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-HT 2 receptor binding sites: ketanserin and ritanserin. 5-HT 1 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-HT 2 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-HT 2 receptors in the nucleus tractus solitarii plays an important role in the modulation of arterial pressure.