This article gave an overview of the 3 main nuclei that play a role in the baroreceptor reflex. It discussed the different neurotransmitters that participates in the modulation and transmission of the signals from one nuclei to another. When I think about the NTS, CVLM and the RVLM I only think about glutamate and GABA because these are the primary players. I never think about the other transmitters that bind to their specific receptors and effect the presynaptic release of glu and GABA . Some of the information that was presented about the RVLM was new to me. For instance I did not realize that there was a respiratory region within the RVLM. The respiratory region can also affect SNA.
The most interesting statement mentioned in the paper was whether the RVLM was a network or pacemaker. I know that it has netwrok characteristics because inputs from other region can modulate the activity of the RVLM. As for the Pacemaker, I can't recall any papers that have said this. Maybe I have read papers and I never really thought about the RVLM in these terms. Is the RVLM a network or Pacemaker? Can someone give me some input or may even a link to an article that may help clarify this?
Great questions Mary and it would be good to have a discussion on this (somewhat) ongoing controversy. It stems from some observations in brainstem slice preparations from neonatal rats in which input to the cells has obviously severed. Guyenet and colleaguess observed spontaneous activity in the cells that they attributed some inherent leak current in the cells that produced spontaneous depolarization. Although the idea had some momentum evidence against this idea came from Lipski's laboratory who performed intracellular recordings of RVLM neurons in vivo (very difficult). Instead of observing spontaneous action potentials they saw excitatory and inhibitory post synaptic potentials indicative of synaptic activity driving the cells. The limitation of the pacemaker theory is that it hasn't really been demonstrated in adult animals in vivo. However the fact that blocking endogenous glutamate or (in some studies) synaptic transmission does not change blood pressure does make one pause when thinking about what regulates the resting level of activity of RVLM neurons. In short, it is still one of the fundamentally unanswered questions in our field. -Pat
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