Antagonism of methylphenidate-induced stereotyped gnawing in mice

Dopamine receptor occupancy in vivo: behavioral correlates using NNC-112, NNC-687 and NNC-756, new selective dopamine D1 receptor antagonists

The ability of dopamine D2, mixed D1/D2 and selective D1 receptor antagonists, including NNC-112, NNC-687, NNC-756, to inhibit the in vivo binding of [3H]SCH 23390 or [3H]raclopride to dopamine receptors was studied in mice and rats. Furthermore, the dopamine-antagonistic effects of these drugs were also studied in various behavioral models. Significant levels of in vivo receptor blockade were required for antagonism of typical dopamine agonist-mediated behaviors. However, fewer D1 than D2 receptors had to be blocked to produce similar antagonistic effects. Thus, there may be a greater receptor reserve for D2 receptors than for D1 receptors.

Partial and full dopamine D1 receptor agonists in mice and rats: relation between behavioural effects and stimulation of adenylate cyclase activity in vitro

The dopamine (DA) D1 agonists, SK&F 83959, SK&F 75670, SK&F 38993, SK&F 81297 and SK&F 80723, had variable abilities to stimulate adenylate cyclase activity in rat striatal homogenates. Their efficacies, in relation to the effect of 100 microM DA were 0, 33, 69, 68 and 81%, respectively. In rats, all compounds induced (1) contralateral circling behaviour after unilateral 6-hydroxy-DA lesions, (2) ipsilateral circling behaviour after midbrain hemitransection after cotreatment with the D2 agonist quinpirole and (3) oral stereotypies after their combination with quinpirole. Maximum effects and rank order of potencies were similar in the three test models. In mice SK&F 83959, SK&F 75670 and SK&F 38393 inhibited methylphenidate-induced gnawing behaviour and induced no or only weak hypermotility. SK&F 81297 induced marked hypermotility which was partially inhibited by SK&F 83959 and SK&F 75670 and was completely blocked by the D1 antagonist, SCH 23390. It is concluded that no relation could be demonstrated between the efficacy to stimulate adenylate cyclase and to induce circling behaviours and stereotypies in rats. In contrast, a relation between biochemical and behavioural efficacies was found in the mouse models. The results suggest that different subtypes of D1 receptors mediate the behavioural effects reported in this study.

Characterization of tiagabine (NO-328), a new potent and selective GABA uptake inhibitor

Tiagabine (NO-328) (R(-)-N-[4,4-bis(3-methylthien-2-yl)but-3-enyl]nipecotic acid, hydrochloride) is a new centrally acting GABA uptake inhibitor. The anticonvulsant activity of tiagabine was evaluated against seizures induced by methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), pentylenetetrazol, bicuculline, maximal electrostimulation (MES), or high intensity sound. The sedative actions of tiagabine were evaluated in tests for traction, rotarod performance and exploratory behavior. Finally, interoceptive properties of tiagabine were assessed using diazepam-, CGS 9896-, pentylenetetrazol-, or amphetamine-discriminating rats. Tiagabine was an effective anticonvulsant in doses which did not produce sedation or motor debilitation, although it was not potent against MES. In a manner similar to other anti-epileptic drugs, tiagabine potentiated dopaminergic function (methylphenidate-induced gnawing in mice) although it did not substitute for amphetamine in amphetamine-trained animals. Furthermore, although tiagabine antagonized DMCM-induced convulsions, it exhibited neither CGS 9896 or diazepam-like interoceptive effects, nor did it block (or potentiate) pentylenetetrazol-discrimination. Thus, GABA uptake inhibition represents a novel rationale for a valproate-like anticonvulsant drug therapy.

Discriminative stimulus effects of a low dose of apomorphine in the rat

The discriminative stimulus (DS) effect of apomorphine was investigated in rats trained in a two-lever, food-reinforcement procedure. Rats were given subcutaneous injections of saline or 0.1 mg/kg apomorphine HCl, 15 min before training sessions. The training dose of apomorphine was chosen to activate dopamine autoreceptors selectively. Stimulus generalization studies demonstrated that the DS effects generalized completely to other direct-acting dopaminergic agonists such as N-n-propylnorapomorphine (NPNA), pergolide, lergotrile, and bromocriptine. The indirect-acting dopamine agonists, (+)amphetamine, cocaine, and methylphenidate produced predominantly saline-appropriate lever responses. The DS effect of apomorphine at the training dose was incompletely antagonized by haloperidol or metoclopramide. The dopaminergic antagonists tested, however, also partially generalized to apomorphine. Both enantiomers of 3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP) produced apomorphine-appropriate lever choice with the (-) enantiomer being slightly more potent. The discriminative property of this (0.1 mg/kg) dose of apomorphine has characteristics consistent with selective dopamine autoreceptor activation.

Ontogeny of GABA-ergic and dopaminergic mediation of gnawing behavior in the mouse

The ontogenetic course of dopaminergically mediated gnawing and the potentiation of this behavior by muscimol (a GABA receptor agonist) was explored in developing and young adult mice using a time-sampling (in 5-, 8-, 11-, and 14-day-old pups), or a corrugated paper procedure (in 14-, 17-, 20-, 23-, 26-, 35-, and 53-day-old animals). In experiment 1, the older mice group (14-53 days), displayed a dose-dependent gnawing behavior after methylphenidate, a dopamine indirect agonist (20, 30, 50 mg/kg). Similarly, in 5-, 8-, 11-, and 14-day-old pups, methylphenidate (10, 20, 50 mg/kg) evoked stereotyped gnawing (or indissociable gnawing-licking in 5-day-old pups), with maximal effects after the two lower doses at 8-11 days of age (experiment 2). Muscimol pretreatment (dosages ranging from 0.025 to 1.3 mg/kg) induced a clear-cut potentiation of gnawing elicited by methylphenidate (10 or 20 mg/kg) as early as 8 days of age (experiments 3 and 4). However, muscimol did not potentiate gnawing in 5-day-old pups treated with 10 or 2.5 mg/kg methylphenidate. The effectiveness of methylphenidate in inducing gnawing-licking among 5-day-old pups confirms the early maturation of central dopamine receptors reported in the literature. It is speculated that the absence of potentiating action of muscimol on methylphenidate-induced gnawing-licking at this age may be due to a functional immaturity of the GABAergic striato-nigro-tectal system, which is thought to transmit dopaminergic striatal stereotyped response at the output stations (recent review by Scheel-Krüger 1986).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological differentiation of dopamine D-1 and D-2 antagonists after single and repeated administration

In single-dose experiments neuroleptics antagonize dopamine (DA)-agonist-induced stereotypies in animals. The antagonistic potency correlates with their clinical antipsychotic effects. In a series of experiments where DA-agonist-induced stereotyped gnawing in mice and rats was inhibited by neuroleptics it was shown that the antagonistic effect of butyrophenones was greatly attenuated by concomitant treatment with anticholinergics. The effect of phenothiazines was slightly attenuated and that of thioxanthenes and SCH 23390 remained unchanged. After repeated administration a differentiation is also seen in the ability of the antagonists to suppress DA-agonist-induced stereotypies. The differentiation in these experiments is similar to that seen in dopamine D-1 and D-2 receptor binding. The compounds can be classified into three pharmacological subgroups: butyrophenones (e.g., haloperidol) with affinity for D-2 receptors; phenothiazines (e.g., fluphenazine and perphenazine) with affinity for both D-2 and D-1 receptors but with preference for the D-2 receptors; and thioxanthenes (e.g., cis(Z)-flupentixol and cis(Z)-clopenthixol) with equal affinity for D-1 and D-2 receptors, and the selective D-1 antagonist SCH 23390. This compound has the same antistereotypic effect as is seen with the neuroleptics. We have also investigated the effect of the above-mentioned neuroleptics and SCH 23390 after 12 days' treatment and 3-5 days withdrawal. They were given either alone or in combination. When they were given alone a clear differentiation was seen between the groups when mice were tested for methylphenidate antagonism. The thioxanthenes and SCH 23390 retain their ability to antagonize the stereotyped gnawing; the phenothiazines show a reduced effect; and the butyrophenones have almost lost their ability to antagonize the stereotyped behavior.

Pharmacological effects of a specific dopamine D-1 antagonist SCH 23390 in comparison with neuroleptics

Neuroleptics such as thioxanthenes (cis(Z)-flupentixol and cis(Z)-clopenthixol) and phenothiazines (fluphenazine and perphenazine), which block both dopamine (DA) D-1 and D-2 receptors and the butyrophenones (haloperidol and spiroperidol), which block D-2 receptors only, are equipotent both behaviorally and clinically. A new compound SCH 23390 which selectively blocks DA D-1 receptors, resembles many neuroleptics in its pharmacological profile: antistereotypic effects in mice, rats and dogs, cataleptogenic effect and inhibitory effect on amphetamine circling. In contrast SCH 23390 has no effect on apomorphine-induced vomiting in dogs and little effects on 6-OHDA-denervated supersensitive DA receptors, stimulated by the DA agonist 3-PPP. In a series of experiments where methylphenidate-induced stereotyped gnawing in mice was inhibited by neuroleptics, it was shown that concomitant treatment with scopolamine or diazepam attenuated the effect of butyrophenones (D-2 antagonists). The same treatment attenuated the effect of phenothiazines, to a lesser extent, and hardly attenuated the effect of thioxanthenes and SCH 23390 at all. It is concluded that DA D-1 receptors are as important as D-2 receptors for the expression of neuroleptic activity in most animal models believed to be predictive of antipsychotic and extrapyramidal side-effect potential. However, the D-1 antagonist is less sensitive than D-2 antagonists to antimuscarinic compounds and benzodiazepines.

Dopamine receptor agonistic and antagonistic effects of 3-PPP enantiomers

The pharmacological profile of the enantiomers of the proposed selective dopamine (DA) autoreceptor agonist 3-PPP [3-(3-hydroxyphenyl)-N-n-propylpiperidine] has been studied. In vitro both enantiomers showed weak DA agonistic activity, and (--)-3-PPP some DA antagonistic effect on DA-stimulated adenylate cyclase activity. Both enantiomers in low doses had a similar profile in vivo: Inhibition of locomotor activity of mice and rats, induction of contralateral circling behaviour in 6-hydroxy-DA-lesioned rats and an emetic effect in dogs. At higher doses, differential effects of the enantiomers were found: (+)-3-PPP induced hyperactivity, weak stereotyped behaviour and ipsilateral circling in hemitransected rats. (--)-3-PPP had depressant effects in high doses, inhibited d-amphetamine-induced hyperactivity and d-amphetamine-, methylphenidate- and apomorphine-induced stereotyped licking/biting in rats and antagonized apomorphine-induced emesis in dogs. However, (+)-3-PPP also showed a weak antagonistic activity against d-amphetamine-induced hyperactivity and d-amphetamine- and apomorphine-induced stereotypy in rats and inhibited apomorphine-induced emesis in dogs. It is suggested that both enantiomers have significant effects on postsynaptic DA receptors in high doses: (--)-3-PPP with weak antagonistic activity in some test models and (+)-3-PPP with agonistic and antagonistic effect. Since these effects of (+)-3-PPP were of low intensity at high doses, (+)-3-PPP may be a partial DA agonist at postsynaptic receptors in high doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacodynamic effects and possible therapeutic uses of THIP, a specific GABA-agonist

THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) is a potent and specific GABA receptor agonist which does not influence the GABA uptake system or GABA metabolizing enzymes. The specificity for the GABA receptor is also demonstrated by lack of action on monoaminergic, cholinergic, histaminergic or opiate receptors. Since in recent years GABA receptor stimulants-among others THIP--have become available many have speculated as to what clinical indication GABA-ergic stimulation might be an important element. The first suggestion was that GABA-ergic drugs by an inhibitory effect on the dopamine neurons would improve the antischizophrenic effect of neuroleptics and improve tardive dyskinesia. Furthermore, studies on brains of deceased Parkinson and Huntington's chorea patients have demonstrated a low level of GABA and its synthesizing enzyme glutamic acid decarboxylase (GAD) in the basal ganglia. Also in epilepsy and diseases with dementia a deficit in the GABA system has been proposed. Therefore a therapeutic strategy for these diseases may be supplementary treatment with drugs which increase GABA receptor activity. Furthermore, recent results in humans have shown that GABA agonists perhaps also could be of benefit in mania and depressions. When considering the neurophysiological elements of nociception and muscle tone it is also reasonable to suggest that GABA-ergic stimulation may reduce pain perception and muscle tone.

A study of inhibition of cholera toxin-induced intestinal hypersecretion by neuroleptics

Various types of neuroleptics and other agents were examined for inhibitory effect in cholera toxin-induced hypersecretion in ligated loops of mice jejunum. Several agents belonging to the phenothiazine group or thioxanthene group were inhibitory. Only three other neuroleptics, loxapin, haloperidol and penfluridol, inhibited the hypersecretion. Among the miscellaneous agents the calcium antagonist nifedipine was inhibitory. The potencies of the neuroleptics did not correlate with the dopamine antagonistic potencies. The results indicate that the site of antisecretory action of the drugs is to be found outside the central nervous system.

Narcotic analgesics and stereotyped behaviour in mice

In this paper we have studied the effects of morphine, codeine, fentanyl, pentazocine, etorphine and fluphenazine (all drugs injected i.p.) on stereotyped behaviour induced by methylphenidate 60 mg/kg i.p., as well as induced by apomorphine 5 mg/kg s.c. in mice. It was found that all used analgesics and fluphenazine dose--dependently inhibited the intensity of methylphenidate--induced gnawing in mice. This effect of analgesics, but not that of fluphenazine was antagonized by naloxone (0.8 mg/kg i.p.) and nalorphine (10 mg/kg i.p.). Climbing behaviour induced by apomorphine was not reduced by narcotic analgesics, but fluphenazine inhibited this effect dose--dependently. These findings give the behavioural support that analgesics applied have antidopaminergic activity in mice.

An automated method for studying stereotyped gnawing

Stereotyped behavior in rats, consisting of compulsive, repetitive sniffing and gnawing, caused by high doses of amphetamine-like psychostimulants, may serve as an animal model for psychosis. Previous methods for measuring behavioral stereotypies of this kind have required continuous observation and rating of the behaviors or semiquantitative techniques that fail to produce a continuous record of the behaviors. The present paper describes a simple automated method that provides a continuous quantitative record of the specific gnawing behavior induced in rats by methylphenidate, an amphetamine-like psychostimulant. The apparatus described and the test procedures developed are compatible with a wide variety of common counters and recorders.

Differential effects of methylphenidate and d-amphetamine on stereotyped behavior in the rat

Different equimolar doses of d-amphetamine and methylphenidate were compared for their potency in eliciting stereotyped behavior in rats. Although at lower doses d-amphetamine appeared more effective in causing stereotyped gnawing, repetitive body movements, and sniffing, at higher doses methylphenidate at certain times caused a greater incidence of gnawing than did d-amphetamine. Understanding these differences and comparing related biochemical correlates may lead to a better definition of mechanisms underlying psychostimulant effects.

Dopaminergic supersensitivity: influence of dopamine agonists, cholinergics, anticholinergics, and drugs used for the treatment of tardive dyskinesia

Single and repeated administration of neuroleptics induce supersensitivity to dopamine agonists like apomorphine and methylphenidate. The degree of this supersensitivity depends on the period of the preceding administration of the neuroleptic. In the development phase additional administration of apomorphine can reverse the hyperdopaminergic behaviour, whereas addition of cholinergic/anticholinergic treatment does not modify the enhanced receptor response. In the supersensitivity phase additional treatment with deanol does not modify the supersensitivity. Pheobarbital, diazepam, and muscimol increase and cis (Z)-flupenthixol decreases the supersensitivity. It is concluded that supersensitivity induced by neuroleptics is time-dependent and that it can be prevented by additional treatment with DA-agonists but not by cholinergic/anticholinergic treatment. In the supersensitivity phase, the syndrome is suppressed by dopamine antagonists but enhanced by GABA-agonists, benzodiazepine and phenobarbital.

Behavioral evidence for supersensitivity after chronic bromocriptine administration

Behavioral evidence for tolerance and supersensitivity during and after chronic (30 day) administration of bromocriptine (BRC) or bromocriptine + L-dopa in mice was assessed by measuring wheel running (WR) behavior during and after chronic drug administration, and apomorphine- and methylphenidate-(MP-)induced stereotyped gnawing after termination of chronic injections. In both BRC and BRC + L-dopa groups, tolerance developed fairly quickly to the depressing effect of BRC on WR seen on day 1 of drug administration. Mice receiving BRC showed significant increases in WR by week 2 of chronic drug administration, which persisted for at least two days after the termination of chronic injections. During the first week after termination of chronic injections, low doses of both apomorphine and MP induced significantly more stereotyped gnawing in BRC and BRC + L-dopa mice than in the control mice or the mice treated with L-dopa alone. This behavioral evidence for dopaminergic supersensitivity after chronic BRC administration may have relevance for the clinical use of BRC in combination with L-dopa or other dopamine agonists.

Effects of methylphenidate on schedule dependent and schedule induced behavior

The effects of methylphenidate, 1.5, 3.0, 6.0 and 12.0 mg/kg, on lever pressing, schedule induced licking, and drinking were studied. The generator schedule was a fixed interval 1 min food reinforcement schedule. The effects were assessed when animals were reduced to 80% body weight by partial food deprivation and when allowed to recover body weight under conditions of ad lib eating. Results indicate that under body weight conditions methylphenidate significantly decreases schedule induced licking and drinking but does not affect lever pressing.

An open field study of stereotyped locomotor activity in amphetamine-treated rats

It is said that amphetamine induces stereotypy and locomotion in rats; however, the present paper shows amphetamine-induced stereotyped locomotion by analyzing the route of locomotion in an open field. Details of the analysis are given, normal as well as stereotypic features are discerned, and the results are discussed in relation to contemporary views on locomotion and exploration and on the mechanisms of amphetamine effect.

Effect of cholingeric drugs on methadone-induced catalepsy and stereotypies in rats treated chronically with methadone

The effects of antimuscarinic (atropine, scopolamine, methylscopolamine), muscarinic (RS86, pilocarpine), antinicotinic (mecamylamine, hexamethonium) and nicotinic (nicotine) cholinergic drugs on the catalepsy and stereotypies induced by acute methadone in rats treated chronically with methadone were studied. The antimuscarinic drugs potentiated and the muscarinic drugs antagonized the cataleptic effect of methadone, whereas the antimuscarinic drugs tended to antagonize and the muscarinic drugs potentiated the methadone-induced stereotypies. Nicotine initially slightly potentiated, and mecamylamine antagonized the cataleptic effect of methadone. The actions of the cholinergic drugs on the extrapyramidal motor effects of methadone were most probably central, because methylscopolamine and hexamethonium had only very weak actions. These results show that the effects of antimuscarinic and muscarinic drugs on the catalepsy and stereotypies induced by methadone are opposite to their effects on the catalepsy and stereotypies produced by drugs which are thought to act on the postsynaptic dopaminergic receptors.

On the supersensitivity of dopamine receptors, induced by neuroleptics

Different neuroleptics caused dopamine receptor blockade (antagonism against methylphenidate-induced compulsive gnawing) for varying lengths of time. When the receptor blockade had expired, supersensitivity to dopamine agonists (occurrence of apomorphine-induced compulsive gnawing and enhancement of methylphenidate-induced gnawing) developed and persisted for varying periods of time. The degree and duration of supersensitivity was related to the degree and duration of the preceding receptor blockade. Inhibition of catecholamine or 5-HT synthesis had no influence on development of supersensitivity. Stimulation with a dopamine agonist, apomorphine, during the period of the development of supersensitivity did not modify the enhanced receptor supersensitivity. A cholinergic-dopaminergic balance was shown to be involved in the manifestation of compulsive behavior during the supersensitivity phase. Tolerance to the dopamine antagonistic effect of a neuroleptic also developed after a single neuroleptic treatment, most likely due to increased sensitivity of the receptors for the dopamine agonist. It is concluded, that the dopamine receptor blockade induced by a single dose of a neuroleptic agent is a dynamic phenomenon which in the course of time is replaced by an increased sensitivity of the receptors to dopamine agonists. Noradrenergic or 5-HT neuron systems do not seem to be involved in the neuroleptic-induced supersensitivity, whereas a dopaminergic-cholinergic balance is operative in the supersensitivity situation.

Pimozide: a review of its pharmacological properties and therapeutic uses in psychiatry

Pimozide 1-(1-[4,4-bis(4-fluorophenyl)butyl]-4-peperidinyl)-2-benzimidazolone, is the first of a new series of psychotropic drugs, the kiphenylbutylpiperidines. It is advocated for once-daily use as maintenance therapy in chronic schizophrenia and for the treatment of psychic and functional disorders induced by personality traits. Published data suggest that in chronic schizophrenia, pimozide 4 to 6mg daily is indistinguishable from maintenance doses of chlorpromazine, fluphenazine, flupenthixol, perphenazine, or thioidazine. Patient groups have usually been to small to allow statistically significant differences to be apparent, but in some trials pimozide was significantly superior to trifluoperzine and to haloperidol. On present evidence, pimozide has no place in the hyperactive, aggressive type of patient or in treating the acute phase of schizophrenia, probably because of its relative lack of sedative properties compared with many antipsychotic drugs. The incidence and severity of extrapyramidal reactions with pimozide are low, but suitably designed controlled studies are needed to determine whether its use leads to a reduction in the requirement for antiparkinsonian medication. In anxious patients, pimozide seems to offer no advantages over currently available anxiolytic agents, either in terms of efficacy or incidence of side-effects. Claims for a specific effect against anxiety associated with psychosis or disturbed personality traits remain unproven.