Nirenberg M J, Chan J, Liu Y, Edwards R H, Pickel V M
Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021, USA.
J Neurosci. 1996 Jul 1;16(13):4135-45. doi: 10.1523/JNEUROSCI.16-13-04135.1996.
Midbrain dopaminergic neurons are known to release dopamine from somata and/or dendrites located in the substantia nigra (SN) and the ventral tegmental area (VTA). There is considerable controversy, however, about the subcellular sites for somatodendritic dopamine storage in these regions. In the present study, we used dual-labeling electron microscopic immunocytochemistry to localize the vesicular monoamine transporter-2 (VMAT2), a novel marker for sites of intracellular monoamine storage, within identified dopaminergic (tyrosine hydroxylase-containing) neurons in the rat SN and VTA. In dopaminergic perikarya, immunogold labeling for VMAT2 was localized to the Golgi apparatus, tubulovesicles that resembled smooth endoplasmic reticulum (SER), and the limiting membranes of multivesicular bodies. In dopaminergic dendrites, VMAT2 was extensively localized to tubulovesicles that resembled saccules of SER, and less frequently localized to isolated small synaptic vesicles (SSVs) or large dense-core vesicles (DCVs). In rare cases, VMAT2-immunoreactive SSVs were clustered within the cytoplasm of an SN or a VTA dendrite. Dopaminergic dendrites in the VTA contained a significantly higher number of immunogold particles for VMAT2 per unit than those in the SN. Together, these observations support the proposal that dopamine is stored in and may be released from dendritic SSVs and DCVs, but suggest that the SER is the major site of dopamine storage within midbrain dopaminergic neurons. In addition, they provide new evidence that dopaminergic dendrites in the VTA may have greater potential for reserpine-sensitive storage and release of dopamine than those in the SN.
已知中脑多巴胺能神经元可从位于黑质（SN）和腹侧被盖区（VTA）的胞体和/或树突释放多巴胺。然而，关于这些区域中胞体树突状多巴胺储存的亚细胞位点存在相当大的争议。在本研究中，我们使用双标记电子显微镜免疫细胞化学方法，在大鼠SN和VTA中已鉴定的多巴胺能（含酪氨酸羟化酶）神经元内定位囊泡单胺转运体2（VMAT2），这是一种细胞内单胺储存位点的新型标记物。在多巴胺能胞体中，VMAT2的免疫金标记定位于高尔基体、类似滑面内质网（SER）的管状小泡以及多囊泡体的界膜。在多巴胺能树突中，VMAT2广泛定位于类似SER囊泡的管状小泡，较少定位于孤立的小突触小泡（SSV）或大的致密核心囊泡（DCV）。在罕见情况下，VMAT2免疫反应性SSV聚集在SN或VTA树突的细胞质内。VTA中的多巴胺能树突每单位所含VMAT2免疫金颗粒数量明显高于SN中的。总之，这些观察结果支持多巴胺储存于树突状SSV和DCV并可能从中释放的观点，但表明SER是中脑多巴胺能神经元内多巴胺储存的主要位点。此外，它们提供了新的证据，表明VTA中的多巴胺能树突比SN中的多巴胺能树突在利血平敏感的多巴胺储存和释放方面可能具有更大的潜力。
