Liang F Q, Sohrabji F, Miranda R, Earnest B, Earnest D
Department of Human Anatomy and Medical Neurobiology, College of Medicine, College Station, Texas, 77843-1114, USA.
Exp Neurol. 1998 Jun;151(2):184-93. doi: 10.1006/exnr.1998.6804.
Photic entrainment of mammalian circadian rhythms occurs because the pacemaker in the suprachiasmatic nuclei (SCN) of the hypothalamus is endowed with a rhythmic sensitivity to photic signals conveyed by the retinohypothalamic tract. Since brain-derived neurotrophic factor (BDNF) has been implicated in the functional modulation of other retinal targets, the rat SCN was examined for expression and cellular distribution of this neurotrophin and TrkB, the tyrosine kinase receptor that preferentially binds BDNF. The rat SCN was found to express the mature BDNF peptide and mRNA by Western blotting, enzyme-linked immunosorbent assay (ELISA), and reverse transcription-polymerase chain reaction (RT-PCR) analyses. BDNF-immunoreactivity and hybridization signal for its mRNA were coextensively localized within a number of SCN cells throughout the rostrocaudal axis of each nucleus. In addition, some cells intercalated within the optic chiasm were distinguished by expression of BDNF immunoreactivity or mRNA. Immunostaining for the TrkB receptor was also evident in the SCN within terminals or fibers predominantly located along the SCN/optic chiasm interface and within scattered perikarya near the medial border of each nucleus. Combined in situ hybridization and immunocytochemical analysis revealed that BDNF mRNA-expressing cells within the ventrolateral SCN were often closely apposed to TrkB-positive fibers extending from the optic chiasm. These findings raise the possibility that target-derived interactions between BDNF and TrkB receptors could play a role in the circadian modulation of SCN pacemaker sensitivity to photic input transmitted by the retinohypothalamic tract.
哺乳动物昼夜节律的光诱导现象之所以会发生，是因为下丘脑视交叉上核（SCN）中的起搏器对视网膜下丘脑束所传递的光信号具有节律性敏感性。由于脑源性神经营养因子（BDNF）已被证明参与了其他视网膜靶标的功能调节，因此对大鼠SCN进行了检测，以研究这种神经营养因子及其酪氨酸激酶受体TrkB（优先结合BDNF）的表达和细胞分布。通过蛋白质免疫印迹法、酶联免疫吸附测定（ELISA）和逆转录聚合酶链反应（RT-PCR）分析发现，大鼠SCN表达成熟的BDNF肽和mRNA。BDNF免疫反应性及其mRNA的杂交信号在每个核的 rostrocaudal 轴上的许多SCN细胞中共同定位。此外，一些夹在视交叉内的细胞通过BDNF免疫反应性或mRNA的表达得以区分。TrkB受体的免疫染色在SCN内也很明显，主要位于SCN/视交叉界面沿线的终末或纤维中，以及每个核内侧边界附近的散在核周体中。原位杂交和免疫细胞化学联合分析显示，腹外侧SCN内表达BDNF mRNA的细胞通常与从视交叉延伸而来的TrkB阳性纤维紧密相邻。这些发现提出了一种可能性，即BDNF与TrkB受体之间源自靶标的相互作用可能在SCN起搏器对视网膜下丘脑束所传递的光输入的昼夜调节中发挥作用。
