MEDIAL FRONTAL-CORTEX LESIONS SELECTIVELY ATTENUATE THE HOT PLATE RESPONSE - POSSIBLE NOCIFENSIVE APRAXIA IN THE RAT

Lesions in the cingulate cortex have attenuated pain-related behavior in humans. We wished to evaluate an animal model of this effect by stu dying the effects of bilateral lesions within the medial frontal corte x, including rat cingulate cortex, on performance in 3 behavioral test s: the formalin, hot-plate, and tail-flick tests. Average hot-plate la tencies, but not formalin test scores or tail-flick latencies, were si gnificantly increased by an average of 82% in rats with medial frontal cortex lesions, as compared to sham-operated control rats. Motor func tion, as tested by righting and foot lifting responses and clinical ob servation, was not impaired. No effects were seen on hot-plate latenci es, tail-flick latencies, and formalin pain scores in sham-operated ra ts. These results suggest that the medial frontal cortex of the rat me diates certain types of supraspinally organized responses to noxious h eat pain. Lesions that include the medial frontal and anterior cingula te cortex appear to disrupt the integration of increasing heat nocicep tive input with motor responses that are necessary to execute quickly the escape behavior in the hot-plate test.