Potential Role of the Amygdala and Posterior Claustrum in Exercise Intensity-dependent Cardiovascular Regulation in Rats

Abstract Tuning of the cardiovascular response is crucial to maintain performance during high-intensity exercise. It is well known that the nucleus of the solitary tract (NTS) in the brainstem medulla plays a central role in cardiovascular regulation; however, where and how upper brain regions form circuits with NTS and coordinately control cardiovascular responses during high-intensity exercise remain unclear. Here focusing on the amygdala and claustrum, we investigated part of the mechanism for regulation of the cardiovascular system during exercise. In rats, c-Fos immunostaining was used to examine whether the amygdala and claustrum were activated during treadmill exercise. Further, we examined arterial pressure responses to electrical and chemical stimulation of the claustrum region exhibiting exercise intensity-dependent activation. We also confirmed the anatomical connections between the amygdala, claustrum, and NTS by retrograde tracer injections. Finally, we performed simultaneous electrical stimulation of the claustrum and amygdala to examine their functional connectivity. c-Fos expression was observed in the amygdala and the posterior part of the claustrum (pCL), but not in the anterior part, in an exercise intensity-dependent manner. pCL stimulation induced a depressor response. Using a retrograde tracer, we confirmed direct projections from the amygdala to the pCL and NTS. Simultaneous stimulation of the central nucleus of the amygdala and pCL showed a greater pressor response compared with the stimulation of the amygdala alone. These results suggest the amygdala and pCL are involved in different phases of exercise. More speculatively, these areas might coordinately tune cardiovascular responses that help maintain performance during high-intensity exercise.