NGF receptor (p75)-immunoreactivity within hypoglossal motor neurons following axotomy in monkeys

The expression of the p75 nerve growth factor receptor (NGFR) was examined in Rhesus and Cebus monkeys following complete unilateral transections of the hypoglossal nerve. In unoperated and sham-lesioned monkeys, NGF receptor-immunoreactivity was always undetectable within hypoglossal motor neurons. In contrast, monkeys receiving unilateral transections of the hypoglossal nerve displayed numerous NGFR-immunoreactive neurons within ipsilateral hypoglossal motor neurons 1 week post-lesion. The peak expression of NGFR-immunoreactive hypoglossal neurons was seen 4 weeks following the lesion and although fewer, these neurons were still observed in large numbers 10 weeks post-lesion. By 16 weeks post-lesion only a few NGFR-immunoreactive motor neurons were observed. A small number of NGF receptor-immunoreactive neurons were also seen within the contralateral hypoglossal nucleus at post-lesion weeks 4 and 10. These data demonstrate that adult hypoglossal motor neurons express detectable levels of p75 nerve growth factor receptor following hypoglossal nerve transection in monkeys in a manner similar to that previously reported in non-primate species. The synthesis of p75 NGF receptors in these neurons may represent a regeneration-mediated re-expression of NGF receptors which only normally occurs during development.