Serotonergic hypotensive mechanism in rats: involvement of bulbospinal fibres.

The present study concerns the involvement of descending bulbospinal serotonergic pathways in blood pressure regulation in both normotensive and neurogenically hypertensive rats. We found that direct stimulation of serotonergic receptors of the spinal cord induced a depressor response which was prevented by prior catecholaminergic denervation in anaesthetized normotensive rats. Twenty-four hours after neurogenic hypertension, depletion of the serotonergic system provoked a further increase in blood pressure in conscious rats. We suggest that stimulation of pre-synaptic serotonergic receptors localized on spinal catecholaminergic neurons decreases blood pressure. This hypotensive mechanism could be activated after baroreflex deafferentation to prevent a further increase in blood pressure.