Nonphosphorylated neurofilament protein is expressed by scattered neurons in the human vestibular brainstem

Vestibular information is critical for the maintenance of balance and posture and for the control of eye movements. The eighth nerve carries vestibular information to four brainstem nuclei called the vestibular nuclear complex (VNC); these nuclei relay vestibular signals to several additional brainstem nuclei. The structure, connections, effects of lesions and neuronal response properties of the vestibular brainstem have been studied in many nonhuman species. The development of bipedal locomotion in humans mandates differences in the vestibular control of balance and suggests that there may also be differences in the organization of the human vestibular brainstem. While the four nuclei of the VNC are described in human, there is a lot of variability among reports in their borders and extent. Further, there are several nuclei described in the human brainstem that are not present in other species. We have been using immunohistochemistry to study the patterns of expression of several different proteins to define and compare the organization of the vestibular brainstem in animals and humans. We here describe the expression of nonphosphorylated neurofilament protein (NPNFP) in the human vestibular brainstem. As in the cat, NPNFP is expressed by scattered cells within multiple regions of the vestibular brainstem and in cranial nerve nuclei. NPNFP expression in other cortical and subcortical regions suggests that it is expressed by projection neurons. For vestibular brainstem, these may be vestibulospinal, vestibulo-oculomotor or vestibulocerebellar neurons. Studies of other brain regions suggest that brainstem neurons expressing NPNFP may be especially vulnerable in different neurological disorders including Alzheimer's disease or to alterations in sensory input.