EFFECT OF PRENATAL STRESS ON OPIOID COMPONENT OF EXPLORATION IN DIFFERENT EXPERIMENTAL SITUATIONS

Prenatal stress interferes with the expression of opioid systems in ra ts. The present study determined the effect of prenatal stress on the opioid-influenced component of exploratory behavior, defined as the di fference between the behavior of vehicle-treated and naloxone-treated rats, in three novel situations previously shown to cause different de grees of arousal. Pregnant rats were stressed three times weekly an a random basis by noise and flashing lights. Experiments were performed on 60-70-day-old offspring (male and female) of control and stressed d arns. Fifteen minutes after injection of vehicle or naloxone (1 mg/kg) , the proportion of time spent in eight different behavioral parameter s, including locomotion, rearing, sniffing, hole poking, pivoting, and grooming, was assessed during 4 min of exposure to an open field, eit her with or without prior exposure to a hole box. The magnitude of the depressant effect of naloxone on exploration depended on the nature o f the environment, previous experience of the animal in another situat ion, and the parameter of exploration assessed. The opioid-influenced component of locomotion and rearing was significantly reduced by prena tal stress, particularly in female rats. Further studies using a cross -fostering design are needed to assess the relative contributions of p re-and postnatal factors to the reduction of opioid activity in prenat ally stressed rats. More specific opioid antagonists could be used to determine the nature of the opioid receptors involved. (C) 1997 Elsevi er Science Inc.