Rostral ventral medulla 5-HT1A receptors selectively inhibit the somatosympathetic reflex

The role of the 5-hydroxytryptamine (5-HT1A) receptors in the rostral ventr olateral medulla (RVLM) on somatosympathetic, baroreceptor, and chemorecept or reflexes was examined in anesthetized rats. Microinjection of the select ive 5-HT1A agonist 8-hydroxy-di-n-propylamino tetralin (8-OH-DPAT) decrease d arterial blood pressure and splanchnic sympathetic nerve activity (SNA). Electrical stimulation of the hindlimb evoked early and late excitatory sym pathetic responses. Bilateral microinjection in the RVLM of 8-OH-DPAT marke dly attenuated both the early and late responses. This potent inhibition of the somatosympathetic reflex persisted even after SNA and arterial blood p ressure returned to preinjection levels. Preinjection of the selective 5-HT 1A antagonist NAN-190 in the RVLM blocked the sympathoinhibitory effect of 8-OH-DPAT and attenuated the inhibitory effect on the somatosympathetic ref lex. 8-OH-DPAT injected in the RVLM did not affect baroreceptor or chemorec eptor reflexes. Our findings suggest that activation of 5-HT1A receptors in the RVLM exerts a potent, selective inhibition on the somatosympathetic re flex.