Selective lesion of Cl neurons in the rostral ventrolateral medulla (RVLM)

The RVLM plays a key role in regulating cardiovascular function. Two populations of spinally-projecting pre-sympathetic RVLM neurons have been distinguished based on neurochemical phenotype, one of which belongs to the C1 catecholamine cell group. An understanding of the cardiovascular functions of C1 and non-C1 RVLM neurons has been hampered by the inability to produce selective lesions of one or the other subpopulation. We now describe the use of saporin toxin coupled to an antibody to dopamine-ß-hydroxylase (DBH) for making selective lesions of the C1 cell group. Saporin-antiDBH (Advanced Targeting Systems, lot #ATS3-1) was injected unilaterally into the RVLM of halothane-anesthetized rats. Following a 2 wk survival, rats were perfused with paraformaldehyde-lysine-periodate fixative and brains were processed for immunocytochemical localization of C1 neurons. Injection of 20 ng of toxin in a 200 nl volume produced an extensive and selective loss of C1 neurons. The cardiovascular effects of local injection of glutamate and clonidine were tested in a separate group of chloralose-anesthetized, paralyzed ventilated rats with unilateral C1 lesions. Glutamate (1 nmol in 100 nl) evoked a similar increase in mean arterial pressure when injected into the lesioned RVLM compared to the intact RVLM (26±4 mm Hg on the lesioned side and 30±4 mm Hg on the intact side; n=7; p>0.05), providing evidence against non-selective destruction of the RVLM. In contrast, the depressor response elicited by injection of clonidine (4 nmol) into the lesioned RVLM was markedly reduced (-7±4 mm Hg for the lesioned side compared to -43±10 mm Hg for the intact side; p<0.05). These results indicate that it is possible to selectively destroy the Cl cell group; this should provide a useful approach for determining the role of the Cl cell group in cardiovascular regulation.