ATTENUATION AND RECOVERY OF NERVE GROWTH-FACTOR RECEPTOR MESSENGER-RNA IN DORSAL-ROOT GANGLION NEURONS FOLLOWING AXOTOMY

The actions of nerve growth factor (NGF) are mediated by two receptor proteins, trk and p75. Recent evidence indicates that NGF upregulates the expression of both trk and p75 in responsive neurons including rat dorsal root ganglion (DRG) neurons, Axotomy by disconnecting the neur on from its source of target-derived NGF is predicted to lead to the d ownregulation of trk and p75 expression, However, previous studies of the effects of axotomy on trk and p75 mRNA expression in rat DRG have yielded discrepant results, We report that following sciatic nerve cru sh, trk and p75 mRNA levels in L4-L6 DRG decrease to similar to 50% of control levels at 4-14 days, return to control levels by 30 days, and are increased by similar to 30% at 60 days, Similar changes are obser ved following nerve transection although mRNA levels are slower in ret urning to normal and do not exceed control levels at later timepoints. Thus, trk and p75 expression decline early following target disconnec tion and later recover irrespective of target reinnervation. These obs ervations indicate that target derived NGF is required for the mainten ance of NGF receptor expression in adult rat DRG neurons and that non- target derived factors can appropriate this function following periphe ral nerve injury. (C) 1996 Wiley-Liss, Inc.