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Fig. 1. The scaffold of axon tracts in the embryonic Xenopus forebrain. (A) The major axon tracts and nuclei of the Xenopus forebrain at 40 h post-fertilization are represented schematically to show the bilateral symmetry of the axon scaffold. The rostral end of the neural tube is curved about the cephalic flexure (c.f.). The dorsal surface of the diencephalon contains the epiphysis (epi). For abbreviations, see below. (B) Double-immunolabeling of control Xenopus forebrains for the NOC-2+ subpopulation of axons (red) and acetylated α-tubulin to show all axons (blue). Axons expressing both NOC-2 and acetylated α-tubulin appear pink. (C) Schematic representation of the trajectory of the NOC-2+ subpopulation of axons in one half of the Xenopus forebrain (arrows). This trajectory is bilaterally symmetrical. The axons in each brain hemisphere arise in the nPT and course within the AC, POC, SOT, ventral TPOC, VLT and VC. Scale bar = 60 μm. AC, anterior commissure; POC, post-optic commissure; nPT, nucleus of the presumptive telencephalon; nTPOC, nucleus of the tract of the post-optic commissure; SOT, supraoptic tract; TPOC, tract of the post-optic commissure; DVDT, dorsoventral diencephalic tract; epi, epiphysis; nTPC, nucleus of the tract of the posterior commissure, PC, posterior commissure; TPC, tract of the posterior commissure; VC, ventral commissure; VLT, ventral longitudinal tract. |
