Synaptic adjustment after deafferentation of the superior colliculus of the rat.

Eyes were removed from rats shortly after birth, when there are few formed synapses in the colliculus. It was found that synaptogenesis continues to give a near-normal ratio of terminals containing either spheroidal or flattened vesicles. After eye removal in adult rats, however, reinvasion of synaptic sites vacated by degenerate optic terminals occurs, with an incomplete return toward a normal proportion of synaptic types.