ROLE OF BDNF IN THE PHOTIC CONTROL OF CIRCADIAN RHYTHMS

拟议研究的广泛目标是深入了解哺乳动物昼夜节律生物学的一个新领域：神经营养因子在SCN蝉功能中的作用。最近的研究结果表明，神经营养因子，脑源性神经营养因子（BDNF0），可以增强大脑其他区域的神经元信号传导。我们的中心假设是BDNF通过调节光输入及其对昼夜节律调解机制的影响在SCN中发挥类似的作用。为了解决这一假设，拟议的研究将确定：使用免疫化学和通道追踪方法，支配SCN的视网膜下丘脑束（RHT）纤维或接受RHT输入的细胞是否表达TrkB酪氨酸激酶受体（BDNF的同源受体），以及啮齿动物SCN中BDNF和TrkB表达的改变或BDNF作用的抑制是否会产生可预测的光对轮跑行为昼夜节律的相移效应的变化。实验将确定：1)在RHT纤维或接受RHT神经支配的细胞上，通过电子和/或光镜观察到TrkB受体免疫反应性在腹侧SCN的定位，并在盲化后减弱；2)当外源性BDNF注入SCN时，当蝉对光线不敏感时，光线可以在主观白天诱导相移；3)杂合敲除小鼠BDNF和TrkB表达的转基因缺陷（BDNF +/-和TrkB +/-）减弱了主观夜间光的相移效应；4)将酪氨酸激酶抑制剂K252a输注到光的移相效应中；5)给予TrkB-IgG融合蛋白，清除内源性BDNF，类似地阻断光诱导的相移。这些研究将为BDNF在调节光对SCN的影响中的作用提供关键支持。鉴于它有可能推进我们对昼夜节律如何以一种时间依赖的方式被光调节的认识，这项研究已经应用于开发治疗、诊断和理解人类心理健康和表现障碍的策略，这些障碍是由身体过程的内部不同步引起的，包括情感障碍、痴呆和衰老过程中的生理衰退。

The broad objective of the proposed research is to gain insight into a new area in mammalian circadian biology: the role of neurotrophins in SCN cicadian function. Recent findings indicate that the neurotrophin, brain- derived neurotrophic factor (BDNF0, enhances neuronal signaling in other brain regions. Our central hypothesis is that BDNF plays a comparable role in the SCN by regulating photic input and its effects on the circadian peacemaker mechanism. To address this hypothesis, the proposed studies will determine: whether retinohypothalamic tract (RHT) fibers innervating the SCN or cells receiving RHT input express TrkB tyrosine kinase receptors, the cognate receptor for BDNF, using imunochistochemical and tract tracing methods and whether alterations in BDNF and TrkB expression or inhibition of BDNF action in the rodent SCN produce predictable changes in the phase-shifting effect of light on the circadian rhythm of wheel-running behavior. Experiments will be conducted to determine whether: 1) localization of TrkB receptor immuno reactivity in the ventral SCN by electron and/or light microscopy is observed on RHT fibers or on cells receiving RHT innervation and is diminished after blinding; 2) infusion of exogenous BDNF into the SCN enables light to induce phase shifts during the subjective day when the cicadian peacemaker is normally insensitive to light; 3) transgenic deficits in BDNF and TrkB expression in heterozygous knock-out mice(bdnf+/- and trkB+/-) abate the phase-shifting effect of light during the subjective night; 4) infusion of the tyrosine kinase inhibitor, K252a, into the phase-shifting effect of light; 5) administration of TrkB-IgG fusion protein, which scavenges endogenous BDNF, similarly blocks light-induced phase shifts. These studies will purvey critical support of the role of BDNF in regulating the effects of light on the SCN peacemaker. In view of it's potential to advance our knowledge of how circadian rhythms are regulated by light in a time-dependent manner, this research has applied relevance for developing strategies in the treatment, diagnosis and understanding of disorders in human mental health and performance that result from internal desynchronization of body process, including affective disorders, dementia and physiological decline during aging.