The effect of sound stimulation during gestation on the behavior of rat offspring

Abstract

The role of a fetal response (direct mediation) in the effects of sound stimulation during gestation on the postnatal behavior of rat offspring was studied. By deafening the mother and so eliminating a maternal stress response to sound stimulation, conditions were optimized for examining direct effects. -- Prior to mating, female hooded rats were either experimentally deafened or left intact (hearing condition). Beginning on the 13th day of gestation, some of the deaf mothers and some of the hearing mothers were presented with an 85db (re 20μN/m²) white noise stimulus. Another hearing group received a low noise stimulus, a 65db (re 20μN/m²) white noise. The remaining deaf and hearing mothers received the same experimental treatment but without the noise presentation. Experimental treatments continued through the 19th day of gestation. An undisturbed control group was also included in the design. A direct effect of noise stimulation would have to be considered if the deaf noise group differed significantly from its control group, deaf no noise. -- Offspring were tested on three behavioral tests: open-field, shuttle box avoidance, and one-way avoidance. In the open-field, the hearing noise group ambulated significantly more than the control group. All groups ambulated more than the controls. The shuttle box yielded insignificant results. On the one-way avoidance task, response latency scores on a CS pre-exposure were similar to group ambulation scores. An extinction effect occurred only in the hearing noise group which had not extinguished in 200 trials. -- The results of these tests were interpreted as indicating that noise stimulation is predominantly indirectly mediated. An important factor in the treatment effect was the placement of the maternal cages into the experimental chamber. This raised the question of the role of differing levels of novelty in the prenatal stress effect, particularly as this difference may account for contradictory findings in the prenatal stress literature.