Antidepressant versus neuroleptic activities of sulpiride isomers on four animal models of depression

Pharmacological validation of a chronic social stress model of depression in rats: effects of reboxetine, haloperidol and diazepam

Chronic social stress is one of the most important factors responsible for precipitation of depressive disorder in humans. In recent years, the impact of social stress on the development of psychopathologies has been thoroughly investigated in preclinical animal studies. We have shown recently that behavioural effects of chronic social stress in rats can be reversed by citalopram and fluoxetine. This study has been designed for further pharmacological validation of the chronic social stress paradigm as a model of depressive symptoms in rats. For this, rats were subjected to 5 weeks of daily social defeat and were in parallel treatment for a clinically relevant period of 4 weeks with the antidepressant drug reboxetine (40 mg/kg/day) and the neuroleptic drug haloperidol (2 mg/kg/day). The anxiolytic diazepam (1 mg/kg) was administered acutely at the end of the stress period. Stress caused decreased locomotor and exploratory behaviours, decreased sucrose preference and increased immobility in the forced swim test, but did not affect behaviour in the elevated plus maze. Four weeks of oral treatment with reboxetine ameliorated the adverse effects of social stress and normalized behaviours related to motivation and reward sensitivity. The treatment with haloperidol worsened the adverse effects of chronic social stress having effects similar to stress on reward and motivation-related behaviours. Diazepam reduced anxiety-related behaviours as measured in elevated plus maze in control animals having no effects on socially stressed individuals. Neither sucrose preference nor performance in forced swim test was affected by diazepam. The effectiveness and selectivity of the treatment with the antidepressant reboxetine in ameliorating socially induced behavioural disturbances supports the validity of the chronic social stress as a model of depressive-like symptoms in rats.

Antipsychotic and antidepressive effects of second generation antipsychotics: two different pharmacological mechanisms?

Second generation antipsychotics display antidepressive effects in schizophrenic patients that are more pronounced than those of traditional neuroleptics and that go beyond antidepressive effects secondary to the reduction of positive symptoms. The antidepressive potential of second generation antipsychotics is presumably related to their pharmacological mechanisms, which differ from those of traditional neuroleptics. Among others, 5-HT(2A) antagonism is of special relevance for most of the new antipsychotics in this respect. But also special interactions with the dopaminergic system, as is the case with amisulpride and aripiprazole, or noradrenalin- and/or serotonin-reuptake-inhibition, as with ziprasidone and zotepine, should be considered. It can be summarised that the antipsychotic and antidepressive effects of second generation antipsychotics are mostly based on different pharmacological mechanisms. This might be especially true for direct antidepressive effects, i. e. antidepressive effects that are not mediated by the reduction of positive symptoms.

The role of dopamine in the mechanism of action of antidepressant drugs

The present paper reviews evidence on the effect of antidepressant treatments on dopamine transmission. Chronic treatment with antidepressant drugs potentiates the behavioural stimulant responses elicited by the stimulation of dopamine receptors, including reward-related behaviours. Moreover, antidepressants affect dopamine release in several brain areas. The reviewed literature is discussed in terms of the possible mechanisms underlying antidepressant-induced supersensitivity to dopamine-mediated behavioural responses, and of the possible implications for the therapeutic effect of these drugs. It is concluded that the potentiation of dopaminergic neurotransmission induced by chronic antidepressant treatments might contribute to their therapeutic effect.

Chronic administration of l-sulpiride at non-neuroleptic doses reduces the duration of immobility in experimental models of "depression-like" behavior

It has been shown that long-term administration of l-sulpiride induces a down-regulation of beta receptor-associated adenylate cyclase activity in the frontal cortex of rats, and adaptive response that is typically associated with the chronic administration of antidepressants. Here we show that in two animal models of "depression-like" behavior (forced swim in rats and tail suspension in mice), the long-term (21 days) administration of l-sulpiride at a non-neuroleptic dose (2 mg/kg IP twice a day) significantly decreases the duration of immobility, the effect being similar to that of desipramine (20 mg/kg IP). The same dose (2 mg/kg) of l-sulpiride, acutely administered, has no effect at all. On the other hand, either chronic (21 days) or acute administration of neuroleptic doses of l-sulpiride have an opposite effect, and indeed increase the duration of immobility. These results are an in vivo support to the in vitro findings suggesting that low doses of l-sulpiride may have antidepressant-like activity.

Disposition of enantiomers of sulpiride in humans and rats

Pharmacokinetics of sulpiride enantiomers after intravenous administration of (+/-)-, (+)-, and (-)-sulpiride was examined in humans and rats. Pharmacokinetics profiles were similar in (+)- and (-)-enantiomers after intravenous administration of (+/-)-sulpiride. Metabolic inversion at a chiral centre was not observed after intravenous administration of each enantiomer in rats.

Possible role of dopamine D1 receptor in the behavioural supersensitivity to dopamine agonists induced by chronic treatment with antidepressants

The effect of chronic treatment with antidepressants (ADs) on the behavioral responses to LY 171555, a selective D2 receptor agonist, SKF 38393, a selective D1 receptor agonist, and B-HT 920, a selective DA autoreceptor agonist, was studied in rats. In normal rats small, intermediate and high doses of LY 171555 produced hypomotility, hyperactivity and stereotypies, respectively. Chronic but not acute pretreatment with imipramine (IMI) greatly potentiated the motor stimulant effect of LY 171555, but failed to modify its stereotypic and sedative effect. The potentiation of the motor stimulant effect of LY 171555 was observed also after chronic, but not acute, treatment with desmethylimipramine (DMI), mianserin (MIA) or repeated electroconvulsive shock (ECS). Chronic treatment with IMI failed to modify the effect of SKF 38393 (motor stimulation, grooming and penile erection), but reversed the sedative effect of B-HT 920 into a motor stimulant response. The motor stimulant response to LY 171555 in IMI-pretreated animals was suppressed by L-sulpiride, a D2 antagonist, and by a combination of reserpine with alpha-methyltyrosine (alpha-MT), but it was only partially antagonized by high doses of SCH 23390, a selective D1 antagonist. The results indicate that chronic treatment with ADs potentiates the behavioural responses mediated by the stimulation of postsynaptic D2 receptors in the mesolimbic system and suggest that this behavioural supersensitivity is due to enhanced neurotransmission at the D1 receptor level.

Amperozide and emotional behaviour

The new putatively antipsychotic drug amperozide is characterized pharmacologically by a specific limbic mode of action. Thus amperozide is a potent antagonist of muricidal behaviour (ED50 = 0.16 mg/kg) as well as aggression between isolated male mice. Although amperozide displays anxiolytic properties in Vogel's conflict test as well as an antidepressive effect in the despair test, the drug does not interfere with motor coordination or cause sedation (ED50 greater than 50 mg/kg). These results could make amperozide very interesting as an antipsychotic drug in the clinic, with effect on both positive and negative symptoms.

An overview of investigational antidepressants

This article provides a brief overview for the clinician of investigational antidepressant compounds. In the last decade, there have been a large number of compounds introduced, and many of these, some identified only by a compound number, are still in research and development. The present overview is not meant to be exhaustive, but focuses on the major classes of newer antidepressant drugs.

Is the forced swimming test a suitable model for revealing antidepressant activity?

The forced swimming test is reviewed. This test appears to be suitable for detecting antidepressant activity in rats but not in mice. Difference in experimental procedure may account for the different sensitivity to drugs of the two animal species.

Alterations in peripheral and central dopamine receptor sensitivity after subchronic treatment with fluphenazine and sulpiride

The effects of subchronic treatment with the antipsychotic drugs fluphenazine and sulpiride on the sensitivity of peripheral neuronal dopamine receptors and central dopamine autoreceptors were evaluated. The ability of apomorphine, a dopamine agonist, to inhibit electrically induced sympathetic vasoconstriction in pithed rats, and apomorphine-induced inhibition of spontaneous locomotor activity in awake rats were used as indices of peripheral and central dopamine receptor sensitivity, respectively. A single injection of fluphenazine decanoate, a long-acting preparation of fluphenazine, enhanced the central locomotor inhibitory effect of low doses of apomorphine 4 and 6 weeks after drug administration, whereas the antidopaminergic effect on peripheral dopamine receptors was prolonged and persisted at least up to 6 weeks. In another set of experiments rats were treated with fluphenazine hydrochloride and sulpiride for 10 days and subsequently challenged with apomorphine after various withdrawal times. Both antipsychotic drugs augmented the inhibitory effect of apomorphine in the periphery, although the time courses of the potentiation were different. Both treatments also enhanced the locomotor inhibitory effect of apomorphine. These results are in line with our previous finding that long-term treatment with dopamine antagonists can induce neuronal dopamine receptor up-regulation also outside the central nervous system. Peripheral neuronal dopamine receptors thus show similar adaptive responses to long-term blockade as central dopamine autoreceptors, and may serve as a useful experimental model in studies concerned with mechanisms of dopaminergic autoregulation in the central nervous system.

Behavioral consequences of antidepressant treatment in rodents

This review discusses the effects of antidepressant drugs on behaviors that are changed during the clinical treatment of depression. We first consider whether there is a similar subjective state produced by antidepressant drugs that might be akin to the mood changes caused clinically by these drugs. We thus review the evidence that antidepressant drugs can produce a distinctive enough subjective state to serve as a discriminative stimulus, and then discuss the nature of the cue produced. Secondly, we discuss whether there is any evidence that antidepressants enhance the rewarding aspects of stimuli since this aspect of behavior is reported to change during the successful treatment of depression. In this section we review the effects on electrical brain stimulation, water and food intake, exploratory and social behaviors. Finally, because of the proposed role of stress in the aetiology of depression, we review the effects of antidepressants on the responses to acute and chronic stress.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published from 1980 to 1984 but data from many earlier papers are also tabulated.

Effect of chronic administration of antidepressants on duration of immobility in rats forced to swim

Chronic administration of imipramine and desipramine significantly reduced the duration of immobility in rats forced to swim in comparison with acute administration. However, amitriptyline did not potentiate the reductive effect of chronic administration. Chlorimipramine, a selective serotonin uptake inhibitor, did not affect the duration of immobility in both the acute and chronic administration. On the other hand, the chronic administration of chlorpromazine, haloperidol and diazepam enhanced the duration of immobility, whereas their acute administration had no effect on it. Sulpiride reduced and enhanced the duration of immobility by the acute and chronic administration, respectively. The present results suggest that the chronic administration of drugs to rats in a forced swimming test can clarify the characteristics of the psychotropic drugs.