Selective Optogenetic Activation of Rostral Ventrolateral Medullary Catecholaminergic Neurons Produces Cardiorespiratory Stimulation in Conscious Mice

Abstract

Activation of rostral ventrolateral medullary catecholaminergic (RVLM-CA) neurons e.g. by hypoxia is thought to increase sympathetic outflow thereby raising blood pressure (BP). Here we test whether these neurons also regulate breathing and cardiovascular variables other than BP. Selective expression of ChR2-mCherry by RVLM-CA neurons was achieved by injecting Cre-dependent vector AAV2-EF1α-DIO-ChR2-mCherry unilaterally into RVLM of dopamine-beta-hydroxylaseCre/0 (DβHCre/0) mice. Photostimulation of RVLM-CA neurons increased breathing in anesthetized and conscious mice. In conscious mice, photostimulation primarily increased breathing frequency and this effect was fully occluded by hypoxia (10% O2). In contrast, the effects of photostimulation were largely unaffected by hypercapnia (3 and 6% CO2). The associated cardiovascular effects were complex (slight bradycardia and hypotension) and, using selective autonomic blockers, could be explained by co-activation of the sympathetic and cardiovagal outflows. ChR2-positive RVLM-CA neurons expressed VGLUT2 and their projections were mapped. Their complex cardiorespiratory effects are presumably mediated by their extensive projections to supraspinal sites such as the ventrolateral medulla, the dorsal vagal complex, the dorsolateral pons, and selected hypothalamic nuclei (dorsomedial, lateral, paraventricular nuclei). In sum, selective optogenetic activation of RVLM-CA neurons in conscious mice revealed two important novel functions of these neurons, namely breathing stimulation and cardiovagal outflow control, effects that are attenuated or absent under anesthesia and are presumably mediated by the numerous supraspinal projections of these neurons. The results also suggest that RVLM-CA neurons may underlie some of the acute respiratory response elicited by carotid body stimulation but contribute little to the central respiratory chemoreflex.

C1 neurons: the body's EMTs

“…In mouse slices, fictive respiration is strongly activated by ␣ 1 -adrenergic receptor stimulation, but unresolved species differences persist and these experiments have not demonstrated whether the C1 neurons or other catecholaminergic neurons regulate breathing (190,199). Using optogenetics, we have shown that selective C1 neuron stimulation activates breathing in conscious mice (1). Barosensitive C1 neurons presumably contribute to the ventilatory baroreflex; i.e., the breathing stimulation elicited by hypotension, well described in conscious humans (173).…”

“…FN, facial motor nucleus; Mo5 trigeminal motor nucleus; NA, nucleus ambiguus; tpz, trapezoid body. The axonal projections of the C1 neurons are based primarily on the result of virus-based tracing methods in rat and mouse (1,30 adrenergic neurons that also target the regions innervated by the C1 cells (e.g., A5 neurons in the intermediolateral cell column). Most C1 cells (90%) lack a plasmalemmal monoamine transporter suggesting that these cells, unlike their noradrenergic counterparts, lack the means of replenishing their catecholamine stores via reuptake (40,107).…”

“…Indirect connections between the C1 cells and the respiratory centers may occur via C1 projections to the retrotrapezoid nucleus, the lateral parabrachial region, the periqueductal gray matter or even via hypothalamic nuclei such as the dorsomedial nucleus/perifornical region (1,30).…”

Arcuate neuropeptide Y inhibits sympathetic nerve activity via multiple neuropathways

“…48) appeared to remain undisturbed, and SNA rose above baseline. Additionally, the DMH receives a sizable brainstem NPY (catecholaminergic) projection (49,50), which could contribute to basal NPY tone and be disinhibited by DMH BIBO3304. This is in contrast to brainstem NPY inputs to the PVN, which may be rare in the mouse (51).…”

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

“…14,43 Present and previous 15 evidence shows that targeted destruction of C1 cells virtually eliminated the sympathoexcitatory response to peripheral chemoreceptor activation in anesthetized rats. Furthermore, selective acti vation of C1 cells by channelrhodopsin2 has been shown to increase breathing, sympathetic activity, and blood pres sure, [44][45][46] whereas inhibition of C1 cells by activation of the allostatin receptor did the opposite. 47 However, despite the critical role of C1 cells in regulation of cardiorespiratory function, the identity of neurotransmitters and downstream effectors responsible for peripheral chemoreflex control of autonomic function at the level of the ventrolateral medulla remains incomplete.…”