Neuroanatomical effects of neonatal transection of the corpus callosum in hamsters.

Newborn hamsters were subjected to surgical transection of their corpora callosa under hypothermic anesthesia. After completion of their development, one group of animals had their brains prepared for cyto- and myeloarchitectonic analysis. Another group had a small pellet of polyacrylamide gel containing horseradish peroxidase (HRP) implanted in different cortical loci. All were perfused with fixatives and had their brains cut into serial sections. The operated brains showed the following anatomical features: (1) The corpus callosum was partially or totally absent; (2) an abnormal longitudinal bundle was present bilaterally underneath the white matter; and (3) except for the physical displacement of some medial structures, the general architecture of the brain appeared unchanged. Analysis of HRP material revealed that (1) the longitudinal bundle contains cortical fibers, of which at least some are commissural; (2) these cortical fibers display a topographic arrangement within the bundle. Results suggest that brain anatomy of "surgical" acallosal hamsters compares closely with that observed in mice with congenital defects of the corpus callosum, a spontaneous condition which also occurs in humans.