IN-VITRO STUDIES OF AXONALLY-REGULATED SCHWANN-CELL GENES DURING WALLERIAN DEGENERATION

Wallerian degeneration in vivo is associated with marked downregulatio n of myelin protein genes such as P(o) and upregulation of other genes such as nerve growth factor receptor (NGF-R), glial fibrillary acidic protein (GFAP) and neural cell adhesion molecule (N-CAM). This study examines the expression of these genes during Wallerian degeneration i n vitro and how manipulating Ca2+ affects this response. Small explant s of sciatic nerve from normal young adult rats cultured for five days show similar reversal of the myelinating phenotype as found in vivo. If Ca++ is removed from the culture medium through the addition of EGT A, expression of the nerve growth factor receptor and glial fibrillary acidic protein genes is inhibited but downregulation of the P(o) gene still occurs. Explants cultured in medium containing EGTA are still c apable of expressing nerve growth factor receptor if the medium is rep laced by one containing Ca2+. Supplementation of normal medium with dr ugs modulating Ca2+, such as Bepridil which blocks the Na +/- Ca2+ exc hanger or compound 48/80 which inhibits calmodulin, also prevent the e xpression of the nerve growth factor receptor gene during Wallerian de generation in vitro. Treatment of the cervical sympathetic trunk with Bepridil leads to loss of the nerve growth factor receptor immunoreact ivity which is normally present. The results indicate that Ca2+ may pl ay a role in the expression of the nerve growth factor receptor gene d uring Wallerian degeneration and provide some indication that this eff ect may be directly on the Schwann cell rather than operating indirect ly via the axon.