Optogenetic stimulation of PVN‐RVLM neurons increases sympathetic nerve activity in anesthetized rats

Abstract

The hypothalamic paraventricular nucleus (PVN) sends direct projections to the rostral ventrolateral medulla (RVLM). The present study was conducted to examine the effect of optogenetic stimulation of PVN‐RVLM neurons on sympathetic nerve activity in anesthetized rats. Male rats anesthetized with pentobarbital received unilateral microinjection into the PVN with an adeno‐associated virus (AAV) vector that encodes the reporter protein palGFP (control rats, N=4) or the channel rhodopsin variant, ChIEF‐tdTomato (ChIEF rats, N=8). Two‐to‐five weeks later, in the rats anesthetized with a mixture of urethane and α‐chloralose, photostimulation (473 nm wavelength, 8–10 mW) was provided to the RVLM ipsilateral to the PVN into which AAV had been injected. In ChIEF rats, photostimulation of the RVLM at 40 Hz (5‐ms pulse duration) for 2 min significantly (P < 0.05) evoked renal sympathoexcitatory (+126 ± 20% from baseline, means ± SE) and pressor (+13 ± 1 mmHg) responses while this stimulation had no effect in control rats. Moreover, immunofluorescence staining revealed abundant distribution of PVN‐derived, tdTomato‐labeled axons in the ipsilateral RVLM as compared with that in the contralateral RVLM. Confocal imaging further showed close association of tdTomato‐labeled axons with tyrosine hydroxylase‐positive neurons in the RVLM. These observations suggest that excitation of the PVN‐RVLM monosynaptic pathway elicits sympathoexcitation via, at least in part, stimulation of RVLM catecholaminergic neurons, potentially playing a role in sympathetic adjustments to stress such as exercise.Support or Funding InformationJSPS KAKENHI 15H05367 & 16K15190 (SK); 16H05128 & 15H05932 (KN).