Monosynaptic Glutamatergic Activation of Locus Coeruleus and Other Lower Brainstem Noradrenergic Neurons by the C1 Cells in Mice

Abstract

The C1 neurons, located in the rostral ventrolateral medulla (VLM), are activated by pain, hypotension, hypoglycemia, hypoxia, and infection, as well as by psychological stress. Prior work has highlighted the ability of these neurons to increase sympathetic tone, hence peripheral catecholamine release, probably via their direct excitatory projections to sympathetic preganglionic neurons. In this study, we use channelrhodopsin-2 (ChR2) optogenetics to test whether the C1 cells are also capable of broadly activating the brain's noradrenergic system. We selectively expressed ChR2(H134R) in rostral VLM catecholaminergic neurons by injecting Cre-dependent adeno-associated viral vectors into the brain of adult dopamine-␤-hydroxylase (D␤H)Cre/0 mice. Most ChR2-expressing VLM neurons (75%) were immunoreactive for phenylethanolamine N-methyl transferease, thus were C1 cells, and most of the ChR2-positive axonal varicosities were immunoreactive for vesicular glutamate transporter-2 (78%). We produced light microscopic evidence that the axons of rostral VLM (RVLM) catecholaminergic neurons contact locus coeruleus, A1, and A2 noradrenergic neurons, and ultrastructural evidence that these contacts represent asymmetric synapses. Using optogenetics in tissue slices, we show that RVLM catecholaminergic neurons activate the locus coeruleus as well as A1 and A2 noradrenergic neurons monosynaptically by releasing glutamate. In conclusion, activation of RVLM catecholaminergic neurons, predominantly C1 cells, by somatic or psychological stresses has the potential to increase the firing of both peripheral and central noradrenergic neurons.

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

“…The present study also provides evidence that A5 neurons facilitate arousal from non-REM sleep. This observation is consistent with our hypothesis that central noradrenergic neurons contribute to C1 cell-mediated arousal (3,38,42) (Fig. 8).…”

“…C1 cell stimulation reproduces most of the effects of hypoxia: arousal from non-REM sleep, sighs, and increases in breathing and BP (22). C1 cells innervate and excite major wake-promoting systems, the orexinergic and noradrenergic neurons, including the locus coeruleus (A6), A5, A2, and A1 (3,15,42 hypoxia can be suppressed by increasing FI CO 2 or by arterial acidification with acetazolamide, a carbonic anhydrase inhibitor (10,11). Both treatments are potent stimulants of RTN activity (9); hence, increased RTN activity may actually suppress sighs, as CO 2 does.…”

Tyrosine Hydroxylase Expression in Type II Cochlear Afferents in Mice

“…since TH expression alone is not a guarantor of catecholaminergic synaptic transmission. For example, TH-positive neurons in locus ceruleus generate glutamatergic postsynaptic currents (Holloway et al 2013) while TH-positive neurons in striatum are GABA-ergic and do not release dopamine (Xenias et al 2015).…”

Neurônios catecolaminérgicos do tronco encefálico participam dos ajustes respiratórios induzidos por hipóxia e hipercapnia.

“…No entanto, embora os neurônios C1 expressem o fenótipo catecolaminérgico, evidências funcionais e anatômicas indicam que estes neurônios utilizam o glutamato como principal neurotransmissor Guyenet et al, 2013;Holloway et al, 2013;Abbott et al, 2014;Holloway et al, 2015). Os terminais que expressam PNMT, os quais também expressam glutamato, formam contato sináptico assimétrico, consistente com a ultraestrutura de sinapses excitatórias glutamatérgicas clássicas, reforçando a hipótese de que os neurônios C1 atuam por meio de sinapses glutamatérgicas (Milner et al, 1987;Milner et al, 1988;Agassandian et al, 2012;Depuy et al, 2012;Abbot et al, 2014).…”

“…Os terminais que expressam PNMT, os quais também expressam glutamato, formam contato sináptico assimétrico, consistente com a ultraestrutura de sinapses excitatórias glutamatérgicas clássicas, reforçando a hipótese de que os neurônios C1 atuam por meio de sinapses glutamatérgicas (Milner et al, 1987;Milner et al, 1988;Agassandian et al, 2012;Depuy et al, 2012;Abbot et al, 2014). Além disso, tem sido consistentemente demonstrado que as respostas promovidas pela ativação seletiva dos neurônios catecolaminérgicos do grupamento C1 são desencadeadas por sinalização glutamatérgica Guyenet et al, 2013;Holloway et al, 2013;Abbott et al, 2014;Holloway et al, 2015). Embora o glutamato pareça ser o neurotransmissor responsável pelas respostas desencadeadas pelo grupamento C1, outros neuropeptídios co-expressos na região (por exemplo o neuropeptídio Y, a substância P, o hormônio liberador de tireotrofina, a anfetamina, e o polipeptídio ativador de adenilato ciclase pituitário) também podem contribuir para estas respostas (Stornetta 2009;Guyenet et al, 2013).…”