Involvement of median preoptic nucleus and medullary noradrenergic neurons in cardiovascular and sympathetic responses of hemorrhagic rats

Abstract

The infusion of hypertonic saline solution (HSS) is known to be beneficial to the treatment of hypovolemic hemorrhage (HH). The central mechanism of HSS-induced cardiovascular and autonomic recovery of animals subjected to HH remains unclear. Hence, the present study evaluated the involvement of median preoptic nucleus (MnPO) and medullary noradrenergic neurons (A1 and A2) in HSS-induced cardiovascular and sympathetic responses in hemorrhagic rats. The wistar rats were subjected to specific lesion of noradrenergic neurons through the nanoinjections of anti-DβH-saporin into caudal ventrolateral medulla (A1 neurons) and nucleus of the solitary tract (A2 neurons). After recovery, mean arterial pressure (MAP) and renal sympathetic nervous activity were recorded. The HH was performed through blood withdrawal until a MAP of 60 mmHg was attained. In sham rats, HSS infusion (3M NaCl) reestablished MAP without change in HH-induced sympathoinhibition. The muscimol (agonist of GABAA receptor) was nanoinjected in MnPO during HH and MnPO inhibition abolished the recovery of MAP and HSS-induced sympathoinhibition. Simultaneous lesions of A1 and A2 abolished MAP restoration and sympathoinhibition after HSS infusion. These results suggest that the recovery of MAP and HSS-induced sympathoinhibition in hemorrhaged rats depend on intact neural projections from A1 and A2 to MnPO.

Cardiovascular Effect of Cuneiform Nucleus During Hemorrhagic Hypotension

“…Hemorrhage (HEM) is a life-threatening incident due to the loss of intravascular volume caused by hypotension with two compensatory and non-compensatory phases ( Evans, Ventura, Dampney, & Ludbrook, 2001 ; Standl, Annecke, Cascorbi, Heller, Sabashnikov, & Teske, 2018 ). The compensatory phase is performed by the elicit of baroreceptors signaling hypotension to the Nucleus of the Solitary Tract (NTS) followed by the activation of vasomotor neurons in Rostral Ventrolateral Medulla (RVLM), an important area in cardiovascular modulation, that excites the sympathetic neurons and maintains blood pressure in normal condition ( Naves et al, 2018 ; Palkovits, 1999 ). If blood loss continues, the non-compensatory phase, as the next phase, is started, in which sympathetic drive abruptly reduces and arterial pressure falls.…”

Mapping of afferent and efferent connections of phenylethanolamine N‐methyltransferase‐expressing neurons in the nucleus tractus solitarii

“…They receive visceral afferents and transmitted information to multiple autonomic units of the medulla, midbrain pontine, thalamus and hypothalamus, and anterior forebrain, such as the CeA, DMH, LH, PVH, ARC, and PAG, to regulate cardiovascular activity, 31 feeding behavior, 11 emotional regulation, 32 and processes such as water intake and salt metabolism. 33 Unfortunately, there has been no comprehensive neural pathways' analysis of adrenergic neurons expressing PNMT, as one of the important neuronal types within the NTS, which constraining the further in‐depth research into the pivotal role of PNMT neurons in physiological regulation. Current relevant neuroanatomical studies mostly outdated and relied on non‐specific chemical tracers, which were unable to reveal cell‐specific synaptic connections to distinct neurons.…”

“…Throughout all this time, research on the neural connectivity of the NTS catecholaminergic neurons has always been highly regarded, given its crucial roles in various brain functions. They receive visceral afferents and transmitted information to multiple autonomic units of the medulla, midbrain pontine, thalamus and hypothalamus, and anterior forebrain, such as the CeA, DMH, LH, PVH, ARC, and PAG, to regulate cardiovascular activity, 31 feeding behavior, 11 emotional regulation, 32 and processes such as water intake and salt metabolism 33 . Unfortunately, there has been no comprehensive neural pathways' analysis of adrenergic neurons expressing PNMT, as one of the important neuronal types within the NTS, which constraining the further in‐depth research into the pivotal role of PNMT neurons in physiological regulation.…”