Behavioral, Electrophysiological and Immunohistochemical Study on the Neuronal Plasticity of the Visual System in the Rat with Monocular Enucleation

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In a series of our behavioral and electrophysiological experiments, it has been demonstrated that monocular enucleation in early postnatal days results in expanded uncrossed visual pathways (expanded UXVPs) to the ipsilateral visual cortex, both via the dorsal lateral geniculate nucleus (LGNd) and via the superior colliculus (SC) in the albino rat. The present study was then aimed to elucidate the function of the expanded UXVPs by evaluating the grating visual acuity and to investigate the neural mechanism of the expanded UXVPs by way of c-fog immunohistochemistry, and the following findings were obtained.1. In the behavioral experimet using a vertical-horizontal discrimination learning, the grating visual acuity of the UXVPs was 0.73 cycles/degree in the rat with monocular enucleation at birth (OEB) and 0.44 in the rat monocularly enucleated at maturity (OET), indicating that the expanded UXVPs results high visual resolution capacity in OEBs.2. In the immunohistochemical experiment, patterned visual stimulation was used to investigate the feasibility of stimulus-dependent induction of the immediate early gene c-fos in neurons of the UXVPs following callosal transection. The 50 mu m-thick coronal sections were incubated with the primary antiserum raised in sheep against the Fos protein, and then with biotinylated rabbit anti-sheep secondary antibody, and with the avidin biotinylated horseradish peroxidase complex. The DAB reaction was intensified with nickel ammonium sulfate. In the expanded UXVPs of the OEB rat, the Fos-like immunoreactive (FLI) cells were substantially detected in the stratum griseum superficiale (SGS) of the SC and the visual cortex (VC), whereas patterned visual stimulation induced only few FLI neurons in the SGS and the VC of the regular UXVPs of the OET rat,