Chronic stress impairs recall of extinction of conditioned fear

• Published in: Neurobiology of learning and memory 2006-05, Vol.85 (3), p.213-218
• Main Authors: Miracle, Angela D., Brace, Michael F., Huyck, Kellie D., Singler, Samantha A., Wellman, Cara L.
• Format: Article
• Language: English
• Subjects: Affectivity. Emotion; Animal; Animals; Biological and medical sciences; Chronic Disease; Conditioning (Psychology); Dendrites - physiology; Extinction; Extinction, Psychological; Fear; Fear conditioning; Fundamental and applied biological sciences. Psychology; Habituation, Psychophysiologic; Learning. Memory; Male; Medial prefrontal cortex; Memory; Mental Recall; Personality. Affectivity; Prefrontal Cortex - physiology; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Rat; Rats; Rats, Sprague-Dawley; Stress, Psychological - psychology
• ISSN: 1074-7427; 1095-9564
• DOI: 10.1016/j.nlm.2005.10.005

Chronic restraint stress produces retraction of apical dendrites of pyramidal neurons in medial prefrontal cortex. To begin to examine the functional significance of this dendritic reorganization, we assessed the effects of chronic restraint stress on a prefrontally mediated behavior, extinction of conditioned fear. After bar press training to obtain a baseline of activity against which to measure freezing, rats were either unstressed or stressed via placement in a plastic restrainer (3 h/day for 1 week). After an additional day of bar press training, rats underwent fear conditioning and extinction. Rats received five habituation trials to a 30-s tone (4.5 kHz, 80 db) followed by seven pairings of tone and footshock (500 ms, 0.5 mA). One hour later, rats received tone-alone extinction trials to criterion. The next day, rats received 15 additional extinction trials. Percent freezing was assessed during all phases of training. Stress did not significantly affect unconditioned responding to tone, acquisition of conditioned fear, or initial extinction, but significantly increased freezing on extinction day 2. Thus, consistent with the regressive dendritic changes seen in medial prefrontal cortex, one week of restraint stress specifically impaired recall of extinction, a pattern of deficits typical of animals with impaired medial prefrontal function.