Hattori T, Takada M, Moriizumi T, Van der Kooy D
Department of Anatomy, University of Toronto, Ontario, Canada.
J Comp Neurol. 1991 Jul 15;309(3):391-401. doi: 10.1002/cne.903090308.
These experiments were designed to examine a paradox present in the literature with regard to the fine structure of nigrostriatal dopamine terminals within the rat striatum. Previous studies have shown that anterograde transport of tritiated labeled proteins from the substantia nigra to the striatum over short survival times primarily labels asymmetric synapses (and that these asymmetric synapses are preferentially vulnerable to selective dopaminergic neurotoxins such as 6-hydroxydopamine). In contrast, fine structural immunohistochemical studies with antibodies to tyrosine hydroxylase and dopamine have consistently labeled primarily symmetric synapses en passant within the striatum. We have now confirmed that these two seemingly contradictory types of labeled synapses (radio- and immuno-labeled) can both be present, but most often separate from one another, in single ultrathin sections. However, we also found that radiolabeled unmyelinated axons were usually double-labeled by tyrosine hydroxylase immunohistochemistry. Employing longer survival times (10 days after the nigral isotope injections) in order to enhance the ratio of "en passant" to terminal labeling produced a large increase in the occurrence of radiolabeled striatal axonal varicosities with the result that many symmetric synapses en passant were double-labeled with both the autoradiographic and the immunohistochemical markers. Given that more than 95% of the nigrostriatal projection arises from dopamine fluorescent neurons, it would appear that both the asymmetric and symmetric terminals belong to the same type of neuron. Thus, we suggest that single dopaminergic neurons in the substantia nigra make two types of synaptic contact with striatal cells: 1) symmetric synapses en passant, which can be stained with tyrosine hydroxylase and dopamine and which contact dendritic spine necks, and 2) asymmetric terminal boutons of unknown chemical nature which end on dendritic spine heads. We conclude that both the asymmetric terminal and symmetric en passant synapses take origin from a single nigrostriatal dopaminergic neuronal population and that dopaminergic transmitter markers occur only in one of these synaptic types in the rat striatum.
这些实验旨在研究文献中关于大鼠纹状体内黑质纹状体多巴胺终末精细结构的一个矛盾之处。以往研究表明，在短存活时间内，从黑质向纹状体进行的氚标记蛋白的顺行运输主要标记不对称突触（并且这些不对称突触优先易受选择性多巴胺能神经毒素如6-羟基多巴胺的影响）。相比之下，用酪氨酸羟化酶和多巴胺抗体进行的精细结构免疫组织化学研究一直主要标记纹状体内的对称突触。我们现在已经证实，这两种看似相互矛盾的标记突触（放射性和免疫标记）在单个超薄切片中都可以存在，但大多数情况下彼此分开。然而，我们还发现放射性标记的无髓轴突通常被酪氨酸羟化酶免疫组织化学双重标记。采用更长的存活时间（黑质同位素注射后10天）以提高“沿途”标记与终末标记的比例，导致放射性标记的纹状体轴突膨体的出现大幅增加，结果许多沿途对称突触被放射自显影和免疫组织化学标记双重标记。鉴于超过95%的黑质纹状体投射来自多巴胺荧光神经元，看来不对称和对称终末都属于同一类型的神经元。因此，我们认为黑质中的单个多巴胺能神经元与纹状体细胞形成两种类型的突触联系：1）沿途对称突触，可被酪氨酸羟化酶和多巴胺染色，与树突棘颈部接触；2）化学性质未知的不对称终末小体，终止于树突棘头部。我们得出结论，不对称终末和对称沿途突触均起源于单一的黑质纹状体多巴胺能神经元群体，并且多巴胺能递质标记仅出现在大鼠纹状体中的这些突触类型之一中。
