Effects of prenatal cocaine exposure and maternal separation on heart rate, orienting response habituation, and retention.

Effects of the presence or absence of the dam during testing and the retention interval on pretone heart rate (HR) and habituation and retention of an HR orienting response to tone were examined in prenatally cocaine-exposed and nontreated Sprague Dawley rat pups in two experiments. On postnatal day 16, each pup received two test sessions, separated by a 4-hr retention interval during which pups were either isolated or placed with their dam and siblings. For testing, each pup was placed in the test apparatus in the presence or absence of an anesthetized dam where, after a 15-min adaptation period, 10 tone presentations were given, each separated by a 65-s intertrial interval, with HR measured during a 5-s pretone period and throughout the 10-s tone for each trial. Experiment 1 used offspring from the regular breeding colony and observed the typical HR lowering effect of maternal presence during testing, an effect that was surprisingly potentiated, however, following the retention interval in animals that were isolated during this interval. This apparent potentiation by prior isolation of the HR lowering effect of the dam was confirmed in Experiment 2 in nontreated offspring, but did not emerge convincingly in offspring of either dams subcutaneously injected with 40 mg/kg of cocaine HCl daily from gestational days 8 to 20 (C40) or dams injected with saline and pair-fed 4 days (PF4) to mimic the acute anorexic effects of cocaine administration. Consistent with prior work, C40 offspring also were found to exhibit better retention of the habituated orienting response than offspring of NT dams and to some extent PF4 dams as well, a retention effect that was not significantly influenced, however, by social context during the retention interval.