Recovery of visual behaviors in adult hamsters with the peripheral nerve graft to the sectioned optic nerve.

In adult hamsters, the autologous peripheral nerve (PN) was grafted to the sectioned optic nerve to make a bridge to the superior colliculus (SC). Three behavioral tasks were used to test functional recovery of the restored retinocollicular pathway. First, change of spontaneous ambulating activity to a decrease in environmental luminance was examined in an open field. PN-grafted hamsters showed a significant increase to 186% in ambulating activity just after light off, though it was lower than that in normal hamsters (489%). Second, a classical conditioning of total body movements was tested using an increase in luminance as a conditioned stimulus (CS) paired with foot shocks. In normal hamsters the magnitude of movements during CS increased in the acquisition period and then decreased in the extinction period in both the second and the third sessions, while the magnitude remained unchanged in a blind control. PN-grafted hamsters showed an increase in the magnitude only in the third session, although it was statistically barely significant (P = 0.0619). Following section of the grafted nerve, the conditioned response disappeared completely. And third, a shuttle-box avoidance task was examined using a flickering light as CS. Normal hamsters showed improved avoidance scores, while blind controls did not. PN-grafted hamsters showed a slight increase in the score, which was similar to that in the one-eyed control. Anterogradely transported labeling of WGA-HRP, injected into the vitreous body of the grafted eye, was observed in the graft and the superficial layers of SC. These results confirm and extend our previous finding that PN-grafted hamsters can restore some visual function and further suggest that the extent of recovered visual function is as good as in one-eyed animals.