Rittase W Bradley, Dong Yu, Barksdale DaRel, Galdzicki Zygmunt, Bausch Suzanne B
Department of Pharmacology, Uniformed Services University School of Medicine, Bethesda, MD 20814, United States.
Department of Anatomy, Physiology and Genetics, Uniformed Services University School of Medicine, Bethesda, MD 20814, United States.
Mol Cell Neurosci. 2014 May;60:63-71. doi: 10.1016/j.mcn.2014.04.002. Epub 2014 Apr 23.
Emerging evidence suggests that neuronal responses to N-methyl-d-aspartate (NMDAR) activation/inactivation are influenced by subunit composition. For example, activation of synaptic NMDAR (comprised of GluN2A>GluN2B) phosphorylates cAMP-response-element-binding protein (CREB) at Ser 133, induces BDNF expression and promotes neuronal survival. Activation of extrasynaptic NMDAR (comprised of GluN2B>GluN2) dephosphorylates CREB (Ser 133), reduces BDNF expression and triggers neuronal death. These results led us to hypothesize that chronic inhibition of GluN2B-containing NMDAR would increase CREB (Ser 133) phosphorylation, increase BDNF levels and subsequently alter downstream dynorphin (DYN) and neuropeptide Y (NPY) expression. We focused on DYN and NPY because these neuropeptides can decrease excitatory neurotransmission and seizure occurrence and we reported previously that seizure-like events are reduced following chronic treatment with GluN2B antagonists. Consistent with our hypothesis, chronic treatment (17-21days) of hippocampal slice cultures with the GluN2B-selective antagonists ifenprodil or Ro25,6981 increased both CREB (Ser 133) phosphorylation and granule cell mossy fiber pathway DYN expression. Similar treatment with the non-subtype-selective NMDAR antagonists d-APV or memantine had no significant effect on either CREB (Ser 133) phosphorylation or DYN expression. In contrast to our hypothesis, BDNF levels were decreased following chronic treatment with Ro25,6981, but not ifenprodil, d-APV or memantine. Blockade of BDNF actions and TrkB activation did not significantly augment hilar DYN expression in vehicle-treated cultures and had no effect in Ro25,6981 treated cultures. These findings suggest that chronic exposure to GluN2B-selective NMDAR antagonists increased DYN expression through a putatively pCREB-dependent, but BDNF/TrkB-independent mechanism.
新出现的证据表明，神经元对N-甲基-D-天冬氨酸（NMDAR）激活/失活的反应受亚基组成的影响。例如，突触NMDAR（由GluN2A>GluN2B组成）的激活使环磷酸腺苷反应元件结合蛋白（CREB）的丝氨酸133位点磷酸化，诱导脑源性神经营养因子（BDNF）表达并促进神经元存活。突触外NMDAR（由GluN2B>GluN2组成）的激活使CREB（丝氨酸133）去磷酸化，降低BDNF表达并触发神经元死亡。这些结果使我们推测，长期抑制含GluN2B的NMDAR会增加CREB（丝氨酸133）磷酸化，提高BDNF水平，随后改变下游强啡肽（DYN）和神经肽Y（NPY）的表达。我们关注DYN和NPY，因为这些神经肽可以减少兴奋性神经传递和癫痫发作，并且我们之前报道过，用GluN2B拮抗剂进行长期治疗后癫痫样事件会减少。与我们的假设一致，用GluN2B选择性拮抗剂艾芬地尔或Ro25,6981对海马切片培养物进行长期治疗（17 - 21天），可增加CREB（丝氨酸133）磷酸化以及颗粒细胞苔藓纤维通路DYN表达。用非亚型选择性NMDAR拮抗剂D-APV或美金刚进行类似治疗，对CREB（丝氨酸133）磷酸化或DYN表达均无显著影响。与我们的假设相反，用Ro25,6981进行长期治疗后BDNF水平降低，但用艾芬地尔、D-APV或美金刚治疗则不然。阻断BDNF作用和TrkB激活在未处理的培养物中并未显著增加海马门区DYN表达，在Ro25,6981处理的培养物中也没有作用。这些发现表明，长期暴露于GluN2B选择性NMDAR拮抗剂可通过一种可能依赖磷酸化CREB但不依赖BDNF/TrkB的机制增加DYN表达。
