DEEP LESIONS OF THE FRONTAL POLE ELIMINATE SHOCK INDUCED HYPERALGESIA IN RATS. T.E. King*, R.L. Joynes, D. E. Minke, H. Penland, 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 (King et al., J. Exp. Psychol.: Anim. Beh. Proc., 22, 1996). Tail withdrawal to radiant heat is inhibited (hypoalgesia) while vocalization thresholds to both heat and shock are lowered (hyperalgesia). Prior work indicates that hyperalgesia represents an unconditioned response and enhances the acquisition of both conditioned freezing and an avoidance response to thermal pain (King et al., 1996).
The present experiment examines whether lesions of the frontal pole affect the induction of shock-induced hyperalgesia. Rats received either deep lesions of the frontal pole that extended to the lateral septum, shallow lesions that were limited to the the overlying cortex, or sham operations. A week later, they were placed in restraining tubes. Half the rats received three 1-mA (0.75-s) tailshocks. Tailshock induced hyperalgesia in both sham operated and shallow lesioned subjects. Hyperalgesia was not observed in deep lesioned rats. We also assessed the impact of deep lesions on conditioned freezing. We found that they eliminated the conditioned freezing elicited by reexposure to the shock context 24 hrs later. Supported by MH54557 to J.W.G.
Published in Society for Neuroscience Abstracts, 23, 1997, 161.