Muscarinic Acetylcholine Receptor-2 in the Cerebellar Fastigial Nucleus is Involved in Acetylcholine-Mediated Blood Pressure Regulation in Rats

Our previous investigations have revealed that microinjection of acetylcholine (ACh) into the cerebellar fastigial nucleus (FN) induces a systemic blood pressure (BP) depressor response and that the muscarinic ACh (mACh) receptor contributes substantially to this process. This study was determined to explore the role of muscarinic ACh receptor-2 (M2 receptor) in ACh-mediated BP regulation and its underlying electrophysiological mechanism. ACh mixed with methoctramine hydrate (MCT, a selective M2 receptor antagonist) and normal saline (0.9% NaCl) were separately microinjected into the FN of anaesthetized rats, and the mean arterial pressure during the reactive time (the duration for BP to return to its basal level) was calculated; the responses of cholinergic reagents to the inward currents in FN neurons were also examined via patch-clamp recording in vitro; in addition, the receptor expression in the FN was confirmed by immunohistochemistry. The results demonstrated that MCT effectively blocked the ACh-mediated BP depressor response and the ACh-induced inward currents in FN neurons; moreover, M2 receptors were unequivocally distributed in the FN. Taken together, the results indicate that M2 receptors in the FN may be involved in ACh-mediated BP down-regulation by tuning neuronal excitation.