Changes during Maturation and Metamorphosis in the Synaptic Organization of the Tadpole Retina Inner Plexiform Layer

Abstract

ELECTROPHYSIOLOGICAL studies have shown that there is considerable variation in the degree of processing of visual information carried out by the retinas of different species, apparently correlated with anatomical difference between species. In amphibian and avian retinas with complex receptive fields there seem to be more conventional (amacrine cell) synapses than in mammalian retinas with simple organization. Moreover, the greater density of serial-conventional synapses, in which a presynaptic amacrine process is also postsynaptic to another amacrine process, is particularly striking in complex retinas. The density of ribbon (bipolar cell) synapses remains fairly constant from species to species¹. The fact that tadpoles apparently make little use of visual cues, whereas adult frogs depend on them for survival, suggests that electrophysiological and anatomical retinal reorganization occurs during metamorphosis. There is some evidence for this^2,3. Here I report changes in retinal synaptic organization found in Rana pipiens both during maturation and metamorphosis and as a result of a hormone pellet implantation.