Abdominal vagal inputs to catecholamine neurons in the ventrolateral medulla.

Stimulation of the abdominal vagus nerve increases arterial pressure and causes secretion of vasopressin. We have shown in rabbits that the arterial pressure increases are mediated by activation of barosensitive bulbospinal neurons in the C1 region of the rostral medulla. Secretion of vasopressin involves activation of neurons in the A1 region of the caudal ventrolateral medulla. Neuroanatomical studies with Fos indicate that approximately 50% of the C1 area cells are C1 neurons. Approximately 70% of the A1 area cells are A1 neurons. These neurons may mediate physiological responses occurring during abdominal malaise resulting from ingestion of toxins. Our discovery of a major excitatory input to A1 and C1 neurons from the abdominal vagus should prove useful in studies of the function of these neurons.