Prenatal psychological stress effects on offspring behaviour in rats

Prenatal stress in rats: effects on plasma corticosterone, hippocampal glucocorticoid receptors, and maze performance

The present experiments were designed to investigate the effects of maternal stress on cognitive and endocrine parameters in the adult offspring. Pregnant rats were stressed daily during the last week of pregnancy (days 15-19) by restraint, and the performance of their offspring in the Morris water maze was recorded. Plasma corticosterone levels after swimming and the status of hippocampal glucocorticoid receptors (GRs) were determined. During acquisition of the task, prenatally stressed (PS) males - but not females - showed longer escape latencies than non-stressed controls when swimming in cold (10 degrees C) but not in warm (20 degrees C) water. This sex- and prenatal stress-specific difference was even more pronounced during reversal learning of the task. In contrast, PS females - but not males - had higher basal corticosterone levels and a lower density of hippocampal corticosteroid receptors than non-stressed controls. In all animals irrespective of treatment, swimming in the water maze causes an increase of corticosterone that was smaller on day 8 of swimming than on day 1. After swimming in cold water, the rise in corticosterone levels in females was steeper and returned faster to baseline values than after swimming in warm water. A similar pattern could be seen in PS females when compared to their non-stressed controls. The data suggest that prenatal stress impairs spatial learning in males but not in females. Basal and stress-induced increases in corticosterone levels, however, were altered in PS females and not in PS males; i.e., prenatal stress-induced changes in corticosterone secretion were not paralleled by prenatal stress-induced deficits in spatial learning.

Prenatal stress alters immune function in the offspring of rats

Pregnant rats were either exposed to restraint under bright lights for 45 min three times daily (n = 7) or were left undisturbed (n = 8) during Days 14-21 of gestation. Offspring were tested for cellular immune responses as measured by Concanavalin A-stimulated proliferation and Natural Killer (NK) cytotoxicity of splenocytes as juveniles or adults, or were tested for specific humoral immune responses to in vivo challenge with the antigen Keyhole Limpet Hemocyanin (KLH) as adults. Results indicated that: (a) Proliferation did not vary as a function of sex or prenatal treatment in either juvenile or adult offspring; (b) in juveniles NK cytotoxicity was marginally lower in males as compared to females, and was also marginally reduced by prenatal stress in males but not females, whereas in adults, NK cytotoxicity was marginally enhanced by prenatal stress in both sexes; and (c) prenatally stressed offspring of both sexes had higher levels of anti-KLH antibodies as compared to controls.

Water maze performance and hippocampal weight of prenatally stressed rats

Prenatally stressed rats were tested for water maze performance with the water temperature kept at 18 degrees C (low stress) or cooled down to 12 degrees C (high stress). When the platform had been removed from the pool and the water was kept at 12 degrees C, prenatally stressed males--but not females--spent more time searching for the platform in the correct quadrant of the pool than their controls. Prenatal stress reduced hippocampal weight in both sexes.

Prenatal stress effects on exploratory activity and stress-induced analgesia in rats

Pregnant rats were exposed three times daily to immobilization stress during gestational Days 15-19. The behavior of their offspring was compared with the behavior of offspring from unstressed control mothers. Although the stress procedure decreased the weight gain of mothers during pregnancy, it slightly but significantly increased the weight of their offspring at birth and at weaning. On postnatal Day 10, prenatally stressed pups returned to their home cage more quickly than did prenatally unstressed control pups during a nest odor discrimination task, but no differences between groups in the number of correct responses were found. On postnatal Days 70-72, prenatally stressed offspring showed increased exploratory activity in a complex tunnel maze compared with control offspring. On postnatal Day 80, analgesia induced by stress (swimming for 3 min in cold water) was determined (tail flick latency). The degree of stress-induced analgesia was smaller in prenatally stressed rats than in control rats. These data suggest that the effects of prenatal stress on behavior are most clearly discernable when such animals are confronted with a novel or stressful situation.