A role for serotonin in the elaboration of a differential pattern of activity in sympathetic nerves to kidney and skeletal muscle vasculature.

The role of serotonin (5-HT) in the elaboration of patterns of regional sympathetic discharge evoked from the ventral medulla was examined in cats under Saffan anesthesia. A differential response pattern consisting of an increase in renal sympathetic nerve activity simultaneous with no change in activity to skeletal muscle vasculature was evoked from a group of ventral medullary neurons by microinjection of D,L-homocysteic acid. Subsequent intrathecal administration of the 5-HT receptor antagonist methysergide (200 micrograms) attenuated or abolished the excitatory response to the kidney on restimulation of the medulla, without affecting sympathetic activity to muscle. Methysergide did not affect an excitatory response evoked in the outflow to both the kidney and skeletal muscle vasculature from an adjacent region of the ventral medulla. These results indicate a role for 5-HT in the elaboration of a specific differential pattern of sympathetic response evoked from medullary neurons.