AGE-RELATED REDUCTION OF THE SATELLITE CELL SHEATH AROUND SPINAL GANGLION NEURONS IN THE RABBIT

The volumes of the nerve cell bodies and those of the enveloping satel lite cell sheaths from spinal ganglia of young adult and aged rabbits were determined by morphometric methods using the electron microscope. The mean volume of the nerve cell bodies was greater in the old rabbi ts than in young adults; this is probably related to the larger body s ize of the old animals. The mean volume of the satellite cell sheaths was, however, smaller in the aged rabbits than in the young adults. Co nsequently the volume ratio between the satellite cell sheaths and the related nerve cell bodies was significantly smaller in the aged anima ls. Since satellite cells play an important role in the support of the neuron, the reduction in volume of the perineuronal sheath could be a ssociated with a decrease in the trophic activity of satellite cells t owards the enveloped neuron with consequences for neuronal activity. F urthermore, in the satellite cell sheaths of old rabbits, the number a nd extension of gaps that leave the neuronal surface directly exposed to the basal lamina were significantly increased. Since spinal ganglia lack a blood-nervous tissue barrier, only the satellite cell sheath c ontrols the traffic of material to the nerve cell body. Because the ne uronal surface unprotected by the satellite cell envelopment is signif icantly more extensive in the spinal ganglia of old rabbits than in th ose of young adults, the nerve cells of the former are more exposed to potential damage by harmful substances. A dense undercoating was seen very frequently beneath the portions of the neuronal plasma membrane not covered by satellite cells.