Debski E A, Constantine-Paton M
Biology Department, Yale University, New Haven, CT 06511.
Brain Res Dev Brain Res. 1993 Mar 19;72(1):21-39. doi: 10.1016/0165-3806(93)90156-5.
Accessibility in early development and the presence of a retinotopic map have made the amphibian optic tectum a popular system for exploration of the role of synaptic function in central map refinement. Although a great deal is known about the development of retinal innervation of the tectum, little information exists about the development of non-retinal tectal inputs. Since these other afferent systems may contribute to the synaptic drive of developing tectal cells and thereby be involved in the activity-dependent refinement of the retinotectal map, we sought to determine whether these inputs are present at the early tadpole stages when the first retinal axons refine their synaptic order within the tectal neuropil. Rhodamine-labelled latex beads, retrogradely transported from injection sites in the optic tecta, were used to identify tectal afferent projections. Projection patterns in very young tadpoles were identical to those found in juvenile frogs and heavily labelled regions included areas of the posteroventral tegmental field, the posterior tuberculum, the ventromedial thalamic nucleus, the ventral part of the ventrolateral thalamic nucleus, the suprachiasmatic nucleus and discrete regions within the central and anterior thalamic nuclei. Ipsilateral nucleus isthmi cells were also labelled, indicating the existence of an isthmo-tectal projection in even the youngest animals examined. Additionally, substance P-like immunoreactive tecto-isthmal fibers were traced from the optic tectum to the nucleus isthmi. The presence of these connections suggests that feedback from the nucleus isthmi and/or input from the other brain areas projecting to the tectum may play a role in modulating the cellular mechanisms that underlie the formation of the visual map.
在早期发育过程中的可及性以及视网膜拓扑图的存在，使得两栖类动物的视顶盖成为探索突触功能在中枢地图精细化过程中作用的热门系统。尽管人们对顶盖的视网膜神经支配发育已经了解很多，但关于非视网膜顶盖输入的发育情况却知之甚少。由于这些其他传入系统可能会对发育中的顶盖细胞的突触驱动产生影响，从而参与视网膜顶盖图的活动依赖性精细化过程，我们试图确定在最早的蝌蚪阶段，当第一批视网膜轴突在顶盖神经毡内完善其突触顺序时，这些输入是否存在。从视顶盖的注射部位逆行运输的罗丹明标记乳胶珠被用于识别顶盖传入投射。极幼龄蝌蚪的投射模式与幼蛙中的模式相同，标记密集的区域包括后腹侧被盖区、后结节、腹内侧丘脑核、腹外侧丘脑核腹侧部分、视交叉上核以及中央和前丘脑核内的离散区域。同侧峡核细胞也被标记，这表明在所检查的最幼龄动物中也存在峡核 - 顶盖投射。此外，从视顶盖追踪到峡核的P物质样免疫反应性顶盖 - 峡核纤维也被发现。这些连接的存在表明，峡核的反馈和/或其他投射到顶盖的脑区的输入可能在调节视觉地图形成的细胞机制中发挥作用。
