Expansion of suprasylvian cortex projection in the superficial layers of the superior colliculus following damage of areas 17 and 18 in developing cats.

Abstract

Tritiated proline and leucine were injected into areas 17 and 18 of intact cats and into the medial bank of the lateral suprasylvian (LS) cortex of intact cats and cats from which areas 17 and 18 had been removed on postnatal day 1 (P1), P28, or in adulthood (A). The density of label transported to the superior colliculus was quantified using image-analysis equipment. The results from the intact cats confirmed previous reports that areas 17 and 18 project most heavily to stratum zonale (SZ) and stratum griseum superficiale (SGS) and LS cortex projects most heavily to stratum opticum (SO) of the superior colliculus. However, in cats with lesions of areas 17 and 18, the projections from LS cortex showed an age-dependent reorganization. LS projections to SGS and SZ were enhanced following ablation of areas 17 and 18 on P1, and projections to SGS were enhanced following an ablation on P28. The pattern of LS-collicular projection following ablations incurred in adulthood was indistinguishable from the pattern presented by intact cats. This study demonstrates that the LS corticocollicular projection expands in SGS and possibly substitutes for inputs eliminated by the removal of areas 17 and 18 from the immature brain. This enhanced pathway may contribute to compensatory neuronal changes and to spared behaviors that accompany damage of immature cortex.