Postnatal development of geniculocortical projections in the tree shrew

We examined the postnatal development of retrogradely labeled cells in the tree shrew lateral geniculate nucleus (LGN) following cortical injections of horseradish peroxidase. Results show that at birth (P0) when the LGN is still unlaminated: (1) the mature proportion of relay cells and interneurons already exists, (2) relay cells present are larger than interneurons, and (3) relay cells are topographically connected with the cortex. Aside from changes in absolute LGN soma size, the primary postnatal change noted (from P0 to P7) was an apparent decline in the relative width of the labeled LGN projection column, suggesting a refinement in topography.