GABA neuron systems in hypothalamus and the pituitary gland. Immunohistochemical demonstration using antibodies against glutamate decarboxylase.

The distribution of gamma-aminobutyric acid (GABA) nerve fibers and cell bodies in the rat hypothalamus and pituitary gland was immunohistochemically examined using antibodies against the GABA-synthesizing enzyme glutamate decarboxylase (GAD). The dense network of GAD-positive nerve fibers was observed to be essentially evenly distributed throughout the hypothalamus. A plexus of GABA terminals was also demonstrated both in the median eminence and with in the posterior and intermediate lobes of the pituitary. Three distinct clusters of magnocellular GABA neurons were discovered in the posterior hypothalamus. In the addition, GAD immunoreactive cell bodies were observed in many other hypothalamic nuclei, such as the arcuate nucleus and in the perifornical region. The results provide a morphological basis by which GABA of hypothalamic origin may regulate the neuroendocrine system.