Apomorphine-induced aggressiveness and [3H]citalopram binding after antidepressant treatment in rats

Gestational treatment with cocaine and fluoxetine alters oxytocin receptor number and binding affinity in lactating rat dams

Cocaine administered chronically throughout gestation has been correlated with deficits in maternal behavior, increased maternal aggressive behavior and decreased oxytocin levels in rats. In addition to its effects on oxytocin levels, cocaine is a potent serotonergic, dopaminergic and noradrenergic reuptake inhibitor. Alterations in the dopaminergic and serotonergic systems have been suggested as possibly having a role in cocaine-induced maternal aggression. This study was in part, an attempt to understand some of the mechanisms by which cocaine increases postpartum aggression, particularly as they relate to changes in the oxytocin system. Oxytocin receptor number and binding affinity in the medial preoptic area of the hypothalamus, ventral tegmental area, hippocampus and amygdala were determined for lactating rat dams on postpartum day 6 (PPD 6) that were gestationally treated with cocaine, fluoxetine, saline or an amfonelic acid/fluoxetine drug combination. Cocaine and fluoxetine treatment both resulted in a significant up-regulation of oxytocin receptor number and lower receptor affinity in the amygdala of lactating rat dams compared to saline controls and the amfonelic acid/fluoxetine combination treatment group. Cocaine treatment also resulted in a significant down-regulation of oxytocin receptors in the medial preoptic area and both cocaine and fluoxetine treated dams had the highest affinity for oxytocin receptors in this brain region. Results of the present study support previous data indicating that alterations in oxytocinergic and perhaps serotonergic system dynamics in the amygdala may play a role in cocaine-induced postpartum aggression.

Additive effect of clonidine and fluoxetine on apomorphine-induced aggressive behavior in adult male Wistar rats

BACKGROUND

Fluoxetine, a selective serotonin reuptake inhibitor, has been reported to be superior in its antiaggressive properties as compared with other antidepressants. The objective of the study was to investigate whether the effect of a minimal effective dose of fluoxetine could be potentiated by the alpha2-adrenergic agonist clonidine.

METHODS

Vehicle (1.0 mL/kg), clonidine (0.1 mg/kg), fluoxetine (10 mg/kg), and their combination [clonidine (0.1 mg/kg) plus fluoxetine (10 mg/kg)] were injected into apomorphine-pretreated (1.0 mg/kg, once daily during 12 days) aggressive adult male Wistar rats.

RESULTS

Repeated apomorphine treatment induced a gradual development of aggressive behavior. Combined clonidine and fluoxetine treatment attenuated the intensity of aggressive behavior, while these drugs alone had only a weak tendency toward reduction of aggression. Latency before the first attack was unchanged.

CONCLUSIONS

Our experiments confirm that combined clonidine and fluoxetine treatment elicits an additive antiaggressive effect on apomorphine-induced aggressive behavior in rats.

Acute trazodone and quipazine treatment attenuates apomorphine-induced aggressive behaviour in male rats without major impact on emotional behaviour or monoamine content post mortem

We have studied the effect of acute trazodone (3--20 mg kg(-1)) and quipazine (1--3 mg kg(-1)) treatment on the apomorphine-induced (1 mg kg(-1), once daily over 2 weeks) aggressive behaviour in male Wistar rats. All doses of trazodone and quipazine tested attenuated the aggressiveness as evidenced by the abolished intensity of aggressive behaviour and increased time of latency before the first attack. The acute trazodone (3--10 mg kg(-1)) or quipazine (1--3 mg kg(-1)) treatment had no or only a minor effect on rat behaviour in the elevated plus-maze, open field, and forced swimming test. Concomitant apomorphine (1 mg kg(-1)) plus trazodone (3 mg kg(-1)), but not apomorphine (1 mg kg(-1)) plus quipazine (1 mg kg(-1)), treatment slowed the development of aggressive behaviour. Repeated apomorphine treatment moderately reduced the dopamine post mortem and increased the DOPAC and HVA contents in striatum. Other monoamines or their metabolites were unchanged. Neither trazodone and quipazine treatment nor forced swimming stress induced any changes in the monoamine contents. In conclusion, our results indicate that acute trazodone and quipazine treatment attenuates the apomorphine-induced aggressive behaviour in male rats, but this phenomenon cannot be implicated in the changes in emotional and motivational behaviour, or in changes of monoamine content post mortem.

The serotonin 5-HT(2A) receptor subtype does not mediate apomorphine-induced aggressive behaviour in male Wistar rats

We have studied the effect of the 5-HT(2A) receptor antagonists on apomorphine-induced aggressive behaviour in male Wistar rats. In acute behavioural experiments with apomorphine-pretreated (1.0 mg/kg, s.c., once daily, 2 weeks) animals, risperidone (0.5 and 1.0 mg/kg) inhibited aggressive behaviour, but ketanserin and ritanserin (0.5-5. 0 mg/kg) had no effect on the latency and intensity of aggressive behaviour. Concomitant risperidone (0.5 mg/kg) and haloperidol (0.03 and 0.3 mg/kg) administration blocked aggressive behaviour completely. In conclusion, our experiments confirm that inhibition of the apomorphine-induced aggressive behaviour is elicited by drugs with dopamine (DA) but not with 5-HT(2A) antagonistic activity. Moreover, it may be concluded that the serotonin 5-HT(2A) receptor subtype does not alter the DA-mediated behaviour.

Apomorphine-induced aggressive behaviour and post-mortem monoamine content in male Wistar rats

The aim of this study was to investigate the monoamine content in post-mortem brain samples of control, apomorphine-aggressive, and apomorphine-non-aggressive adult male Wistar rats. The repeated apomorphine (1.0 mg/kg, (s.c.) once daily during 2 weeks) gradually induced aggressive behaviour in 18 animals out of 24. No unidirectional changes in the brain monoamine contents in four regions (frontal cortex, striatum, hippocampus, and hypothalamus) were detected as measured by high pressure liquid chromatography-electrochemical detection. In conclusion, our present experiment demonstrates that the development and intensity of apomorphine-induced aggressive behaviour do not correlate with the brain post-mortem monoamine content.

Inhibition of amphetamine- and apomorphine-induced behavioural effects by neuropeptide Y Y(1) receptor antagonist BIBO 3304

Neuropeptide Y (NPY) has an important role in the regulation of stress responses and feeding behaviour. There is evidence that some effects elicited by NPY occur due to modulation of action of regular neurotransmitters. The main objective of the present study was to test behavioural effects of the novel neuropeptide Y (NPY) Y(1) receptor antagonist (R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N(2)-(diphe nylacetyl)-argininamide trifluoroacetate (BIBO 3304) on dopamine-dependent behaviour. Intracerebroventricular administration of BIBO 3304 (1, 10, 50 nmol) had no effect on locomotor activity as measured by number of rearings and number of squares visited in an open field test in rats, but at 50 nmol dose defecation was significantly increased. BIBO 3304 (10 nmol) reduced amphetamine-induced increases in horizontal and vertical activity whereas its S-configurated enantiomer BIBO 3457 was inactive. In an open field test BIBO 3304 (10 nmol) inhibited purposeless running in rats sensitized to direct dopaminergic agonist apomorphine (0.5 mg/kg, s.c.). BIBO 3304 (10 nmol but not 1 nmol, i.c.v.) reduced fighting in apomorphine-induced aggression paradigm. Apomorphine-induced aggression was reduced by another, structurally similar, but less potent NPY Y(1) receptor antagonist BIBP 3226 (10 nmol, i.c.v.). A lower dose of BIBP 3226 (1 nmol, i.c.v.) was inactive. Concomitant administration of BIBO 3304 (10 nmol) with low doses of apomorphine (0.5 mg/kg s.c.) over the course of 10 days failed to prevent the development of apomorphine-induced aggressiveness. These data demonstrate that behavioural response to indirectly (amphetamine) and directly (apomorphine) acting dopaminergic stimulants is inhibited by NPY Y(1) receptor antagonists and suggest that NPY Y(1) receptor activation might be important in pathophysiology of disorders associated with hyperactivity of dopaminergic pathways, such as psychosis, schizophrenia and drug abuse. We propose that the effects of BIBO 3304 on amphetamine/apomorphine-induced locomotion and apomorphine-induced aggressiveness are due to modulation of postsynaptic dopaminergic responses rather than direct effects of NPY Y(1) receptor antagonists on dopamine or NPY release.

Modulatory role of 5-HT3 receptors in mediation of apomorphine-induced aggressive behaviour in male rats

We have studied the effects of serotonin (5-HT) 5-HT3 receptor agonists 1-phenylbiguanide (1-PBG) and 1-(m-chlorophenyl)biguanide (mCPBG), and antagonists 3-tropanyl-3,5-dichlorobenzoate (MDL-72222) and tropisetron (3-tropanyl-indole-3-carboxylate HCl; ICS-205930) on apomorphine-induced aggressive behaviour in normal or DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride] pre-treated male Wistar rats. DSP-4 (50 mg/kg) pre-treatment significantly accelerated the development of apomorphine-induced aggressive behaviour. mCPBG (1.0 and 10 mg/kg) did not modify the aggressiveness, but 1-PBG (3.0 and 30 mg/kg) attenuated the aggressiveness in normal but not DSP-4 pre-treated rats. MDL-72222 (0.4 and 4.0 mg/kg) attenuated the aggressive behaviour in normal rats, tropisetron (0.3 mg/kg) had an antiaggressive effect only by citalopram (10 mg/kg) challenge. MDL-72222 and tropisetron were ineffective in DSP-4 pre-treated rats. In conclusion, our results indicate that the 5-HT3 receptors modulate the apomorphine-induced aggressive behaviour and the 5-HT3 receptor antagonists have moderate antiaggressive effect in this test.