*K. K. COWANSAGE1, D. E. BUSH1, B. S. MCEWEN2, J. E. LEDOUX1;
1Ctr Neural Sci, New York Univ, New York, NY, 2Lab of Neuroendocrinology, Rockefeller Univ, New York, NY

Fear conditioning is an amygdala-dependent form of Pavlovian learning that endows an initially neutral conditioned stimulus (e.g. a tone) with fear-eliciting properties by association with an aversive unconditioned stimulus (e.g. a footshock). Recent findings indicate that acute or chronic stress exposure can alter the potency of subsequently formed fear memories. However, effects of stress on fear conditioning vary considerably depending on the fear conditioning parameters, type of stress, stress duration, and recovery period used. We therefore directly compared the effects of acute pre-exposure to shock stress, restraint stress, and forced swim stress on fear conditioning in rats. Male Sprague-Dawley rats were randomly assigned to one of four stress groups (no stress, restraint stress, shock stress, or swim stress). Restraint stress entailed firm confinement within cone-shaped plastic bags; shock stress consisted of 15 unsignaled footshock (1sec, 1mA) presentations, given at random intervals (mean ITI 60sec); swim stress involved forced exposure to a water pool (25°C; depth 30cm); no stress controls were handled briefly and returned to home cages. Fear conditioning commenced after 15 min recovery from stress and consisted of two 20-sec tone (5kHz, 80dB SPL) presentations that each co-terminated with a mild footshock (0.5sec, 0.5mA). Testing for tone-elicited freezing, in the absence of footshock, took place in a distinct context one day later. Results showed that freezing was significantly impaired in rats pre-exposed to acute swim stress, but restraint and shock stress had no effect. This effect of swim stress was still apparent, although slightly weaker, when a 60-min recovery period was used. Pretreatment with naloxone (2.5 mg/kg/ml, i.p.; 5 min before stress) did not reverse the effect of swim stress. Further experiments are underway to investigate the time course and physiological mechanisms underlying the stress-induced attenuation of fear conditioning.
Support Contributed By: P50 MH058911;R01 MH046516 ;R37 MH38774;K05 MH067048

Program No. 370.6/KK24
Poster presentation:Monday, Oct 16, 2006, 10:00 AM -11:00 AM
Location: Georgia World Congress Center: Halls B3-B5