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Sci Adv. 2016 Aug 17;2(8):e1501723. doi: 10.1126/sciadv.1501723. eCollection 2016 Aug.

A novel GABA-mediated corticotropin-releasing hormone secretory mechanism in the median eminence.

Author information

1
Department of Neurophysiology, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan.; Second Division, Department of Medicine, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan.
2
Department of Neurophysiology, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan.
3
Second Division, Department of Medicine, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan.
4
Department of Genetic and Behavioral Neuroscience, Gunma University Graduate School of Medicine, Maebashi, Gunma 371-8511, Japan.
5
Laboratory of Information Biology, Graduate School of Information Sciences, Tohoku University, Sendai, Miyagi 980-8579, Japan.
6
Department of Family and Community Medicine, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan.

Abstract

Corticotropin-releasing hormone (CRH), which is synthesized in the paraventricular nucleus (PVN) of the hypothalamus, plays an important role in the endocrine stress response. The excitability of CRH neurons is regulated by γ-aminobutyric acid (GABA)-containing neurons projecting to the PVN. We investigated the role of GABA in the regulation of CRH release. The release of CRH was impaired, accumulating in the cell bodies of CRH neurons in heterozygous GAD67-GFP (green fluorescent protein) knock-in mice (GAD67(+/GFP)), which exhibited decreased GABA content. The GABAA receptor (GABAAR) and the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1), but not the K(+)-Cl(-) cotransporter (KCC2), were expressed in the terminals of the CRH neurons at the median eminence (ME). In contrast, CRH neuronal somata were enriched with KCC2 but not with NKCC1. Thus, intracellular Cl(-) concentrations ([Cl(-)]i) may be increased at the terminals of CRH neurons compared with concentrations in the cell body. Moreover, GABAergic terminals projecting from the arcuate nucleus were present in close proximity to CRH-positive nerve terminals. Furthermore, a GABAAR agonist increased the intracellular calcium (Ca(2+)) levels in the CRH neuron terminals but decreased the Ca(2+) levels in their somata. In addition, the increases in Ca(2+) concentrations were prevented by an NKCC1 inhibitor. We propose a novel mechanism by which the excitatory action of GABA maintains a steady-state CRH release from axon terminals in the ME.

KEYWORDS:

Corticotropin releasing hormone; K+-Cl- cotransporter; Na+-K+-2Cl- cotransporter; arcuate nucleus; median eminence; paraventricular nucleus; γ-aminobutyric acid

PMID:
27540587
PMCID:
PMC4988769
DOI:
10.1126/sciadv.1501723
[Indexed for MEDLINE]
Free PMC Article

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