Development of the Marsupial Primary Visual Pathway
Events underlying development of the mammalian primary visual system have only recently begun to be described in detail. Four approaches have been used. In eutherians, pioneering developments in the use of in utero surgery have allowed examination of various aspects of fetal development (e. g. rat: Bunt and Lund 1981; cat: Williams and Chalupa 1982, Shatz 1983; monkey: Rakic 1977). More recently, tissue slices of diencephalon from eutherian embryos have been maintained in vitro to study development of retino-geniculate organisation (Sretavan and Shatz 1984). Altricial mammals such as rat, hamster and ferret have also provided opportunities to study some aspects of development (e.g. Perry et al. 1983, Sengelaub et al. 1986, Linden et al. 1981); however, at birth, the visual system is advanced since optic axons invade target tissue by mid-gestation (e. g. Bunt and Lund 1983, Linden et al. 1981). By contrast, in marsupials, the eye and brain form almost entirely post-natally. Marsupials therefore provide a unique opportunity to explore events taking place at the earliest, crucial stages of central nervous system development without surgical intervention to the mother (e. g. Sanderson et al. 1982, Cavalcante and Rocha-Miranda 1978, Beazley and Dunlop 1983, Wye-Dvorak 1984, Reynolds et al. 1985, Braekevelt et al. 1986, Harman et al. 1987, Nelson 1987). Compared to eutherians, the developmental sequence in marsupials is considerably protracted (Dunlop and Beazley 1984), and allows separation of specific events.
KeywordsOptic Nerve Ganglion Cell Retinal Ganglion Cell Optic Nerve Head Ganglion Cell Layer
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