Hoogland P V, Wouterlood F G, Welker E, Van der Loos H
Department of Anatomy, Vrije Universiteit, Amsterdam, The Netherlands.
Exp Brain Res. 1991;87(1):159-72. doi: 10.1007/BF00228517.
By means of tracing with the lectin Phaseolus-vulgaris leucoagglutinin (PHA-L), we examined in the thalamus of the mouse, the axon terminals of fibers originating in the barrel cortex. Vibratome sections of the brain were subjected to PHA-L immunocytochemistry and processed for light and electron microscopy. We observed small (0.5-0.8 microns in diameter) varicosities of labeled fibers in the nucleus ventrobasalis (VB) and the nucleus posterior (PO) as well as labeled giant terminals (3-5 microns in diameter) in PO. The analysis involved examination of serial sections and computer-aided reconstruction of several terminals. The small varicosities in VB appear to be small axon terminals forming distinct asymmetric synapses with small dendritic profiles. Some labeled terminals are apposed to, but not synaptically related with, the cell bodies of neurons in VB that are retrogradely labeled with PHA-L. The small varicosities seen with the light microscope in PO are terminals forming asymmetric synapses with dendritic shafts. The giant terminals in PO appear as large, vesicle-filled profiles forming part of synaptic glomeruli, i.e. complexes of one corticothalamic terminal engulfing several excrescences of a single dendrite. A giant terminal forms several asymmetric synapses (about 8) with these excrescences, as well as numerous (up to 15) puncta adhaerentia. The glomeruli are enveloped in glial lamellae, and they are often found at the bifurcations of primary dendritic segments. We suggest that the small terminals in VB are in the service of feedback signalling from the barrel cortex to its principal thalamic relay nucleus; the functional importance of this projection may reside in increased spatio-temporal discrimination. We interpret the giant terminals in PO as elements serving feed-forward processing, allowing the barrel cortex to influence, via PO, parts of the motor pathway modulating the animal's ongoing behavior.
通过用凝集素菜豆白细胞凝集素（PHA-L）进行追踪，我们在小鼠丘脑内检查了起源于桶状皮层的纤维的轴突终末。对脑振动切片进行PHA-L免疫细胞化学处理，并进行光镜和电镜观察。我们在腹后内侧核（VB）和后核（PO）中观察到标记纤维的小（直径0.5 - 0.8微米）膨体，以及在PO中标记的巨大终末（直径3 - 5微米）。分析包括对连续切片的检查以及几个终末的计算机辅助重建。VB中的小膨体似乎是与小的树突轮廓形成明显不对称突触的小轴突终末。一些标记终末与用PHA-L逆行标记的VB中神经元的胞体相邻，但无突触联系。在光镜下在PO中看到的小膨体是与树突干形成不对称突触的终末。PO中的巨大终末表现为大的、充满囊泡的轮廓，形成突触小球的一部分，即一个皮质丘脑终末包绕单个树突的几个赘生物的复合体。一个巨大终末与这些赘生物形成几个不对称突触（约8个），以及许多（多达15个）粘着斑。突触小球被神经胶质板包裹，并且它们经常出现在初级树突段的分支处。我们认为VB中的小终末用于从桶状皮层向其主要丘脑中继核的反馈信号传递；该投射的功能重要性可能在于增强时空辨别能力。我们将PO中的巨大终末解释为用于前馈处理的元件，使桶状皮层能够通过PO影响调节动物当前行为的运动通路的部分。
