BDNF-TrkB Pathway Mediates NMDA receptor NR2B Subunit Phosphorylation in the Supraoptic Nuclei Following Progressive Dehydration

• Published in: Journal of neuroendocrinology 2011-10, Vol.23 (10), p.894-905
• Main Authors: Carreño, Flávia Regina, Walch, Joseph D, Dutta, Mayurika, Nedungadi, Thekkethil P., Cunningham, J. Thomas
• Format: Article
• Language: English
• ISSN: 0953-8194; 1365-2826
• DOI: 10.1111/j.1365-2826.2011.02209.x

We studied the effects of water deprivation on the phosphorylation of TrkB and NMDA receptor subunits in the supraoptic nucleus (SON) of the rat. Laser capture microdissection and qRT-PCR was used to demonstrate BDNF and TrkB gene expression in vasopressin SON neurones. Immunohistochemistry confirmed BDNF staining in vasopressin neurones, while staining for phosphorylated TrkB was increased following water deprivation. Western Blot analysis of brain punches containing the SON revealed that tyrosine phosphorylation of TrkB (pTrkBY 515 ), serine phosphorylation of NR1 (pNR1S 866 or pNR1) and tyrosine phosphorylation of NR2B subunits (pNR2BY 1472 or pNR2B) were significantly increased in WD animals compared to control. Access to water for 2 h reduced pTrkBY 515 content to control levels without affecting pNR1 or pNR2B. Four hours of rehydration was needed to reduce pNR1 and pNR2B to control. To test whether increased phosphorylation of TrkB in this study is mediated by BDNF, a group of animals were instrumented with right SON cannula coupled to mini-osmotic pumps filled with vehicle or TrkB-Fc fusion protein which prevents BDNF binding to TrkB. In the left SON contralateral to the cannula, TrkB phosphorylation was significantly enhanced following WD. Separate analysis of the right SON, which received TrkB-Fc, showed that the TrkB receptor phosphorylation following WD was significantly attenuated. While increased pNR1S 866 following WD was not affected by local infusion of TrkB-Fc, pNR2BY 1472 was significantly reduced. Co-immunoprecipitation revealed an increased physical interaction between Fyn kinase and NR2B and TrkB in the SON following water deprivation. Thus, activation of TrkB in the SON following WD may affect cellular excitability through the phosphorylation of NR2B subunits.