Haloperidol-induced emotional defecation: a possible model for neuroleptic anxiety syndrome

Influence of aversive stimulation on haloperidol-induced catalepsy in rats

Catalepsy - an immobile state in which individuals fail to change imposed postures - can be induced by haloperidol. In rats, the pattern of haloperidol-induced catalepsy is very similar to that observed in Parkinson's disease (PD). As some PD symptoms seem to depend on the patient's emotional state, and as anxiety disorders are common in PD, it is possible that the central mechanisms regulating emotional and cataleptic states interplay. Previously, we showed that haloperidol impaired contextual-induced alarm calls in rats, without affecting footshock-evoked calls. Here, we evaluated the influence of distinct aversive stimulations on the haloperidol-induced catalepsy. First, male Wistar rats were subjected to catalepsy tests to establish a baseline state after haloperidol or saline administration. Next, distinct cohorts were exposed to open-field; elevated plus-maze; open-arm confinement; inescapable footshocks; contextual conditioned fear; or corticosterone administration. Subsequently, catalepsy tests were performed again. Haloperidol-induced catalepsy was verified in all drug-treated animals. Exposure to open-field, elevated plus-maze, open-arm confinement, footshocks, or administration of corticosterone had no significant effect on haloperidol-induced catalepsy. Contextual conditioned fear, which is supposed to promote a more intense fear, increased catalepsy over time. Our findings suggest that only specific defensive circuitries modulate the nigrostriatal system mediating the haloperidol-induced cataleptic state.

Dopaminergic mechanisms underlying catalepsy, fear and anxiety: do they interact?

Haloperidol is a dopamine D2 receptor antagonist that induces catalepsy when systemically administered to rodents. The haloperidol-induced catalepsy is a state of akinesia and rigidity very similar to that seen in Parkinson's disease. There exists great interest in knowing whether or not some degree of emotionality underlies catalepsy. If so, what kind of emotional distress would permeate such motor disturbance? This study is an attempt to shed some light on this issue through an analysis of ultrasound vocalizations (USVs) of 22 kHz, open-field test, and contextual conditioned fear in rats with some degree of catalepsy induced by haloperidol. Systemic administration of haloperidol caused catalepsy and decreased exploratory activity in the open-field. There was no difference in the emission of USVs between groups during the catalepsy or the exploratory behavior in the open-field test. In the contextual conditioned fear, when administered before training session, haloperidol did not change the emission of USVs or the freezing response. When administered before testing session, haloperidol enhanced the freezing response and decreased the emission of USVs on the test day. These findings suggest that the involvement of dopaminergic mechanisms in threatening situations depends on the nature of the aversive stimulus. Activation of D2 receptors occurs in the setting up of adaptive responses to conditioned fear stimuli so that these mechanisms seem to be important for the emission of 22 kHz USVs during the testing phase of the contextual conditioned fear, but not during the training session or the open-field test (unconditioned fear stimuli). Catalepsy, on the other hand, is the result of the blockage of D2 receptors in neural circuits associated to motor behavior that appears to be dissociated from those directly linked to dopamine-mediated neural mechanisms associated to fear.

Classical and novel approaches to the preclinical testing of anxiolytics: A critical evaluation

Over 80% of current anxiety studies employ one of the tests that were developed earlier than, or concurrently with the elevated plus-maze, i.e. before 1985. Considering 1985 as a historical reference point, we briefly review here 115 new tests and models of anxiety, the development of which was likely prompted by the poor predictive validity of classical tests as shown here by the comparison of preclinical and clinical findings with putative novel anxiolytics. The new approaches comprise major innovations to classical tests, the pre-test application of manipulations that mimic etiological factors of anxiety disorders, and entirely new approaches including anxiety disorder-specific tests. Thus, intensive test development over the last 27 years created a large pool of novel approaches. However, these are infrequently used and as such, their impact on anxiolytic drug development remains low. We suggest here that test/model development should step over the intensive phase when several new methods are proposed each year and should start selecting and establishing the methodologies that would successfully replace or complement classical tests. We propose here a novel strategy for improving the validity of anxiety testing that includes the retrospective analysis of the predictive validity of new procedures (as opposed to classical pharmacological validation), and a call for concerted international efforts at both the conceptual and practical levels. Similar endeavors proved recently successful with other psychiatric disorders.

Translating laboratory discovery to the clinic: from nicotine and mecamylamine to Tourette's, depression, and beyond

The early development of novel nicotinic drugs for Tourette's and depression was a very long journey in discovery, which began with basic behavioral neuroscience studies aimed at understanding how cholinergic and dopaminergic systems interact in the basal ganglia to control goal directed movement. These early rodent studies with nicotine and dopamine antagonists formed the basis for investigating a potentially improved treatment for children suffering from Tourette's syndrome (TS). Clinically, the research trajectory first focused on studies employing the use of nicotine gum to potentiate the therapeutic effect of the dopamine receptor antagonist, haloperidol, in patients with TS. These projects led to the discovery of a new use for a decades-old blood pressure medication, mecamylamine, a nicotine antagonist, which also appeared to provide symptomatic relief in some TS patients when used clinically and was found to reduce symptoms of mood instability and depression. This unexpected discovery led to a new hypothesis regarding the mechanism of action of antidepressants as well as a series of successful independent trials employing mecamylamine, and its active enantiomer, TC5214, as an augmenting agent in the treatment of major depression. This article is a chronological mini review of these basic and clinical translational studies on nicotinic therapeutics for Tourette's syndrome and depression over the past 25 years.

Involvement of dopamine D1/D2 receptors on harmane-induced amnesia in the step-down passive avoidance test

Ingestion of harmane and other alkaloids derived from plant Peganum harmala has been shown to elicit profound behavioural and toxic effects in humans, including hallucinations, excitation, feelings of elation, and euphoria. These alkaloids in the high doses can cause a toxic syndrome characterized by tremors and convulsions. Harmane has also been shown to act on a variety of receptor systems in the mammalian brain, including those for serotonin, dopamine and benzodiazepines. In animals, it has been reported to affect short and long term memory. In the present study, effects of dopamine D1 and D2 receptor antagonists on the harmane (HA)-induced amnesia and exploratory behaviors were examined in mice. One-trial step-down and hole-board paradigms were used for the assessment of memory retention and exploratory behaviors in adult male NMRI mice respectively. Intraperitoneal (i.p.) administration of HA (5 and 10 mg/kg) immediately after training decreased memory consolidation, while had no effect on anxiety-like behavior. Memory retrieval was not altered by 15- or 30 min pre-testing administration of the D1 (SCH23390, 0.025, 0.05 and 0.1 mg/kg) or D2 (sulpiride 12.5, 25 and 50 mg/kg) receptor antagonists, respectively. In contrast, SCH23390 (0.05 and 0.1 mg/kg) or sulpiride (25 and 50 mg/kg) pre-test administration fully reversed HA-induced impairment of memory consolidation. Finally, neither D1 nor D2 receptor blockade affected exploratory behaviors in the hole-board paradigm. Altogether, these findings strongly suggest an involvement of D1 and D2 receptors modulation in the HA-induced impairment of memory consolidation.

Preclinical behavioral models for predicting antipsychotic activity

Schizophrenia is a major psychiatric disease that is characterized by three distinct symptom domains: positive symptoms, negative symptoms, and cognitive impairment. Additionally, treatment with classical antipsychotic medication can be accompanied by important side effects that involve extrapyramidal symptoms (EPS). The discovery of clozapine in the 1970s, which is efficacious in all three symptom domains and has a reduced propensity to induce EPS, has driven research for new antipsychotic agents with a wider spectrum of activity and a lower propensity to induce EPS. The following chapter reviews existing behavioral procedures in animals for their ability to predict compound efficacy against schizophrenia symptoms and liability to induce EPS. Rodent models of positive symptoms include procedures related to hyperfunction in central dopamine and serotonin (5-hydroxytryptamine) systems and hypofunction of central glutamatergic (N-methyl-d-aspartate) neurotransmission. Procedures for evaluating negative symptoms include rodent models of anhedonia, affective flattening, and diminished social interaction. Cognitive deficits can be assessed in rodent models of attention (prepulse inhibition (PPI), latent inhibition) and of learning and memory (passive avoidance, object and social recognition, Morris water maze, and operant-delayed alternation). The relevance of the conditioned avoidance response (CAR) is also discussed. A final section reviews animal procedures for assessing EPS liability, in particular parkinsonism (catalepsy), acute dystonia (purposeless chewing in rodents, dystonia in monkeys), akathisia (defecation in rodents), and tardive dyskinesia (long-term antipsychotic treatment in rodents and monkeys).

Subjective and behavioural consequences of striatal dopamine depletion in schizophrenia--findings from an in vivo SPECT study

Dysphoria is an integral part of the symptomatology of a variety of clinical states, though there is little empirical data available on the qualitative and quantitative aspects of this phenomenon. The purpose of the study was to administer alphamethyl paratyrosine (AMPT), a catecholamine depleting agent as a chemical probe to induce dysphoria, and document the ensuing changes in mental status. AMPT (4-5 g/day) was administered to a group of medication-free schizophrenic patients (n=13) over a 48 hour period, and changes in their mental status were monitored at 12 hour intervals with the Profile of Mood States (POMS), Addiction Research Center Inventory (ARCI), Drug Attitude Inventory (DAI) and other standardized rating scales. All of the subjects experienced dysphoric responses of variable severity. The profile of changes included blunted pleasure responsivity, clouded thinking, loss of motivation and lowered vigilance. Subtle subjective changes were experienced soon after the first dose of AMPT and the dysphoria steadily worsened, resulting in social withdrawal and personal distress. Subjective responses were the earliest to manifest, followed by akathisia, akinesia and rigidity. We conclude that AMPT induced dopamine depletion is a safe, rapid, reliable and reversible method of studying dysphoric states in humans. The technique is helpful in examining the phenomenology of dysphoria, the temporal relationship between subjective and behavioural consequences of dopamine depletion, and the role of dopamine in mediating subtle aspects of pleasure responsivity, which is in turn crucial to the understanding of treatment non-adherence in schizophrenia and the origins of comorbid substance abuse.

The chick separation stress paradigm: a validation study

To expand the generalizability of the chick separation stress paradigm as a high-throughput anxiolytic screen, six positive drug probes (doses in mg/kg: meprobamate 15-120, pentobarbital 2.5-20.0, chlordiazepoxide 2.5-15.0, buspirone 2.5-10.0, imipramine 1-15, and clonidine 0.10-0.25) and five negative drug probes (amphetamine 0.5-4.0, scopolamine 0.2-1.6, caffeine 5-20, chlorpromazine 1-30, and haloperidol 0.03-1.00) were evaluated in the test. Seven-day-old chicks received intramuscular injections of either vehicle or drug probe 15 min prior to tests in either a mirror (low-stress) or a no-mirror (high-stress) condition for a 3-min observation period. The dependent measures were distress vocalizations to index separation stress and sleep onset latency to index sedation. All positive drug probes attenuated distress vocalizations in a dose-dependent manner, except buspirone. All positive drug probes affected sleep onset latency in a dose-dependent manner, except buspirone and imipramine. In all cases, the anxiolytic-like effect of positive drug probes was greater than its sedative effect. None of the negative drug probes affected either distress vocalizations or sleep onset latency, except for the highest dose of amphetamine, which caused pronounced stereotypy. These findings demonstrate that this anxiolytic screen is sensitive to a wide range of positive pharmacological probes and insensitive to a wide range of negative pharmacological probes.

Neuroleptic dysphoria: towards a new synthesis

RATIONALE

Neuroleptic dysphoria (ND) is a subtle and under-recognized side effect of antipsychotic drugs. It is an all-inclusive descriptive phrase that encompasses a variety of unpleasant subjective changes in arousal, mood, thinking and motivation induced by neuroleptic drugs. Understanding this phenomenon has wide ranging clinical and research implications.

OBJECTIVE

The present review examined the themes identified in the original studies from the neuroleptic era in the light of recent findings from neuroimaging research, cumulative experience with second generation antipsychotic drugs, and new concepts such as pleasure responsivity, hedonic regulation and subjective tolerability.

METHODS

Empirical studies on neuroleptic drugs involving clinical populations treated for schizophrenia, Tourette's disorder and stuttering, studies performed on normal healthy volunteers and selected experimental studies in animals, are reviewed.

RESULTS

Dysphoric responses occur early during treatment and typically manifest as a dislike towards medication (drug aversiveness). Dysphoria persisting over time, may lead to adverse clinical consequences such as treatment non-adherence, substance abuse, poor clinical outcome, increased suicidality and compromised quality of life. Interference with the physiological processes of hedonic capacity by the neuroleptics due to their dopaminergic blocking action in the prefrontal cortex and the shell of nucleus accumbens is the putative mediating mechanism underlying the occurrence of dysphoric responses. Second generation antipsychotic drugs with an atypical receptor blocking profile are less likely to elicit dysphoric responses.

CONCLUSION

Viewing neuroleptic dysphoria within a broader spectrum of disorders of subjective tolerability and exploring its neurobiological mechanisms is relevant to addressing the nuances of antipsychotic therapy, and could help unravel the questions surrounding the pathophysiology of depression, substance abuse and other dysphoric clinical states.

Comparative evaluation of conventional and novel antipsychotic drugs with reference to their subjective tolerability, side-effect profile and impact on quality of life

This study compared the effectiveness of conventional and novel antipsychotic drugs from a patient's perspective. Five comparable groups of schizophrenic patients (n=230) clinically stabilized on conventional antipsychotic drugs, risperidone, olanzepine, quetiapine or clozapine for a period of 6months or longer were cross-sectionally evaluated. Patients' clinical symptom profile, subjective responses and attitudes toward drugs, prevalence of dysphoria, akathisia, abnormal involuntary movements and Parkinsonian symptoms, and quality of life were ascertained using standardized rating scales. Between-group differences were examined with analysis of variance and chi-square tests. Patients receiving novel antipsychotic drugs experienced fewer side-effects, reported positive subjective responses and favourable attitudes toward their treatment, and revealed a lower prevalence of neuroleptic dysphoria. The differences were statistically significant (p<0.05) with the risperidone, olanzepine and quetiapine groups. Self-rated quality of life, measured with the sickness impact profile, was also significantly better among patients receiving novel antipsychotic drugs. These perceived benefits, however, were not reflected in the clinician rated (objective) measures of psychosocial functioning and quality of life. These findings substantiate the general notion that novel antipsychotic medications are uniformly better tolerated as indicated by the measures of subjective responses, side-effects and self rated quality of life.

Animal models of acute drug-induced akathisia - a review

Akathisia is a complex neurobehavioural side effect of neuroleptics and some other drugs which is characterised by subjective report and objective manifestations of restlessness. Its pathophysiology is poorly understood and there are many limitations to its investigation in humans. This paper reviews the various attempts that have been made in modelling acute akathisia in animals. Homologous as well as isomorphic models have been attempted, but most models are partial as they reproduce either the subjective or the objective features of the syndrome. None of the available models has been fully validated. Neuroleptic-induced defecation in the rat, even though constrained by a lack of symptom similarity and thereby face validity, has been most studied as a model of subjective akathisia. Rat models of restlessness, in particular those involving the use of serotonergic drugs or lesions of the ventral tegmentum or medial prefrontal cortex, are interesting partial models that should be further investigated. Neuroleptic-induced akathisia is observed in primates and has been modelled in dogs, and these should be studied further for their validation. It is also necessary to consider the subtypes of akathisia in the attempts to develop these models.

Effects of specific dopamine D1 and D2 receptor antagonists and agonists and neuroleptic drugs on emotional defecation in a rat model of akathisia

An increase in emotional defecation in rats in a well-habituated environment induced by neuroleptic drugs (NDef) has been proposed as a model for neuroleptic-induced akathisia. We examined the effects of dopamine receptor antagonists and agonists on this model. A selective dopamine D1 antagonist (SCH 23390) and a selective D2 antagonist (raclopride) induced increased defecation at higher doses, and demonstrated a synergistic effect at lower doses. Selective D1 (SKF 82958) and D2 (quinpirole) agonists did not have a significant effect on defecation, nor did they reverse the effect of haloperidol. In a further pilot study, we explored the effects of typical and atypical neuroleptics on this model. The haloperidol and risperidone treated rats produced more faecal boli than those treated with clozapine, thioridazine and chlorpromazine, with the former being non-significantly greater than the vehicle-treated group. The results of our studies suggest that NDef is most probably an effect of central dopamine antagonism that is not specific to D1 or D2 receptors, but that the two receptor subtypes have a synergistic effect. It is unlikely to be due to actions of neuroleptics on 5HT2 or alpha1 receptors as has sometimes been suggested. The results have implications for our understanding of the pathogenesis of akathisia.

Anxiolytic effects of dopamine receptor ligands: I. Involvement of dopamine autoreceptors

The anxiolytic-like properties of dopamine agonists and antagonists with different receptor profiles were investigated in the ultrasonic vocalization test in rats after subcutaneous administration. Only dopamine D2 receptor agonists inhibited ultrasonic vocalization with the following ED50 values: apomorphine (0.07 mg/kg), quinelorane (0.01 mg/kg), quinpirole (0.04 mg/kg), pramipexole (0.09 mg/kg), roxindole (0.04 mg/kg), talipexole (0.04 mg/kg), (+/-)-7-OH-DPAT (0.05 mg/kg), (+/-)-PPHT (0.03 mg/kg), (-)-TNPA (0.06 mg/kg), PD128907 (0.13 mg/kg). The D2 antagonists haloperidol, mazapertine, raclopride, remoxipride, L745870, U99194A, U101958 and S(-)-DS121, the partial agonists PD143188 and preclamol, the selective D1 agonist R(+)-SKF38393 and the D1 antagonist SCH23390, and the uptake inhibitors GBR12909, GBR12935 and indatraline lacked significant inhibitory effects on ultrasonic vocalization. Because at least some of the D2 receptor agonists investigated have selectivity for dopamine autoreceptors, it is speculated that the dopamine autoreceptor may be a target for the development of new antianxiety drugs.

The effects of beta-adrenoceptor antagonists on a rat model of neuroleptic-induced akathisia

Neuroleptic-induced defecation in rats in a well-habituated environment has been proposed as a model of the subjective component of akathisia. In this study, we examined the effects of two lipophilic beta-adrenoceptor antagonists - the non-selective drug propranolol and the relatively beta1-selective metoprolol - and one non-selective hydrophilic drug nadolol in this model. Young male Wistar rats were randomly assigned to one of eight groups (n = 12 in each group) and treated with haloperidol or vehicle, with or without one of the beta-antagonists. Haloperidol-treated rats had higher bolus counts than vehicle-treated rats, and this increase was significantly reversed by the lipophilic but not the hydrophilic beta-antagonists. This finding is consistent with the reported anti-akathisia effects of these drugs in humans, suggesting that this effect is central in origin and achievable with relatively selective beta1-antagonism. The B-antagonist drugs significantly reduced the cataleptic effect of haloperidol and this effect warrants further examination.

Effects of typical and atypical antipsychotic drugs on freezing behavior induced by conditioned fear

A typical antipsychotic drugs (atypical APDs), such as clozapine, ORG5222, and olanzapine, have been suggested to possess anxiolytic activity in the conflict test and elevated plus-maze test, while several studies have suggested that typical APDs are not anxiolytic in several models of anxiety. We investigated the effects of typical and atypical APDs on the acquisition and expression of conditioned fear-induced freezing. Drugs were administered subcutaneously to male Sprague-Dawley rats 30 min before foot shock stress (the VI60s schedule, 2.5 mA for 30 min). Twenty-four hours after foot shock, freezing behavior of rats was observed in the shock chamber without shocks. The atypical APD clozapine (0.3-10 mg/kg) dose-dependently inhibited the acquisition of conditioned freezing. Candidates for atypical APDs, ORG5222 (0.1-1 mg/kg), olanzapine (1-10 mg/kg), and raclopride (3-30 mg/kg), also reduced the acquisition of conditioned freezing in a dose-dependent manner. Typical APDs, haloperidol (3 mg/kg), spiperone (0.1-1 mg/kg) and nemonapride (1 mg/kg) had significant inhibitory effects on the acquisition of conditioned freezing, but their effects were reduced at higher doses. Chlorpromazine, a typical APD, showed about 50% inhibition of the acquisition of conditioned freezing at the dose of 10 mg/kg, but did not reveal significant inhibition at any of the doses (3-30 mg/kg). The ED50S (mg/kg) for inhibiting the acquisition of conditioned freezing significantly correlated with the Ki values for D4 dopaminergic receptors, but not with the Ki values for other monoamine and acetylcholine receptors. On the other hand, clozapine or haloperidol did not change the expression of conditioned freezing. These results suggest that protective effects of clozapine and other antipsychotic drugs on the acquisition of conditioned freezing may be mediated by blockade of D4 receptors.

Effect of prolonged treatment with haloperidol on "emotional" defecation and movement in rats in a well-habituated environment

Sixteen adult male Wistar rats were administered either haloperidol (n = 8), 0.5 mg/kg, or saline (placebo) (n = 8) by subcutaneous injection three times per week for 6 weeks, and were again injected after a 6-week drug-free period. The study was conducted in a well-habituated, distinctive environment to which the rats were introduced 1 hour before the injection on each occasion. The fecal bolus counts 1 hour before and 2 hours after drug injection were obtained, as well as movement counts repeatedly in epochs of 90 seconds upon introduction to the cages and after the injections. Haloperidol produced an overall increase in defecation in the 2 hours after drug injection compared with placebo. The post-drug bolus counts for haloperidol-treated rats were lower in week 2 compared with week 1, but the difference from placebo for this reduction was not significant, and it did not persist beyond week 4. The haloperidol-treated group showed a significant increase in the predrug bolus counts from week 5, suggesting a conditioned response to the cage environment. The haloperidol-treated rats were markedly less mobile than the placebo-treated rats, and with repeated exposure to haloperidol, they tended to develop hypomotility earlier. No tolerance to the movement effect was observed. The defecation and movement effects of haloperidol at 12 weeks were no different from those at week 1. This study supports earlier work indicating that haloperidol produces a dysphoric effect in rats, and it suggests that this effect does not habituate over 6 weeks of repeated administration. It does not replicate the motor aspect of akathisia seen in humans.

Behavioral consequences of predictable vs. unpredictable shocks in rats

Adult, male, Sprague-Dawley rats were given either predictable or unpredictable footshocks coupled with predictable or unpredictable warning stimuli in a factorially designed experiment. The effect of footshocks on different parameters of motility was studied immediately, 1 h and 24 h later. Footshock-induced stress caused increases in the motility of rats, and this increase persisted for 24 h. Of the parameters studied, distance travelled and time spent in ambulatory behavior were significantly affected, but there was no difference between the predictably and unpredictably shocked animals in the pattern or time course of stress-induced locomotion changes. The defecation scores recorded in footshocked rats were lower than in controls in both the predictably and unpredictably shocked groups, but there was no difference between the predictably and unpredictably shocked groups. Lack of differences in motility and defecation between the two groups limits the usefulness of these parameters in behavioral experiments based on predictability of noxious stimuli.

Neuroleptic-induced defecation in rats as a model for neuroleptic dysphoria

Two groups of 32 rats were challenged in a well-habituated environment with haloperidol (0.5 mg/kg), haloperidol (0.1 mg/kg), domperidone (0.1 mg/kg), or saline to study the effect of these drugs on defecation--an index of emotionality--and voluntary movements in the 2 hours after the injection. The haloperidol-treated rats in the high-dose condition had significantly more bolus counts in the 2 hours after the injection than were observed in the groups treated with domperidone (a peripheral dopamine D2 receptor antagonist) or placebo. All movements were greatly reduced in the haloperidol-treated rats and, in this group, the ones with more bolus counts did not differ in their activity levels from those with fewer bolus counts. There was a trend for the rats that were less mobile at 10 minutes after the injection to produce more boli in the 2-hour period. Our study, therefore, replicates the findings of Sanberg (1980) and Russell et al. (1987a, 1987b) that haloperidol increases "emotional" defecation in rats in well-habituated environments, but the same model does not replicate the motor component of neuroleptic-induced akathisia seen in human subjects.

Correlations of motility, defecatory behavior and striatal dopaminergic activity in rats

The spontaneous motor activity, fecal pellet scores and content of dopamine and its metabolites, dihydroxyphenyl acetic acid and homovanillic acid in corpus striatum were measured in a group of randomly selected Sprague-Dawley rats. The spontaneous motility, fecal pellet scores and neurochemical parameters measured showed significant variations. The correlations between these parameters were investigated. A significant correspondence was seen between the motility, fecal pellet scores and the striatal dopaminergic activity. The implications of the behavioral models of motility and defecation scores in studying the central dopaminergic function is discussed. It is suggested that striatal dopaminergic activity may be responsible not only for motor activity but also may contribute to the de novo emotionality as expressed by the defecation scores in rats.

Effects of specific dopaminergic agonists and antagonists in the open-field test

It has been found that dopaminergic transmission could be involved in some aspects of anxiety. The present study aims to explore this hypothesis further, using specific DA1 (SKF 38393) and DA2 (bromocriptine) agonists or DA1 (SCH 23390), and DA2 (zetidoline) antagonists in the open-field test. The results confirm previous studies indicating that DA1 and DA2 agonists predominantly increase locomotor activity, while DA1 and DA2 antagonists predominantly decrease it. However, at low doses, the four drugs increase the peripheral ambulation score significantly and, with the exception of zetidoline, also increase the central ambulation score. The observations made with zetidoline confirm the hypothesis that a specific presynaptic DA2 antagonism could be determinant for the disinhibitory effects of low doses of neuroleptics. A collateral action on 5HT transmission is also suggested to explain an hypothetic anxiolytic action of DA agonists and SCH 23390 at lower doses.

Effect of chronic hypoxic treatment on the retention of fixed-interval responding

The present experiments aimed to study the effects of hypoxic treatment (10 min on 3.5% oxygen) on the stabilized performance of rats in a fixed-interval schedule (FI 60 s). The hypoxic treatment was given once a day, for 3 days, immediately after the FI session. The results showed that the operant performance was disturbed from the very first posthypoxia FI session. There was a sharp drop in response rate, and changes in the temporal distribution of responses occurred. The data obtained greatly limit the importance of nonspecific factors in explaining these changes in performance. The results are discussed with reference to the retrieval hypothesis. In particular, it is suggested that the decreases of performance may be due to an effect of hypoxia on the retrieval mechanisms associated with long-term memory.

Antagonism of 8-OH-DPAT-induced behaviour in rats

Selective activation of the 5-HT1A receptor induces lower lip retraction (LLR) in rats. 8-Hydroxy-dipropylamino tetralin (8-OH-DPAT)-induced LLR could not be antagonised by the 5-HT antagonists methysergide, metergoline or mesulergine. In fact, some 5-HT antagonists induced LLR. However, 8-OH-DPAT-induced LLR could be antagonised by pindolol, spiperone, spiroxatrine and NAN-190, but not by the beta 1-adrenoceptor antagonist metoprolol, the beta 2-adrenoceptor antagonist butoxamine or the dopamine antagonist haloperidol. This antagonism was competitive as the dose-response curve of 8-OH-DPAT was shifted to the right. Pindolol, spiperone, spiroxatrine and NAN-190 all have a high affinity for the 5-HT1A receptor. This indicates that blockade of 8-OH-DPAT-induced LLR is only possible by selective blockade of 5-HT1A receptors. A possible mechanism of action is discussed. The increased defecation induced by 8-OH-DPAT could be antagonised by pindolol and NAN-190. The effect of spiroxatrine and haloperidol on the 8-OH-DPAT-induced increase in defecation was bimodal: an increase after a low and a decrease after a high dose of 8-OH-DPAT. Metoprolol and butoxamine had no effect on the 8-OH-DPAT-induced increase in defecation, thereby excluding an influence of beta-adrenoceptors.

Anxiolytic potential of sulpiride, clozapine and derivatives in the open-field test

Recently acquired data question the sharp dichotomy between anxiolytics and neuroleptics, since disinhibitory effects have been measured in the rat with very low doses of haloperidol and higher doses of atypical neuroleptics in FI and DRL schedules, but also in the open-field test. That the DA transmission in certain brain regions is involved in some aspects of anxiety has recently been suggested. The present study confirms this hypothesis particularly with high doses of sulpiride (80 mg/kg) and clozapine (24 mg/kg) when tested in the open-field test. Moreover, the results show how a slight chemical modification of clozapine can give a direction to pharmacological activity with one derivative still resembling clozapine and the second one resembling haloperidol. As neuroleptics do not seem to influence the synthesis and utilization of GABA, the higher entry score observed with them would seem to depend above all on DA antagonism in the mesolimbic system.

The effects of cocaine on multivariate locomotor behavior and defecation

The present study utilized a multifactorial open-field analysis (Digiscan activity) to assess behavioral changes induced by various doses of cocaine known to stimulate locomotion. The measures that were implemented included ambulation, rearing, stereotypic behavior, rotational movements and changes in defecation levels. Thirty-two male Sprague-Dawley rats were habituated to Digiscan-16 Animal Activity Monitors (Omnitech Electronics, Columbus, OH) before being injected with 0.0, 10, 20 or 30 mg/kg cocaine. Rats were kept on a reversed light/dark schedule and tested in the middle of the dark cycle. It was found that cocaine consistently increased activity measures; most prominently affecting the rotational and ambulatory indices. Interestingly, this 'activity print' appeared to be dose-dependent and specific to cocaine. Open-field defecation levels were compared to home-cage levels as an additional behavioral correlate. Defecation decreased under all doses of cocaine as compared to control levels (saline injection). This result is attributed to cocaine's weakly sympathomimetic effect.

Neuroleptic-induced emotional defecation: effects of pimozide and apomorphine

Neuroleptics, such as haloperidol, have been found to produce dysphoria, anxiety and akathisia in humans. In animals, these effects have rarely been reported since the decreased movement produced by these drugs can confound the study of many behavioral indices of emotionality. In fact, most investigators have found a decrease in emotional defecation in rats given neuroleptics in novel environments, supporting their action as a major tranquilizer. We have found, however, that in rats a profound increase in emotional defecation can result from haloperidol administration in well habituated environments, such as the homecage. In male rats, defecation was measured for a one hour test period following various doses of the neuroleptic, pimozide, and the dopamine receptor agonist, apomorphine. Apomorphine and pimozide (a dopamine receptor antagonist) were both found to increase levels of fecal boli excretions. In addition, when apomorphine was combined with haloperidol, defecation levels were also increased suggesting that this phenomenon is not directly mediated by dopamine receptors. It is suggested that this drug-induced defecation is a consequence of the agent's interaction with the affective state of the animal, creating a dysphoric or anxious state in the animal.

Neuroleptic-induced emotional defecation: effects of scopolamine and haloperidol

Most investigators have found a decrease in emotional defecation in rats given neuroleptics in novel environments, supporting their action as a major tranquilizer. We have found, however, that in rats a profound increase in emotional defecation can result from neuroleptic administration in well habituated environments, such as the homecage. Anticholinergics are known to be effective in treating the side effects associated with neuroleptic administration in humans. Therefore the present study determined the effects of anticholinergic treatment in this animal model. In male rats, defecation was measured for a 1-h test period in their homecage following various doses of the central and peripheral anticholinergics, scopolamine, and n-methylscopolamine, respectively. A decrease in fecal excretions and an attenuation of haloperidol-induced defecation was found following administration of scopolamine. n-Methylscopolamine reduced defecation at all doses. When n-methylscopolamine was combined with haloperidol, both fecal mass and number decreased significantly. Since both anticholinergic agents reduced haloperidol-induced defecation it is suggested that their effectiveness is mediated through peripheral mechanisms.