Further Characterization of Forebrain Serotonin Receptors Mediating Tachycardia in Conscious Rats

It has been shown recently that activation of forebrain serotonin 1A (5-HT 1A) receptors, likely within the preoptic area, elicits a slight increase in blood pressure and a substantial tachycardia. The present studies were designed to characterize: (1) the requirement of the 5-HT 1A receptor agonist R(+)-8-hydroxy-2-(di- n-propylamino) tetralin [R(+)8-OH-DPAT]-induced tachycardia on the integrity of serotonergic innervation of the preoptic area, (2) the ability of the 5-HT 1A receptor partial agonist buspirone to elicit cardiovascular responses when microinjected into the preoptic area, (3) the role of 5-HT 2 and 5-HT 3 receptors in the preoptic area in cardiovascular regulation, and (4) the site specificity of the tachycardia produced by R(+)8-OH-DPAT. The data suggest that activation of 5-HT 1A receptors, but not 5-HT 2 or 5-HT 3 receptors, within or very near the preoptic area increases blood pressure and heart rate in conscious rats. Furthermore, the full response is dependent on afferent serotonergic innervation, suggesting a presynaptic modulatory role for 5-HT in the preoptic area.