The C1 neurons are a nodal point for blood pressure control and other autonomic responses. Here we test whether these rostral ventrolateral medullary catecholaminergic (RVLM-CA) neurons use glutamate as a transmitter in the dorsal motor nucleus of the vagus (DMV). After injecting Cre-dependent adeno-associated virus (AAV2) DIO-Ef1α-channelrhodopsin2(ChR2)-mCherry (AAV2) into the RVLM of dopamine-β-hydroxylase Cre transgenic mice (DβHCre/0), mCherry was detected exclusively in RVLM-CA neurons. Within the DMV >95% mCherry-immunoreactive(ir) axonal varicosities were tyrosine hydroxylase (TH)-ir and the same proportion were vesicular glutamate transporter 2 (VGLUT2)-ir. VGLUT2-mCherry colocalization was virtually absent when AAV2 was injected into the RVLM of DβHCre/0;VGLUT2flox/flox mice, into the caudal VLM (A1 noradrenergic neuron-rich region) of DβHCre/0 mice or into the raphe of ePetCre/0 mice. Following injection of AAV2 into RVLM of TH-Cre rats, phenylethanolamine N-methyl transferase and VGLUT2 immunoreactivities were highly colocalized in DMV within EYFP-positive or EYFP-negative axonal varicosities. Ultrastructurally, mCherry terminals from RVLM-CA neurons in DβHCre/0 mice made predominantly asymmetric synapses with choline acetyl-transferase-ir DMV neurons. Photostimulation of ChR2-positive axons in DβHCre/0 mouse brain slices produced EPSCs in 71% of tested DMV preganglionic neurons (PGNs) but no IPSCs. Photostimulation (20 Hz) activated PGNs up to 8 spikes/s (current-clamp). EPSCs were eliminated by tetrodotoxin, reinstated by 4-aminopyridine, and blocked by ionotropic glutamate receptor blockers. In conclusion, VGLUT2 is expressed by RVLM-CA (C1) neurons in rats and mice regardless of the presence of AAV2, the C1 neurons activate DMV parasympathetic PGNs monosynaptically and this connection uses glutamate as an ionotropic transmitter.
All Science Journal Classification (ASJC) codes