Acid sensitivity and ultrastructure of the retrotrapezoid nucleus in Phox2b‐EGFP transgenic mice

Abstract

SummaryThe retrotrapezoid nucleus (RTN) contains non-cholinergic non-catecholaminergic glutamatergic neurons that express the transcription factor Phox2b (chemically coded or "cc" RTN neurons). These cells regulate breathing and may be central chemoreceptors. Here we explore their ultrastructure and their acid-sensitivity using two novel BAC eGFP-Phox2b transgenic mice (B/G, GENSAT JX99) in which respectively 36% and 100% of the cc RTN neurons express the transgene in complete or partial anatomical isolation from other populations of eGFP neurons.All but one eGFP-labeled RTN neuron recorded in these mice were acid-activated in slices. These cells contained VGLUT2 mRNA and 50% contained preprogalanin mRNA (determined by singlecell PCR in the B/G mouse). Two neuronal subgroups were revealed which differed in discharge rate at pH 7.3 (Type I ~2; Type II ~4 Hz) and the degree of alkalization that silenced the cells (Type I: 7.4 -7.6; Type II: 7.8 -8.0). Medial to the RTN, C1 neurons recorded in a tyrosinehydroxylase-GFP mouse were pH-insensitive between pH 6.9 -7.5.Ultrastructural studies demonstrated that eGFP-labeled RTN neurons were surrounded by numerous capillaries and were often in direct contact with glial cells, pericytes and the basement membrane of capillaries. Terminals contacting large proximal eGFP-dendrites formed mainly symmetric, likely inhibitory, synapses. Terminals on more distal eGFP-dendrites formed preferentially asymmetric, presumably excitatory, synapses.In sum, C1 cells are pH-insensitive whereas cc RTN neurons are uniformly acid-sensitive. The RTN neurons receive inhibitory and excitatory synaptic inputs and may have unfettered biochemical interactions with glial cells and the local microvasculature.

Breathing without CO2Chemosensitivity in ConditionalPhox2bMutants

“…) profile counts to estimate total cell numbers essentially as described previously (Lazarenko et al, 2009). Statistical analysis was done using a twotailed t test and XLSTAT software with ␣ set at 0.05.…”

Neural mechanisms underlying respiratory rhythm generation in the lamprey

“…This oscillator may display burst activity involving endogenous I NaP -dependent properties, as it occurs in the preBötC ThobyBrisson et al, 2009;Molkov et al, 2010). In addition, it contains glutamatergic neurons that express NK1 receptors, but it is not sensitive to opioids (Mulkey et al, 2004;Onimaru et al, 2008;Takakura et al, 2008;Lazarenko et al, 2009;Thoby-Brisson et al, 2009; for reviews, see Feldman et al, 2013;Guyenet and Mulkey, 2010). In conclusion, similarly to other neurophysiological features (Ericsson et al, , 2013Stephenson-Jones et al, 2011, 2012a, 2012b, the basic oscillatory and neuromodulatory mechanisms of the respiratory network seem to be highly evolutionary conserved regardless of their location and their inspiratory or expiratory function.…”

Respiratory and autonomic dysfunction in congenital central hypoventilation syndrome

“…One region that is involved in central respiratory chemoreception is the retrotrapezoid nucleus (RTN) (Guyenet et al 2010;Guyenet and Bayliss 2015;Nattie 2011). This region is located in the ventrolateral surface of the medulla with neurons that have a genetic lineage (derived from neurons that express PHOX2B, Atoh-1, and Egr-2) and express different phenotypes (PHOX2B, NK1 receptors, VGlut2, TASK-2, GPR4, and galanin but not GABA, glycine, acetylcholine, or catecholamines) (Kumar et al 2015;Lazarenko et al 2009;Ruffault et al 2015;Takakura et al 2008Takakura et al , 2014Wang et al 2013). In this concise review, we discuss, on the basis of clinical and genetic studies in human respiratory disease and evidence from neurophysiology and experimental animal models, how a restricted number of neurons, located in the VMS, expressing and depending on the PHOX2B transcription factor could be essential in the control of breathing and autonomic regulation.…”