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

Daniel A. Mandel and Ann M. Schreihofer Am J Physiol Heart Circ Physiol 295: H1772–H1779, 2008. First published August 29, 2008; doi:10.1152/ajpheart.216.2008. We know that the CVLM is important providing inhibitory input to RVLM. It has been shown that GABAergic input from CVLM that is not baroreceptor sensitive. This study investigates what is driving the baro-independent input that is coming from CVLM. They inhibited the baroreceptors by lower AP using SNP and then they inhibited the NTS bilateral using muscimol, AP did not change in response to muscimol in NTS. Finally, CVLM was inhibited with muscimol resulting in an increase in AP, SNA and HR. In order to determine whether the baro-independent neuronal activity was driven by glutamatergic input, the glutamate receptor antagonist, kynurenate was bilaterally microinjected into CVLM. After they confirmed that the NTS was blocked they gave kynurenate into the CVLM bilaterally. This lead to increased AP, SNA and HR. In order to whether the central respiratory drive was playing a role in the control of baro-independent gabaergic neurons activity, While AP was lowered with SNP and NTS was blocked with muscimol, in vagotomized rats, PCO2 was altered. When PCO2 was increased this greater increases in SNA in response to kynurenate in CVLM were observed. These data suggest, that baro-independent neuronal activity is driven by glutamate and a possible source of this glutamatergic driven may be from central respiratory areas.-MD