Neurobiological constituents of active, passive, and variable coping strategies in rats: Integration of regional brain neuropeptide Y levels and cardiovascular responses

Authors

Darby F. Hawley, Massimo Bardi, Ashley M. Everette, Torrence J. Higgins, Kelly M. Tu, Craig H. Kinsley, Kelly G. Lambert

Abstract

Effective coping strategies build resilience against stress-induced pathology. In the current study, young male rats were categorized as active, passive, or variable copers by observing their responses to being gently restrained on their backs (i.e., the back-test). The rats were subsequently exposed to chronic unpredictable stress, which included several ethologically relevant stressors such as predator odors and calls, for approximately three weeks. During this time, the variable copers, defined as rats that demonstrated a variable as opposed to a rigid response to stress, exhibited more seemingly adaptive responsiveness in three successive forced swim tests than the more consistently responding passive and active copers. This behavioral flexibility was accompanied by increased neuropeptide Y-immunoreactivity in the bed nucleus of the stria terminalis (BNST) and the amygdala and increased fos-immunoreactivity in the BNST. Additionally, the alterations in fecal corticosteroid levels and cardiovascular measures (systolic blood pressure and tail blood volume) between baseline and stress conditions differed according to coping strategy. Factor analysis indicates that variable copers were characterized by a distinct cardiovascular and neural response to the stress exposure. These results suggest that this animal coping model may be useful in discerning the adaptive nature of particular response strategies in the face of environmental exigencies.