Age-dependent changes in the midsized neurofilament subunit in sensory-motor systems of the cat brainstem: an...

This study documents age-related changes in the immunoreactivity of the medium-molecular weight subunit of neurofilaments in sensory and motor neurons in the brainstem of the cat. In old age, there was a clear decrease in immunoreactivity in the following brainstem sensory and motor nuclei: sensory trigeminal, gracile, cuneate, and facial motor. Only a few neuronal perikarya and dendrites were labeled in these nuclei in old cats; moreover, when present, the labeling was weak. In contrast, in adult cats, these nuclei contained intensely stained neuronal perikarya and dendrites. In other sensory and motor nuclei of the brainstem, there was an obvious age-related increase in the immunoreactivity of the medium-molecular weight subunit of neurofilaments in the perikarya. Despite different patterns of age-related alterations in immunoreactivity within perikarya and dendrites in distinct brainstem regions, most sensory and motor axons in old cats were smaller than those in adult cats. A decrease in the medium-molecular weight neurofilament subunit in the dendrites may be the basis for the dendritic atrophy that has been shown to occur in sensory nuclei in old animals. The decrease in axonal size is likely to be one of the causes of the decrease in axonal conduction velocity, in these neurons, that was reported in our previous studies.