A novel means of Y cell identification in the developing lateral geniculate nucleus of the cat

We examined the postnatal development of putative Y cells in the dorsal lateral geniculate nucleus (dLGN) using the SMI-32 antibody, which has been demonstrated in the adult cat to stain cells with Y cell morphology. At birth, SMI-32 stained cells were concentrated in the interlaminar zones. During postnatal development, the SMI-32 staining gradually becomes more disperse and by P21 stained cells are found throughout the A and magnocellular C laminae. By the end of the first postnatal week, and in all later ages examined, the SMI-32 stained cells were significantly larger than the overall population of Nissl stained cells and interneurons (stained with an antibody against glutamic acid decarboxylase). Postnatal SMI-32 staining revealed a dramatic increase in soma sizes and the expansion of putative geniculate Y cell dendritic arbors that continued past the second postnatal month. In contrast, the growth of interneurons appeared to be complete by 3-4 postnatal weeks, at which time cell somas stained with SMI-32 have only reached a little over one half of their adult size. Similar to the adult cat, SMI-32 appears to selectively stain the Y cell population during development and may provide a useful morphological marker to examine the participation of Y cells in the developing postnatal circuitry of the dLGN. This further establishes the cat dLGN as a novel model system to study the normal function and pathological reorganization of neurofilaments.