By: Tseng et al
The rhythmicity is an important feature of the sympathetic nervous system. It's what keeps the system functioning at a stable pace. This rhythm has been showed to be controlled by the heart beat, respiratory regulation, and the baroreflex loop. Blood pressure is directly controlled by this loop. The RVLM has been showed to contribute to this rhythm by tonically driving SNA. The purpose of this study was to investigate which types of RVLM neurons contribute to the low frequency (LF) SNA rhythm in rats. To do this they studied the neuronal activities of RVLM neurons, SNA, and BP at the same time. Coherence analysis was used to correlate LF rhythms of SNA with neuronal firing frequency.
Recordings of SNA, BP, and RVLM activity were recorded simultaneously. RVLM neuronal firing and SNA were compared to each other using a cross-correlation computation. Phenylephrine was used to denervate the baroreflex loop. Once infused, BP, SNA, and HR were significantly decreased. 51 neurons were recorded from the RVLM. They were sorted by their responsiveness to raised BP (inhibited, excited, non-responsive)
41% of neurons recorded were correlated with the LF SNA rhythm. When removing baroreceptor input, neurons were still correlated to the LF SNA rhythm which suggests that vasomotor RVLM neurons contribute to the existence of the LF SNA rhythm. When the baroreflex was denervated, SNA was only reduced, but didn't go to 0. This explains that there are other sources for the LF component of SNA that exist. 62% of RVLM neurons that contributed to the LF SNA rhythm that are barosensitive were sympathoexcitatory. The conclusion of the study is that RVLM neurons have the ability to generate the LF SNA rhythm and also the LF BP rhythm.
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