Organization and regulation of paraventricular nucleus glutamate signaling systems: N-methyl-D-aspartate receptors.
Stress activation of the hypothalamo-pituitary-adrenocortical (HPA) axis is mediated in part by glutamatergic neurotransmission. The precise nature of glutamate effects on stress-integrative hypothalamic paraventricular nucleus (PVN) neurons remains to be determined. Therefore, the current study was designed to delineate the organization of glutamate/NMDA receptor systems in the PVN and to assess regulation of PVN glutamate receptor subunit expression by chronic intermittent stress and glucocorticoids. Immunohistochemical studies verified that N-methyl-D-aspartate (NMDA) receptor subunit proteins NR1 and NR2A/2B are expressed in the medial parvocellular PVN, indicating the potential for NMDA receptor regulation of corticotropin-releasing hormone (CRH) release. Dual-label confocal analysis revealed that CRH neurons are apposed by vesicular glutamate transporter 2 (VGLUT2)-containing terminals, consistent with glutamatergic innervation from hypothalamus and/or brainstem. In situ hybridization analysis revealed a significant and selective stress-induced decrease (37%) in NR2B subunit mRNA expression in the CRH-containing region of the PVN. No changes were observed for NR1 or NR2A mRNAs. In contrast, none of the subunits investigated showed altered expression following adrenalectomy with or without low/high-dose corticosterone replacement. Thus, the observed stress regulation is likely mediated by neurogenic mechanisms in the PVN and upstream stress-transducing neurocircuitry. Because a loss of NR2B subunit inclusion in NR receptors would likely confer increased Ca(++) conductance and faster deactivation kinetics, the stress-induced decrease in NR2B mRNA is consistent with enhanced glutamate signaling in the PVN following chronic stress and, perhaps, increased basal HPA activity and more rapid and/or more robust HPA responses to stress.
Ziegler
Dana R
DR
Department of Psychiatry, University of Cincinnati, Cincinnati, Ohio 45267-0559, USA. drz@jhu.edu
Cullinan
William E
WE
Herman
James P
JP
D000315:Adrenalectomy; D000818:Animals; D005938:Glucocorticoids / Q000494:pharmacology; D018698:Glutamic Acid / Q000502:physiology*; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008297:Male; D026901:Membrane Transport Proteins / Q000378:metabolism; D010286:Paraventricular Hypothalamic Nucleus / Q000166:cytology / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000187:drug effects / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013315:Stress, Psychological / Q000378:metabolism; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2
D005938:Glucocorticoids; D026901:Membrane Transport Proteins; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; C493475:Slc17a6 protein, rat; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D018698:Glutamic Acid