The sympathoregulatory region of the mouse rostral brainstem relies on both GABA and glycine to generate inhibitory currents

Presympathetic neurons in the ventrolateral and ventromedial medulla (VLM/VMM) control the sympathetic tone, and GABA and glycine were identified as inhibitory neurotransmitters. Although glycinergic inhibition of presympathetic neurons in the VLM/VMM has been shown and evidence suggests that both GABA and glycine inhibit sympathetic tone; the sources of glycinergic inputs and mechanism of glycine release is unknown. Here, we tested whether presympathetic neurons in the VLM/VMM receive glycinergic inputs. Glycine is recycled by glycine transporter 2 (GlyT2), which is a reliable marker of glycinergic neurons. Therefore, GlyT2Cre mice were cross bred with channelrhodopsin (ChR2) mice to generate GlyT2ChR2/EYFP mice to be able to selectively stimulate GlyT2-expressing fibers. We found that glycinergic fibers were abundant throughout the rostral brainstem, and GlyT2-expressing neurons were distributed within the ventral gigantocellular nucleus and medial reticular formation. Presympathetic neurons in the VLM/VMM were retrogradely labeled with pseudorabies virus (PRV-RFP) and whole-cell, patch clamp recordings were conducted in brainstem slices. Our study demonstrates that inhibitory synaptic currents recorded from presympathetic VLM/VMM neurons are mediated by GABA and glycine. We found that increasing the activity of inhibitory synapses facilitates glycine release. Light stimulation of GlyT2ChR2/EYFP fibers triggered monosynaptic evoked currents composed of GABA and glycine and we found that sustained glycine release depends on glycine uptake mediated by GlyT2. In addition, we used a combination of monosynaptic and transsynaptic viral tracings to identify the location of presympathetic glycinergic neurons in the ventral brainstem, and immunostaining to reveal the expression of GlyR α1, α3, and β subunits in VLM/VMM neurons. Our study identified that GlyT2-expressing neurons rely on release of both GABA and glycine to generate inhibitory currents. However, potential role and the necessity for both neurotransmitters in the control of presympathetic VLM/VMM neurons require additional studies This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.