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The retrotrapezoid nucleus stimulates breathing by releasing glutamate in adult conscious mice
Author(s) -
Holloway Benjamin B.,
Viar Kenneth E.,
Stornetta Ruth L.,
Guyenet Patrice G.
Publication year - 2015
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/ejn.12996
Subject(s) - optogenetics , neuroscience , stimulation , biology , catecholaminergic cell groups , brainstem , population , glutamate receptor , dopamine , chemistry , medicine , catecholaminergic , biochemistry , receptor , environmental health
The retrotrapezoid nucleus ( RTN ) is a bilateral cluster of neurons located at the ventral surface of the brainstem below the facial nucleus. The RTN is activated by hypercapnia and stabilises arterial P co 2 by adjusting lung ventilation in a feedback manner. RTN neurons contain vesicular glutamate transporter‐2 ( Vglut2 ) transcripts ( Slc17a6 ), and their synaptic boutons are Vglut2‐immunoreactive. Here, we used optogenetics to test whether the RTN increases ventilation in conscious adult mice by releasing glutamate. Neurons located below the facial motor nucleus were transduced unilaterally to express channelrhodopsin‐2 (ChR2)–enhanced yellow fluorescent protein, with lentiviral vectors that employ the Phox2b‐activated artificial promoter PRS x8. The targeted population consisted of two types of Phox2b‐expressing neuron: non‐catecholaminergic neurons (putative RTN chemoreceptors) and catecholaminergic (C1) neurons. Opto‐activation of a mix of ChR2‐expressing RTN and C1 neurons produced a powerful stimulus frequency‐dependent (5–15 Hz) stimulation of breathing in control conscious mice. Respiratory stimulation was comparable in mice in which dopamine‐β ‐ hydroxylase (DβH)‐positive neurons no longer expressed Vglut2 ( D β H Cre/0 ;;Vglut2 fl/fl ). In a third group of mice, i.e. D β H +/+ ;;Vglut2 fl/fl mice, we injected a mixture of PRS x8‐Cre lentiviral vector and Cre‐dependent ChR2 adeno‐associated virus 2 unilaterally into the RTN ; this procedure deleted Vglut2 from ChR2‐expressing neurons regardless of whether or not they were catecholaminergic. The ventilatory response elicited by photostimulation of ChR2‐positive neurons was almost completely absent in these mice. Resting ventilatory parameters were identical in the three groups of mice, and their brains contained similar numbers of ChR2‐positive catecholaminergic and non‐catecholaminergic neurons. From these results, we conclude that RTN neurons increase breathing in conscious adult mice by releasing glutamate.