EVIDENCE FOR BEHAVIORAL SENSITIZATION TO COCAINE IN PREWEANLING RAT PUPS

While chronic intermittent administration of stimulants often induces behavioral sensitization in adulthood, stimulant sensitization has rar ely been reported prior to weaning [around postnatal day (P) 21]. Cons istent pairing of drug administration with the test context often faci litates sensitization in adults: yet young animals have been typically returned to the home cage immediately post-injection. To determine wh ether promoting context-dependent sensitization might facilitate expre ssion of sensitization in preweanlings, Sprague-Dawley rats were injec ted daily from P14 to P20 with 0, 5, 15, or 30 mg/kg cocaine HCl and p laced for 30 min in either the experimental chamber or home cage. On P 21 (test day), subjects were challenged with either 15 mg/kg cocaine o r saline prior to placement in the experimental chamber. Significant s ensitization of cocaine-induced stereotyped head movements was evident in animals given 15 or 30 mg/kg chronically in the experimental chamb er, but not when these same doses were given in the home cage. Less co nsistent evidence for cocaine-induced sensitization was seen when exam ining locomotion, although trends for sensitization of this behavior w ere seen in animals chronically injected in either the test chamber or home cage. Thus, preweanlings can exhibit cocaine sensitization, part icularly in terms of stereotypy when tested shortly after the chronic exposure period, with expression of this sensitization being facilitat ed by pairing the chronic injections with the test context.