EVIDENCE INESCAPABLE SHOCK PRODUCES HYPERALGESIA IN RATS. M. W. Meagher, E. D. Crown, & J. W. Grau. Dept. of Psychology, Texas A&M University, College Station, TX 77843.

An extended exposure to shock produces a constellation of behavioral effects collectively known as learned helplessness. Maier & Watkins (1998; Psychol. Rev., 105,83) have suggested that the behavioral consequences of stress have parallels to the effects of illness, and that the depressive-like symptoms of learned helplessness might reflect a form of sickness behavior. Supporting this, they have shown that inescapable shock produces physiological signs of illness (e.g., fever) that last over 24 hrs.

Evidence suggests illness induces hyperalgesia. Yet, inescapably shocked rats exhibit longer tail-flick latencies to radiant heat. However, evidence from our laboratory suggests that reflex inhibition sometimes reflects a selective inhibition of protective reflexes rather than decreased pain (King et al., 1996, J. Exp. Psychol.: Anim. Behav. Proc., 22, 265). Given this, we assessed the impact of inescapable shock exposure (80, 5-s, 1 mA tailshocks) on other measures of pain. A day after shock treatment, rats were returned to the apparatus and both vocalization and tail-flick latencies were assessed. Previously stressed subjects exhibited lower vocalization thresholds to a noxious thermal stimulus, and outcome indicative of hyperalgesia. As in prior studies, tail-flick latencies were increased. We are currently examining whether the shift in vocalization thresholds is modulated by stressor controllability. Supported by MH54557 to J.W.G. & M.W.M.

Society for Neuroscience Abstracts, 25 (1999), 688.

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