Prenatal maternal stress in Mus musculus: effects on the offspring, and the role of the mother

Abstract

The aim of this project was to examine certain aspects of prenatal stress, by providing a more comprehensive study of one strain of animal in one laboratory than hitherto presented. The stressor employed was that of crowding during the last third of gestation, and special attention was given to the problem of distinguishing between prenatally and postnatally-caused alterations to the offspring. In order to assess the mother's role in postnatal mediation of these changes, the behaviour towards the young of both stressed and non-stressed dams raising either type of litter was monitored throughout the lactation period. Differences were observed in the ways in which frequencies and diurnal rhythms of behaviour changed as the young matured, and efforts have been made to relate these to observed differences in offspring.
As to the effects on the offspring themselves, their emotionality" was examined employing three common methods - the open-field test, the holeboard test and a passive avoidance test. The results indicated that prenatal stress may differentially affect male and female offspring, and that the importance of prenatal versus postnatal influences on emotionality is likewise sex-dependent. The sexuality of female offspring was investigated, with measures being taken of puberty onset, adult ovarian cyclicity, and receptivity. While the results of this section were not clear-cut, they did indicate that prenatal stress may act to reduce responsiveness (to e.g., pheromonal stimuli) in female offspring. An investigation of adrenocortical function was also carried out, examining the daily corticosterone rhythm and its onset, and also the adrenocortical response to mild stress. Rhythm onset was advanced in prenatally-stressed animals, and while no differences were observed in the adult corticosterone rhythm of males, that of females suggested that prenatal stress may alter pituitary-gonadal function. A theoretical model for the mediation of prenatal stress effects, based upon the results obtained in this work and elsewhere, is presented.