Differential cardiorespiratory control elicited by activation of ventral medullary sites in mice

Abstract

We studied the respiratory and blood pressure responses to chemical stimulation of two regions of the ventral brainstem in mice: the rostral and caudal ventrolateral medulla (RVLM and CVLM, respectively). Stimulation of the RVLM by microinjections of the excitatory amino acid L-glutamate induced increases in diaphragm activity and breathing frequency, elevation of blood pressure (BP), and a slight increase in heart rate (HR). However, activation of the CVLM induced a decrease in breathing frequency, mainly due to prolongation of expiratory time (TE), and hypotension associated with a slight slowing of HR. Because adrenergic mechanisms are known to participate in the control of respiratory timing, we examined the role of alpha(2)-adrenergic receptors in the RVLM region in mediating these inhibitory effects. The findings demonstrated that blockade of the alpha(2)-adrenergic receptors within the RVLM by prior microinjection of SKF-86466 (an alpha(2)-adrenergic receptor blocker) significantly reduced changes in TE induced by CVLM stimulation but had little effect on BP responses. These results indicate that, in mice, activation of the RVLM increases respiratory drive associated with an elevation of BP, but stimulation of CVLM induces prolongation of TE via an alpha(2)-adrenergic signal transduction pathway.

Maps of cardiovascular and respiratory regions of rat ventral medulla: Focus on the caudal medulla

“…Bourassa et al (2009) commented that although the rostrocaudal extent of the most extensively investigated vasopressor RVLM are now clear the other axes are poorly defined. Medullary regions have been explored using chemical stimulation in several species including mice (Tolentino- Silva et al, 2000), cats (McAllen and May, 1994), rabbits Goodchild and Dampney, 1985;Goodchild et al, 1982Goodchild et al, , 1984 and rats (Minson et al, 1987;Ross et al, 1984;Ruggiero et al, 1994;Willette et al, 1983) and when common areas are assessed for the most part (see below) have been found to share similar contours perhaps not surprisingly considering the fundamental processes conducted by the medulla.…”

Transcriptional Factor Aryl Hydrocarbon Receptor (Ahr) Controls Cardiovascular and Respiratory Functions by Regulating the Expression of the Vav3 Proto-oncogene

“…leads to the stimulation of GABAergic cells present in this region (59). As a result, the microinjection of this neurotransmitter in this brainstem area leads to hypotension and bradypnea due to enhanced inhibitory GABAergic signaling from L-glutamate-stimulated CVLM neurons.…”

Nicotinic acetylcholine receptor subunit mRNA expression in adult and developing rat medullary catecholamine neurons

“…It receives extensive peripheral afferents from multiple visceral modalities and projections from various areas of the central nervous system (CNS) that regulate visceral function (Altschuler et al, 1989;Lawrence and Jarrott, 1996;Rogers and Hermann, 1985;Rogers et al, 2003). The VLM controls both sympathoexcitatory and inhibitory circuits in order to maintain autonomic ho-meostasis (Averill, 2000;Blessing and Li, 1989;Granata, 2003;Tolentino-Silva et al, 2000). The DMV receives information from the abdomen and supplies parasympathetic motor preganglionic fibers to the viscera, mediating CNS control of gastric motility and vagovagal reflexes (Guo et al, 2001;Gwyn et al, 1985).…”