Habituation of sympathetic sudomotor and vasomotor skin responses: neural and non-neural components in healthy subjects

Objective Sympathetic skin response (SSR) and skin vasomotor response (SVR) habituation was thought to be induced by neural mechanisms. Here, we investigate the hypothesis that non-neural mechanisms could also be involved. Methods We recorded sympathetic skin nerve activity (SSNA) from median nerve by microneurography and the corresponding SSR and SVR in 16 healthy subjects. Superficial electrical stimulation of the opposite median nerve was used to induce arousal responses. Results Throughout stimulation, SSNA, SSR and SVR amplitude showed a significant reduction. During the first ten stimuli, SSNA showed a marked decrease highly correlated to SSR and SVR changes. During the subsequent 20 stimuli SSNA did not change whereas SSR and SVR significantly decreased. SVR was significantly influenced by skin temperature changes. Conclusions Both neural and non-neural mechanisms are involved in SSR and SVR habituation. The neural mechanisms were predominant during the first part of stimulation whereas non-neural mechanisms prevailed during the last part of stimulation. Significance During repeated arousal stimuli SSR and SVR amplitude changes did not reflect the strength of the corresponding sympathetic nerve traffic and must be interpreted with caution.