Involvement of the 5-HT(1A) receptor of the cuneiform nucleus in the regulation of cardiovascular responses during normal and hemorrhagic conditions

OBJECTIVE(S): The 5-hydroxytryptamine1A (5-HT(1A)) receptor is one of the serotonin receptors in the brain, which regulates cardiovascular responses, especially in hemorrhage. Presence of this receptor in the cuneiform nucleus (CnF) has been shown. The present study evaluates the cardiovascular effect of this receptor of the CnF in normal and hypotensive hemorrhagic rats. MATERIALS AND METHODS: Agonist (8-OH-DPAT) and antagonist (WAY-100635) of 5-HT(1A) microinjected into the CnF in basal and hemorrhagic conditions and cardiovascular responses were evaluated. Hemorrhage induced by blood withdrawal from the femoral artery and 2 min after that drugs microinjected. Time course and peak changes (∆) of the mean arterial pressure (MAP), systolic blood pressure (SBP) and heart rate (∆HR) were obtained and compared to the control and hemorrhage groups. RESULTS: In basal condition, 8-OH-DPAT significantly decreased ∆SBP, ∆MAP and ∆HR compared to the control (P<0.05-P<0.01), while way-100635 did not have a significant effect. Hypotension and tachycardia induced by hemorrhage ameliorated by agonist (P<0.05-P<0.01), while antagonist deteriorated hypotension (P<0.05) but attenuated tachycardia (P<0.01). CONCLUSION: This study shows that 5-HT(1A) receptor of the CnF involves in regulation of the cardiovascular responses. However, this effect in basal and hemorrhage conditions is different.