Bilateral pericruciate cortical innervation of the red nucleus in cats with adult or neonatal cerebral hemispherectomy.

We studied remodeling of the remaining corticorubral projections in adult cats sustaining a left cerebral hemispherectomy in adulthood or neonatally using cortical injections of [3H]leucine-proline. Injection sites and terminal fields were reconstructed from autoradiography-processed tissue. In all cats, the label filled similar extents of ares 4 gamma and 3a of the right frontal cortex. We used sections at 8 coronal planes throughout the red nucleus (RN) for computer-assisted analysis of visually estimated density and topography of distribution of terminal label, and for calculation of RN cross-sectional area. Additionally, at 3 coronal planes we further quantified terminal label using computerized procedures (number of particles for surface area). In all lesioned cats we found terminal label in the RN contralateral to the injection site with a topographic distribution similar to that of the RN ipsilateral to the injection in normal or lesioned cats and in absence of any significant shrinkage of the nucleus. The difference between the 2 age-at-lesion groups was that in the cats with neonatal ablation the density of contralateral terminal label was about double that seen in adult-lesioned subjects. However, the amount of contralateral labeling in adult-lesioned cats was substantial and represented a significant increase over the minimal labeling seen in normal cats. There were no differences between groups in labeling or size of the RN ipsilateral to the injection site. For reasons discussed, we interpret the label on the side of the hemispherectomy as representative of reinnervation of the cortically deafferented RN by crossing collaterals of fibers arising in the remaining motor cortex and not as lesion-sustained persistent prenatal connections.

Behavioral observations of sensory substitution in neonate macaques (Macaca arctoides).

The ability of neonate macaque monkeys to learn to respond to artificial spatial sensory information was studied through the use of compact, head-worn, electronic spatial sonars with audible displays, which translate spatial information into auditory dimensions specifying distance, direction, and surface characteristics. Three animals were born in the dark and raised without vision for 1 to 3 months while wearing either the Binaural Sensory Aid (Animal 1; Kay, 1974) or the Trisensor (Animals 2 and 3; Easton & Jackson, 1983) airborne sonars. Each animal demonstrated alertness to information transmitted by the devices in spontaneous reaching or reinforced discrimination tasks, and more device-related, perceptual-motor activities were observed when the sensors were switched on than when they were switched off. The results show that neonate monkeys can learn effective use of information obtained from sensory substitution devices through unstructured interaction with the environment.

Reorganization of pericruciate cortical projections to the spinal cord and dorsal column nuclei after neonatal or adult cerebral hemispherectomy in cats.

This is a quantitative study of changes in distribution and density of terminals of the corticospinal tract in the cervical spinal cord and dorsal column nuclei (DCN) in cats with left cerebral hemispherectomy performed neonatally or in adulthood. Kittens received hemispherectomy at a mean of 12.1 postnatal days and were compared, as adults, to adult-lesioned cats of similar survival time. All animals, including controls, received injections of [3H]leucine-proline and were sacrificed 5 days later. Injection sites and terminal fields were reconstructed from autoradiography-processed tissue. The label filled comparable extents of areas 4 gamma and 3a of the right cerebral cortex. Coronal sections from upper and lower cervical cord levels, and from the brainstem (cuneate and gracile nuclei) were studied. Computer-image processing procedures were used to count labeled particles from multiple sites of the dorsal horn and DCN, bilaterally. In the spinal cord of intact and adult-hemispherectomized cats, most terminals were found in lamina VI, and adjacent laminae V and VII contralateral to the injection side. The major finding was that neonatal-lesioned cats showed a significant increase in axon terminals in areas ipsilateral to the injection. The topography of distribution of the novel terminals was similar to that in the contralateral side and the originating fibers appeared to have crossed the midline from that side. A similar reorganization occurred in the gracile nucleus where, in intact and adult-lesioned cats, the cortical terminals also predominated in the side contralateral to the injection. In contrast, neonatal-lesioned animals showed a significant increase in terminal density ipsilateral to the cortical injection. These findings are discussed as an alternative mechanism for postlesion remodeling of the corticospinal tract in animals with the pyramidal crossing completed at the time of birth.

Reorganization of cerebellorubral terminal fields following hemispherectomy in adult cats.

Tritiated amino acids were injected into the right nucleus interpositus of the cerebellum and the projections to the red nucleus were mapped autoradiographically in adult cats with ablation of the left cerebral hemisphere and in intact controls. In intact animals cerebellorubral terminals were found along the entire rostrocaudal extent of only the left red nucleus. The fields occupied a larger area and were apparently more dense toward the middle third of the nucleus. An outstanding change in hemispherectomized cats was a significant expansion of the terminal fields into the dorsal quadrants. Possibilities for morphological reorganization are discussed.

Evidence for a crossed corticorubral projection in cats with one cerebral hemisphere removed neonatally.

Tritiated amino acids were injected into the right pericruciate cortex and the projections to the red nucleus were mapped autoradiographically in 10 intact and 6 adult cats with one cerebral hemisphere (left side) removed neonatally. In the intact cats only projections to the ipsilateral red nuclei were seen. The terminals were distributed along the entire rostrocaudal extent, but the density of the label was greater in the ventral and medial aspects of the nucleus. In the hemispherectomized cats projections to both red nuclei were found. The topography of the terminals was similar to that seen in intact animals. This finding, together with other changes which we have described, suggests that an extensive structural reorganization may occur after removal of one cerebral hemisphere in cats.