Environmental enrichment promotes fiber sprouting after deafferentation of the superior colliculus in the adult rat brain.

Exposure to an enriched environment has proven to be beneficial in the recovery of function after brain lesions, but the underlying mechanisms remain only partly understood. One possibility is that environmental enrichment stimulates the reorganization of areas and fiber tracts that have been spared by the injury. Here we evaluate the effects of enriched environment on the sprouting of undamaged retinal afferents into the deafferented superior colliculus (SC) after a partial retinal lesion in adult rats. Anterograde tracing of retinal axons demonstrated a significant increase in fiber sprouting in the denervated SC of animals reared in enriched environment compared to animals reared in standard conditions. Environmental enrichment also promoted a substantial recovery of synaptic sites within the deafferented SC as shown by both synapsin I and vesicular glutamate transporter 2 immunostaining. These data provide evidence that environmental enrichment stimulates axonal plasticity and synaptic reorganization following brain injury.