The mammalian superior colliculus (SC) and its vertebrate homologue, the optic tectum, have long been favorite models for study of developmental processes in brain. These studies range from those focusing upon the initial stages of axon outgrowth of retinal ganglion cells to those examining the final formation of topographically correct synaptic connections in the SC. The early stages in the formation of this pathway are directed by chemotaxic molecules, both attractants and repellents,
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which operate largely independently of activity or visual experience. The later stages of development, particularly the refinement of axonal connections that result in a precise topographic map of the retina onto SC, are dependent upon both impulse activity and visual experience, as well as upon a variety of signaling molecules operating at both the presynaptic terminal and within the postsynaptic target. This chapter reviews these later stages of development, including evidence for the involvement of various receptors and channels, and the changes in physiology of the synapse that accompany this refinement.