The discharge of a subset of serotonergic raphe magnus cells is influencedby baroreceptor input

In order to determine whether serotonergic cells in the medullary raphe mag nus (RM) receive baroreceptor input, cells were tested for their responses to descending aortic occlusion, aortic nerve stimulation, or systemic pheny lephrine administration in the lightly anesthetized rat. Serotonergic cells were identified physiologically by a quantitative analysis of their slow a nd steady discharge. Greater than 40% of the serotonergic RM cells tested r esponded to brief occlusion of the descending aorta at the level of the coe liac arteries, a stimulus that elevated blood pressure by about 30 mmHg. Si milarly, about 40% of the serotonergic RM cells responded to stimulation of the aortic nerve, a nerve that contains primarily baroreceptor afferents f rom the aortic arch. Greater than 70% of RM serotonergic cells responded to phenylephrine administration which elevated blood pressure by an average o f 50 mmHg. Serotonergic cell responses to all methods of baroreceptor activ ation were small in magnitude and were largely restricted in time to the st imulus duration. The results indicate that a subset of serotonergic cells i n RM are influenced by baroreceptor activity. (C) 2001 Published by Elsevie r Science B.V.