Williams, Adrian Lloyd; (2000) Growth dynamics in the developing lateral geniculate nucleus. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Binocularly segregated maps develop from stages where projections from the two eyes initially overlap. Differential growth of the lateral geniculate nucleus may regulate their segregation. This hypothesis has been tested using novel shape modelling techniques to quantify the 3D structure of the ferret LGN at successive developmental stages. Spatio-temporal aspects of LGN shape change have been compared with different measurements of its cellular population. Mature shape arises prior to the full maturation of its cellular constituents, and is probably influenced by the substantial volumetric expansion which occurs to the nucleus. Cellular bodies contribute little to volumetric expansion, and it is suggested that non-somatic factors such as axon arbors, or the late proliferation of glial cells play a more important role. The nucleus rotates laterally by 70° during the first three postnatal weeks. Prior to evaluating spatial shape changes, LGN models were normalised to account for rotation. Specific patterns of shape change transpire, consistent with the nucleus accommodating ocular segregation. Following segregation, only isotropic growth occurs. It has not been possible to show a dependant relationship between LGN growth and ocular segregation, either in terms of model transformations, or local changes between LGN structure and terminal field regions. The role of retinal afferents in regulating LGN shape and its cellular population have been explored using monocular enucleation. Varying degrees of abnormalities occur to the cellular population, but contributions made by cells to LGN growth are similar to the normal animal. LGN structure does not develop fully, and the temporal course of shape change is considerably advanced. The results demonstrate that a possible role for differential LGN growth in ocular segregation cannot be ruled out.

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