Freund T F, Martin K A, Somogyi P, Whitteridge D
J Comp Neurol. 1985 Dec 8;242(2):275-91. doi: 10.1002/cne.902420209.
The precise location of physiologically identified specific afferent input on the different types of cell in the visual cortex and the identification of the neurotransmitters of these cells are essential to a better understanding of the first stage of cortical processing. A combination of anatomical, neurochemical, and physiological methods was used to identify the cortical neurones that receive synaptic input from X- and Y-type afferents, which are thought to originate from cells of the lateral geniculate nucleus. One method relied on chance contacts made between single physiologically characterised axons, which had been injected with horseradish peroxidase (HRP), and the processes of cells impregnated by the Golgi method. These experiments revealed that both X and Y axons formed synapses on the dendrites of spiny stellate cells in layer 4. Y axons in both areas 17 and 18 established multiple synaptic contacts on basal dendrites of layer 3 pyramidal cells. One X axon contacted the apical dendrite of a layer 5 pyramidal cell and one Y axon contacted the dendrite of a large cell with smooth dendrites in layer 3. The maximum number of synapses made between one axon and a single postsynaptic cell was eight, although in most cases it was only one. It was concluded that one axon only provides a small fraction of the geniculate afferent input to an individual cell. A second method revealed that the somata in layer 4 in synaptic contact with the HRP-filled axon terminals were GABA-immunoreactive, and therefore might be involved in inhibitory processes. From light microscopic data it was found that somata receiving contacts from X axons in area 17 were significantly smaller (average diameter 15 microns) than those contacted by the Y axons in areas 17 and 18 (average diameter 24 microns). Somatic contacts were extremely rare in layer 6. These data show that the X and Y afferents may activate separate subsets of inhibitory neurones.
在视觉皮层中，生理上确定的特定传入输入在不同类型细胞上的精确位置以及这些细胞的神经递质的确定，对于更好地理解皮层处理的第一阶段至关重要。结合解剖学、神经化学和生理学方法来识别接受来自X型和Y型传入纤维突触输入的皮层神经元，这些传入纤维被认为起源于外侧膝状体核的细胞。一种方法依赖于单个经生理特征化的轴突（已注射辣根过氧化物酶（HRP））与用高尔基方法浸渍的细胞的突起之间的偶然接触。这些实验表明，X轴突和Y轴突都在第4层棘状星状细胞的树突上形成突触。17区和18区的Y轴突在第3层锥体细胞的基底树突上建立了多个突触联系。一条X轴突与第5层锥体细胞的顶树突接触，一条Y轴突与第3层中具有光滑树突的大细胞的树突接触。一条轴突与单个突触后细胞之间形成的突触的最大数量为8个，尽管在大多数情况下只有1个。得出的结论是一条轴突只为单个细胞提供一小部分膝状体传入输入。第二种方法表明，与充满HRP的轴突终末有突触接触的第4层细胞体是GABA免疫反应性的，因此可能参与抑制过程。从光学显微镜数据发现，17区接受X轴突接触的细胞体（平均直径15微米）明显小于17区和18区接受Y轴突接触的细胞体（平均直径24微米）。在第6层中体细胞接触极为罕见。这些数据表明，X和Y传入纤维可能激活抑制性神经元的不同亚群。
