Depressor pathway involved in somatosympathetic reflex in cats

The present study aimed to identify direct vasodepressor pathways from the rostral ventrolateral medulla (RVLM) to the spinal cord and their role in mediation of somatosympathetic reflexes. Vasopressor and depressor areas were identified by stimulating various sites of RVLM electrically and/or chemically in anesthetized cats. Electrical lesions on the pressor areas abolished the pressor response evoked by peripheral C-fiber activation while the depressor response remained. Electrical lesions on the depressor areas decreased the depressor response evoked by A delta-fiber stimulation. To characterize the neurons involved, 17 medullospinal sympathetic neurons were identified electrophysiologically. While most of them were sympathoexcitatory, three medullospinal tract cells were found to be sympathoinhibitory neurons. From these results we concluded that a minor group of neurons in the RVLM is sympathoinhibitory and is involved in mediation of somatosympathetic depressor response.