Recent advances in basic aging research on the nervous system in Japan

Recent studies on aging of the nervous system are reviewed with special reference to neuronal cell death, compensatory reaction, trophic factors, brain cholinergic systems and the autonomic nervous system. Studies on spinal motoneurons labeled with a tracer substance transported retrogradely demonstrated differential age effect on different types. Compensatory reactions were also seen among surviving motoneurons. Motoneuronal survival appears to be correlated with the amount of activity. However, the causal relationship between them is not yet conclusive. The effects of nerve growth factor on sympathetic and dorsal-root ganglion cells seem to be well preserved in the aged, although there are some controversial findings on the ratio of NGF-dependent neurons versus NGF-independent neurons. It has been shown that acidic fibroblast growth factor or other substances may prevent degeneration of the basal forebrain cholinergic neurons and improve memory and learning performance in aged animals. The cholinergic system also regulates the regional cerebral blood flow, and this function seems to be well maintained in aged rats. Microneurography techniques have revealed increased activity of postganglionic sympathetic nerves innervating muscles in aged human subjects. The activity of preganglionic sympathetic nerves innervating the adrenal gland and the section rate of noradrenaline have been shown to increase in the aged rat. These changes might cause high blood pressure in the aged, although some species differences have been noted between humans and rats.