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Behav. Sci. 2012, 2(2), 57-78; doi:10.3390/bs2020057

Physiological Consequences of Repeated Exposures to Conditioned Fear

1 Department of Integrative Physiology, University of Colorado at Boulder, Boulder, CO 80309-0354, USA 2 Center for Neuroscience, University of Colorado at Boulder, Boulder, CO 80309-0354, USA
* Author to whom correspondence should be addressed.
Received: 5 April 2012 / Revised: 5 May 2012 / Accepted: 14 May 2012 / Published: 18 May 2012
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Activation of the stress response evokes a cascade of physiological reactions that may be detrimental when repeated or chronic, and when triggered after exposure to psychological/emotional stressors. Investigation of the physiological mechanisms responsible for the health damaging effects requires animal paradigms that repeatedly evoke a response to psychological/emotional stressors. To this end, adult male Sprague Dawley rats were repeatedly exposed (2X per day for 20 days) to a context that they were conditioned to fear (conditioned fear test, CFT). Repeated exposure to CFT produced body weight loss, adrenal hypertrophy, thymic involution, and basal corticosterone elevation. In vivo biotelemetry measures revealed that CFT evokes sympathetic nervous system driven increases in heart rate (HR), mean arterial pressure (MAP), and core body temperature. Extinction of behavioral (freezing) and physiological responses to CFT was prevented using minimal reinstatement footshock. MAP responses to the CFT did not diminish across 20 days of exposure. In contrast, HR and cardiac contractility responses declined by day 15, suggesting a shift toward vascular-dominated MAP (a pre-clinical marker of CV dysfunction). Flattened diurnal rhythms, common to stress-related mood/anxiety disorders, were found for most physiological measures. Thus, repeated CFT produces adaptations indicative of the health damaging effects of psychological/emotional stress.
Keywords: stress; diurnal rhythms; blood pressure; stress-induced hyperthermia stress; diurnal rhythms; blood pressure; stress-induced hyperthermia
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Thompson, R.S.; Strong, P.V.; Fleshner, M. Physiological Consequences of Repeated Exposures to Conditioned Fear. Behav. Sci. 2012, 2, 57-78.

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