Activity-dependent plasticity in the visual systems of frogs and fish

The retinotectal system of lower vertebrates has provided considerable insight into the cellular mechanisms underlying the development and maintenance of orderly visual projections to the brain. This review will briefly summarize some of the data on the activity-dependent components of these mechanisms and incorporate the data into a model for selective synapse stabilization of coactive synapses. The model, based on the Hebbian synapse, is similar to models of long-term potentiation (LTP) of synaptic transmission, which are thought to account for the increased synaptic efficacy observed after associative conditioning paradigms. However, more recent data from two studies, one using confocal microscope analysis of migrating retinal arbors in vivo and the other investigating the requirement for protein kinase activity in map formation, point to a possible divergence in the cellular events underlying synapse stabilization in the developing visual system of the frog and LTP in the mammalian hippocampus.