Modulation of sympathetic nerve activity by microinjection of the 5-HT1A receptor agonist 8-OH-DPAT into the rostroventrolateral medulla

In the present study, renal sympathetic nerve activity was recorded simulta neously with sympathetic nerve activity to skeletal muscle vasculature to d etermine if the sympatho-inhibition evoked by microinjection of the 5-MT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)teralin (8-OH-DPAT) into the rostroventrolateral medulla (RVLM) was uniform or regional. Three patterns of sympatho-inhibition were observed in these sympathetic outflows and the type of response depended upon location of microinjection within the subre trofacial nucleus (SRF). Inhibition of renal nerve activity only was elicit ed by microinjections at rostral sites at the caudal pole of the facial nuc leus. In contrast, inhibition of muscle sympathetic nerve activity was evok ed from more caudal injections at the rostral pole of the inferior olives. Microinjection in the area between these two regions produced inhibition of both sympathetic outflows. This study demonstrates that differential inhib ition of regional sympathetic outflows can be elicited by microinjection of the 5-HT1A receptor agonist 8-OH-DPAT into the RVLM. These data suggests t hat this modulation is due to differences in anatomical arrangement of the medullary neurons rather than differences in neuron sensitivity to the sero tonergic agonist. (C) 1999 Elsevier Science B.V. All rights reserved.