RELATIONSHIP BETWEEN SCHEDULE-INDUCED-POLYDIPSIA AND AMPHETAMINE INTRAVENOUS SELF-ADMINISTRATION - INDIVIDUAL-DIFFERENCES AND ROLE OF EXPERIENCE

It has been suggested that drug abuse belongs to a larger class of add ictive behaviors, including smoking, eating or gambling, which are med iated by common processes. Since laboratory animals can be induced to develop drug self-administration as well as indulge in compulsive eati ng or drinking, the present experiments were designed to find out if t he same animals were susceptible to both behaviors. Only certain rats develop amphetamine intravenous self-administration (SA), and this sus ceptibility can be predicted from their enhanced locomotor response in a novel environment. Furthermore, excessive, non-regulatory drinking, referred to as schedule-induced polydipsia (SIP), in response to the periodic delivery of small amounts of food is only observed in certain rats. Since the propensity to SA has been shown to be influenced by e xperimental factors and testing for SIP was found to modify behavioral and biological parameters related to the propensity for drug-seeking, we also investigated whether experience of SIP influenced the subsequ ent development of SA. In Expt. 1, the rats that developed SA also acq uired SIP, and had a higher locomotor response to novelty. The results of Expt. 2 showed that testing for SIP influenced the predisposition to develop amphetamine SA. When animals were tested for SIP first, the polydipsic rats subsequently failed to acquire SA, and had a reduced locomotor response to novelty. These changes seemed to be specific to the experience of SIP, as individual differences in the locomotor resp onse to novelty were unchanged when animals were housed in standard la boratory conditions over a period of one month between the two tests. First and foremost, the results indicate that the predisposition to de velop amphetamine SA is related to other behaviors with compulsive fea tures, such as SIP. Secondly, these results demonstrate the powerful i nfluence of a specific experience that is thought to have a coping fun ction, in reducing or altering vulnerability to addiction.