The effects of amperozide on cocaine-induced social withdrawal in rats

Peer influences on drug self-administration: social facilitation and social inhibition of cocaine intake in male rats

RATIONALE

One problem facing animal models of intravenous drug self-administration, particularly those examining social manipulations, is that subjects must be removed from the home environment and separated from cagemates during testing. This represents a limitation of animal models because it fails to capture the complex social environments in which drug use often occur.

OBJECTIVES

The aim of this study was to examine intravenous cocaine self-administration in isolated and socially housed rats, with the caveat that the socially housed subjects lived together 24 h/day, including during daily self-administration sessions. As a secondary aim, the study examined the impact of a companion that also self-administered cocaine versus a companion without access to cocaine.

METHODS

Male rats were obtained at weaning and reared in isolated or pair-housed conditions for 6 weeks. Rats were then implanted with intravenous catheters and transferred to custom-built operant conditioning chambers that served as home cages for the remainder of the study. For some socially housed subjects, both rats had simultaneous access to cocaine; for others, only one rat of the pair had access to cocaine.

RESULTS

Cocaine self-administration was facilitated in socially housed rats if both members of the pair had access to cocaine; however, cocaine self-administration was inhibited if only one rat of the pair had access to cocaine.

CONCLUSIONS

These data indicate that the self-administration behavior of a peer, not merely the presence of a peer, determines whether cocaine self-administration is facilitated or inhibited by social contact.

Behavioral evidence for the significance of serotoninergic (5-HT) receptors in cocaine addiction

Cocaine addiction has somatic, psychological, psychiatric, socio-economic and legal implications in the developed world. Presently, there is no medication approved for the treatment of cocaine addiction. In recent years, data from the literature (pre-clinical studies and clinical trials) have provided several lines of evidence that serotonin (5-HT) and 5-HT receptors play a modulatory role in the mechanisms of action of cocaine. Here we review the contribution of 5-HT receptor subtypes to cocaine sensitization, discrimination, conditioned place preference, self-administration, reinstatement of seeking behavior and withdrawal symptoms in laboratory animals. Additionally, the consequences of chronic cocaine exposure on particular 5-HT receptor-assigned functions in pre-clinical studies are presented.

Effects of cocaine and putative atypical antipsychotics on rat social behavior: an ethopharmacological study

The effects of cocaine, amperozide, clozapine, olanzapine and cocaine/atypical antipsychotic combinations on aggression, affiliation and defensive behaviors was examined. Acute cocaine (30.0 mg/kg) decreased basal aggression and affiliation yet increased basal defense. Amperozide (1.0, 3.0 and 5.0 mg/kg) decreased basal aggression, affiliation and defense had no effect on the cocaine-induced decrease in affiliation, and accentuated the cocaine-induced decrease in aggression. Near basal levels of defense were observed for animals treated with either amperozide, clozapine (3.0 and 10.0 mg/kg but not 30.0 mg/kg) or olanzapine followed by cocaine. Clozapine (3.0, 10.0 and 30.0 mg/kg) decreased basal aggression and affiliation. Clozapine (30.0 mg/kg but not 3.0 or 10.0 mg/kg) decreased basal defense. Clozapine attenuated the cocaine-induced decrease in aggression. Although 3.0 and 10.0 mg/kg clozapine attenuated the cocaine-induced decrease in affiliation, 30.0 mg/kg clozapine accentuated this cocaine-induced effect. Olanzapine (1.0, 3.0 and 10.0 mg/kg) decreased basal aggression, affiliation and defense. Olanzapine had no effect on the cocaine-induced decrease in aggression. Olanzapine (3.0 mg/kg but not 1.0 or 10.0 mg/kg) attenuated the cocaine-induced decrease in affiliation. Thus, acute cocaine administration had an antiaggressive effect, suppressed affiliative behavior and enhanced defensive behavior. Amperozide, clozapine and olanzapine have anticonflict and anxiolytic effects, as well as potent and specific antiaggressive effects.

Acute effects of amperozide and paroxetine on social cohesion in male conspecifics

The effects of acute administration of the selective 5-hydroxytrypamine (5-HT; serotonin) uptake inhibitor, paroxetine, and the potent 5-HT(2A) receptor antagonist, N-ethyl-4-[4',4'-bis(rho-flourophenyl)butyl]-1-piperazinecarboxamide (amperozide) on social cohesion was determined by using a tether paradigm, in which the movement of one of a pair of rats was restricted to one-half of an observation chamber. Administration of 0.1mg/kg paroxetine, 1.0, 3.0, and 5.0mg/kg amperozide but neither 1.0 nor 10.0mg/kg paroxetine increased time spent in contact with the untreated, tethered rat. Whereas only the lowest dose of paroxetine (0.1mg/kg) promoted social cohesion, all doses of amperozide (1.0, 3.0, and 5.0mg/kg) promoted social cohesion. The amperozide-induced increases in time spent in contact were greater than the paroxetine-induced increases in seconds spent in contact, regardless of dose. Acute administration of amperozide is more effective than acute administration of paroxetine in promoting social cohesion between pairs of male conspecifics. Amperozide may be an effective alternative treatment for patients with social anxiety disorder suffering from adverse side effects of paroxetine. Amperozide may prove to be a more effective treatment for social anxiety disorder than paroxetine, which is supported by our results.

(+/-)-3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy') increases social interaction in rats

A series of experiments administered a low dose range (0, 1.25, 2.5 and 5 mg/kg) of (+/-)-3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy') to rats and assessed them in a variety of standard tests of anxiety. These tests included the emergence and elevated plus-maze tests, social interaction, cat odor avoidance and footshock-induced ultrasonic vocalizations. MDMA increased anxiety-related behaviours in the emergence and elevated plus-maze tests at all dose levels. A 5 mg/kg dose of MDMA also significantly reduced the time spent in close proximity to an anxiogenic cat odor stimulus. The 5 mg/kg dose also significantly reduced footshock-induced ultrasonic vocalizations. In the social interaction test, MDMA decreased aggressive behaviours at all doses tested, while the highest dose (5 mg/kg) also significantly increased the duration of social interaction. These results indicate that MDMA has both anxiogenic and anxiolytic effects depending upon the test situation employed. The facilitation of social interaction produced by MDMA in rats concurs with human experience of MDMA as a uniquely prosocial drug.