TEMPORAL DYNAMICS OF THE
CARDIOVASCULAR AND THERMOGENIC RESPONSE
TO SOCIAL STRESS IN RATS.

Sietse F. de Boer, Andrea Sgoifo, Peter Meerlo, Bauke Buwalda, and Jaap M. Koolhaas.
Department of Animal Physiology, University of Groningen
P.O. Box 14, 9750 AA Haren, The Netherlands.

INTRODUCTION Epidemiological studies in humans emphasize that major uncontrollable psychosocial stressors are important precipitating/predisposing factors in the development of affective (anxiety, depression) and somatic (cardiovascular) disorders. A striking aspect of these ilnesses is that both the symptoms and the responsivity to pharmacological treatment evolve over time, even remarkably long after the preceding stressful event. However, few animal models of affective disorders have considered the time course of stress-induced changes in behavior and physiology.

METHODS In our experimental approach in male rats we focus on the analysis of the temporal dynamics of the behavioral, physiological and neurochemical consequences of a single, 60 min lasting social defeat by a dominant male conspecific. The animals are provided i.p.with a small biotelemetric transmitter (DSI) for continuous chronic recording of ECG, heartrate, bloodpressure, temperature and activity using DSI Labpro acquisition and analysis software.

RESULTS As part of the classical response to an acute stressor, the social defeat induces strong behavioral (defense) reactions and associated physiological (tachycardia, hypertension, hyperthermia), neuroendocrine (increased corticosterone, catecholamine, prolactin, testosterone) Most of these responses diminish within minutes to a few hours after termination of the social stressor. However, more sustained recordings indicate that social defeat induces changes in various behavioral and physiological parameters each of which may have different course in time ranging from several days to weeks. During the first 7-14 days after the event, there is a decrease in general activity, growth, sexual interest and open field exploration as well as a reduction in the circadian variation of body temperature, heart-rate and blood-pressure. In addition, behavioral provocation tests show a gradually developing and long-lasting (at least up to 5 weeks) enhancement of behavioral (immobility reaction to sudden silence) and physiological (sudden-silence evoked bradycardia and handling/novelty-induced hyperthermia and tachycardia) responsiveness to mild environmental stimuli.

DISCUSSION These long-term temporal dynamics of the social stress responses and its consequences may provide an important fundamental approach of the etiology and symptomatology of stress-related disorders.