Persistence of experience-induced homeostatic synaptic plasticity through adulthood in superficial layers of mouse visual cortex

It is well established that sensory cortices of animals can be modified by sensory experience, especially during a brief early critical period in development. Theoretical analyses indicate that there are two synaptic plasticity mechanisms required: input- specific synaptic modifications and global homeostatic mechanisms to provide stability to neural networks. Experience- dependent homeostatic synaptic plasticity mechanisms have subsequently been demonstrated in the visual cortex of juvenile animals. Here, we report that experiencedependent homeostatic synaptic plasticity persists through adulthood in the superficial layers of the mouse visual cortex. We found that 2 d of visual deprivation in the form of dark rearing is necessary and sufficient to cause an increase inAMPAreceptor- mediated miniature EPSC amplitude in layer 2/ 3 neurons. This increase was rapidly reversed by 1 d of light exposure. This reversible change in synaptic strength persisted in adult mice past the critical period for ocular dominance plasticity, which is reported to end at similar to 1 month of age in rodents. Interestingly, the mechanism of homeostatic synaptic modifications in 3- month- old mice differed from that in young mice ( 3 weeks old) in that the multiplicative nature of synaptic scaling is lost. Our results demonstrate that the superficial layers of adult mouse visual cortex retain the ability to undergo reversible experience- dependent homeostatic synaptic plasticity.