THE ROLE OF ANXIETY IN SHOCK-INDUCED HYPERALGESIA IN RATS. A. Sieve*, T. King, E. Crown, M. Meagher, and J. Grau. Dept. of Psychology, Texas A&M Univ., College Station, TX 77843
Previous experiments have shown that exposure to a few moderate tailshocks (3, 0.75 sec, 1mA) elicits hyperalgesia in rats, as measured by lowered vocalization thresholds to heat and shock, and enhanced acquisition of both conditioned freezing to a weak shock, and an avoidance response to thermal pain. (King, et al., J. of Exp. Psychol.: Anim. Beh. Proc., 22, 1996). King et al. suggested that shock exposure enhances pain because it induces anxiety. The present experiments test this hypothesis.
After confirming that the anxiogenic DMCM produces anxiety on the elevated plus maze and social interaction test, we tested the effects of our shock procedure on these behavioral measures. Though traditional measures of anxiety found no difference between shocked and unshocked rats, the frequency of aggressive behaviors was higher in shocked rats. Next, we tested the effects of pharmacologically manipulated anxiety on heat and shock thresholds. The anxiolytic Midazolam attenuated the shock-induced hyperalgesia. However, DMCM increased heat and shock thresholds and reduced conditioned freezing to a weak shock, suggesting that the drug reduced pain. It is possible that a negative affective state of anger or pain, rather than anxiety, induces the hyperalgesia to shock. Supported by MH54557 to J. W. G. and M. W. M.
Published in Society for Neuroscience Abstracts, 24 (1998),1901.