Cardiovascular responses produced by microinjection of serotonin-receptor agonists into the paraventricular nucleus in conscious rats

Activation of serotonin (5-hydroxytryptamine, 5-HT) receptors in the brain produces cardiovascular responses by altering autonomic outflow. The parave ntricular nucleus (PVN) contains a modest density of 5-HT receptors and has connections to autonomic centers. Experiments were designed to determine w hether cardiovascular responses were produced by the administration of 5-HT 2- and 5-HT1A-receptor agonists into the PVN of conscious rats. The microin jection of the 5-HT2-receptor agonist DOI [(+/-)-1-(2,5-dimethoxy-4-iodophe nyl)-2-aminopropane HCl] into the PVN produced dose-dependent (1-10 nmol) i ncreases in heart rate and blood pressure; the peak responses were +39 +/- 10 beats/min and +6 +/- 2 mm Hg, respectively. Both responses were blocked by the concomitant administration of the selective 5-HT2-receptor antagonis t LY53857 into the PVN. By contrast, the microinjection of the selective 5- HT1A-receptor agonist R(+)-8-OH-DPAT [R(+)8-hydroxy-2-(di-n-propylamino) te tralin HBr; 1-10 nmol] into the PVN did not affect blood pressure or heart rate. These data suggest that 5-HT neurons projecting from the raphe nuclei to or near the PVN can participate in the central control of the cardiovas cular system by way of 5-HT2 receptors. Apparently 5-HT neurons terminating in the PVN can increase blood pressure and heart rate and produce sympatho adrenal activation, metabolic and hormonal responses consistent with those observed in several different stress paradigms.