Capsaicin-sensitive primary afferents mediate responses to cold in rats with a peripheral mononeuropathy.

Persistent sensitivity to noxious and innocuous somatic stimuli results from peripheral nerve injury. Following chronic constriction injury (CCI) of the sciatic nerve in the rat, the hind paw ipsilateral to the injury displays significantly decreased response latencies to a noxious heat stimulus (thermal hyperalgesia), compared with the contralateral uninjured paw. The ligated paw also shows increased lifting and duration of lifting from a cooled (4 +/- 1 degrees C) surface. To characterize the peripheral nerve component of increased sensitivity to cold, CCI rats were systemically injected with the potent capsaicin analog resiniferatoxin (RTX). Twenty-four hours following RTX injection response latencies to noxious heat were significantly increased for both the ligated and unligated hind paws. In addition, increased responsiveness of the ligated paw to the cold surface was significantly attenuated. The results demonstrate that the enhanced responsiveness to cold and heat following a CCI are mediated in part by RTX-sensitive primary afferents.