Vesicular glutamate transporter 2 is required for the respiratory and parasympathetic activation produced by optogenetic stimulation of catecholaminergic neurons in the rostral ventrolateral medulla of mice in vivo.

Eur J Neurosci. 2014 Jan;39(1):98-106. doi: 10.1111/ejn.12421. Epub 2013 Nov 18. Abbott SB, Holloway BB, Viar KE, Guyenet PG. As we all know, The RVLM communicates by releasing glutamate on to all of its targets, including respiratory groups... Or so we thought we knew. It turns out that this has really only been implied, suggested, hinted at, and supported - which resulted in us all believing it to be true regardless of the fact that direct evidence for it was pretty much absent. That's what this group set out to change with this paper - they wanted to directly link RVLM neuron activity with activation of target regions through glutamatergic transmission. To do this, they crossed DBH-Cre mice with mice that had the sequence for part of VGLUT2 flanked by loxP sites. The offspring mice then had selective knockout of VGlut2 in the DBH-expressing cells, including the C1 neurons. Animals were injected with a virus that would cause expression of Channelrhodopsin2 (ChR2) conditional to expression of Cre - which would be the DBH-expressing cells, which were the same cells that had deleted their own VGLUT2. They found that their ChR2 expression worked well and that RVLM cells in brainstem slices could be stimulated with light. They extended this to show that it worked in vivo as well. They found that in mice with intact VGLUT2, photostimulation of the RVLM could increase breathing frequency, but knockout mice did not show the effect. They found the same effect when they monitored the activity of the Vagus, presumably because RVLM neurons are known to directly innervate the dorsal motor nucleus of the vagus. Finally, they used prazosin to block A1-adrenoreceptors and found that this blockade did not change the results of photostimulation in either strain, suggesting that none of the effects were mediated by catecholaminergic signaling. -DH