Cholinergic regulation of arterial pressure by the C1 area of the rostral ventrolateral medulla

Abstract

In anesthetized, paralyzed rats intravenous administration of the acetylcholinesterase inhibitor physostigmine (PHY) (100 micrograms/kg) evoked a dose-related rise in arterial pressure (AP) and heart rate (HR) and an associated increase in sympathetic nerve activity (SNA). The responses to PHY were blocked by electrolytic lesions of, or microinjection of kainic acid into, a specific site in the rostral ventrolateral medulla containing a cluster of neurons immunoreactive for the adrenaline-synthesizing enzyme phenylethanolamine N-methyltransferase and corresponding to the C1 area of the nucleus reticularis rostroventrolateralis (RVL). The C1 area and its surround contain a heretofore unrecognized network of varicose neuronal processes and perikarya labeled immunocytochemically with a monoclonal antibody to the ACh-synthesizing enzyme, choline acetyltransferase (CAT). PHY increased, by over 3-fold, the spontaneous activity of reticulospinal cardiovascular neurons in the C1 area which excite preganglionic sympathetic neurons in the intermediolateral spinal column. The effects of PHY on AP, SNA, and the discharge of reticulospinal neurons were blocked by systemic administration of the muscarinic antagonist scopolamine. Microinjections within the C1 area of the RVL of scopolamine, the M2-selective muscarinic receptor antagonist AF-DX 116, or the high-affinity choline uptake inhibitor hemicholinium-3 blocked the pressor effects of PHY. The nicotinic antagonist hexamethonium and the M1-selective muscarinic receptor antagonist pirenzepine were without effect. We conclude that (1) the increases in AP, HR, and SNA elicited by the systemic administration of PHY result from the augmented action of ACh released from cholinergic terminals within the C1 area of the RVL; (2) the locally released ACh acts through muscarinic receptors of the M2 subtype within the C1 area to produce excitation of intrinsic reticulospinal sympathoexcitatory neurons, thereby increasing the activity of sympathetic preganglionic neurons and consequently elevating AP and HR; and (3) while the specific function of the cholinergic innervation of the C1 area in cardiovascular regulation is unknown, it may contribute to the tonic regulation of AP.

Central Command Regulation of Circulatory Function Mediated by Descending Pontine Cholinergic Inputs to Sympathoexcitatory Rostral Ventrolateral Medulla Neurons

“…[7][8][9][10][11][12][13][14][15][16][17][18] Systemic or central administration of acetylcholinesterase inhibitors or muscarinic agonists increases blood pressure, 7-11 lowers body temperature, 12 and alters respiration. 13,14 Pressor responses can be evoked via activation of muscarinic receptors (mAChR) within several cardiovascular nuclei, including the posterior hypothalamus, 7 nucleus of the solitary tract, 15 and rostral ventrolateral medulla (RVLM).…”

“…13,14 Pressor responses can be evoked via activation of muscarinic receptors (mAChR) within several cardiovascular nuclei, including the posterior hypothalamus, 7 nucleus of the solitary tract, 15 and rostral ventrolateral medulla (RVLM). 10,11 Effects of central mAChR activation on cardiovascular reflexes are less well understood. 8,16,17 Sympathoexcitatory and hypertensive effects of intravenously administered physostigmine are largely mediated by excitation of RVLM neurons.…”

Effects of Microinjected Carbachol on the Antinociceptive Response to Noxious Heat Stimuli.

“…1,2) In addition, the RVLM modulates one of the physiological functions of antinociception via cholinergic neurons. 3,4) Immunohistochemical studies have shown that the RVLM is extensively innervated with cholinergic neurons 5) that mainly project from the pedunculopontine tegmental nucleus (PPT), 6) then efferently extend to the spinal cord. In fact, small-medium cholinergic neurons and choline acetyltransferase mRNA have been identified in small cells of the NRGC/nucleus reticularis paragigantocellularis (NRPG).…”

A Carbamate-Type Cholinesterase Inhibitor 2-sec-Butylphenyl N-Methylcarbamate Insecticide Blocks L-Type Ca2+ Channel in Guinea Pig Ventricular Myocytes

“…Intravenous injection of physostigmine, a typical ChE inhibitor, produces hypertension followed by respiratory arrest via inhibition of ChE activity in the medulla oblongata (4). Since the hypertension is inhibited by the microinjection of muscarinic blockers into the ventral medulla (25,26), the response appears to be elicited by the accumulation of ACh in the medulla (27). Intravenous injection of BPMC also inhibited ChE activity in the medulla (4).…”