Systemic and regional haemodynamic responses to microinjection of 5-HT agonists in the rostral ventrolateral medulla in the rat.

In anaesthetised rats bilateral microinjection of 2 nmol 5-HT or the agonists 5-carboxyamidotryptamine (5-CT), 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) into nucleus paragigantocellularis lateralis produced a fall in blood pressure and heart rate, an increase in hindlimb vascular conductance but no significant change in renal conductance. In contrast, alpha-methyl-5-HT injected into the same region had no such effects. It is suggested that these cardiovascular effects are mediated by activation of 5-HT1A receptors. The possibility that there may be differences between species with respect to central 5-HT receptor-mediated cardiovascular effects is also discussed.