Exposure to Predator Odor Reduces Locomotor Activity Levels in Adult Male Rats: Lack of Effect of Hippocampal Lesion

The hippocampus has been implicated in mediating responses to predators. Involvement of the hippocampus was tested in the present study in which a multivariate analysis of the locomotor activity of intact and hippocampectomized (destruction of dentate and CA1 cells) laboratory rats, Rattus norvegicus, was conducted following exposure to a predator odor. Levels of various activity variables were monitored in an automated activity monitoring system following a brief 3-min exposure to 2-propylthietane (weasel odor), caproic acid (goat odor), toluene (organic solvent), and a no-odor condition in hippocampal-lesioned (using colchicine) and sham-operated control male rats. Rats of both groups displayed reduced levels of total distance, movement time, vertical activity, and number of movements following exposure to weasel odor and toluene in comparison to the no-odor condition. Exposure to goal odor resulted only in reduced levels of vertical activity and number of movements. There were no differences in activity levels between hippocampal-lesioned and sham-operated rats during baseline activity recording or following exposure to any of the odors. However, hippocampal-lesioned rats spent less lime in the center of the activity boxes than sham-operated control rats across all conditions. This study demonstrates that laboratory rats show marked changes in locomotion in response to the odor of a predator and suggests that an intact hippocampus is not essential for mediating these responses.