UBC Theses and Dissertations
Naturally occurring variations in defensive burying behavior are associated with differences in central neuropeptide expression in the male rat Linfoot, Ian
The shock prod defensive burying test has proven incredibly reliable and instrumental in determining the underpinnings of normal anxiety in rodents. Largely ignored in tests of defensive burying, however, is the capacity for individual animals to display marked variations in active and passive coping behaviors. To unmask the neurobiological correlates of this behavioral differentiation, rats were exposed to a mousetrap that was remotely triggered upon approach to remove the quality of pain. This design invited striking variations in defensive burying behavior levels, in which some rats either buried robustly or showed little to no levels of defensive burying. Furthermore, differences in burying behavior were associated with marked differences in the central expression of arginine vasopressin (AVP) and oxytocin (OT). Thus, relative to animals showing no significant levels of defensive burying activity, rats showing sustained elevations in defensive burying expressed higher levels of AVP mRNA and increased numbers of androgen receptor positive cells in the medial amygdala and posterior bed nuclei of the stria terminalis, brain regions that integrate emotional appraisal and sensory information. In contrast, animals showing little to no defensive burying responses expressed relatively higher levels of AVP and OT mRNA within the supraoptic nucleus and subregions of the paraventricular nucleus of the hypothalamus responsible for neuroendocrine and autonomic function. CRH mRNA levels did not vary as a function of burying activity in the central nucleus of the amygdala, the anterior division of the bed nuclei of the stria terminalis, nor in the paraventricular nucleus. These findings suggest a role for central AVP and OT in mediating differential defensive behaviors, and demonstrate the utility of using a pain free test of conditioned defensive burying as a framework for exploring individual differences in behavioral coping and neuroendocrine capacity.
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