Shostak Yuri, Ding Yuchuan, Casagrande Vivien A
Department of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee 37232, USA.
J Comp Neurol. 2003 Jan 27;456(1):12-28. doi: 10.1002/cne.10436.
As in other primates, the lateral geniculate nucleus (LGN) of owl monkeys contains three anatomically and physiologically distinct relay cell classes, the magnocellular (M), parvocellular (P), and koniocellular (K) cells. M and P LGN cells send axons to the upper and lower tiers of layer IV, and K cells send axons to the cytochrome oxidase (CO) blobs of layer III and to layer I of primary visual cortex (V1). Our objective was to compare the synaptic arrangements made by these axon classes. M, P, and K axons were labeled in adult owl monkeys by means of injections of wheat germ agglutinin-horseradish peroxidase into the appropriate LGN layers. The neurochemical content of both pre- and postsynaptic profiles were identified by postembedding immunocytochemistry for gamma-aminobutyric acid (GABA) and glutamate. Our key finding is that the synaptic arrangements made by M, P, and K axons in owl monkey exhibit more similarities than differences. They are exclusively presynaptic, contain glutamate and form asymmetric synapses mainly with glutamate-positive dendritic spines. The majority of the remaining axons synapse with glutamatergic dendritic shafts. There are also differences between LGN pathways. M and P terminals are significantly larger and more likely to make multiple synapses than K axons, although M and P axons do not differ from each other in either of these characteristics. Of interest, a larger percentage of M and K axons than P axons make synapses with GABAergic dendritic shafts. Cells directly postsynaptic to M and K axons are known to exhibit orientation selectivity and, in some cases, direction selectivity. Cells postsynaptic to P axons do not show these properties, but instead tend to reflect their LGN inputs more faithfully; therefore, it is possible that these physiologic differences seen in the cortical cells postsynaptic to different LGN pathways reflect the differential involvement of inhibitory circuits.
与其他灵长类动物一样，夜猴的外侧膝状核（LGN）包含三种在解剖学和生理学上截然不同的中继细胞类型，即大细胞（M）、小细胞（P）和颗粒细胞（K）。M和P LGN细胞将轴突发送到第IV层的上下层，K细胞将轴突发送到第III层的细胞色素氧化酶（CO）斑以及初级视觉皮层（V1）的第I层。我们的目标是比较这些轴突类型形成的突触排列。通过将小麦胚芽凝集素-辣根过氧化物酶注射到成年夜猴的适当LGN层中，标记M、P和K轴突。通过对γ-氨基丁酸（GABA）和谷氨酸进行包埋后免疫细胞化学鉴定突触前和突触后轮廓的神经化学内容。我们的主要发现是，夜猴中M、P和K轴突形成的突触排列相似之处多于差异。它们仅为突触前，含有谷氨酸并主要与谷氨酸阳性树突棘形成不对称突触。其余大多数轴突与谷氨酸能树突干形成突触。LGN通路之间也存在差异。M和P终末明显大于K轴突，并且比K轴突更有可能形成多个突触，尽管M和P轴突在这两个特征上彼此没有差异。有趣的是，与P轴突相比，M和K轴突中有更大比例与GABA能树突干形成突触。已知直接位于M和K轴突突触后的细胞表现出方向选择性，在某些情况下还表现出方向选择性。位于P轴突突触后的细胞不显示这些特性，而是倾向于更忠实地反映其LGN输入；因此，在不同LGN通路突触后的皮层细胞中看到的这些生理差异可能反映了抑制性回路的不同参与情况。
