DEVELOPMENT OF THE ANTERIOR COMMISSURE IN THE OPOSSUM - MIDLINE EXTRACELLULAR-SPACE AND GLIA COINCIDE WITH EARLY AXON DECUSSATION

While the anterior commissure has been shown to be an important route of information transfer in the forebrain, relatively little is known a bout its anatomical development, Glial substrates and extracellular sp aces have been associated with the maturation of other large-fiber tra cts, such as the corpus callosum and retinofugal pathway. The present study examined early stages in the maturation of the commissure in the gray short-tailed opossum, Monodelphis domestica. Monodelphis offspri ng are born after a short 14-day gestation, and, unlike in rats and mi ce, the anterior commissure develops entirely during the postnatal per iod, A number of techniques were employed: the carbocyanine dye Dil wa s used to label early axons in the region, semithin plastic sections w ere used to examine the extracellular environment of the developing co mmissure, and immunocytochemistry for glial fibrillary acidic protein (GFAP) was used to characterize glial components. Results suggest that the first commissural fibers that cross the midline pass through a re gion of large extracellular spaces and may use GFAP-immunoreactive cel ls and processes as guides during their midline decussation. (C) 1997 John Wiley & Sons, Inc.