Vasoactive intestinal polypeptide (VIP) containing cells in the developing rat occipital hemisphere.

Numerous cells were observed to show intense vasoactive intestinal polypeptide (VIP) immunoreactivity from birth to postnatal day 8 in the subventricular zone of the rat occipital hemisphere. This cell population was markedly reduced by postnatal day 8, but isolated clusters of VIP cells persisted into adulthood. In addition, long, L-shaped VIP fibers were seen in the hemispheric wall up to postnatal day 16, but not in the adult. Parallel to the reduction in number of the subventricular VIP cells an increasing number of VIP cells appeared in the neo- and allocortex, developing by postnatal day 12 all the features of the mature cortical bipolar fusiform neurons. As possible alternatives, the migration of subventricular VIP cells into the cortex, the transient character of the subventricular VIP population or the expression of VIP by radial glia are discussed.