Investigation of therapy for neonatal hypoxic-ischemic brain damage

胶质细胞源性神经营养因子(GDNF)是1993年发现的一种对中脑多巴胺能神经元有很强的神经营养作用的神经营养因子。随后的研究揭示了其对运动神经元的营养作用和对脑水肿的有益作用。本研究探讨了胶质细胞源性神经营养因子在新生大鼠缺氧缺血性脑损伤中的作用：(1)脑实质内注射2-μ-g和4-μ-g对7日龄大鼠脑缺血/缺氧性损伤有明显的保护作用，并呈剂量依赖关系。(2)免疫细胞化学方法检测新生大鼠出生后1~14天和21天脑内胶质细胞源性神经营养因子的表达。结果揭示了GDNF在神经元和非神经元细胞中表达的发育变化特征，提示GDNF可能在脑生长和分化的不同阶段起关键作用。脑脊液EL ISA检测显示，GDNF水平从伤后1天开始迅速升高，至伤后7~9天达到峰值，之后逐渐下降。(3)在7日龄大鼠缺氧缺血性脑损伤模型中，伤后3h和48h出现两个高峰。免疫细胞化学研究表明，前者为神经元产生GDNF，后者为迁移中的星形胶质细胞。(4)从PND1开始连续3d给予地塞米松(0.5 mg/kg)可显著增加PND3-5时脑脊液中GDNF的水平。而早期给予地塞米松治疗的新生大鼠脑脊液中GDNF水平在第10天低于对照组。(5)建立新生大鼠上臂丛神经麻痹模型，观察其行为学和组织学变化。局部应用浸泡了4μg神经营养因子的明胶可显著改善动物的行为和组织学损伤。

Glial cell line-derived neurotrophic factor (GDNF) was discovered as a potent neurotrophic factor to the dopaminergic neurons in the midbrain at 1993. The subsequent studies revealed its trophic effect on the motor neuron and beneficial effect on brain edema. We have investigated the involvement of GDNF in neonatal hypoxic-ischemic brain damage as follows.(1) Intraparenchymal administration of 2μg and 4μg of GDNF provided remarkable protection against ischemia/hypoxia-induced brain damage in 7-day-old rats in a dose-dependent manner.(2) Expression of GDNF in developing rat brain form post natal day (PND) 1 to 14 and on PND 21 was examined immunocytochemically. The results revealed the characteristic developmental shifts in GDNF expression in neuronal and non-neuronal cells, which indicated that GDNF may be of critical importance at different stages of brain growth and differentiation. ELISA of the cerebrospinal fluid (CSF) revealed a rapid rise in GDNF levels from PND 1 to peak levels at PND 7-9, and thereafter, the levels gradually decreased.(3) In hypoxic-ischemic brain damage model of 7-day-old rat, brain GDNF levels took two peak, 3 and 48 hours after the insult. Immunocytochemical study showed that the former peak was represented by GDNF production in neurons and the latter peak was corresponded by that in migrating astrocytes.(4) Administration of dexamethasone (0.5 mg/kg) for 3 days beginning from PND 1 significantly increased GDNF levels in the CSF at PND 3-5. However, GDNF levels in the CSF in the group which receive dexamethasone in the early life were lower than that in the control group at PND 10.(5) We established the neonatal rat model mimicking upper brachial plexus palsy in newborn, in which the behavioral and histological changes could be evaluated. Topical application of gelform soaked with 4μg of GDNF dramatically improved the behavioral and histological impairment.