NEURAL STEM CELLS AND XENOBIOTIC RESPONSE

中枢神经系统在胚胎期和出生后早期经历了非凡的增殖生长。传统上认为，一旦产生了完整的神经元补体，中枢神经系统神经元就不会再增殖。然而，少量新的神经元和神经胶质细胞已被证明是在整个生命过程中产生的。最近的研究表明，神经元和胶质细胞可能起源于脑室和脊髓中央管的室管膜层。关于这些干细胞对神经毒性损伤的反应性知之甚少。我们假设位于室管膜的神经干细胞通过增殖和后代分化为神经细胞来响应神经毒性刺激，并且这些新产生的细胞在大脑对神经毒性损伤的反应中发挥作用。为了验证这一假设，我们提出解决三个具体问题：(1)室管膜细胞是否在毒性诱导的邻近大脑区域神经元损失的反应中增殖？(2)室管膜细胞的后代是否迁移到神经毒性损伤区域并整合到大脑中？(3)未成熟大脑的神经干细胞对神经毒性损伤的反应是否与成人的神经干细胞相同？将使用三种模型神经毒物来比较室管膜细胞在直接损伤（尿素）、邻近心室系统的海马神经元损伤（三甲基锡）和远程损伤嗅觉系统（硫酸锌）后的反应性。室管膜细胞将通过脑室内注射DiI和饮用水中给予BrdU进行双重标记，并通过免疫荧光和免疫细胞化学确定其运动和命运。室管膜细胞复制的后代将使用针对神经元、星形胶质细胞或少突胶质细胞的特异性标记的抗体来表征。将同时对幼年动物和成年动物进行检查，以确定这种反应是否与年龄有关。拟议研究的目的是表征室管膜干细胞对神经毒物的细胞反应的贡献。结果可能阐明脑损伤适应性的年龄依赖性差异，并可能为神经毒性损伤的治疗性修复提供策略。

The central nervous system undergoes extraordinary proliferative growth during embryonic and early postnatal life. It is traditionally held that once the full complement of neurons is produced, there is no further proliferation of CNS neurons. However, a small number of new neurons and glia have been demonstrated to be generated throughout life. Recent studies suggest that neuronal and glial cells may arise from the ependymal layer lining the ventricles of the brain and central canal of the spinal cord. Little is known regarding the responsiveness of these stem cells to neurotoxic injury. We hypothesize that neural stem cells located in the ependyma respond to neurotoxic stimuli by proliferation and differentiation of progeny into neural cells, and that these newly produced cells play a role in the brain's response to neurotoxic injury. To test this hypothesis, we propose to address three specific questions: (1) Do ependymal cells proliferate in response to toxicant-induced loss of neurons from neighboring regions of the brain? (2) Do progeny of ependymal cells migrate to areas of neurotoxic damage and become integrated into the brain? (3) Do neural stem cells of immature brains respond to neurotoxic injury in the same manner as neural stem cells in adults? Three model neurotoxicants will be used to compare the responsiveness of ependymal cells following direct injury (urea), damage to hippocampal neurons adjacent to the ventricular system (trimethyltin) and remote injury to the olfactory system (zinc sulfate). Ependymal cells will be double- labelled by intraventricular injection of DiI and with BrdU administered in drinking water, and their movement and fate determined by immunofluorescence and immunocytochemistry. The progeny from ependymal cell replication will be characterized using antibodies to specific markers for neurons, astrocytes, or oligodendroglia. Juvenile and adult animals will be examined in parallel to determine whether the response is age-dependent. The goal of the proposed study is to characterize the contributions of ependymal stem cells to cellular responses to neurotoxicants. Results may elucidate age-dependent differences in brain adaptability to injury, and may suggest strategies for therapeutic repair of neurotoxic damage.