Reversal and stabilization of synaptic modifications in a developing visual system

Persistent synaptic modi. cations are essential for experience-dependent refinement of developing circuits. However, in the developing Xenopus retinotectal system, activity-induced synaptic modi. cations were quickly reversed either by subsequent spontaneous activity in the tectum or by exposure to random visual inputs. This reversal depended on the burst spiking and activation of the N-methyl-D-aspartate subtype of glutamate receptors. Stabilization of synaptic modi. cations can be achieved by an appropriately spaced pattern of induction stimuli. These findings underscore the vulnerable nature of activity-induced synaptic modi. cations in vivo and suggest a temporal constraint on the pattern of visual inputs for effective induction of stable synaptic modifications.