Paraventricular nucleus (PVN) neurons projecting to the rostral ventrolateral medulla (RVLM) contain both oxytocin and glutamate

Abstract

The PVN is crucial to the CNS regulation of sympathetic outflow. Glutamate is the prevalent excitatory neurotransmitter in the CNS, including the PVN. Oxytocin (OT) is specifically produced by PVN and supraoptic nucleus neurons, and microinjection of OT into the RVLM induces a pressor response. The current study is aimed at determining whether glutamate PVN neurons projecting to the RVLM contain OT as a co‐transmitter. Real time RT‐PCR analyses of PVN tissues from 4‐6 week‐old Sprague‐Dawley (SD) rats revealed the presence of OT and phosphate‐activated glutaminase (PAG; specific marker of glutamate neurons) mRNAs. Microinjection of AAV2‐PAG‐eGFP (200 nL; 1.2 x 1012 gc/mL) bilaterally into PVN of 5 week‐old SD rats produced glutamate neuron‐specific expression of GFP within two weeks. Isolation and ex‐vivo culture of PVN cells from these rats produced GFP labeled neurons, and single‐cell PCR analysis of these revealed that 8 out of 13 (61.53%) were OT‐positive. To identify the phenotype of the GFP expressing glutamate neurons that project to RVLM, fluorescent retrobeads were microinjected bilaterally into the RVLM of SD rats that had received injections of AAV2‐PAG‐eGFP into the PVN. Immunocytochemistry indicated that GFP‐ and retrobead‐labeled PVN neurons contained immunoreactive OT. Thus we conclude that RVLM‐projecting PVN neurons contain both OT and glutamate as major excitatory neurotransmitters.