Fitzpatrick D, Conley M, Luppino G, Matelli M, Diamond I T
Department of Anatomy, Duke University, Durham, North Carolina 27706.
J Comp Neurol. 1988 Jun 1;272(1):43-67. doi: 10.1002/cne.902720105.
The distribution and sources of putative cholinergic fibers within the lateral geniculate nucleus (GL) of the tree shrew have been examined by using the immunocytochemical localization of choline acetyltransferase (ChAT). ChAT-immunoreactive fibers are found throughout the thalamus but are particularly abundant in the GL as compared to other principal sensory thalamic nuclei (medial geniculate nucleus, ventral posterior nucleus). Individual ChAT-immunoreactive fibers are extremely fine in caliber and display numerous small swellings along their lengths. Within the GL, ChAT-immunoreactive fibers are more numerous in the layers than in the interlaminar zones and, in most cases, the greatest density is found in layers 4 and 5. Two sources for the ChAT-immunoreactive fibers in the GL have been identified--the parabigeminal nucleus (Pbg) and the pedunculopontine tegmental nucleus (PPT)--and the contribution that each makes to the distribution of ChAT-immunoreactive fibers in GL was determined by combining immunocytochemical, axonal transport, and lesion methods. The projection from the Pbg is strictly contralateral, travels via the optic tract, and terminates in layers 1, 3, 5, and 6 as well as the interlaminar zones on either side of layer 5. The projection from PPT is bilateral (ipsilateral dominant) and terminates throughout the GL as well as in other thalamic nuclei. Lesions of the Pbg eliminate the ChAT-immunoreactive fibers normally found in the optic tract but have no obvious effect on the density of ChAT-immunoreactive fibers in the contralateral GL. In contrast, lesions of PPT produce a conspicuous decrease in the number of ChAT-immunoreactive fibers in the GL and in other thalamic nuclei on the side of the lesion but have no obvious effect on the number of ChAT-immunoreactive fibers in the optic tract. These results suggest that there are two sources of cholinergic projections to the GL in the tree shrew which are likely to play different roles in modulating the transmission of visual activity to the cortex. The Pbg is recognized as a part of the visual system by virtue of its reciprocal connections with the superficial layers of the superior colliculus, while the PPT is a part of the midbrain reticular formation and is thought to play a non-modality-specific role in modulating the activity of neurons throughout the thalamus and in other regions of the brainstem.
通过使用胆碱乙酰转移酶（ChAT）的免疫细胞化学定位技术，对树鼩外侧膝状核（GL）内假定的胆碱能纤维的分布和来源进行了研究。在整个丘脑中均发现了ChAT免疫反应性纤维，但与其他主要感觉丘脑核（内侧膝状核、腹后核）相比，GL中的此类纤维尤为丰富。单个ChAT免疫反应性纤维的管径极细，且在其长度上有许多小的膨体。在GL内，ChAT免疫反应性纤维在各层中的数量多于层间区，并且在大多数情况下，第4层和第5层中的密度最大。已确定GL中ChAT免疫反应性纤维的两个来源——副视束核（Pbg）和脑桥脚被盖核（PPT）——并通过结合免疫细胞化学、轴突运输和损伤方法，确定了它们各自对GL中ChAT免疫反应性纤维分布的贡献。来自Pbg的投射严格对侧，经视束传导，并终止于第1、3、5和6层以及第5层两侧的层间区。来自PPT的投射是双侧的（同侧占优势），并终止于整个GL以及其他丘脑核。Pbg损伤消除了视束中通常存在的ChAT免疫反应性纤维，但对同侧GL中ChAT免疫反应性纤维的密度没有明显影响。相反，PPT损伤导致损伤侧GL和其他丘脑核中ChAT免疫反应性纤维的数量显著减少，但对视束中ChAT免疫反应性纤维的数量没有明显影响。这些结果表明，树鼩中向GL投射的胆碱能纤维有两个来源，它们可能在调节视觉活动向皮层的传递中发挥不同作用。Pbg因其与上丘表层的相互连接而被视为视觉系统的一部分，而PPT是中脑网状结构的一部分，被认为在调节整个丘脑和脑干其他区域神经元的活动中发挥非模态特异性作用。
