The development of callosal and corticocorcal innervation in the neocortex of the hamster

The development of cortical afferentation by callosal and ipsilateral corticocortical fibers was studied in hamsters by transport of wheat germ agglutinin conjugated to horseradish peroxidase. Elongation of callosal axons (and possibly also of corticocortical fibers) started a couple of days before birth and extended through the first postnatal days. After a "waiting" period of a few days, axons were seen innervating restricted target sectors of the cortex. The zones of origin of these projections were initially exuberant, but they were subsequently trimmed down to overlap with the corresponding terminal fields

The neurogenesis of the callosal population of cortical cells in hamsters

The neurogenesis of the callosal subpopulation of cortical cells was determined in hamsters by associating incorporation of [3H]- thymidine injected on different embryonic days with horseradish peroxidase retrograde labelling in adulthood. Despite the great radial dispersion of migratory destinations of neurons born simultaneously, it was found that callosal birthdates in cortical area 6 extend from day E13 to day E15, a period that corresponds to the neurogenesis of layers III-V, where most callosal neurons come to be located in adults