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  • Title: Ibotenic acid lesions of the substantia nigra pars reticulata ipsilateral to a visual cortical lesion fail to restore visual orienting responses in the cat.
    Author: Ciaramitaro VM, Wallace SF, Rosenquist AC.
    Journal: J Comp Neurol; 1997 Jan 27; 377(4):596-610. PubMed ID: 9007195.
    Abstract:
    Unilateral removal of all known visual cortical areas in the cat renders the animal hemianopic in the contralateral visual field as measured by visual perimetry and other behavioral tests. We have shown that visual orientation behavior can be restored to the previously blind hemifield by destruction of a critical zone in the substantia nigra pars reticulata contralateral to a cortical lesion (Wallace et al., J. Comp. Neurol. 296:222-252, 1990). The model proposed to explain this recovery postulates that damage to the crossed nigrotectal projection disinhibits the superior colliculus ipsilateral to the cortical lesion and this leads to recovery. If disinhibition can account for recovery, then destruction of the uncrossed nigrotectal projection, which is known to exert a tonic inhibition on the superior colliculus, should also result in recovery. We made unilateral visual cortical ablations and ipsilateral ibotenic acid lesions of the substantia nigra pars reticulata. Visual orienting behavior was assessed in animals for a period of 4 to 31 weeks. Contrary to the prediction of the model, we failed to observe a recovery of visual orienting behavior in the blind hemifield in any of 23 animals.
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