Stages of growth of hamster retinofugal axons: implications for developing axonal pathways with multiple targets

摘要: Neurons in many regions of the CNS (e.g., cortical areas, thalamic nuclei) are heterogeneous with regard to their afferent and efferent connections. Using hamster retinofugal system as a model, we investigated mechanisms by which such connectional heterogeneity arises during ontogeny. Retinal ganglion cell axons were labeled 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (Dil) paraformaldehyde-fixed tissue. The fluorescent label was photoconverted diaminobenzidine reaction product. morphology axons, including trajectories, branching patterns, growth cones, studied at level dorsal lateral geniculate nucleus (LGd) from embryonic day 14 adulthood. In adult hamsters, retinal cells (RGCs) spatially segregated into superficial optic tract, situated just beneath pia, an internal tract consisting fascicles running parallel pia within geniculate. All project midbrain, but only emit collaterals LGd. During development, both divisions LGd, postnatal 15, virtually entirely eliminated, whereas those have elaborated terminal arbors. Thus, among different classes RGCs respect connections emerges selective stabilization, each class, unique subset initially widespread set shared all classes. Thalamic RGC emerge along established axon trunks, not bifurcation growing tip. This occurs after grown past thalamus and, presumably, entered targets midbrain. Growth cones tips elongating trunks larger size more “complex” compared on collaterals. Axons develop 3 morphologically distinct states. First, they elongate most distant Then, simultaneously unbranched or poorly branched multiple targets. Finally, elaborate arbors definitive eliminate other developmental strategy may be paradigmatic for formation long pathways Furthermore, these data document, single-axon level, steps elaboration withdrawal transient neuronal projections.