Cardiovascular responses to disinhibition of rostral ventrolateral medulla (RVLM) following unilateral RVLM blockade in sedentary or physically active, sinoaortic denervated rats (875.13)

Abstract

The RVLM is a bilateral region in the brainstem important for sympathetic control of arterial pressure (AP). Although tonically active, both RVLMs receive strong γ‐amino‐butyric acid (GABA)‐mediated inhibition, due in part to tonic arterial baroreceptor input. Previous studies report that unilateral inhibition of the RVLM in sinoaortic denervated (SAD) rabbits leads to dramatic decreases in AP and sympathetic nerve activity (SNA), demonstrating the importance of the baroreflex to resting AP. Following SAD, a strong GABAergic input to RVLM persists and likely suppresses the activity of the RVLM in the absence of baroreceptor input. However, whether this inhibition is altered in sedentary (SED) and active conditions is unknown. The current study was aimed at testing the hypothesis that inhibition of one RVLM in SAD rats would result in enhanced non‐barosensitive GABAergic input in the remaining intact RVLM, and this input would be greater in the SEDs compared to the active rats (i.e., 12 weeks of chronic wheel running on average =WR ). In Inactin‐anesthetized SEDs (n=4) and WRs (n=4), AP and splanchnic SNA were recorded following surgical SAD. Following inhibition of one RVLM (muscimol 2mM, 90nl), bicuculline (5mM, 90nl) was microinjected into the contralateral RVLM. Preliminary data indicate that changes in mean AP appeared to be higher in the SEDs (∆60±12mmHg) compared to the WRs (∆44±15mmHg). Due to small sample size, however, we were unable to support our finding statistically. Splanchnic SNA responses between SEDs (∆52%±16) and WRs (∆49%±23) did not appear to differ. These preliminary data suggest that in the absence of baroreceptor input, MAP and SNA are significantly reduced due to strong non‐barosensitive GABAergic input to the intact RVLM. However, non‐barosensitive GABAergic input may be altered in response to sedentary and active conditions.Grant Funding Source: Supported by R01‐HL096787; R01‐ HL096787‐S1