Abstract
OBJECTIVES: Cholinergic neurons are important neurons in the Pedunculopontine tegmental nucleus (PPT). In this study, nicotinic receptor of the PPT in central cardiovascular regulation in the anesthetized rat was evaluated. MATERIALS AND METHODS: Saline, acetylcholine (Ach; doses: 90 and 150 nmol), hexamethonium (Hexa; doses: 100 and 300 nmol) and higher doses of Hexa (300 nmol) + Ach (150 nmol) microinjected into the PPT. The femoral artery was cannulated and cardiovascular responses were continuously recorded by a power lab system. After injection of drugs, peak changes of mean arterial pressure (∆MAP), systolic blood pressure (∆SBP) and heart rate (∆HR) calculated and compared with saline group. RESULTS: The ∆SBP and ∆MAP significantly decreased by two doses of Ach (P<0.05 to P<0.001) but ∆HR did not change. Two doses 100 (P<0.05) and 300 nmol (P<0.01) of Hexa significantly increased ∆HR but did not alter the ∆MAP or ∆SBP. Co-injection of Hexa + Ach significantly strengthened the ∆HR induced by Hexa alone (P<0.01) but did not affect ∆MAP or ∆SBP. CONCLUSION: These results indicate that nicotinic receptor of the PPT has an inhibitory effect on ∆HR with no significant effect on ∆MAP or ∆SBP.