RESUMO
We studied the attributes of cytochrome c oxidase (CytOx)-rich blobs and ocular dominance columns (OD) in human V1 associated with monocular retinal lesions. Interblob distance, blob cross-sectional area, OD width, and OD arrangement pattern were analyzed in CytOx-reacted tangential sections of flat-mounted V1 preparations. Monocular deprivation induces differential expression of CytOx in the corresponding ODs in V1. We were thereby able to identify the V1 regions associated with the lesioned area in the retina, assign which OD was associated with each eye, and assign the corresponding blob in Layer III as deprived or nondeprived of visual input. We found that nondeprived blobs are more conspicuously stained than blobs outside the lesioned area. Notably, we found a selective expansion of blobs associated with the nonlesioned eye, whereas blobs associated with the deprived eye showed no significant change in size. Blob size in the latter condition was similar to the one observed in normal participants. These effects were present throughout the representation of the lesion in V1, suggesting that the underlying plasticity mechanisms do not depend on eccentricity. Retinal lesion caused no change in interblob distance, which was comparable to the normal brain (i.e., participants with no retinal lesion). This indicates that blob center is a stable hallmark of cortical organization. Finally, the width of ODs associated with the nonlesioned eye tended to be larger compared with ODs of the lesioned eye. However, this effect did not reach statistical significance. The stability of ODs thereby contrasts with blob plasticity, suggesting that the retinal lesion-triggered imbalance in the thalamocortical projection to Layer IVc has a limited impact on OD CytOx reactivity. On the other hand, we argue that ocular imbalance supports intracortical lateral competition that increases CytOx reactivity in the periblob region associated with the nonlesioned eye, accounting for the blob expansion we observe.
RESUMO
We studied the time course of changes of cytochrome oxidase (CytOx) blob spatial density and blob cross-sectional area of deprived (D) and nondeprived (ND) portions of V1 in four capuchin monkeys after massive and restricted retinal laser lesions. Laser shots at the border of the optic disc produced massive retinal lesions, while low power laser shots in the retina produced restricted retinal lesions. These massive and restricted retinal lesions were intended to simulate glaucoma and diabetic retinopathy, respectively. We used a Neodymium-YAG dual frequency laser to make the lesions. We measured Layer III blobs in CytOx-reacted tangential sections of flat-mounted preparations of V1. The plasticity of the blob system and that of the ocular dominance columns (ODC) varied with the degree of retinal lesions. We found that changes in the blob system were different from that of the ODC. Blob sizes changed drastically in the region corresponding to the retinal lesion. Blobs were larger and subjectively darker above and below the non deprived ODC than in the deprived columns. With restricted lesions, blobs corresponding to the ND columns had sizes similar to those from non-lesioned areas. In contrast, blobs corresponding to the deprived columns were smaller than those from nonlesioned areas. With massive lesions, ND blobs were larger than the deprived blobs. Plastic changes in blobs described here occur much earlier than previously described.
