Serotonin receptors in the rat nucleus tractus solitarii and cardiovascular regulation.

The effects of local application in the nucleus tractus solitarii of different serotonin receptor agonists and antagonists were investigated in anesthesized rats. Unilateral microinjection of serotonin produced an acute and transient hypotension and bradycardia which could be totally blocked by antagonists acting preferentially upon 5-HT2 receptor binding sites: ketanserin and ritanserin. 5-HT1 receptor agonists such as RU-24969 and 8-hydroxy-2-(di-n-propylamino)tetralin failed to reproduce the acute cardiovascular effects of serotonin. Bilateral microinjection of 5-HT2 receptor antagonists produced an increase in the level and in the variability of arterial pressure but did not block the baroreceptor reflex arc. The data suggest that serotonin acting upon 5-HT2 receptors in the nucleus tractus solitarii plays an important role in the modulation of arterial pressure.