Aim: 

Experience-dependent plasticity in the visual cortex declines after the critical period. This limits the capacity of the adult visual system to recover from pathological conditions due to developmental defects or damage. Therefore, one outstanding challenge is to find strategies enhancing plasticity in the adult. Here we report that environmental enrichment (EE) or fluoxetine treatment restore plasticity in the adult visual cortex of the rat.

Methods: 

We evaluated recovery of visual functions in adult Long-Evans hooded rats rendered amblyopic by long-term monocular deprivation and then subjected to reverse eye-lid suture (RS) under two different experimental conditions: 1) They were reared in an EE setting for 3 weeks, or 2) They were chronically treated with fluoxetine for 4 weeks (in this case, RS was performed during the last 2 weeks of antidepressant treatment). Visual acuity and ocular dominance were assessed in both groups using electrophysiological recordings or behavioural methods.

Results: 

We found that either EE and fluoxetine administration promoted a full recovery of visual functions in adult amblyopic animals. These effects were accompanied by reduced intracortical inhibition and increased expression of BDNF in the visual cortex. Cortical administration of diazepam totally prevented amblyopia recovery, indicating that the reduction of intracortical inhibition directly promotes visual cortical plasticity in the adult.

Conclusions: 

Our results highlight a potential clinical application for EE and antidepressants in neurological disorders in which neuronal plasticity is compromised because of excessive intracortical inhibition.