Brain stem control of arterial pressure in chronic arterial baroreceptor-denervated rats

Authors: Ann M. Schreihofer, Satoru Ito, and Alan F. Sved

Unlike acute denervation, chronic denervation condition lead  normal sympathetic vasomotor tone. So the authors wanted to examine what is driving sympathetic vasomotor tone. Methods: Sinoaortic denervation (SAD) or NTS lesion was done and the rats were allowed to recovery for one week. Then several microinjecion protocols were done while recording BP responses. Results: BP responses to α₁  adrenergic  injections relieved no differences between control and chronic SAD rats. This data suggests that vascular reactivity is not altered in response to chronic denervation. They also did a spinal transection at the T1 level and BP responses were no different between the control and chronic SAD rats. These results demonstrate that supraspinal regions are still response for control of BP under chronic SAD conditions. In order to investigate the role that RVLM is playing in the control of BP under chronic SAD conditions, they microinjected muscimol into RVLM bilaterally. Results showed that control and NTS lesioned and chronic SAD rats had similar responses. This showed that the RVLM is important to the control of sympathetic vasomotor tone under both intact and chronic SAD conditions. Next they wanted to investigate CVLM GABAergic input to RVLM. After inhibition of CVLM with muscimol they saw no differences between groups. This showed that even after removal of barorecptor inputs to the brain stem, the CVLM is still able to maintain the same level of GABAergic input to RVLM. They saw similar differences for glutamergic input to CVLM between groups. Demonstrating that the same of activation of CVLM neurons is occurring  even in the absence of baroreceptors. 

Conclusion: Under chronic SAD conditions, the CVLM receives baroindependent glutamergic input. This allows for the CVLM to still provide gabaergic input to RVLM in order to maintain BP in chronic denervated rats.