Cataleptic and anticataleptic effects of muscimol and gabaculine injected into globus pallidus and substantia nigra, and interactions with haloperidol or benzodiazepines

Case Report: Successful Treatment of Refractory Interstitial Lung Disease With Cyclosporine A and Pirfenidone in a Child With SLE

Interstitial lung disease (ILD) as an initial manifestation of lupus is rare, especially in young children. Here, we report a case of a 3-year-old boy who presented with fever, shortness of breath, and facial erythema. Clinical examination suggested a diagnosis of active systemic lupus erythematosus (SLE) with butterfly rash, anemia, positive antinuclear antibody, positive anti-double-stranded DNA, and hypocomplementemia. On retrospective review of the patient’s records, multiple chest computed tomography (CT) images showed non-specific interstitial pneumonia + organizing pneumonia pattern, with no further autoimmune work-up during the visit to a respiratory department. In our opinion, persistent interstitial pneumonia may be a clue to connective tissue disease. The patient received steroid treatment for 1 year, and the radiological and immunological resolution was noted. However, he still suffered from cough and dyspnea. After a 1-year follow-up, he was hospitalized again for SLE relapse. While continuing corticosteroid therapy, the patient was given combination therapy consisting of cyclosporine A (CsA) and monthly-pulse cyclophosphamide for 6 months, and decreased proteinuria was noted. However, the patient’s respiratory symptoms and pulmonary radiologic findings did not improve significantly. With continued steroid therapy, the patient was started on a daily regimen of CsA and pirfenidone. Both drugs were sufficiently effective to allow gradual reduction of steroid dosage. After 2 years of treatment, marked improvements in symptoms, pulmonary function and chest CT images were observed. Our experience with this case emphasizes that prompt work-up for connective tissue disease (CTD) should be considered in young children with ILD, and pirfenidone might be a useful add-on therapy with immunosuppressive agents for refractory CTD-ILD in pediatric patients. Nevertheless, further clinical trials including larger numbers of patients need to assess the efficiency and safety of this combination therapy for refractory CTD-ILD.

A Clinical Risk Model to Predict Rapidly Progressive Interstitial Lung Disease Incidence in Dermatomyositis

Background: Rapidly progressive interstitial lung disease (RP-ILD) is a fatal complication of dermatomyositis (DM) and clinically amyopathic DM (CADM). The objective of this study was to evaluate risk markers associated with RP-ILD incidence in patients with DM/CADM and to develop a RP-ILD risk prediction (RRP) model.

Methods: The clinical records of 229 patients with DM/CADM from Peking University People's Hospital, and 97 patients from four other independent clinical centers were retrospectively reviewed. Univariate and multivariate logistic regression analyses were performed to identify independent risk factors associated with later RP-ILD incidence to build a risk score model. The concordance index (C-index) and calibration curve were calculated to evaluate the predictive accuracy of the RRP model.

Results: A multiparametric RRP model was established based on weighted clinical features, including fever (yes, 5; no, 0), periungual erythema (yes, 6; no, 0), elevated CRP (yes, 5; no, 0), anti-MDA5 antibody (positive, 8; negative, 0), and anti-Ro-52 antibody (positive, 6; negative, 0). Patients were divided into three risk groups according to the RRP total score: low, 0–9; medium, 10–19; high, 20–30. The C-index and calibration curve of the RRP model showed a promising predictive accuracy on the incidence of RP-ILD.

Conclusion: The RRP model might promisingly predict the incidence of RP-ILD in DM/CADM patients to guide early individual treatment and further improve the prognosis of DM/CADM patients.

Pharmacological characteristics of zolpidem-induced catalepsy in the rat

Zolpidem is a non-benzodiazepine hypnotic drug acting preferentially at α1-containing GABAA receptors expressed in various parts of the brain, including the basal ganglia. The aim of the present study was to provide preliminary characteristics of zolpidem-induced catalepsy in Wistar rats. Zolpidem (2.5-10.0mg/kg), but not diazepam and midazolam, produced dose-dependent cataleptic responses in the bar test, which were similar to those produced by a reference antipsychotic drug, haloperidol. Zolpidem-induced catalepsy was abolished by a benzodiazepine site antagonist, flumazenil (5.0mg/kg), D2/3 receptor agonist, quinpirole (1.0mg/kg), and a non-competitive NMDA receptor antagonist, MK-801 (0.1mg/kg), but not by a non-selective opioid receptor antagonist, naltrexone (3.0mg/kg). The present results indicate that systemic injections of zolpidem may produce short-lasting, neuroleptic-like catalepsy in the rat.

Distinct changes in evoked and resting globus pallidus activity in early and late Parkinson's disease experimental models

The main clinical manifestations of Parkinson's disease are caused by alterations of basal ganglia activity that are tied in with the progressive loss of mesencephalic dopaminergic neurons. Recent theoretical and modeling studies have suggested that changes in resting neuronal activity occurred later in the course of the disease than those evoked by phasic cortical input. However, there is no empirical support for this proposal. Here we report a marked increase in the responsiveness of globus pallidus neurons to electrical motor cortex stimulation, in the absence of noticeable changes in resting activity, in anesthetized rats that had consistently shown a deficit in forelimb use during behavioral testing before the experiments, and had approximately 45% dopamine neurons spared in the substantia nigra. Pallidal neurons were also over-responsive to motor cortex stimulation and lost spatial selectivity for cortical inputs in rats with extensive nigrostriatal damage. After partial lesions, over-responsiveness was mainly due to an increased proportion of neurons showing excitatory responses, while extensive lesions led to an increased likelihood of inhibitory responding neurons. Changes in resting neuronal activity, comprising pauses disrupting tonic discharge, occurred across different global brain states, including an activated condition which shares similarities with natural patterns of cortical activity seen in awake states and rapid eye-movement sleep, but only after massive nigrostriatal degeneration. These results suggest that a loss of functional segregation and an abnormal temporal encoding of phasic cortical inputs by globus pallidus neurons may contribute to inducing early motor impairment in Parkinson's disease.

Motor effects of GABA(A) antagonism in globus pallidus: studies of locomotion and tremulous jaw movements in rats

RATIONALE

Although most rodent studies related to parkinsonian symptoms have focused on locomotion, tremulous jaw movements also have been used as a rodent model of tremor for investigating the circuitry of the basal ganglia.

OBJECTIVE

There are multiple pathways involved in the generation of parkinsonian symptoms. The globus pallidus is a basal ganglia relay nucleus, and the present study was conducted to investigate the effect of pallidal GABA antagonism on locomotion and tremulous jaw movements.

METHODS

Suppression of locomotion and induction of tremulous jaw movements were produced by repeated (i.e., 14 day) systemic administration of the dopamine D2 antagonist haloperidol, and by acute systemic injection of the muscarinic agonist pilocarpine. The GABA(A) antagonist bicuculline was injected into the globus pallidus, and its effects on locomotion in haloperidol- and pilocarpine-treated rats were assessed in the first group of experiments. In the second group of experiments, the effects of intrapallidal infusions of bicuculline on haloperidol- and pilocarpine-induced jaw movements were observed.

RESULTS

Pallidal GABA antagonism stimulated locomotion when no other treatment was present, and also when animals were coadministered haloperidol or pilocarpine. Bicuculline suppressed haloperidol-induced jaw movements in a dose-related manner, and had no effect on pilocarpine-induced jaw movements.

CONCLUSIONS

These results support the notion that there are distinct pathways conveying basal ganglia outflow and demonstrate that the striatopallidal pathway is involved in the generation of the haloperidol-induced tremulous jaw movements. These findings are consistent with some features of current models of basal ganglia function and may lead to an understanding of the specific mechanisms that generate parkinsonian symptoms.

Endomorphin-1: induction of motor behavior and lack of receptor desensitization

The endomorphins are recently discovered endogenous agonists for the mu-opioid receptor (Zadina et al., 1997). Endomorphins produce analgesia; however, their role in other brain functions has not been elucidated. We have investigated the behavioral effects of endomorphin-1 in the globus pallidus, a brain region that is rich in mu-opioid receptors and involved in motor control. Bilateral administration of endomorphin-1 in the globus pallidus of rats induced orofacial dyskinesia. This effect was dose-dependent and at the highest dose tested (18 pmol per side) was sustained during the 60 min of observation, indicating that endomorphin-1 does not induce rapid desensitization of this motor response. In agreement with a lack of desensitization of mu-opioid receptors, 3 hr of continuous exposure of the cloned mu receptor to endomorphin-1 did not diminish the subsequent ability of the agonist to inhibit adenylate cyclase activity in cells expressing the cloned mu-opioid receptor. Confirming the involvement of mu-opioid receptors, the behavioral effect of endomorphin-1 in the globus pallidus was blocked by the opioid antagonist naloxone and the mu-selective peptide antagonist Cys(2)-Tyr(3)-Orn(5)-Pen(7) amide (CTOP). Furthermore, the selective mu receptor agonist [d-Ala(2)-N-Me-Phe(4)-Glycol(5)]-enkephalin (DAMGO) also stimulated orofacial dyskinesia when infused into the globus pallidus, albeit transiently. Our findings suggest that endogenous mu agonists may play a role in hyperkinetic movement disorders by inducing sustained activation of pallidal opioid receptors.

Dystonic posturing and circling behaviors induced by dopaminergic agents in rats with unilateral globus pallidus lesions

The present study examined the behavioral effects of dopamine receptor agonists, antagonists, or N-methyl-D-aspartate (NMDA) glutamate receptor antagonist in rats with a unilateral excitotoxic lesion of the globus pallidus (GP). After the unilateral GP lesions were made by injections of the ibotenic acid, drugs were systemically given and the elicited behaviors were quantitatively assessed. Systemic administration of haloperidol, but not SCH23390, dose-dependently induced contraversive dystonic posturing in unilateral GP-lesioned rats. On the other hand, systemic administration of quinpirole, but not SKF38393, induced ipsiversive circling. MK-801, only when given at a high dose, unilateral GP-lesioned rat, the D2 receptor agonist and antagonist caused ipsiversive and contraversive posturing or circling, respectively. Since the rotational behavior is induced on the basis of asymmetry of the basal ganglia output activity, there must be a marked difference between the GP ablation and the administration of D2 receptor blockade on the basal ganglia output activity, supporting a speculation that overactivity of the basal ganglia under dopamine depletion is not solely a result of the disinhibition from the inhibitory GP efferents. The present unilateral GP-lesion model appears to be a useful one for the pharmacobehavioral investigation of D2-mediated mechanisms.

Zona incerta-lateral hypothalamus as an output structure for impulses involved in neuroleptic drug-induced catalepsy

Our previous studies showed that the neuronal impulses connected with catalepsy, which have their origin at dopamine D2 receptors in the ventro-rostral part of the nucleus caudatus-putamen in rats, are conveyed to the zona incerta-lateral hypothalamic region. The aim of the present study was to investigate the route of the neuronal impulses between these structures. The experiments were carried out on rats with cannulae chronically implanted in the brain structures. We showed that (1) bilateral injection of bicuculline methiodide (5-50 ng) into the ventro-medial part of the globus pallidus (GPv) and (2) bilateral injection of muscimol (2.5-25 ng) into the substantia nigra pars reticulata (SNR) inhibit, in a dose dependent manner, the catalepsy induced by sulpiride (1 microgram) administered bilaterally into the ventro-rostral part of the nucleus caudatus-putamen. It was also demonstrated that muscimol (25 ng), injected bilaterally into the ventro-medial part of the globus pallidus, induces catalepsy which, in turn, is dose-dependently inhibited by either (1) muscimol (5-25 ng) injected into the substantia nigra pars reticulata, or (2) bicuculline (1.0-2.5 ng) injected into the zona incerta-lateral hypothalamus (ZI-LH). Moreover, even a dose as high as 50 ng of bicuculline, injected into the ventro-medial part of the globus pallidus, had no significant effect on the locomotor activity of rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioural and biochemical effects of muscimol in ethanolamine O-sulphate-treated rats

A behavioural model, accompanied by biochemical analysis, was used to study the effects of the GABA-A receptor agonist muscimol on untreated and ethanolamine O- sulphate (EOS)-treated male rats. The most pronounced effect of muscimol was a lengthening of the duration of investigating behaviour. Pretreatment with EOS for 29 days potentiated this effect. Muscimol decreased the accumulation of GABA in the substantia nigra after 8 days but not after 30 days of EOS treatment, indicating that receptor adaptation might have occurred. We conclude that muscimol influences investigating behaviour and that chronic elevated brain GABA levels potentiate this effect.

Drug effects on active immobility responses: what they tell us about neurotransmitter systems and motor functions

The literature reviewed indicates that active immobility can be promoted by systemic injections of various neurotransmitter systems, as follows: (1) Dopaminergic blockade of both D1 and D2 receptor subtypes. (2) Cholinergic agonism of both muscarinic and nicotinic receptors. (3) Noradrenergic agonism of both alpha-1 and alpha-2 receptors (but these agonists may interfere with haloperidol- and reserpine-induced catalepsy). (4) GABA agonism. (5) Histamine agonism, particularly at the H1 receptor. (6) Opiate agonism, including action of many endogenous opiate peptides, particularly those affecting mu and delta receptors. (7) Agonism by certain other peptides (neurotensin, cholecystokinin). Among the major interactions of neurotransmitter systems that regulate immobility, are the following: (1) Cholinergic-dopaminergic (cholinolytics disrupt catalepsy of dopaminergic blockade and dopaminergic agonists tend to disrupt cholinomimetic catalepsy). (2) Opiate-induced catalepsy is antagonized by the dopamine agonist, apomorphine, but is enhanced by amphetamine. It is also antagonized by certain alpha-2 adrenergic agonists, while it does not seem to be antagonized by anticholinergics. (3) Numerous other interactions have been reported, involving opiates and MSH, serotonin and dopamine mimetics, serotonin and ketamine, GABA and neuroleptics, neurotensin and anticholinergics and histamine. The significance of the multiple neurotransmitter systems is unknown. One possible explanation is that the various neurotransmitter systems participate in mediating the sensory inputs that are involved in triggering immobility and regulate the higher-order limbic and basal ganglia processing reactions that engage a final motor output pathway from the brainstem. The brain is assumed to contain two sets of systems, each with its own, or possibly overlapping, set of neurotransmitter systems, that promote either active immobility or locomotion. The systems reciprocally inhibit each other. Another view, not mutually exclusive, is that output from the locomotor-promoting system provides a negative feedback, via the active immobility pathways, to act as a "brake" on movement, while at the same time maintaining the muscular tonus that is characteristic of active immobility.

The behavioural effects of chronic elevation of rat brain GABA by ethanolamine O-sulphate

This study examined the functional effects of long-term elevated brain GABA concentrations. The increase in GABA was achieved by use of the GABA-aminotransferase (GABA-T) inhibitor, ethanolamine O-sulphate (EOS). Forms of exploratory behaviour pre viously demonstrated to be sensitive to GABAergic receptor stimulation were measured over a 4 week period of EOS treatment. The most pronounced behavioural effect was an increased duration of investigating behaviour following 2-21 days of EOS treatment. This effect was accompanied by an accumulation of GABA in the substantia nigra and the corpus striatum. After 28-30 days of EOS treatment the GABA concentration was still significantly elevated, whereas the investigating behaviour was no longer different from controls.

Delta-9-tetrahydrocannabinol-induced catalepsy in mice is enhanced by pretreatment with flurazepam or chlordiazepoxide

Pretreatment with flurazepam (3 mg/kg s.c.) or chlordiazepoxide (5.5-30 mg/kg s.c.) at an ambient temperature of 34 degrees C, markedly enhanced the cataleptic response of mice to delta-9-tetrahydrocannabinol (THC; 5-20 mg/kg i.p.) as measured in a bar test. Also, the incidence of loss of the righting response was significantly greater in mice receiving a subhypnotic dose of flurazepam (0.3-3 mg/kg s.c.), followed by THC (5-20 mg/kg i.p.), than in animals receiving THC preceded by saline. Loss of the righting response was not associated with any gross reduction in skeletal muscle tone (inclined screen and wire grip tests) and it was proposed that the animals were not anaesthetized but instead could be placed on their backs because flurazepam had enhanced the cataleptic effect of THC. Loss of the righting response produced in mice by pentobarbitone (60 mg/kg i.p.) or by a large dose of flurazepam (300 mg/kg s.c.) was associated with a marked loss of muscle tone and probably indicated the induction of anaesthesia. It is possible that THC interacts with benzodiazepines by increasing synaptic concentrations of gamma-aminobutyric acid (GABA). However, many other possible mechanisms exist and these cannot yet be excluded.

Dopamine dependent behaviours in rats with bilateral ibotenic acid-induced lesions of the globus pallidus

Amphetamine hyperactivity, apomorphine stereotypy and haloperidol catalepsy were studied in rats following selective damage to cell bodies within the globus pallidus (GP). Ibotenic acid-induced bilateral lesions of GP attenuated the spontaneous locomotion of rats, but they did not influence the locomotor response to amphetamine. Apomorphine-induced gnawing and licking but not sniffing were attenuated in rats with GP lesions. The effect of haloperidol on catalepsy was enhanced following the GP lesion. It is concluded that the normal expression of some dopamine-related functions depends to a great degree on the integrity of cells within the GP region.

Brain dopamine activity following intranigral or intrathalamic drug injections in the rat

Stereotaxic injection of muscimol into a restricted region of one substantia nigra of the rat provoked robust circling and a concomitant rise in ipsilateral nigrostriatal dopamine activity, as revealed by a greater accumulation of 3,4-dihydroxyphenylacetic acid and homovanillic acid in the caudate-putamen together with depleted nigral dopamine concentrations. Considered with earlier evidence, these data are taken to indicate that dopamine may be involved in the mediation of this particular rotational behaviour. On the other hand, focal application of bicuculline to the substantia nigra or ventromedial thalamus, or intrathalamic kainate, all evoked a closely similar and vigorous hypermotility (not circling) that could not be correlated with the assorted changes in dopamine utilisation occurring in the substantia nigra, caudate-putamen or nucleus accumbens, either uni- or bilaterally. These changes were therefore probably casually rather than causally related to the mechanisms underlying the behaviour of the animals. Whilst the regional concentrations of noradrenaline were unaltered by these focal drug treatments, the induction of halothane anaesthesia coupled with a unilateral intranigral saline injection produced bilateral elevations in regional dopamine utilisation when assessed 15 min after injection. Such changes were not apparent in tissue taken 30 or 60 min post-injection. We conclude that dopamine cell activity and/or other indices of dopamine utilisation cannot be used to predict the behavioural state of the individual and that an imbalance between the dopamine systems in the two hemispheres does not per se lead to postural or locomotor asymmetry.

The role of the GABA mechanisms of the globus pallidus in mediating catalepsy, stereotypy and locomotor activity

Muscimol, picrotoxin and bicuculline were injected bilaterally through permanently implanted cannulae into either anterior (GPa) or posterior parts of the globus pallidus (GPp) of rats. Both the muscimol injected into the GPa and the picrotoxin injected into the GPp abolished or strongly inhibited spiperone (0.2 mg/kg, IP)-induced catalepsy. Muscimol alone (25-200 ng/0.2 microliter/GP) injected into the GPa evoked a dose-dependent biphasic effect: at first catalepsy (throughout 7.3 min), and then a long-lasting (more than 2 hr) locomotor stimulation and stereotyped sniffing. Muscimol (200 ng/GP) injected into GPp inhibited both the spontaneous motility and amphetamine-induced hyperactivity. Picrotoxin (200 and 400 ng/GP) injections into GPa and GPp produced an increase of the locomotor activity as well as stereotyped sniffing. Picrotoxin started to block muscimol hyperactivity when its own stimulatory action disappeared, thus also for picrotoxin the second phase of action could be detected. The globus pallidus is shown to be a relay station of impulses mediating neuroleptic catalepsy. Furthermore, it is suggested that behavioural changes induced by muscimol resulted from the action of the drug on at least 2 different neuronal systems, both being controlled by GABA receptors. One of them seems to be responsible for inducing neuroleptic-like catalepsy, and the other one for the hyperactivity and blockade of spiperone-catalepsy.

Role of mesencephalic reticular formation in cholinergic-induced catalepsy and anticholinergic reversal of neuroleptic-induced catalepsy

The present experiments investigate the brain sites involved in the elicitation of catalepsy by cholinergic agonists and neuroleptics. Microinjection of acetylcholine chloride (50 micrograms) in combination with eserine (2.5 micrograms) into the ventral mesencephalic reticular formation (MRF) elicited catalepsy. Microinjection of atropine sulfate (5 micrograms) into the same sites reversed the catalepsy of rats treated with haloperidol (1.5 mg/kg) 2 h earlier, but did not reverse morphine-induced (30 mg/kg, 1 h) catalepsy. Haloperidol (25 micrograms) injected into the nucleus accumbens septi (NAS) resulted in catalepsy as severe as that caused by an identical injection into the caudate nucleus. Catalepsy caused by intraNAS haloperidol occurred with a shorter latency than that resulting from intracaudate haloperidol, and was reversed by systemic scopolamine (0.4 mg/kg). On the basis of these results it is suggested that the ventral MRF is a site for the elicitation of catalepsy by cholinergic agonists and for the reversal of neuroleptic-induced catalepsy by anticholinergics, and that neuroleptic-induced catalepsy involves blockade of dopamine receptors in both the NAS and caudate nucleus.

Role of the ventromedial nucleus of the thalamus in motor behaviour--I. Effects of focal injections of drugs

An assortment of drugs was injected into one or both ventromedial nuclei of the thalamus, to see how these influenced stereotypy, locomotion and posture in spontaneously behaving and actively rotating rats. Unilateral intrathalamic muscimol promoted weak ipsiversive circling, while bilateral treatment gave catalepsy. Similar injections of 4-amino-hex-5-enoic acid, which inhibits gamma-aminobutyrate metabolism, raised gamma-aminobutyrate levels in the ventromedial nuclei more than three-fold yet had none of these behavioural effects. The indirectly acting gamma-aminobutyrate agonists flurazepam and cis-1,3-aminocyclohexane carboxylic acid had little effect on posture and locomotion and, like muscimol and 4-amino-hex-5-enoic acid, elicited only very weak stereotypies. Procaine behaved like the gamma-aminobutyrate antagonist bicuculline, provoking vigorous locomotor hyperactivity and teeth chattering if given uni- or bilaterally. Pretreatment of one ventromedial nucleus with muscimol or 4-amino-hex-5-enoic acid, and to a lesser extent flurazepam or cis- 1,3-aminocyclohexane carboxylic acid, gave rise to pronounced ipsilateral asymmetries when combined with a large systemic dose of apomorphine. Contraversive rotations were initiated by unilateral stereotaxic injection of muscimol into the substantia nigra pars reticulata, or with apomorphine from the supersensitive striatum in unilaterally 6-hydroxydopamine lesioned rats. Drug treatments in the ipsilateral ventromedial nucleus showed a similar rank order of potency at inhibiting these circling behaviours, seemingly by reducing apomorphine-induced posture and muscimol-induced hypermotility. The suppression of circling by muscimol in these tests was highlighted by introducing the compound into the ventromedial nucleus at the height of circling activity. Both types of circling stimulus lost the capacity to increase locomotion, but still caused head turning and stereotypy in rats made cataleptic with bilateral ventromedial muscimol. Treating one ventromedial thalamus with muscimol greatly intensified any pre-existing posture directed towards that side, and vice versa. These data suggest that the ventromedial nucleus is not involved with the expression of stereotyped behaviours, but can profoundly influence posture and locomotion, especially in the presence of some other motor stimulus. The recovery of circus movements in rats with impaired ventromedial nucleus function implies this nucleus is not essential for the execution of circling in these models.

A biphasic influence of globus pallidus lesions: spontaneous catalepsy followed by anticataleptic effect

The behavioural and histological effects of unilateral or bilateral lesions induced by kainic acid injections into the globus pallidus were investigated in rats. Both lesions provoked a behavioural syndrome similar to those seen in animals treated systemically with neuroleptics or opiates. Animals displayed akinesia, ptosis, catalepsy, hypothermia and muscular rigidity. Also a marked hypersensitivity to touch, and a sensory neglect to touch and pain limited to hindlegs, adipsia, aphagia and high mortality of lesioned rats were observed. These symptoms were much stronger and lasted longer (catalepsy lasted over 15 days) in bilaterally lesioned animals. Subcutaneous injections of apomorphine in bilaterally lesioned rats abolished akinesia and catalepsy while rigidity and ptosis were unaffected. In unilaterally lesioned rats in which the lesion-induced spontaneous catalepsy already disappeared the spiperone-induced catalepsy was suppressed while in bilaterally lesioned animals which showed still pronounced lesion-induced catalepsy the spiperone-induced catalepsy was unchanged when compared to the sham-operated rats. Our results and the literature data suggest that the lesions of the globus pallidus produce biphasic effects: spontaneous catalepsy and unchanged neuroleptic catalepsy in the first phase and suppression of the neuroleptic catalepsy in the second phase. The role of the globus pallidus as a distal link (for neostriatum and n. accumbens) in neuronal chain forming a matrix of central patterns of catalepsy, akinesia and rigidity is discussed.

Enhancement of cocaine-induced hyperactivity in mice by benzodiazepines: evidence for an interaction of GABAergic processes with catecholaminergic neurons?

The effects of nine benzodiazepines on the locomotor stimulation induced in mice by cocaine (4 mg . kg-1 i.p.) were studied. These benzodiazepines markedly enhanced cocaine-induced hyperactivity. This effect was observed at low doses, e.g. doses at least 8 times lower than those required to depress the stimulation caused by cocaine. Nitrazepam-induced enhancement of the hyperactivity elicited by cocaine was reduced or suppressed by blocking dopaminergic receptors with pimozide (0.015--0.03 mg . kg-1), by interrupting GABAergic transmission with picrotoxin (0.25--0.5 mg . kg-1) or blocking alpha- or beta-adrenergic receptors with prazosin (0.25 mg . kg-1) or dl-propranolol (4 mg . kg-1) respectively. At these doses, neither pimozide, picrotoxin, prazosin nor propranolol were able to modify the spontaneous locomotor activity or the stimulation elicited by cocaine alone. Strychnine (0.25--0.50 mg . kg-1) or methysergide (2 mg . kg-1) failed to alter the enhancement by nitrazepam of cocaine-induced hyperactivity. These results suggest that an interaction of benzodiazepines with some catecholaminergic processes, either directly or through the involvement of a GABAergic link, may account for their facilitatory activity on cocaine-induced locomotor stimulation.

The effects of muscimol and picrotoxin injections into the cat substantia nigra

The behaviour of cats after unilateral injections of muscimol, picrotoxin and bicuculline into the posterior and lateral parts of the substantia nigra was observed. The antagonism between muscimol and picrotoxin was limited to some effects of the drugs: (1) muscimol-induced sniffing, licking and enhanced locomotor activity was attenuated by picrotoxin in contrast to the muscimol-induced contralateral turning which was even enhanced by picrotoxin; (2) picrotoxin-induced balance disorders as well as characteristic motor disturbances in the hind legs remained unaffected following an additional treatment with muscimol. Furthermore, subcutaneously given apomorphine did not affect the picrotoxin-induced balance and hind leg disorders, although the apomorphine-induced stereotyped behaviour itself was enhanced and suppressed by intranigral administration of muscimol and picrotoxin respectively. The conclusion is reached that there are at least two distinct populations of GABA receptors within the substantia nigra: one group controlling or being controlled by dopaminergic neurons and one group operating fully independently of the former neurons. The similarities to experiments on rats are stressed. The mechanism underlying the muscimol-resistant picrotoxin-induced effects (balance disorders and motor disturbance of the hind legs) is discussed.

Naloxone reduces abdominal muscle tone in mice and rats

The effect of naloxone on muscle tone was investigated in mice and rats at various times after administration. The naloxone effect was also tested in diazepam-pretreated animals. Naloxone was found to display muscle relaxant activity. This effect appeared to be additive to that of diazepam.

The effects of GABA-ergic drugs on enkephalin-induced motor seizure phenomena in the rat

1. The relationship between the effects of GABA-ergic drugs and D-ala2-met-enkephalinamide (DALA)-induced myoclonic contractions of inframandibular muscles has been studied in the rat. 2. GABA-ergic drugs altered enkephalin-induced myoclonic contractions in the following manner: (a) The GABA-mimetic drugs, muscimol, gabaculine and baclofen, decreased DALA-induced myoclonic contractions. (b) The GABA antagonist, bicuculline and the anticonvulsant substance, sodium valproate (dipropylacetic acid, DPA) potentiated DALA-induced myoclonic contractions. The potentiating effect of DPA is probably due to its opiate-like activity, since naloxone abolished this effect. 3. The modulatory effect of the GABA-mimetic drug on enkephalin-induced myoclonic contractions may give grounds for further study to test the possible use of other GABA-mimetic drugs and possibly opiate antagonists for the treatment of myoclonic syndromes.

Biphasic effects of direct, but not indirect, GABA mimetics and antagonists on haloperidol-induced catalepsy

At very low doses the GABA agonists SL 76002 and muscimol diminish haloperidol-induced catalepsy. At somewhat higher doses these compounds potentiate catalepsy. Biphasic effects on DA-receptor mediated functions have previously been noted with bicuculline and picrotoxinin. In contrast, manipulation of GABA levels by enzyme inhibition induced only a monophasic effect on dopamine-mediated behaviour. The potentiation of GABA levels by enzyme inhibition induced only a monophasic effect on dopamine-mediated behaviour. The potentiation of haloperidol-induced catalepsy by GABA mimetics is also observed with dipropylacetate, delta-aminovaleric acid and gamma-acetylenic GABA. This GABA-mimetic potentiation of catakepsy was blocked by the coadministration of bicuculline. These results confirm and extend the hypothesis that GABA-neurons influence DA neuron function. Furthermore they suggest that more than one group of GABA receptors influence directly and/or indirectly DA neuronal function, with different resultant effects.