Baro-Activated Neurons With Pulse-modulated Activity in the Rat Caudal Ventrolateral Medulla Express GAD67 mRNA

Ann M. Schreihofer and Patrice G. Guyenet j.neurophysiology 89: 1265-1277, 2003 10, 1152/jn00737.2002 We already know that the CVLM is important because it baro-dependent and independent input to RVLM. This study investigated whether CVLM neurons actually projected to the RVLM and that they were GABAergic. Using extracellular recording, they recorded neuronal activity in the CVLM in response to loading and unloading the baroreceptor along with activating other reflexes. They showed in 17 rats that there are baro- activated neurons in the CVLM that are silenced by decreases in AP and some that were not. They also showed that the majority of the baro- activated neurons displayed an increase in activity in response to phenyl biguanide. They also showed that there were baro-inhibited neurons in the CVLM. These neurons that were baro inhibited also were inhibited by phenyl biguanide. In order to determine the phenotype of the neurons they recorded they did some histology along with in situ hybridization. Once the extracellular recording was completed they filled the cell they were recording from with biotinamide. Sectioning was done and they stained for the biotinamide and once they located the cell they did immuno for GAD67 and ChaT. They found a high density of GAD67 neurons in CVLM and a smaller portion of only ChaT IR neurons in CVLM.TH was also found in the CVLM but this as distinct from the GAD67 and Chat IR neurons. The 12 baro-activated neurons that were GAD 67 IR, 5 were examined for ChaT IR. They found that there was no ChaT IR. As for the baro-inhibited cells they found that all of them were baro-inhibited and none displayed GAD 67 IR. This study demonstrates that baro activated neurons are GABAergic and not only play role in the baroreflex but in the Bezold-jarisch reflex and noxious tail pinch. -MD