NEONATAL AND PREWEANLING RATS ARE ABLE TO EXPRESS SHORT-TERM BEHAVIORAL SENSITIZATION TO COCAINE

The present study assessed the ability of suckling rats to express sho rt-term behavioral sensitization to cocaine prior to weaning. Rat pups , aged either 3, 5, 10, 12, 17 or 19 days at the beginning of the expe riment, were placed in a chamber after daily injection with cocaine (7 .5 or 15 mg/kg, i.p.) for either 2 or 4 consecutive days, and were tes ted for behavioral responsiveness to cocaine in the same chamber 24 h later (at either 7, 14 or 21 days of age). Such a short post-treatment interval was adopted, along with a consistent pairing of the testing context with the drug effect and a sensitive technique of behavioral m easurement (video recording), in order to maximize the possibility of detecting any cocaine sensitization. Locomotion was sensitized at an a ges, after both regimens in 14-day-old pups, but solely after 2 inject ions in 21- and 4 injections in 7-day-old pups. Sensitization was also expressed via behaviors specific to each age. Four cocaine injections augmented cocaine-induced uncoordinated movements of head, paws and b ody (horizontal activity) in 7-day-old pups, and mouth movements in 14 -day-old pups. In 21-day-old pups, sensitization was dose- and regimen -dependently expressed via adult-like stereotyped head movements. In n eonatal 7-day-old pups, cocaine sensitization was also visible as redu ctions in immobility (both injection regimens). Contrary to previous s tudies, these results indicate that, given the use of an appropriate m ethodology, short-term sensitization to the motoric effects of cocaine can be expressed by suckling rats prior to weaning, even after relati vely short regimens of daily injections. (C) 1997 Elsevier Science B.V .