Smiley J F, Williams S M, Szigeti K, Goldman-Rakic P S
Section of Neurobiology, Yale School of Medicine, New Haven, Connecticut 06510.
J Comp Neurol. 1992 Jul 15;321(3):325-35. doi: 10.1002/cne.903210302.
The distribution and synaptic connections of dopamine axons were studied by light and electron microscopy in human cerebral cortex. For this purpose, dopamine immunoreactivity was characterized in apparently normal anteriolateral temporal cortex, which was removed to gain access to the medial temporal lobe during tumor excision or treatment of epilepsy. Nissl sections showed this to be granular neocortex. Dopamine fibers were distributed throughout this cortex, although there were relatively more fibers in layers I-II and in layers V-VIa, compared to layers III-IV and VIb, resulting in a bilaminar pattern of labeling. In all layers, fibers were seen to form numerous varicosities, and to vary in size from thick to very fine. Fibers were relatively straight, sparsely branched and were oriented in various planes within the cortex. However, in layer I, they often ran parallel to the pial surface. In order to analyze the functional interactions of dopamine fibers, individual cortical layers were surveyed for dopamine synapses. These were usually symmetrical (Gray's type II), although 13% of them were asymmetrical. Approximately 60% of dopamine synapses were made with dendritic spines, and 40% with dendritic shafts, and this ratio was similar in all layers. On both spines and shafts, it was common to see dopamine synapses closely apposed to an unlabeled asymmetric input, suggesting a dopamine modulation of excitatory input. Some postsynaptic dendritic shafts had features of pyramidal cells, including formation of spines. Since pyramidal cells are the major type of cortical spiny neuron, they probably represent the main target of dopamine synapses in this cortex. There were also dopamine profiles apposed to membrane densities on unlabeled axon terminals, suggesting another type of synaptic interaction. These findings provide the first documentation of dopamine synapses in the human cortex, and show that they form classical synaptic junctions. The location of these synapses on spines and distal dendrites, and their proximity to asymmetric synapses, suggest a modulatory role on excitatory input to pyramidal cells.
通过光学显微镜和电子显微镜研究了多巴胺轴突在人类大脑皮质中的分布及突触连接。为此，对明显正常的前外侧颞叶皮质进行多巴胺免疫反应特性分析，该皮质是在肿瘤切除或癫痫治疗过程中为暴露内侧颞叶而切除的。尼氏染色切片显示这是颗粒状新皮质。多巴胺纤维分布于整个该皮质，不过与III - IV层和VIb层相比，I - II层和V - VIa层中的纤维相对较多，形成了双分层标记模式。在所有层中，可见纤维形成众多膨体，其大小从粗到非常细不等。纤维相对较直，分支稀疏，在皮质内呈不同平面取向。然而，在I层，它们常与软脑膜表面平行排列。为分析多巴胺纤维的功能相互作用，对各个皮质层进行了多巴胺突触检测。这些突触通常是对称的（格雷氏II型），不过其中13%是不对称的。约60%的多巴胺突触与树突棘形成，40%与树突干形成，且该比例在所有层中相似。在树突棘和树突干上，常见多巴胺突触紧邻未标记的不对称输入，提示多巴胺对兴奋性输入有调节作用。一些突触后树突干具有锥体细胞的特征，包括形成树突棘。由于锥体细胞是皮质棘状神经元的主要类型，它们可能是该皮质中多巴胺突触的主要靶点。也有与未标记轴突终末上的膜致密物相邻的多巴胺结构，提示另一种突触相互作用类型。这些发现首次记录了人类皮质中的多巴胺突触，并表明它们形成经典突触连接。这些突触在树突棘和远端树突上的位置，以及它们与不对称突触的接近程度，提示对锥体细胞兴奋性输入有调节作用。
