Plasticity and interaction after ablations of visual or somatosensory motor cortex or retina in neonatal rats

Abstract

The results obtained following eye enucleation and dorsal occipital cortical (DOC) lesion in normal adult animals are in general agreement with those reported in previous work. The details, however, vary somewhat. A DOC projection to the claustrum and reticularis thalami is reported here for the first time in the rat. Six experiments were performed: (1) DOC lesions followed by eye enucleations. (2) Eye enucleations followed by DOC lesions. (3) Eye enucleations followed by sensorimotor cortical (SMC) lesions. (4) SMC lesions followed by eye enucleations. (5) DOC lesions followed by SMC lesions. (6) SMC lesions followed by DOC lesions. The results obtained from the experimental animals demonstrate a certain degree of plasticity and interaction between the DOC and retinal efferents to the superior colliculus, lateral geniculate nucleus, the pretectal region and the superior colliculus. Thus, following a neonatal left dorsal occipital cortical lesion, the retinal efferents from the right eye produce a denser projection to the contralateral lateralis posterior (LP), nucleus lateralis of the optic tract (NLOT), and the caudal part of the lateral division of the lateral geniculate nucleus pars ventralis (VGN). Following neonatal left eye enucleation, increased ipsilateral projection from the right DOC was noted in the superficial part of the stratum griseum superficiale (SGS), NLOT, pretectal nucleus (PT) and the adjoining stratum griseum intermediate (SGI) of the superior colliculus, lateral geniculate nucleus, pars dorsalis (DGN), and both the medial and lateral halves of the caudal portion of VGN. Following a neonatal DOC lesion a denser projection from the remaining ipsilateral SMC was seen in the medial pretectal nucleus (PTM), PT and deep pretectal nucleus (PTP). Following a neonatal SMC lesion a denser projection from the ipsilateral DOC was seen in the SGI, PT, nucleus medialis of the optic tract (NMOT) and PTM. There was no change in the retinal efferents following neonatal SMC lesions. Nor was there any change in the SMC efferents following neonatal eye enucleations.