Transient CD15 expression reflects stages of differentiation and maturation in the human subcortical central auditory pathway

The expression of the terminal saccharide determinant CD15 (3[al-3]-fucosyl -N-acetyl-lactosamine) was evaluated in the central auditory system of the human developing brain by using monoclonal antibodies against this epitope. CD15 immunoreactivity was first observed in the ventral cochlear nucleus a t 10 weeks of gestation, whereas the dorsal cochlear nucleus became positiv e from 13 weeks of gestation. In both nuclei, the intensity of immunoreacti vity increased until 16 weeks of gestation and lasted until 25 weeks of ges tation. In the inferior colliculi, CD15 was poorly expressed in the central nucleus from 13 to 23 weeks of gestation and later with moderate levels un til birth. Within the medial geniculate nucleus, a biphasic pattern of expr ession was observed with peaks around 14-17 and 21-24 weeks of gestation. H eterogeneous expression in the medial geniculate nucleus, which was associa ted either with neurons or the neuropil, allowed distinction of subnuclei. In many of the auditory pathway structures (e.g., ventral cochlear nucleus and central nucleus of the inferior colliculus), a heterogeneous pattern of CD15 expression in the form of repeating parallel bands, possibly related to tonotopic organization, became transiently apparent around 23 weeks of g estation, whereas in the magnocellular part of the medial geniculate nucleu s, a striking modular or compartmental arrangement of immunoreactive struct ures (which could also be associated with tonotopic organization) was also noted at about 23 weeks of gestation. We propose that the initiation of CD1 5 expression in each nucleus heralds the appearance of functional contacts and that high levels of neuropil labeling are related to the formation of n onstabilized synaptic contacts. Thus, transient CD15 expression in the cent ral auditory system is possibly correlated with phases of functional plasti city in this pathway. (C) 1999 Wiley-Liss, Inc.