Deafferentation Studies on the Glutamic Acid Decarboxylase Content of the Supraoptic Nucleus of the Rat

The localization of the GABAergic neurons which send efferent fibers to the supraoptic nucleus was investigated. For this purpose the activity of glutamic acid decarboxylase, a specific marker for GABAergic neurons, was determined in the supraoptic nucleus after a variety of lesions. The severance of fibers from the mesencephalon and the mediobasal hypothalamus, as well as from the hippocampus, had no effect. However, lesions rostral to the nucleus reduced its activity in glutamic acid decarboxylase by about 40%, as did the infusion of kainic acid into the nucleus accumbens. Thus, the neurons in the supraoptic nucleus seem to receive a large part of their GABAergic afferents from the n. accumbens. In addition to that, GABAergic neurons intrinsic or adjacent to the supraoptic nucleus seem to contribute to the regulation of the release of vasopressin and/or oxytocin.