Determination of the place conditioning and locomotor effects of amperozide in rats: a comparison with cocaine

Amperozide promotes social interactions in rats (Rattus norvegicus) and reduces craving for cocaine and alcohol without producing adverse side effects. Amperozide administration produced a place preference in the dose range from 3.0 to 10.0 mg/kg. Locomotor behavior tended to be suppressed on the days of amperozide pairings, elevated on the days of vehicle pairings, and elevated on test days. Administration of 20.0 mg/kg but neither 2.0 nor 0.2 mg/kg cocaine produced place preference. Rats exhibited a greater place preference for the chamber paired with 2.0 mg/kg and 20.0 mg/kg but not 0.2 mg/kg cocaine compared to the chamber paired with 5.0 mg/kg amperozide. The results indicate that amperozide is appetitive. The most appetitive dose of amperozide (5.0 mg/kg) is less appetitive than the most appetitive dose of cocaine (20.0 mg/kg). More research is needed before conclusions regarding the degree of abuse potential for amperozide can be made.

The failure of some rats to acquire intravenous cocaine self-administration is attributable to conditioned place aversion

Although cocaine administration in humans includes euphoric and anxiogenic effects, the latter are less well understood. Acute cocaine administration produces aversive effects including anxiogenic effects as well as appetitive effects in rats and mice. In the present study the self-administration and conditioned place preference paradigms were used to determine whether the failure of some rats to acquire intravenous cocaine self-administration is attributable to either an interference with learning or an aversion to cocaine. Rats were classified as self-administrators or non-self-administrators based on the mean number of cocaine self-infusions per session and whether or not rats exhibited either a stable high level of responding or a stable low level of responding. Intravenously administered cocaine produced place preference for the self-administrators, while intravenously administered cocaine produced place aversion for the non-self-administrators. The fact that the non-self-administrators showed place aversion is inconsistent with the interpretation that the failure of these rats to readily self-administer is attributable to cocaine-mediated interference of learning. This is the first study in which both the self-administration and the conditioned place preference paradigms have been used in the same animals to demonstrate that the effects of cocaine are appetitive for some rats and aversive for others, and are not an artifact of cocaine's interference with learning.

The effects of atypical antipsychotics and phencyclidine (PCP) on rotorod performance

A series of six experiments were conducted to determine the effects of haloperidol, clozapine, olanzapine, and phencyclidine (PCP) on rotorod performance. Rodents were trained to walk on a rotorod to avoid a mild shock to a criterion of 20 rpm for 3 min. None of the vehicles of any of these drugs disrupted rotorod performance. Haloperidol disrupted rotorod performance at doses of 0.03, 0.1, and 0.3 mg/kg, and olanzapine disrupted rotorod performance at doses of 3.0 and 10.0 mg/kg. Clozapine produced a much milder disruption across all three doses (3.0, 10.0, and 30.0 mg/kg). PCP produced a consistent and severe disruption of rotorod performance at doses of 4.0 and 6.0 mg/kg, but not at a dose of 2.0 mg/kg. Twenty-four hours postinjection there were no residual PCP effects on rotorod performance. Coadministration of either haloperidol or olanzapine with PCP did not reverse PCP-induced disruption in rotorod performance, while clozapine produced a partial reversal at only one dose. These findings indicate that olanzapine functions similarly to classic antipsychotics with respect to their effects on locomotion and balance.

The effects of the naltrexone implant on rodent social interactions and cocaine-induced conditioned place preference

Two experiments were conducted to determine the behavioral properties of the naltrexone implant on: 1) rodent social interactions; and 2) the appetitive properties of cocaine. Rats were surgically implanted with a naltrexone implant (placebo, 10 or 30 mg) and placed into an open field for the recording of social interactions. The naltrexone implants increased latency to initiate contact and decreased pinning, bouts of grooming, and crawl unders on all 7 days. Other rats were surgically implanted with naltrexone (60, 120, or 240 mg) and habituated to a two-chambered conditioned place preference apparatus. After 6 days of conditioning, place preference was computer recorded. Cocaine produced a dose-dependent conditioned place preference in the rats implanted with placebo or 60 mg of naltrexone. The 120 and 240 mg naltrexone implants blocked the emergence of cocaine-induced place preference. The results indicate that naltrexone implants produce significant social behavioral effects within 1 day, and are effective at attenuating the conditioned place preference produced by cocaine.