Intraneural stimulation as a method to study sympathetic function in the human skin.

Intraneural electrical stimulation of sympathetic postganglionic axons was made in human skin nerves combined with recordings of skin resistance and a photoelectric pulse plethysmogram within the innervation zone. Tungsten microelectrodes were used first to record multiunit sympathetic activity in sural or median nerves. After blocking the nerve with local anaesthetics proximal to the recording site the electrodes were then used for intraneural stimulation. Stimulation led to reduction of skin resistance which was frequency dependent. A short train of stimuli reduced skin resistance transiently and the response was potentiated by a single stimulus delivered up to 2.5 min. prior to the train. Vasoconstrictor responses did not always occur and were relatively independent of stimulation frequency. The method may be useful for physiological and pathophysiological studies of sympathetic neuroeffector transmission in man.