c-fos identifies GABA-synthesizing barosensitive neurons in caudal ventrolateral medulla

Jane B. Minson, Ida J. Llewellyn-Smith, John P. Chalmers, Paul M. Pilowsky and Leonard F. Arnold. NeuroReport8, 3015-3021(1997). We know that CVLM provides barosensitive and non-barosensitive GABAergic input to RVLM. This study provides anatomical along with functional support for the previous statement. They microinjected CTB into the RVLM of Wistar rats and infused with PE for 60min. Following the infusion of Phenylephrine, the rats were perfused and used for immunohistochemistry. They looked at 3 things in this study 1.) Barosensitive neurons in the CVLM 2.) Examined whether these barosensitive neurons in CVLM project to the RVLM and 3.) Determined if the barosensitive neurons that were GABAergic or glutamatergic. The results showed that PE increased the BP of the rats and lead to increase Fos expression in CVLM and in the NTS but not in the RVLM. Fos expressing and RVLM projecting neurons were identified and located in the more rostral areas of CVLM. Most of these neurons were located rostral to obex. Next the phenotype of the neurons was investigated, in order to determine if the neurons expressed GAD, PAG and TH. There were no TH and GAD neurons identified. About 40% of Fos positive neurons were also GAD positive. Most of these neurons were located in the rostral portion of the CVLM. There was no difference between fos/ PAG and Fos/ TH when PE infused animals were compared to the saline group. The Fos/ PAG/ TH neurons are located in the caudal regions of the CVLM. The most interesting finding in my opinion is that they were able to identify PAG/ CTB and GAD/ CTB neurons in the CVLM. This suggests that CVLM provides both glutamatergic and GABAergic inputs to RVLM. Even though the PAG/CTB neurons were not Fos positive, maybe CVLM provides a tonic level of glutamate to RVLM. Is this driving the activity of spinally projecting RVLM neurons? Also could this glutamatergic drive be altered in SEDs and WRs? These are questions that we could potentially look into. -MD