INDUCTION OF FOS-LIKE IMMUNOREACTIVITY BY ELECTROCUTANEOUS STIMULATION OF THE RAT HINDPAW

Stimulation of peripheral nerves activates the proto-oncogene c-fos, w hich in turn generates its gene product, Fos. Fos and Fos-like protein s are produced in the central nervous sytem in response to chemical, m echanical, thermal, and electrical manipulation. The present study dem onstrated a relationship between the number of Fos-like-immunoreactive nuclei in the spinal dorsal horn and graded intensities of electrical stimulation applied to the hindpaws of anesthetized and unanesthetize d rats. Stimulation levels within the range of 0.1 to 1.0 mA were chos en on the basis of parameters previously determined in behavioral inve stigations of escape reactions. Focal stimulation at these intensities activates peripheral axons directly, but does not injure or traumatiz e peripheral tissues. There was no evidence of inflammation or edema a s a result of the focal electrical stimulation. As the stimulation int ensity increased, the number and distribution of Fos-like-labeled nucl ei increased with respect to rostral-caudal and laminar orientation. T he threshold for expression of Fos-like immunoreactivity was different for anesthetized and unanesthetized animals. For anesthetized animals , the number of labeled nuclei increased significantly from the contro l level only when 1.0 mA was applied. However, in unanesthetized anima ls, the pattern of labeling was statistically significant at 0.2 mA. T he present study demonstrates that electrical stimulation can evoke th e expression of Fos-like immunoreactivity by activating nociceptors in the absence of tissue injury, and that the use of anesthetics can mod ulate this expression.