GluR5-mediated glutamate signaling regulates hypothalamo–pituitary–adrenocortical stress responses at the paraventricular nucleus and median eminence

Summary 

Glutamate is the main excitatory neurotransmitter in the central nervous system, and plays an excitatory role in generation of hypothalamic–pituitary–adrenocortical (HPA) axis responses to stress. The current study assesses the role of kainate-preferring receptors in glutamatergic excitation of the HPA axis. In situ hybridization and immunohistochemical analyses confirmed the existence of the GluR5 kainate subunit in the paraventricular nucleus of the hypothalamus (PVN). Importantly, GluR5 immunoreactivity was enriched in the external lamina of the median eminence, where it is co-localized with corticotropin releasing hormone (CRH). Intra-PVN infusion of LY382884 increased plasma adrenocorticotropin (ACTH), corticosterone and PVN c-Fos immunoreactivity. Infusions of LY382884 into the median eminence region, on the other hand, reduced restraint induced ACTH release without altering c-Fos expression. Together, these findings provide evidence for glutamate-mediated signaling in control of CRH release at the PVN and median eminence, mediated by way of kainate-preferring receptor complexes.

Abbreviations: ACTH, adrenocorticotropic hormone, AMPA, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, ANOVA, analysis of variance, ATPA, (RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl)propanoic acid, CRH, corticotropin releasing hormone, DAB, diaminobenzidine, GFAP, glial fibrillary acidic protein, HPA, hypothalamic–pituitary–adrenocortical, KPBS, potassium phosphate buffered saline, NMDA, n-methyl-d-aspartate, PVN, paraventricular nucleus of the hypothalamus

Keywords: HPA axis, GluR5, CRH, Rats, Presynaptic, Median eminence