Altered neuronal activity patterns in the visual cortex of the adult rat after partial optic nerve crush--a single-cell resolution metabolic mapping study.

Thallium autometallography (TIAMG) is a novel method for high-resolution mapping of neuronal activity. With this method, we found that a general depression of neuronal activity occurs in response to optic nerve crush (ONC) within the first 2 weeks postinjury in the contralateral dorsal lateral geniculate nucleus (dLGN) as well as in the contralateral primary visual cortex (V1). Interestingly, the neuronal activity recovered thereafter in both brain regions and reached a plateau in the tenth week postinjury in layers IV and V of V1, monocular area (V1m). Several clusters of highly active neurons in V1m were found 6 weeks after ONC in layers IV and V on the side contralateral to the lesion. We reasoned that these clusters appeared due to a reorganization of the corticocolliucular projections. Employing a combination of biotinylated dextran amine retrograde tract tracing from the superior colliculus (SC) with TIAMG in the same animal, we indeed found that the clusters of neurons with high Tl(+) uptake in V1m are spatially in register with those neuronal subpopulations that project to the SC. These data suggest that extensive reorganization plasticity exists in the adult rat visual cortex following ONC.