immediate reduction of LH release. This effect may be the result of an inhibition of GnRH release but also GnRH biosynthesis may be affected. Using competitive reverse transcription-polymerase chain reaction (RT-PCR) we now addressed the question, whether an acute inhibition of the GnRH pulse generator in ovx rats by GABA involves reduction of GnRH biosynthesis as determined by GnRH mRNA levels in micropunches of the POA. To activate either the GABAA or GABAB receptor, we injected intraventricularly (icv) MUS or baclofen (BAC). Intracerebroventricular injection of 10 nmol MUS caused a rapid and lasting inhibition of LH release from about 7.5 ng/ml (pretreatment value) to approximately 1.5 ng/ml. Neither application of BAC or saline (control injections) affected LH secretion. Two hours after icv injections, rats were decapitated and GnRH mRNA levels were determined. MUS induced a pronounced decrease of GnRH levels in the POA (control rats: 2.26 pg GnRH mRNA; MUS-treated rats: 0.85 pg, n = 10/group). BAC was without any effect on GnRH mRNA levels. Thus, we confirm the inhibitory action of GABA on LH release in vivo which is exerted via the A-subtype of the receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Depression of the vestibulospinal reflex adaptation by intravermal microinjection of GABA-A and GABA-B agonists in the cat.

In decerebrate cats the gain of the vestibulospinal reflex (VSR), elicited by sinusoidal roll tilt of the animal at 0.15 Hz, +/- 10 degrees, was tested every 10-15 min during and after a sustained (3 h) period of roll tilt of the head at the parameters indicated above, associated with synchronous roll tilt of the body at 0.15 Hz, +/- 12.5 degrees; this stimulus led to 2.5 degrees of neck rotation, which was thus out of phase with respect to head rotation. In this condition the gain of the VSR progressively increased during the first h of neck-vestibular stimulation, to reach a plateau level at the end of the third h of stimulation. This adaptive process was followed for at least 1 h after stimulation. Microinjection into the zone B of the cerebellar anterior vermis of the GABA-A agonist muscimol (0.25 microliter at 8 micrograms/microliter saline) producing only a slight or negligible depression of the VSR gain in non-adaptive conditions, prevented the occurrence of the adapted increase in gain of the VSR following a 3-h period of sustained head and neck rotation. In addition, intravermal injection of the GABA-A or the GABA-B agonist muscimol or baclofen, respectively, at the same dose indicated above supressed the adapted increase in gain occurring after a 3-h period of continuous neck-vestibular stimulation. The effective sites were located into the zone B of the cerebellar anterior vermis, from which the direct corticocerebellar projection to the lateral vestibular nucleus originates. In conclusion, the results seem to indicate that the adaptive increase in gain of the VSR which occurs in decerebrate cats depend upon plastic changes which affect the Purkinje cells of the cerebellar anterior vermis. These changes were in fact suppressed by GABAergic inhibition of these neurons. The demonstration that the effects of the GABA agonists occurred suddenly makes unlikely the hypothesis that the cerebellar anterior vermis represents either a relay for adaptive changes occurring before it (for instance in the inferior olive) or else the generator of error signals that elicit plasticity in target structures (as in the vestibular nuclei).

The Antagonistic Effect of Cholecystokinin Octapeptide (CCK-8) on Opioid Effects in Cardiovascular Activities Was Mediated by CCK-B Receptor

Previous studies have shown that CCK-8 has distinct antiopioid effect in the central sites related with pain control and blood pressure control. The aim of this study was to explore the receptor mechanism by which CCK-8 antagonized the depressor effect of u-and k-opioid agonists, and to observe whether CCK-8 could antagonize the depressor effect induced by muscimol, a nonopioid substance. The results showed that (ⅰ) The antagonistic effect of CCK-8 on opioid-induced hypotension could be blocked by intrathecal (i.t.) administration of CCK-B antagonist L-365, 260 at nanogram doses, or by CCK-A antagonist devazepide at doses 20—40 times higher than L-365, 260, indicating that it was the CCK-B receptor which mediates the antiopioid effect. (ⅱ) The depressor effect induced by intrathecal muscimol, a GABA agonist, was blocked neither by naloxone nor by CCK-8, supporting the notion that CCK-8 is an endogenous opioid antagonist rather thana universal anti-hypotension agent.

The antagonistic effect of cholecystokinin octapeptide (CCK-8) on opioid effects in cardiovascular activities was mediated by CCK-B receptor.

Previous studies have shown that CCK-8 has distinct antiopioid effect in the central sites related with pain control and blood pressure control. The aim of this study was to explore the receptor mechanism by which CCK-8 antagonized the depressor effect of u- and k-opioid agonists, and to observe whether CCK-8 could antagonize the depressor effect induced by muscimol, a nonopioid substance. The results showed that (i) The antagonistic effect of CCK-8 on opioid-induced hypotension could be blocked by intrathecal (i. t.) administration of CCK-B antagonist L-365, 260 at nanogram doses, or by CCK-A antagonist devazepide at doses 20-40 times higher than L-365, 260, indicating that it was the CCK-B receptor which mediates the antiopioid effect. (ii) The depressor effect induced by intrathecal muscimol, a GABA agonist, was blocked neither by naloxone nor by CCK-8, supporting the notion that CCK-8 is an endogenous opioid antagonist rather than a universal anti-hypotension agent.

Changes in Concentration of Ibotenic Acid and Muscimol in the Fruit Body of Amanita muscaria during the Reproduction Stage

Ibotenic acid (IBO) and muscimol (MUS) in the fruit body of Amanita muscaria during the reproduction stage were investigated. The mean levels of IBO and MUS throughout the fruit were x: 343ppm and x: 22ppm, respectively; most was detected in the cap of the fruit (IBO x: 519ppm, MUS x: 30ppm), then in the base (IBO x: 290ppm, MUS x: 20ppm), with the smallest amount in the stalk (IBO x: 253ppm, MUS x: 17ppm).The concentrations of IBO and MUS in the cap decreased gradually after increasing early on, and those in the stalk decreased gradually, where as in the base there was an increase; the levels in the whole body were nearly constant during maturation. Since the changes were similar in lone and colonial mushrooms, difference of mushroom-growing location had no influence on the concentrations of IBO and MUS. Also, difference of size of the fruit body had no influence on the concentrations of IBO and MUS. The large variations of the IBO and MUS contents may depend on individual differences of growth circumstances. Although the fruit body grew to about 6 times the weight of the base during maturation, the concentration of IBO remained nearly constant.Detection of MUS may reflect the enzymatic decarboxylation of IBO before the analysis, since the changes in the concentration of MUS paralleled those of IBO at a lower level.

Change in Ibotenic Acid and Muscimol Contents in Amanita muscaria during Drying, Storing or Cooking

It is believed by people in mountainous areas that toxins in A. muscaria are reduced by drying, storing or cooking. The main physiologically active substances, ibotenic acid (IBO) and muscimol (MUS), in A. muscaria were therefore investigated. IBO is readily transformed to into MUS through decarboxylation, and MUS is a hallucinogen. Drying A. muscaria in the sun or with a heater caused an increase of MUS in the mushroom, though a lot of precursor IBO was lost. It was suggested that the toxicity of the mushroom would be intensified by processing. IBO and MUS in the mushroom were stable on storage under dry or salt conditions. MUS increased in concentration while IBO decreased during heat-cooking, and the changes were more marked under acidic than alkaline conditions. However, general cooking (within 10 minutes) hardly reduced the toxic substances. Boiling or soaking A. muscaria in water caused most of the IBO and MUS in the mushroom to be released rapidly into the water.