Development of the visual callosal cell distribution in the rat: mature features are present at birth.

In the present study, the early postnatal distribution and subsequent fate of visual callosal neurons were studied in neonatal rat pups. Previous studies had indicated that the adult pattern of visual callosal neurons was sculpted from an initially uniform distribution in the neonatal cortex. To reexamine this issue, we used a sensitive tracer, latex microspheres conjugated either to rhodamine or fluorescein, that was injected into the occipital cortex of one hemisphere in pups on the day of birth (PND 1), PND 6, or PND 12.