Housing conditions fail to affect the intravenous self-administration of amphetamine

Rats were housed either in isolation or in groups of 4 for 6 weeks following weaning (21 days). After this housing period, some of the rats were tested for the acquisition of intravenous self-administration of amphetamine (0.004-0.25 mg/kg/infusion) and others were tested for the locomotor activating effects of amphetamine (0-1.0 mg/kg, IP). In the self-administration tests, both the isolated and grouped rats readily acquired the operant to obtain drug infusions and exhibited dose-dependent behavior. These results are in direct contrast to those we have obtained concerning the influence of the environmental manipulation on cocaine self-administration. In those tests, only isolated rats self-administered cocaine. The results of the locomotor tests indicated that whereas the isolated rats were consistently more active, the dose/response curves for the effects of amphetamine on activity were parallel for the rats reared under the different housing conditions. Thus the environment has specific effects on behavior which may be a reflection of specific neurochemical effects of the manipulation.