Increased dependence of superior colliculus metabolic activity on visual cortex after eye enucleation

Metabolic activity, as previously shown by the 2-deoxy-D-[14C]glucose technique, is depressed in the superior colliculus after eye enucleation and recovers substantially by 30 days. To determine whether or not this recovery involves an increase in visual cortex control over superior colliculus metabolic activity, rats that had undergone either monocular or binocular enucleation 30 days earlier received visual cortex ablations. In the monocularly enucleated group, a bilateral visual cortex lesion produced greater depression in the recovered superior colliculus than in the opposite control colliculus, and increased the metabolic differences between the two colliculi compared with those of rats recovered from monocular enucleation but cortically intact. In the binocularly enucleated group a unilateral cortex lesion produced greater ipsilateral depression than did the same ablation in the otherwise intact rat. These findings led to the conclusion that the recovery in the superior colliculus that follows eye enucleation involved an increase in cortical control over metabolic activity.