Imidazole Receptors and their Endogenous Ligand in the Rostral Ventrolateral Medulla: Relationship to the Action of Clonidine on Arterial Pressure

Over the past few years there has been increasing awareness that a restricted region of the brain residing in the rostral and ventrolateral medulla oblongata (RVL) contains neurons that act tonically to maintain a resting level of arterial pressure (AP) and to integrate many cardiovascular reflexes (Reis et al., 1988, 1989). Interestingly, this area appears to share pharmacological characteristics with the adjacent ventral surface of the medulla (VSM), a region that respiratory physiologists and neuropharma- cologists, notably Feldberg and associates (Feldberg, 1986), have defined as a chemically sensitive area wherein neurotransmitters and drugs, including centrally active antihypertensive agents related to clonidine (Bousquet and Schwartz, 1983), act to control AP.