Glutamatergic inputs to the CVLM independent of the NTS promote tonic inhibition of sympathetic vasomotor tone in rats

Daniel A. Mandel , Ann M. Schreihofer American Journal of Physiology - Heart and Circulatory PhysiologyPublished 1 October 2008Vol. 295no. H1772-H1779DOI: 10.1152/ajpheart.216.2008 In this study they wanted to determine if the NTS was providing baro independent glutamatergic input to CVLM. They also wanted to investigate whether glutamate was driving baroreceptor into to CVLM. Finally they wanted to look at the role respiratory neurons in controlling CVLM neuronal activity. In male S-D rats, they recorded sSNA and AP. They also exposed the brainstem in order to microinjections into NTS and CVLM. So they infused SNP in order to lower AP below baroreceptor reflex threshold. Then they bilaterally blocked the NTS with muscimol. They found that AP did not change however they gave mus into CVLM following NTS blockade and found that they got an increase in AP and sSNA. Next they gave only mus bilaterally into NTS and then they gave either mus or kyn into CVLM. They found that after NTS blockade there was an increase in AP and sSNA and when the CVLM activity was blocked by either giving mus or kyn they saw an increase that was significantly greater than NTS blockade alone. Finally they looked how central respiratory drive would affect CVLM neuronal activity. They found that in the presence of SNP and kyn into the CVLM sSNA was significantly enhanced in response to elevated pCO2. The conclusion based on the data from this article suggests that glutamate is playing a major role in driving the activity of CVLM and that it is not only coming from NTS. Also that NTS glutamergic input to CVLM is being driven by the baroreceptor reflex. Finally the activity of CVLM is also being modulated by central respiratory areas. -MD