Development of attenuated baroreflexes in obese Zucker rats coincides with impaired activation of nucleus tractus solitarius.

Guimaraes PS, Huber DA, Campagnole-Santos MJ, Schreihofer AM. Am J Physiol Regul Integr Comp Physiol. 2014 May;306(9):R681-92. In this paper, they wanted to look at some of the changes that might be responsible for increases in SNA and MAP, and the blunted baroreflex seen in obese zucker rats (OZR) compared to lean zucker rats (LZR). They pharmacologically lowered MAP and saw that while LZR and juvenile OZR (jOZR) had an immediate tachycardia, this response was attenuated in OZR for the first five minutes, but it eventually caught up with the other two grops. They looked at c-Fos expression in the RVLM, and didn't see any differences between the groups. However, when they increased MAP with injections of PE, they saw that OZR had attenuated bradycardia and increases in MAP, possibly due to the fact that they also showed less c-Fos in the NTS. They then moved on to doing microinjections and found that injections of glu in to the CVLM induced similar decreases in SNA, HR, and MAP between all three groups, but injections in to the NTS produced attenuated responses in OZR. The conclusion here was that changes in sensitivity in the NTS, but not the CVLM or the RVLM, seem to be responsible for the systemic effects seen in adult OZR. However, they did also find that jOZR showed greater c-FOS in the NTS than juvenile LZR after injection of PE, which suggests that the changes start occuring in the brainstem early, but don't have systemic effects until the rats become adults. - DH