Vesicular glutamate transporter DNPI/VGLUT2 is expressed by both C1 adrenergic and nonaminergic presympathetic vasomotor neurons of the rat medulla

Abstract

The main source of excitatory drive to the sympathetic preganglionic neurons that control blood pressure is from neurons located in the rostral ventrolateral medulla (RVLM). This monosynaptic input includes adrenergic (C1), peptidergic, and noncatecholaminergic neurons. Some of the cells in this pathway are suspected to be glutamatergic, but conclusive evidence is lacking. In the present study we sought to determine whether these presympathetic neurons express the vesicular glutamate transporter BNPI/VGLUT1 or the closely related gene DNPI, the rat homolog of the mouse vesicular glutamate transporter VGLUT2. Both BNPI/VGLUT1 and DNPI/VGLUT2 mRNAs were detected in the medulla oblongata by in situ hybridization, but only DNPI/VGLUT2 mRNA was present in the RVLM. Moreover, BNPI immunoreactivity was absent from the thoracic spinal cord lateral horn. DNPI/VGLUT2 mRNA was present in many medullary cells retrogradely labeled with Fluoro-Gold from the spinal cord (T2; four rats). Within the RVLM, 79% of the bulbospinal C1 cells contained DNPI/VGLUT2 mRNA. Bulbospinal noradrenergic A5 neurons did not contain DNPI/VGLUT2 mRNA. The RVLM of six unanesthetized rats subjected to 2 hours of hydralazine-induced hypotension contained tenfold more c-Fos-ir DNPI/VGLUT2 neurons than that of six saline-treated controls. c-Fos-ir DNPI/VGLUT2 neurons included C1 and non-C1 neurons (3:2 ratio). In seven barbiturate-anesthetized rats, 16 vasomotor presympathetic neurons were filled with biotinamide and analyzed for the presence of tyrosine hydroxylase immunoreactivity and/or DNPI/VGLUT2 mRNA. Biotinamide-labeled neurons included C1 and non-C1 cells. Most non-C1 (9/10) and C1 presympathetic cells (5/6) contained DNPI/VGLUT2 mRNA. In conclusion, DNPI/VGLUT2 is expressed by most blood pressure-regulating presympathetic cells of the RVLM. The data suggest that these neurons may be glutamatergic and that the C1 adrenergic phenotype is one of several secondary phenotypes that are differentially expressed by subgroups of these cells.

Spinal neurons activated in response to pudendal or pelvic nerve stimulation in female rats

“…VGlut2 and VGlut1 immunoreactivity are widely distributed in the central nervous system and are found in some overlapping regions [34,53,63]. Neurons synthesizing VGlut2 have been identified in the ventral medulla, a region that projects to the lumbosacral spinal cord and is involved in regulating pelvic function [42,60]. VGlut2 also innervates the parasympathetic preganglionic neurons of the lumbosacral spinal cord [38].…”

Immunohistochemical assessment of cyclic guanosine monophosphate (cGMP) and soluble guanylate cyclase (sGC) within the rostral ventrolateral medulla

“…The rostral ventrolateral medulla (RVLM) contributes significant excitatory drive to sympathetic preganglionic neurons and therefore also to vascular tone via two well characterised subpopulations of bulbospinal neurons: the C1 (adrenergic) and non-C1 cell groups [1][2][3]. Glutamate is the major neurotransmitter driving the activity of these neurons [3,4], but the gaseous neurotransmitter nitric oxide (NO) is thought to play a key role in regulating glutamate induced pressor responses, and therefore modulating homeostatic blood pressure mechanisms [5][6][7].…”

Mecanismos purinérgicos no bulbo ventrolateral rostral modulam respostas cardiovasculares e respiratórias promovidas pela ativação dos quimiorreceptores centrais e periféricos.

“…[11][12][13][14] Evidence suggests that both RTN chemore ceptors 9 and C1 cells 15 receive peripheral chemoreceptor drive. The transmitter basis for this drive is thought to depend largely on glutamate because NTS terminals in this region are immu noreactive for vesicular glutamate transporter 2 (VGLUT2, a marker of glutamatergic cells) 16,17 , and bilateral injections of kynurenic acid (glutamate receptor blocker) blunted peripheral chemoreceptor-mediated activation of breathing and blood pressure. 9,18 However, purinergic signaling has also been impli cated in the peripheral chemoreflex, [19][20][21][22] including at the level of the RVLM.…”

“…We focused our observations on the marginal layer of the ventrolateral medulla between Bregma −11.3 and Bregma −12.2 because this region contains chemosensitive 9,10,25,31 neurons and C1 15,17 cells, and it is known to receive a dense input from the cNTS. 9 BDAlabeled varicosities were assumed to be terminals (putative synapse).…”

“…The transmitter basis for this drive is thought to depend largely on glutamate because NTS terminals in this region are immu noreactive for vesicular glutamate transporter 2 (VGLUT2, a marker of glutamatergic cells) 16,17 , and bilateral injections of kynurenic acid (glutamate receptor blocker) blunted peripheral chemoreceptor-mediated activation of breathing and blood pressure.…”