EFFECTS OF CLONIDINE ON SYMPATHOEXCITATORY NEURONS IN THE ROSTRAL VENTROLATERAL MEDULLA

The effects of intravenous and iontophoretic clonidine were determined on the firing rates of sympathoexcitatory neurons in the rostral ventrolateral medulla of the cat. As previously reported in the rat, we found that sympathoexcitatory neurons could be differentiated based on their sensitivity in clonidine. Approximately 50% of the neurons were inhibited by clonidine. There was only a weak correlation between the inhibition of unit activity and whole sympathetic nerve activity. The discharge rates of the remaining neurons were either not altered or were increased by clonidine. Unlike the rat, these two groups of neurons could not be further differentiated on the basis of axonal conduction velocity or discharge frequency. These data are discussed and the effects of clonidine and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on sympathoexcitatory neurons are compared.