SHOCK-INDUCED HYPERALGESIA IN RATS. T.E. King*, R.L. Joynes, M.W. Meagher, J.W. Grau. Dept. of Psychology, Texas A&M University, College Station, TX 77843.
Exposure to a few moderately intense (1 mA) tailshocks has opposite effects on two measures of pain reactivity in rats. Tail-withdrawal to radiant heat is inhibited (hypoalgesia) while vocalization thresholds are lowered (hyperalgesia) to both heat and shock (King et al., J.Exp.Psychol.: Anim. Beh. Proc., 22, 1996). Prior work indicates that hyperalgesia represents an unconditioned response and enhances the acquisition of both conditioned freezing and an avoidance response to thermal pain. The present experiments further explore the behavioral properties of hyperalgesia and the underlying neural mechanisms.
We have shown that hypoalgesia is limited to the distal region of the tail (Prentice et al., Behav. Neurosci., 110, 1996). Experiment 1 shows that rats exhibit hyperalgesia irrespective of where the test stimulus is applied. Experiment 2 examined the shock conditions needed to induce hypo- & hyperalgesia. Exposure to 0.3 mA, but not 0.1 mA, tailshocks elicited both behavioral effects. Evidence indicates that the hypoalgesia is eliminated by both pentobarbital anesthesia and decerebration. Experiments 3 and 4 show that these manipulations also eliminate shock-induced hyperalgesia. Administration of a benzodiazepine (chlordiazepoxide) also attenuated the hyperalgesia. Results from additional pharmacological/physiological manipulations will be reported. Supported by MH48994 to J.W.G.
Published in Society for Neuroscience Abstracts, 22, 1996, 120.