Blockade of amphetamine-induced locomotor activity and stereotypy in rats by spiroperidol but not by an atypical neuroleptic, thioridazine

Locomotor stereotypy is produced by methylphenidate and amfonelic acid and reduced by haloperidol but not clozapine or thioridazine

In addition to its well-known behavioral effects in rats, amphetamine also produces patterned locomotion (referred to below as locomotor stereotypy) in an open field. Locomotor stereotypy may be mediated by different mechanisms than those mediating the better-known behavioral effects of amphetamine. To determine whether the ability to produce locomotor stereotypy is an exclusive property of amphetamine or is a property of many amphetamine-like stimulants, several doses of methylphenidate and amfonelic acid were tested. The ability of both atypical and typical neuroleptics to block amphetamine-induced locomotor stereotypy was also tested. Both amfonelic acid and methylphenidate produced some degree of locomotor stereotypy. In addition, amphetamine-induced locomotor stereotypy was reduced by haloperidol but not by clozapine or thioridazine. These data suggest that locomotor stereotypy is more closely related to focused stereotypy than to hyperlocomotion.

Atypical antipsychotic drugs block selective components of amphetamine-induced stereotypy

Individual items of behavior produced by 1.0 or 5.0 mg/kg d-amphetamine were monitored in rats pretreated 15 minutes earlier with vehicle or with behaviorally relevant doses of haloperidol (0.1 or 0.25 mg/kg), clozapine (1.0 or 5.0 mg/kg), or thioridazine (1.0 or 5.0 mg/kg). Unlike haloperidol, the atypical antipsychotics failed to block all components of either the low- or high-dose response to amphetamine. These drugs, however, did block selective items of amphetamine-induced stereotyped behavior. Clozapine significantly attenuated the sniffing produced by 1.0 mg/kg d-amphetamine as well as the oral behavior (licking and/or biting) produced by 5.0 mg/kg d-amphetamine. Thioridazine, at a dose of 5.0 mg/kg, also reduced oral behavior and selectively blocked repetitive head bobbing. Taken together, these results suggest that although atypical antipsychotic drugs exert some common effects on the amphetamine behavioral response, these drugs do not influence all amphetamine-induced behaviors equally.

Behavioural microanalysis of the role of dopamine in amphetamine anorexia

A microstructural analysis paradigm was used to study amphetamine anorexia. Doses above 0.40 mg/kg significantly reduced food intake by reducing eating time; in contrast, eating rate was increased at these doses. Examination of the frequency distribution of interresponse times (IRTs) revealed a significant shift to shorter IRTs at doses as low as 0.125 mg/kg. Pimozide blocked amphetamine anorexia at 0.5 and 1.0 mg/kg, suggesting that at both doses amphetamine anorexia has a dopaminergic substrate. However, the atypical neuroleptic thioridazine did not antagonize amphetamine. Furthermore, effects of amphetamine were additive with those of apomorphine, administered at a dose known to suppress feeding by inhibiting mesolimbic DA neurons. These results provide evidence against an involvement of the mesolimbic DA system in amphetamine anorexia.

Motivational vs. motor effects of striatal and pallidal gabergic projections to subthalamic and entopeduncular nuclei, ventromedial thalamus, and ventral globus pallidus

Four GABA-terminal sites downstream from the rat corpus striatum were injected bilaterally with either a GABA agonist (muscimol 15-250 ng) or antagonist (picrotoxin 15-300 ng), and the effects on spontaneous locomotor activity or variable-interval hypothalamic self-stimulation were recorded. Significant changes in locomotor activity were produced at all four sites, as in previous studies. Two of the sites tested, the anterior globus pallidus and the thalamic ventromedial nucleus, also receive gabergic projections from the nucleus accumbens or from structures other than the basal ganglia; at these two sites, injection of either muscimol (depressant), or picrotoxin (facilitatory), had the same effect on self-stimulation as on locomotor activity. The two other sites tested, the entopeduncular nucleus and subthalamic nucleus, do not receive projections from the accumbens; in these two structures, muscimol enhanced locomotor activity but abolished self-stimulation; picrotoxin was without significant effect, or was disruptive. These results confirm previous reports that gabergic systems downstream from the striatum can mediate a simple, innate motor sequence (locomotion), but they fail to demonstrate a specific involvement of these pathways in learned behaviour (self-stimulation).

Stimulatory effect of N-methyl aspartate on locomotor activity and transmitter release from rat nucleus accumbens

N-Methyl-aspartate (NMA), an agonist at central glutamate receptors, elicited prolonged and intense locomotor activity when injected into the nucleus accumbens septi (NAS) in subconvulsive doses (3-10 micrograms bilaterally). This effect was antagonised by intra-accumbens injection of the specific NMA antagonist, aminophosphonovaleric acid (APV) in a dose (3.0 micrograms bilaterally) that was without intrinsic effect when given on its own. Intra-accumbens injection of APV also suppressed locomotor hyperactivity elicited by intra-accumbens injection of DA (50 micrograms bilaterally) in rats pretreated with nialamide. In vitro release of [3H]-acetylcholine in accumbens tissue slices was significantly increased in the presence of NMA (30 microM) or N-methyl-D-aspartate (NMDA) (15 microM). Both effects were antagonised by APV (30 microM). Similar results were obtained with tissue slices of rat corpus striatum. These results suggest that locomotor stimulation by intra-accumbens NMA is mediated by an action on the mesolimbic dopaminergic neuron, either directly or via a cholinergic interneuron. In addition, activity at the glutamate synapse may be enhanced by the presence of DA affecting glutamate release and/or reuptake.

A rapid and simple behavioural screening method for simultaneous assessment of limbic and striatal blocking effects of neuroleptic drugs

A simple and rapid screening method, where the ability of neuroleptic drugs to antagonise the abnormal pattern of exploration induced by a low dose of d-amphetamine in a 10 min test, was evaluated. The d-amphetamine 2 mg/kg pretreatment induced both an increased locomotion, thought to reflect an increased dopamine transmission in the nucleus accumbens, and weak stereotypies, thought to reflect an increased dopamine transmission in the neostriatum. Haloperidol, chlorpromazine and thioridazine blocked all ongoing behaviours while clozapine and sulpiride, regarded as causing less extrapyramidal side effects in the clinic, only antagonised the d-amphetamine induced locomotion. The findings support the notion that the common site of action for anti-psychotic drugs is blockade of dopamine receptors outside the neostriatum while the blockade of dopamine receptors within the striatum probably are related to the propensity of these drugs to induce the extrapyramidal side effects. It seems possible with this method to screen neuroleptic drugs for their relative potency in blocking limbic and striatal dopamine receptors simultaneously in one short experiment. The method might be used when new anti-psychotic drugs with low incidences of extrapyramidal side effects are sought for.

Apomorphine anorexia: a behavioural and neuropharmacological analysis

Anorectic effects of apomorphine were studied in a microstructural analysis paradigm. Low doses of apomorphine (less than 0.1 mg/kg SC) reduced food intake, by reducing both the rate of eating and eating time. The neuroleptics haloperidol and thioridazine blocked the effect of apomorphine on eating time, but not on eating rate. Anorectic effects elicited by apomorphine administration to the ventral tegmental area and, to a lesser extent, the substantia nigra were mediated by a selective reduction of eating time. Effects of apomorphine on eating time appear to result from an action at presynaptic dopamine receptors; the mechanism of the effect of apomorphine on eating rate is unclear.

Atypical neuroleptics clozapine and thioridazine enhance amphetamine-induced stereotypy

The effects of the atypical neuroleptics clozapine and thioridazine and the typical neuroleptic pimozide on amphetamine-induced behavior were examined. Pimozide, as expected, blocked both amphetamine-induced locomotion and stereotypy. Thioridazine and clozapine antagonized the increases in locomotion produced by amphetamine, but produced increases in amphetamine-induced stereotypy and lowered the threshold dose for stereotypy. It is suggested that the increased stereotypy might partly account for the decreased locomotion, and that this might be a primary effect of these atypical neuroleptics. The data would also suggest that the use of amphetamine-induced stereotypy as a model for psychosis is inappropriate, as clozapine and thioridazine, which enhance stereotypy, are antipsychotic.

Drug interactions on spontaneous locomotor activity in rats. Neuroleptics and amphetamine-induced hyperactivity

The locomotor activity of female rats was recorded during 10-min sessions in a circular open-field apparatus after the administration of vehicle or drug. Dose-response curves were obtained for seven neuroleptic drugs both alone (spontaneous activity) and in combination with 1.0 mg/kg of d-amphetamine. Haloperidol, pimozide, loxapine, thiothixene, molindone and chlorpromazine all produced graded decreases in spontaneous locomotor activity. Haloperidol, pimozide, loxapine, thiothixene and molindone also produced graded reversals of the hyperactivity produced by d-amphetamine, while chlorpromazine did not. Clozapine neither altered spontaneous activity nor reversed the hyperactivity produced by d-amphetamine. The data indicate that measures of locomotor activity provide important additional information about the actions of neuroleptics and do not necessarily mirror the actions of these drugs on other measures of performance such as lever-pressing for brain stimulation.

The cholecystokinin analogue, caerulein, does not modulate dopamine release or dopamine-induced locomotor activity in the nucleus accumbens of rat

We have investigated the effect of the cholecystokinin (CCK) analogue, caerulein, in the nucleus accumbens on dopamine (DA) release and locomotor activity. Caerulein (10(-9)-10(-4) M) did not affect the resting or K+-evoked release of [14C]DA, although concentrations within this range have been shown to modulate transmitter release in cerebral cortex. When injected bilaterally into the nucleus accumbens, caerulein (30 ng-1 microgram) did not affect spontaneous locomotor activity as compared to vehicle-injected controls. Similarly, bilateral injections of caerulein (1 microgram) into the nucleus accumbens did not modulate locomotor hyperactivity induced by bilateral injections of DA (20 microgram) into the nucleus accumbens. It is concluded that CCK in the nucleus accumbens has no direct effect on dopamine release or dopamine-stimulated locomotor activity.

Anti-conflict and depressant effects by GABA agonists and antagonists, benzodiazepines and non-gabergic anticonvulsants on self-stimulation and locomotor activity

Rats were injected systemically with different classes of gabergic agent in order to investigate gabergic involvement in limbic output. Agonists differed one from another in their effects on variable-interval self-stimulation: clonazepam (in repeatedly-tested rats), chlordiazepoxide and pentobarbitone had a strongly biphasic action, low doses being facilitatory and high doses depressant, whereas other agonists including valproate and 3-APS (homotaurine) were uniformly depressant. The facilitatory effects of the benzodiazepines were dramatically enhanced by GABA antagonists (picrotoxin or pentylenetetrazol) even though antagonists on their own produced a dose-dependent depression that was not reversible by other anticonvulsant drugs. Ventral tegmental electrode placements yielded generally similar results. Depression of self-stimulation observed on initial exposure to clonazepam was reversed by repeated self-stimulation testing in the drugged state but not by repeated daily injections without testing. Locomotor activity (under conflict-free conditions) was unaffected or was depressed both by agonists and by antagonists. Thus, the facilitation of self-stimulation by chlordiazepoxide, pentobarbitone and clonazepam appears to be accounted for in terms of non-gabergic anti-conflict activity by these agents. Self-stimulation and locomotor changes following systemic administration did not disclose facilitatory effects attributable to gabergic efferents from limbic dopamine areas.

Effects of excitatory amino acids on locomotor activity after bilateral microinjection into the rat nucleus accumbens: possible dependence on dopaminergic mechanisms

In order to study the role of excitatory amino acids on motor function, the effects of kainic, quisqualic, and N-methyl-DL-aspartic acids on locomotor activity were determined after their direct injection into the nucleus accumbens. These three amino acids have been used in previous studies to classify receptors for excitatory amino acids in the mammalian spinal cord. After injection into the nucleus accumbens all three amino acids stimulated locomotor activity, with kainic acid being the most potent and N-methyl-DL-aspartic acid the least potent. The maximum intensity of the stimulation produced by kainic and quisqualic acids was greater than that produced by N-methyl-DL-aspartic acid. These results suggest that receptors in the nucleus accumbens, sensitive to kainic and quisqualic acids, play a more important role in the stimulation of locomotor activity than those sensitive to N-methyl-DL-aspartic acid. In addition to the above amino acids, the administration of large doses of L-aspartic and D-glutamic acids also produced hyperactivity, while L-glutamic acid had no effect. To determine whether endogenous dopamine mediates the hypermotility produced by the excitatory amino acids, the response to these amino acids was studied after treatment with reserpine or dopamine receptor blocking agents. Reserpine (5 mg/kg, i.p.), haloperidol (0.8 mg/kg, i.p.) or fluphenazine [5.0 micrograms (total dose) injected into the nucleus accumbens] markedly attenuated the hypermotility induced by excitatory amino acids. These results suggest that the hypermotility produced by excitatory amino acids is mediated through release of dopamine and the subsequent stimulation of dopamine receptors in the nucleus accumbens.

Multiple dopamine receptors and behavior

The therapeutic effects of dopamine (DA) agonists and DA antagonists used in the treatment of schizophrenia (antipsychotics, DA antagonists), Huntington's chorea (DA antagonists) and Parkinson's disease (antiparkinsonian agents, DA agonists) have been thought to result largely from actions on DA receptors located in the striatum (caudate nucleus and putamen). Many of the classical drugs used to treat these disorders are known to have a high incidence of extrapyramidal side effects (EPS). However, a number of drugs, the atypical antipsychotics and antiparkinsonian agents, have been developed which have a low incidence of EPS. It has been of enormous interest to researchers and clinicians alike to determine what characteristics of the atypical antipsychotics and antiparkinsonian agents are responsible for their unique behavioral profile. Because all of the antipsychotics and antiparkinsonian agents act on DA receptors, much attention has focused on potential differences in the interactions of the atypical agents with DA receptors. An hypothesis that has been raised, due to the knowledge that there are multiple subtypes of DA receptors located in the striatum, is that the atypical agents could have their therapeutic actions as a result of an interaction with one specific subtype of DA receptor. This review emphasizes two major points: (1) it is unlikely that the atypical antipsychotics and antiparkinsonian agents interact with only one subtype of DA receptor, or have their therapeutic actions only through that receptor; (2) other pharmacological characteristics of these agents are more critically involved in their unique behavioral effects. The applicability of animal models to assess the pharmacological and behavioral profiles of these agents is discussed, and the relevance to the clinical profiles of these agents is emphasized.

Central dopamine receptor agonist and antagonist actions of the enantiomers of 3-PPP

The two enantiomers of the putative centrally acting dopamine (DA) autoreceptor agonist 3-(3-hydroxyphenyl)-N-n-propylpiperidine, 3-PPP (Hjorth et al. 1981), were pharmacologically evaluated. An extensive series of biochemical and behavioural experiments unexpectedly revealed that both (+)- and (-)-3-PPP showed clear, but differential, effects on the DA receptors. Thus, (+)-3-PPP is a DA agonist with autoreceptor as well as postsynaptic receptor stimulatory properties. In contrast, although (-)-3-PPP similarly activates DA autoreceptors it acts concomitantly as an antagonist at postsynaptic DA receptors. Moreover, both behavioural and biochemical data on motor activity and DA synthesis and turnover suggest a preferential limbic action for the (-)-enantiomer. These results are discussed in terms of the dual antidopaminergic action of (-)-3-PPP coupled with anatomical differences in the feedback organisation in central (viz, limbic vs striatal) DA systems. It is suggested that compounds like (-)-3-PPP may be of potential clinical utility in the treatment of psychotic disorders, whilst lacking the seriously incapacitating motor dysfunctions produced by current neuroleptic therapy.

Feeding stimulated by very low doses of d-amphetamine administered systemically or by microinjection into the striatum

The effects of d-amphetamine over a wide range of doses (0.125-4.0 mg/kg IP) on rat unconditioned behaviour were examined in the presence of food and water (experiment 1), in their absence (experiment 2) and after microinjection (2.0 micrograms in 0.5 microliter) directly into the striatum (experiment 3). In experiment 1 very low doses (0.125 and 0.25 mg/kg) stimulated the intake of food, but not water, and higher doses produced locomotor hyperactivity, rearing, stereotyped sniffing and anorexia. In experiment 2 all doses, including very low doses (0.125 and 0.25 mg/kg), significantly potentiated locomotor activity. In experiment 3, microinjection into the corpus striatum elicited substantial feeding, but not drinking, locomotor activity or stereotyped behaviour. The results suggest that a single graded facilitative mechanism underlies the effects on food intake and other behavioural effects of amphetamine, as implied by a general hypothesis of amphetamine action proposed in the literature, and that these effects may to a large extent be mediated by forebrain dopamine systems.

A comparison of the effects of neuroleptics on phencyclidine-induced behaviors in the rat

The dose-response effects of neuroleptic pretreatment on phencyclidine (PCP; 3 or 5 mg/kg)-induced locomotor activity, stereotyped behaviors and ataxia were quantified in groups of male rats using rating scales recently developed in this laboratory. Three butyrophenone neuroleptics consistently produced dose-dependent antagonism of the behavioral effects of PCP administration. Fluphenazine antagonized the behavioral effects produced by 3 mg/kg PCP but not those produced by 5 mg/kg PCP. Each of the other neuroleptics examined (chlorpromazine, thioridazine, mesoridazine, triflupromazine, cis-flupenthixol) had no consistent antagonistic effect or actually enhanced one or more of the behavioral effects of PCP. Some neuroleptics slightly reduced PCP locomotion or stereotypies at high doses, but these effects were probably a non-specific consequence of the synergistic ataxia-producing properties of these drugs. In a second set of experiments, atropine sulfate pretreatment increased PCP-induced locomotor activity and stereotyped behaviors but had no effect on ataxia; pretreatment with physostigmine produced opposite effects. Combined pretreatment with haloperidol and atropine sulfate significantly reduced only haloperidol antagonism of PCP-induced ataxia, thus suggesting that non-dopoaminergic effects of neuroleptics may interfere with their ability to antagonize PCP.