Differential immunoreactivity of glucocorticoid receptor and GABA in GABAergic afferents to parvocellular neurons in the paraventricular nucleus.

We assessed the distribution of glucocorticoid receptors (GR), GABA (γ-aminobutyric acid) neurons and co-localization of GR in GABA-positive neurons for four hypothalamic sources of GABAergic projections to the parvocellular neurons in the paraventricular nucleus (PVH) from normal, sham-surgery and adrenalectomized male rats subjected to intraperitoneal injections of saline or dexamethasone. Blood samples were collected to measure corticosterone by radioimmunoassay. The distribution of GR, GABA-positive neurons and co-localization of GR in GABA-positive neurons were analyzed by immunofluorescence in sections from the paraventricular nucleus (PVH). In intact and sham rats, dexamethasone induced expression of GABAergic neurons in the regions of the anterior periventricular nucleus (PVa) coincident with anterior (PVHap) and medial (PVHmp) parvocellular subdivisions of thePVH. However, the co-expression of GR in GABAergic neurons was found only in the region of the PVa coincident with PVHmp. These findings confirm that glucocorticoids may directly act on GABAergic neurons through GR. PVHap and PVHmp present differentiated patterns of GABA and GR expression between then. The co-localization of GR in GABA-positive neurons in the region of the PVa coincident with PVHmp demonstrates a critic importance of this region to control the hypothalamus-pituitary-adrenal axis through GABAergic mediation.