Intrinsic gamma-aminobutyric acid neurons in the nucleus of the solitary tract and the rostral ventrolateral medulla of the rat: an immunocytochemical and biochemical study.

Sympathoexcitatory neurons in the C1 adrenergic area of the rostral ventrolateral medulla (RVL) are tonically inhibited by gamma-aminobutyric acid (GABA). To identify the source of this GABAergic input, the distribution of neurons containing glutamate decarboxylase (GAD) was determined immunocytochemically in rats treated with colchicine. Numerous GAD-stained neurons were located in the nucleus of the solitary tract (NTS) and in RVL. Unilateral lesions in NTS did not alter GABA content or GAD activity in RVL, indicating that the afferent projection from NTS to RVL is not GABAergic. Intrinsic GABAergic neurons in RVL may provide tonic inhibition of vasomotor neurons in the C1 area.