Selective optogenetic stimulation of the retrotrapezoid nucleus in sleeping rats activates breathing without changing blood pressure or causing arousal or sighs

Abstract

Burke PG, Kanbar R, Viar KE, Stornetta RL, Guyenet PG. Selective optogenetic stimulation of the retrotrapezoid nucleus in sleeping rats activates breathing without changing blood pressure or causing arousal or sighs. J Appl Physiol 118: 1491-1501. First published April 9, 2015 doi:10.1152/japplphysiol.00164.2015.-Combined optogenetic activation of the retrotrapezoid nucleus (RTN; a CO 2/proton-activated brainstem nucleus) with nearby catecholaminergic neurons (C1 and A5), or selective C1 neuron stimulation, increases blood pressure (BP) and breathing, causes arousal from non-rapid eye movement (non-REM) sleep, and triggers sighs. Here we wished to determine which of these physiological responses are elicited when RTN neurons are selectively activated. The left rostral RTN and nearby A5 neurons were transduced with channelrhodopsin-2 (ChR2 ϩ ) using a lentiviral vector. Very few C1 cells were transduced. BP, breathing, EEG, and neck EMG were monitored. During non-REM sleep, photostimulation of ChR2 ϩ neurons (20s, 2-20 Hz) instantly increased V E without changing BP (13 rats). V E and BP were unaffected by light in nine control (ChR2 Ϫ ) rats. Photostimulation produced no sighs and caused arousal (EEG desynchronization) more frequently in ChR2 ϩ than ChR2 Ϫ rats (62 Ϯ 5% of trials vs. 25 Ϯ 2%; P Ͻ 0.0001). Six ChR2 ϩ rats then received spinal injections of a saporin-based toxin that spared RTN neurons but destroyed surrounding catecholaminergic neurons. Photostimulation of the ChR2 ϩ neurons produced the same ventilatory stimulation before and after lesion, but arousal was no longer elicited. Overall (all ChR2 ϩ rats combined), ⌬V E correlated with the number of ChR2 ϩ RTN neurons whereas arousal probability correlated with the number of ChR2 ϩ catecholaminergic neurons. In conclusion, RTN neurons activate breathing powerfully and, unlike the C1 cells, have minimal effects on BP and have a weak arousal capability at best. A5 neuron stimulation produces little effect on breathing and BP but does appear to facilitate arousal.arousal; A5 noradrenergic neurons; hypercapnia; non-REM sleep; retrotrapezoid nucleus HYPOXIA AND HYPERCAPNIA, ALONE or in combination, activate breathing and, if severe enough, produce arousal (17,60,62,63). The carotid bodies are largely responsible for the hypoxic ventilatory stimulation and for hypoxia-induced arousal because both responses are eliminated by ablating these organelles (17). How and where central nervous system (CNS) hypercarbia elicits the hypercapnic ventilatory reflex (HCVR) are still debated, and the CNS pathways responsible for arousal to hypoxia or hypercapnia are even more conjectural. The prevailing view is that both the HCVR and CO 2 -induced arousal result from the combined action of CO 2 on myriads of CNS pH-sensitive neurons, including serotonergic, noradrenergic, and orexinergic neurons (13,21,29,41,49,59,67).The retrotrapezoid nucleus (RTN) is a key structure for the HCVR. RTN neurons are glutamatergic and seem to operate both as a central respiratory chemorece...

Role of A5 noradrenergic neurons in the chemoreflex control of respiratory and sympathetic activities in unanesthetized conditions

“…Based upon the evidence that A5 neurons are activated during hypoxia and hypercapnia, and by the fact that brainstem noradrenergic neurons are an important component of wake-promoting system and contribute to increase sympathetic tone upon awakening (Li and Nattie, 2006; Burke et al, 2015; Bellesi et al, 2016), additional experiments will be important to investigate the involvement of A5 noradrenergic cells in the arousal responses linked to chemoreflex activation. Moreover, previous studies have evidenced that severe loss of A5 neurons in the A5 area contributes to the manifestation of autonomic disorder associated with the neurodegenerative disease of multiple system atrophy (Benarroch et al, 2008).…”

Proton detection and breathing regulation by the retrotrapezoid nucleus

“…B ) and rostrally they are intermixed with the A5 group of noradrenergic neurons (Burke et al . b ). As shown in Fig.…”

“…; Burke et al . b ). Third, in resting conscious rats, optogenetic inhibition of the same RTN neurons using the archaerhodopsin variant ArchT3.0 (Chow et al .…”

Microcircuits in respiratory rhythm generation: commonalities with other rhythm generating networks and evolutionary perspectives

“…In mammals, each phase of breathing is associated with distinct behaviors and conditions. Inspiration is expressed during eupnea, gasping and sighing, and is associated with olfaction, whisking [94], arousal [95], and specific emotional conditions [96], while postinspiration is associated with swallowing, vocalization, breath-holding and coughing [97 • ]. Thus, it is likely that each respiratory microcircuit is specifically connected to the brain regions that control these behaviors.…”