Bywood P T, Johnson S M
Department of Clinical Pharmacology, Flinders University of South Australia, Adelaide, 5001, Australia.
Exp Neurol. 2000 Mar;162(1):180-8. doi: 10.1006/exnr.2000.7310.
Although differential vulnerability in different regions of the central nervous system is a characteristic feature of neurodegenerative disorders in vivo, its cellular basis is not well understood. In the present study we investigated whether catecholamine neurons in different regions of the substantia nigra (SN) are differentially vulnerable to excitatory amino acid-induced damage in a midbrain slice preparation. Rats were anesthetized by halothane inhalation and killed, the brain was rapidly removed, and 300-microm-thick midbrain slices were cut horizontally on a vibratome. The slices were incubated at 35 degrees C for 2 h in saline buffer containing either kainic acid (KA) or N-methyl-d-aspartate (NMDA) (10-50 microM). They were then fixed and cut into 30-microm sections that were coplanar with the horizontal slice. Individual catecholamine neurons were identified in these thin sections using an antibody to tyrosine hydroxylase coupled to diaminobenzidine. Catecholaminergic neurons in the dorsal and ventral tiers of the SN were readily identified by reference to an atlas of the distribution of catecholamine neurons in the horizontal plane. Using dendritic degeneration as a sensitive index of damage, and submaximal concentrations of KA and NMDA, we found that catecholamine neurons in the dorsal tier were more vulnerable than those in the ventral tier. For example, KA (10 microM) caused a significant reduction in the proportion of neurons with dendrites in the dorsal tier (from 60 to 34%) without altering the dendritic arbor of ventral tier neurons. After treatment with 50 microM KA, only 11% of dorsal tier neurons retained any dendrites while 45% of ventral tier neurons retained their dendrites. These differences were statistically significant (P<0.001). A similar differential vulnerability was apparent in slices treated with NMDA; neurons in the dorsal tier lost dendrites before detectable damage in the ventral tier. An understanding of the comparative anatomical, neurochemical, and physiological properties of vulnerable (dorsal tier) and resistant (ventral tier) catecholamine neurons in rat SN may provide significant insights into the mechanisms and treatment of neurodegenerative disorders involving catecholamine neurons.
虽然中枢神经系统不同区域的易损性差异是体内神经退行性疾病的一个特征，但对其细胞基础的了解并不充分。在本研究中，我们调查了黑质（SN）不同区域的儿茶酚胺能神经元在中脑切片制备中对兴奋性氨基酸诱导损伤的易损性是否存在差异。通过吸入氟烷对大鼠进行麻醉并使其致死，迅速取出大脑，并在振动切片机上水平切取300微米厚的中脑切片。将切片在含有 kainic 酸（KA）或 N - 甲基 - D - 天冬氨酸（NMDA）（10 - 50微摩尔）的盐缓冲液中于35摄氏度孵育2小时。然后将其固定并切成与水平切片共面的30微米切片。使用与二氨基联苯胺偶联的酪氨酸羟化酶抗体在这些薄片中鉴定单个儿茶酚胺能神经元。参照儿茶酚胺能神经元在水平面分布的图谱，很容易识别出SN背侧层和腹侧层的儿茶酚胺能神经元。以树突退变作为损伤的敏感指标，并使用亚最大浓度的KA和NMDA，我们发现背侧层的儿茶酚胺能神经元比腹侧层的更易受损。例如，KA（10微摩尔）导致背侧层有树突的神经元比例显著降低（从60%降至34%），而未改变腹侧层神经元的树突分支。用50微摩尔KA处理后，背侧层只有11%的神经元保留任何树突，而腹侧层有45%的神经元保留其树突。这些差异具有统计学意义（P < 0.001）。在用NMDA处理的切片中也明显存在类似的易损性差异；背侧层的神经元在腹侧层出现可检测到的损伤之前就失去了树突。了解大鼠SN中易损（背侧层）和抗损伤（腹侧层）儿茶酚胺能神经元的比较解剖学、神经化学和生理学特性，可能为涉及儿茶酚胺能神经元的神经退行性疾病的机制和治疗提供重要见解。
