Neural recognition molecule NB-2 of the contactin/F3 subgroup in rat: Specificity in neurite outgrowth-promoting activity and restricted expression in the brain regions

NB-2, a neural cell recognition molecule of the contactin/F3 subgroup, prom oted neurite outgrowth of the cerebral cortical neurons but not the hippoca mpal neurons. NB-2 in rat became apparent after birth at protein level, rea ching a maximum at postnatal day 14 in the cerebrum and postnatal day 3 in the cerebellum. NB-2 in the cerebellum declined abruptly thereafter. In sit u hybridization demonstrated that NB-2 mRNA was highly expressed in regions implicated in the central auditory pathway, including the cochlear nuclei, superior olive, inferior colliculi, medial geniculate nuclei, and auditory cortex. In addition, a high level of NB-2 expression was observed in the a ccessory olfactory bulb, thalamic nuclei, facial nucleus, and inferior oliv e. By immunohistochemistry, intense immunoreactivity against NB-2 was also detected in the auditory pathway. Thus, NB-2 is expressed in highly restric ted brain regions, including the auditory system, suggesting that it plays specific roles in the development and/or maturation of the regions. (C) 200 1 Wiley-Liss, Inc.