GABAA receptor subunit expression within hypophysiotropic CRH neurons: A dual hybridization histochemical study

Dual hybridization histochemical studies were conducted to investigate the extent of colocalization of mRNA transcripts encoding the α1–2 and β1–3 subunits of the gamma aminobutyric acid (GABA)A receptor with those for corticotropin-releasing hormone (CRH) within the rat hypothalamic paraventricular nucleus (PVN). A vast majority of CRH neurons (>94.5%) were found to express transcripts specific for the the α2, β1 and β3 subunits; mRNAs for the α1 and β2 subunits of the GABAA receptor were detected within 53.3% and 65.7% of PVN CRH neurons, respectively. The results may have important implications for studies aimed at understanding GABAergic influences upon the hypothalamic-pituitary-adrenocortical (HPA) axis. Hypophysiotropic CRH neurons serve as the origin of the final common pathway for glucocorticoid secretion in response to stressful stimuli, and GABAergic afferents have been implicated in afferent control of these neurons. The subunit composition of GABAA receptors at this key regulatory locus may affect the efficacy of a major inhibitory input, and thus the magnitude and/or duration of stress-induced glucocorticoid secretion. The present findings reveal basal expression patterns of transcripts encoding several subunits of the GABAA receptor within stress-integrative CRH neurons, data which may be used to guide regulatory studies of GABAergic influences on the HPA axis under a variety of conditions. J. Comp. Neurol. 419:344–351, 2000. © 2000 Wiley-Liss, Inc.