Bevan M D, Francis C M, Bolam J P
MRC Anatomical Neuropharmacology Unit, Oxford, United Kingdom.
J Comp Neurol. 1995 Oct 23;361(3):491-511. doi: 10.1002/cne.903610312.
Neurons of the subthalamic nucleus play a key role in the normal physiology and the pathophysiology of the basal ganglia. In order to understand better how the activity of subthalamic neurons and hence the output of the basal ganglia are controlled, we have reexamined the topography and examined in detail the synaptology and neurochemical nature of the two major excitatory projections to the subthalamic nucleus, that from the cortex and from the parafascicular nucleus of the thalamus. The approach was to use anterograde neuronal tracing and postembedding immunocytochemistry for amino acid transmitters. In confirmation of previous findings the cortical and thalamic projections were topographically organized, although the topography was more finely organized, and the projections more extensive, than previously demonstrated. Cortical and thalamic terminals made asymmetrical synaptic contacts with the dendrites and spines of subthalamic neurons. The thalamic terminals contacted larger postsynaptic targets, and therefore presumably more proximal regions of subthalamic neurons, than did the cortical terminals. Quantitative analysis of the postembedding immunolabelled sections revealed that the cortical and thalamic terminals were significantly enriched in glutamate-immunoreactivity when compared to identified gamma-aminobutyric acid (GABA)-positive terminals, supporting physiological studies that suggest that these projections use glutamate as their neurotransmitter. In addition a small population of nonanterogradely labelled terminals that formed asymmetrical synapses and were immunopositive for GABA were identified. A larger population of terminals that formed symmetrical synapses were also immunopositive for GABA and were probably derived from the globus pallidus. The latter type of terminal was found to make convergent synaptic input with cortical or thalamic terminals on the dendrites and spines of subthalamic neurons, indicating that the "indirect pathways" by which information flows through the basal ganglia converge at the level of individual neurons in the subthalamic nucleus.
底丘脑核的神经元在基底神经节的正常生理学和病理生理学中起着关键作用。为了更好地理解底丘脑神经元的活动以及基底神经节的输出是如何被控制的，我们重新审视了其拓扑结构，并详细研究了投射到底丘脑核的两条主要兴奋性投射的突触学和神经化学性质，这两条投射分别来自皮层和丘脑束旁核。研究方法是使用顺行性神经元追踪技术以及针对氨基酸递质的包埋后免疫细胞化学方法。正如之前研究所证实的，皮层和丘脑的投射具有拓扑结构组织，尽管这种拓扑结构比之前所显示的更加精细，投射范围也更广。皮层和丘脑的终末与底丘脑神经元的树突和棘形成不对称性突触联系。与皮层终末相比，丘脑终末与更大的突触后靶点接触，因此推测与底丘脑神经元更靠近近端的区域接触。对包埋后免疫标记切片的定量分析显示，与已确定的γ-氨基丁酸（GABA）阳性终末相比，皮层和丘脑终末的谷氨酸免疫反应性显著增强，这支持了生理学研究，即表明这些投射以谷氨酸作为神经递质。此外，还鉴定出一小部分未被顺行标记的终末，它们形成不对称突触且对GABA免疫阳性。大量形成对称性突触的终末也对GABA免疫阳性，可能来自苍白球。发现后一种类型的终末在底丘脑神经元的树突和棘上与皮层或丘脑终末形成汇聚性突触输入，这表明信息流经基底神经节的“间接通路”在底丘脑核的单个神经元水平上汇聚。
