Visual deprivation in adulthood engages presynaptic plasticity of thalamocortical synapses

Synaptic plasticity between neurons in first order thalamus and layer 4 cortex is greatest during an early postnatal critical period and was thought to decrease irreversibly with age. However, here we show that robust and reversible plasticity can be induced in adult mice at synapses between dLGN axons and visual cortex layer 4 neurons by prolonged dark exposure (DE) and light reintroduction (LRx). Unexpectedly, the experience-dependent change in synaptic strength was mediated by a change in presynaptic structure, organization and function. DE/LRx declusters/clusters synaptic vesicles and reorganizes presynaptic molecular geometry. Furthermore, DE/LRx decreases/increases visually-evoked and spontaneous calcium signaling and neurotransmitter release probability in dLGN axonal boutons. The presynaptic plasticity mechanism described here has a high threshold for engagement which would allow maintenance of synapse stability across a wide activity range, and reactivation of thalamocortical plasticity in extraordinary conditions.