Cardiovascular responses induced by the activation of muscarinic receptors of the pedunculopontine tegmental nucleus in anesthetized rats.

Background: The cardiovascular effects of nicotinic receptors of cholinergic system in the pedunculopontine tegmental nucleus (PPT) were shown.

Objective: In the following, the cardiovascular effects of the muscarinic receptor, another receptor in this system, were examined.

Methods: Rats were divided into eight groups: 1) control; 2 and 3) Ach (acetylcholine, an agonist) 90 and 150 nmol; 4 and 5) Atr (atropine; a muscarinic antagonist) 3 and 9 nmol; 6) Atr 3 + Ach 150; 7) Atr 9 + Ach 150; and 8) Atr 3 + hexamethonium (Hexa; 300 nmol) + Ach 150. After anesthesia, cannulation of the femoral artery was performed, and then the mean arterial pressure (MAP), systolic blood pressure (SBP), and heart rate (HR) were recorded using a power lab apparatus.

Results: Following drug microinjection, the maximum change (Δ) in MAP, SBP, and HR was calculated and analyzed. Both doses of Ach (90 and 150) significantly decreased ΔMAP and ΔSBP but could not change ΔHR. Neither of the doses of Atr significantly affected ΔMAP, ΔSBP, and ΔHR. Co-injection of Atr 3 + Ach 150 only increased ΔHR, but Atr 9 + Ach 150 decreased ΔMAP and ΔSBP than Ach 150 alone. The effect of the co-injection of Atr 9 + Hexa 300 + Ach 150 was also the same as the Atr 9 + Ach 150 group.

Conclusion: The present results revealed that cholinergic muscarinic receptors in the PPT have an inhibitory effect on MAP and SBP with no important effect on HR.