Nerve growth factor receptor (p75)-immunoreactivity in the normal adult feline trigeminal system and following retrogasserian rhizotomy.

The 75 kDa protein nerve growth factor receptor [NGFr(p75)] is a neurotrophin receptor that is able to bind different members of the neurotrophin family of molecules implicated in affecting neuronal survival. Here we describe the light microscopic distribution of NGFr(p75)-immunoreactivity (IR) within the feline trigeminal brainstem sensory nuclear complex and trigeminal ganglion of normal adult subjects and in subjects 10 and 30 days following retrogasserian rhizotomy. Within the trigeminal ganglion of normal subjects, numerous fibers and most of the neuronal cell bodies showed NGFr(p75)-IR that varied in intensity, while cells and fibers with NGFr(p75)-IR were less numerous within the mesencephalic trigeminal nucleus. Within the main sensory and spinal trigeminal nuclei, NGFr(p75)-IR formed a reproducible pattern that varied between the different subnuclei. The NGFr(p75)-IR consisted both of dense pockets and a low level NGFr(p75)-IR that was selective to the trigeminal neuropil. Following rhizotomy, most of the NGFr(p75)-IR was lost from the main sensory and spinal trigeminal nuclei, except in regions where the upper cervical roots and cranial nerves VII, IX, and X project. In contrast, examination of the central root that was still attached to the trigeminal ganglion showed increased NGFr(p75)-IR in fibers and supporting cells, as did the motor root within the peripheral mandibular division. These results indicate that the majority of the NGFr(p75)-IR within the main sensory and spinal trigeminal nuclei originates from primary trigeminal afferents and that retrogasserian rhizotomy leads to an up-regulation of NGFr(p75)-IR in the part of the central root that is contiguous with the ganglion.