Effects of neonatal corticosterone and environmental enrichment on retinal ERK1/2 and CREB phosphorylation in adult mice

Exposure to Stimulating Environments (SE) during development may improve neuroplasticity in central nervous system, protect against neurotoxic damage, and promote neuronal recovery in adult life. While biochemical mechanisms of SE-promoted neuronal plasticity are well known in the brain, much less is known on the signaling cascade governing plasticity and neuroprotection in the retina. In order to investigate if in the retina signaling molecules involved in neuronal plasticity are affected by SE, neonatal CD-1 mice were exposed to moderate corticosterone levels (NC), supplemented through maternal milk during the first postnatal week, or to environmental enrichment (EE) conditions (physical and social stimuli) from early adolescence. Our results showed that both NC and EE increased the phosphorylation level of Extracellularly Regulated Kinase 1/2 (ERK1/2) and cAMP response element-binding protein (CREB) in the adult retinal tissue. Furthermore, we observed that activated ERK1/2 was restricted to Müller cells, while pCREB was mostly present in the nuclei of retinal neurons. Neither NC, nor EE modified the expression of GFAP, a marker of Müller cells activation. In conclusion our results indicate that both NC and EE activate ERK1/2 and CREB in the retina and provide a biochemical background for the neuroprotective activity exerted by SE against retinal damage. Furthermore, they support the role of Müller glia as a key cell determinant of retinal neuroplasticity.