Sensory and sympathetic nerve contributions to the cutaneous vasodilator responses to a noxious heat stimulus

Abstract

We investigated the roles of sensory and sympathetic nerves on the cutaneous vasodilator response to a localized noxious heating stimulus. In a two‐part study, forearm sites were instrumented with microdialysis fibers, local heaters and laser‐Doppler probes. Skin sites were heated from 33°C to 42°C or rapidly to 44°C (noxious). In Part 1, we tested sensory nerve involvement using EMLA cream. Treatments were as follows: control 42°C, EMLA 42°C, control 44°C, and EMLA 44°C. At EMLA treated sites, the axon reflex was reduced compared to the control sites during heating to 42°C (p<0.05). There were no differences during the plateau phase (p>0.05). At both the sites heated to 44°C, the axon reflex and nadir became indistinct. The EMLA treated sites were lower compared to the control sites during the plateau phase (p<0.05). In Part 2, we tested the role of sympathetic nerves in response to the noxious heating using bretylium tosylate (BT). Treatments were as follows: control 42°C, BT 42°C, control 44°C, and BT 44°C. Treatment with BT at the 42°C sites resulted in a marked reduction in both the axon reflex and secondary plateau (p<0.05). At the 44°C sites the axon reflex and nadir became indistinct, and the plateau phase was reduced at the BT treated sites (p<0.05). These data suggest that both sensory and sympathetic nerves are involved during the vasodilator response to a noxious heat stimulus. Supported by University of Alabama.