Induction of nerve growth factor receptor (p75 NGFr) mRNA within hypoglossal motoneurons following axonal injury

Abstract

The hypoglossal nerve is a useful model system for analysis of gene expression in injured motoneurons. In particular, we sought to determine whether the increased appearance of the low affinity nerve growth factor receptor (p75 NGFr) observed immunocytochemically following nerve injury can be directly correlated to increased levels of the p75 NGFr mRNA. The present study also examined the relative effects of nerve crush versus nerve transection on the expression of p75 NGFr mRNA. In sham-operated or intact animals, p75 NGFr mRNA is detected rarely and then only at levels slightly higher than background. Following unilateral transection or crush of the rat hypoglossal nerve, the levels of p75 NGFr mRNA increase in a time dependent fashion that parallels the appearance of the protein as reported previously. Moreover, this increase in p75 NGFr mRNA following transection is dependent on a signal from the injured site, since blockage of axonal transport with vincristine also blocks the increased p75 NGFr mRNA levels. When comparing the effect of nerve crush to nerve transection, we observed that the intensity of the response was greater in the crush paradigm versus that observed following transection. The duration of the response following nerve crush was shorter than that observed following transection of the nerve. The increase in p75 NGFr mRNA after crush was most robust 4 days postlesion and appeared more robust primarily due to a 90–150% increased number of motoneurons expressing p75 NGFr mRNA when compared to nerve transection. These data suggest that nerve crush is more effective than nerve transection in eliciting increased p75 NGFr mRNA levels.