The development of behavioral and endocrine abnormalities in rats after repeated exposure to direct and indirect stress

Willie Mark Uren Daniels¹, Joachim de Klerk Uys¹, Petra van Vuuren¹, Daniel Joseph Stein²

¹Division of Medical Physiology, Faculty of Health Sciences, University of Stellenbosch, South Africa; ²Department of Psychiatry, Faculty of Health Sciences, University of Cape Town, South Africa

Abstract: The present study compared the effects of direct and indirect stress on the behavior and hypothalamic-pituitary-adrenal axis of rats. Animals were placed in a two compartment box. In one compartment the direct stressed rat was subjected to electric foot shocks randomly applied for 10 minutes (0.5 mA of 1 s duration). In the adjacent compartment, the indirect stressed rats witnessed the application of these electric foot shocks. Our data showed substantial behavioral changes in the open field test, but limited effects in the elevated plus maze. The findings suggested that single and repeated stress exposure may have different consequences, that the effects of stress exposure may develop over time and persist for an extended period, and that both direct and indirect stressed rats displayed a hyposensitive HPA axis following acute restraint stress. Overall our observations moderately indicate direct exposure to elicit behavioral changes, and both direct and indirect exposure to stress to result in aberrations within the neuroendocrine system. With additional development our stress models may be considered for studying the complex interrelationship between an external stressor, and the experience of the organism.

Keywords: direct vs indirect stress, behavior, open field, elevated plus maze, HPA axis, stress response