Visual input induces long-term potentiation of developing retinotectal synapses

Early visual experience is essential in the refinement of developing neural connections. In vivo whole-cell recording from the tectum of Xenopus tadpo les showed that repetitive dimming-light stimulation applied to the contral ateral eye resulted in persistent enhancement of glutamatergic inputs, but not GABAergic or glycinergic inputs, on tectal neurons. This enhancement ca n be attributed to potentiation of retinotectal synapses. It required spiki ng of postsynaptic tectal cells as well as activation of NMDA receptors, an d effectively occluded long-term potentiation (LTP) of retinotectal synapse s induced by direct electrical stimulation of retinal ganglion cells. Thus, LTP-like synaptic modification can be induced by natural visual inputs and may be part of the underlying mechanism for the activity-dependent refinem ent of developing connections.