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The sympathetic drive to the cardiovascular system depends on the integrity of neurons in the medulla oblongata. The adrenergic neurons of the C1-area of the cortical ventrolateral medulla are tonically active and provide the background excitation of the spinal preganglionic neurons, which relay to the postganglionic sympathetic neurons. The noradrenergic neurons of the A1-area of the caudal ventrolateral medulla act as tonic inhibitors of the sympathetic discharge; they mediate the depressor response to centrally acting alpha-adrenergic agonists such as clonidine. Imbalance between those two types of neuronal control systems leads to increased sympathetic discharge and hence elevated arterial blood pressure.