EFFECTS OF PRENATAL EXPOSURE TO COCAINE ON HEART-RATE AND NONASSOCIATIVE LEARNING AND RETENTION IN INFANT RATS

Nonassociative learning and retention were assessed in terms of habitu ation of a heart-rate (HR) orienting response (bradycardia) to a tone in 16-day-old male and female rats prenatally exposed to cocaine and i n control offspring. Offspring were derived from Sprague-Dawley dams g iven daily subcutaneous injections of 40 mg/kg/3 cc cocaine HCl (C40) from gestational days 8-20, pair-fed control dams given saline injecti ons (PF), and nontreated control dams (LC). Each pup was adapted to th e test apparatus for 15 min prior to being given 10 presentations of a pulsing tone, each separated by a 65-sec intertrial interval, with HR measured during a 5-sec pretone period and throughout the 10-sec tone for each trial. To assess retention, subjects were given 10 additiona l tone trials either 1, 2, 4, or 6 hr later. C40 male offspring displa yed significantly lower basal HR following the initial 15-min isolatio n period than either LC or PF offspring, whereas prenatal treatment ha d no effect on basal HR among females. Although no differences were se en in rate of habituation, prenatal cocaine exposure was observed to a ffect retention of the habituated orienting response. Whereas LC and P F offspring retained habituation of the orienting response for less th an 4 hr, C40 offspring exhibited no forgetting after a 4-hr interval, and showed significant loss of the habituation response only after a 6 -hr interval. (C) 1994 Wiley-Liss, Inc.