Ageing of the spinal ganglion neurons in the rat: a radioautographic study following injection of [3H]lysine

Mitochondria in Perineuronal Satellite Cell Sheaths of Rabbit Spinal Ganglia: Quantitative Changes during Life

We studied quantitative changes in mitochondria of perineuronal satellite cell sheaths (SCSs) of rabbit spinal ganglia from young to extremely advanced age (1, 3.6, 6.7 and 8.8 years). The mitochondrial structure did not differ in the four age groups, while mitochondrial size increased progressively and significantly with age. The mean percentage of cytoplasmic volume occupied by mitochondria decreased progressively and significantly from young to old animals. This decrease was mainly due to a progressive and significant reduction in the total mitochondrial volume. Lipofuscin accumulation had a negligible influence on this reduction. These results suggest that the ability of SCSs to produce energy decreases with age and that the reduced ability of spinal ganglion neurons to respond to high energy demands in old age may be in part due to the diminished contribution of perineuronal satellite cells.

The perineuronal glial tissue of spinal ganglia. Quantitative changes in the rabbit from youth to extremely advanced age

The volumes of the nerve cell bodies and those of the enveloping satellite cell sheaths from spinal ganglia were determined by morphometric methods applied to electron micrographs in young, adult, old and very old rabbits. The mean volume of the nerve cell bodies increased progressively with age; this is probably related to the increase with age of the body size of the rabbits studied. The mean volume of the satellite cell sheaths did not differ significantly in young, adult and old animals, but was significantly smaller in very old animals. It is extremely unlikely that this marked reduction in the volume of the satellite cell sheath is the result of a pathological process. The mean value of the volume ratio between the satellite cell sheaths and the related nerve cell bodies did not differ significantly in young and adult animals, but was significantly smaller in old and very old animals. This ratio was particularly low in very old animals. Our analysis showed that in each age group the volume of the satellite cell sheath is linearly related to the volume of the related nerve cell body. This result suggests that in rabbit spinal ganglia the quantitative relations between glial and nervous tissue are tightly controlled throughout life. It is suggested that ganglionic neurons release signals to influence and control the volume of their associated glial tissue. Since satellite cells have important support roles for the neurons they surround, it is likely that the marked reduction in the volume of perineuronal sheaths in the extremely advanced age is accompanied by a reduction of those roles, with negative consequences for neuronal activity.

Changes with age in the Golgi apparatus of rabbit spinal ganglion neurons

We studied the Golgi apparatus in spinal ganglion neurons of rabbits aged 12, 42 and 79 months. We found no structural changes, no indications of fragmentation, no indications of peripheral displacement affecting this organelle with advancing age. The volume of the perikaryon increased significantly with age, whereas the total volume of the Golgi apparatus remained essentially constant. Hence the mean percentage of perikaryal volume occupied by the Golgi apparatus decreased with age. This decrease was only in very minor part a consequence of lipofuscin accumulation, so that the ratio between the total volume of the Golgi apparatus and the functionally active volume of cytoplasm decreased with age. This decrease could be related to the reduced neuronal metabolism that occurs during ageing. It is possible that the delivery to the axon of newly synthesized proteins destined for fast transport is one of the Golgi apparatus roles that decrease with age. Finally, we found that the age-related quantitative changes in the Golgi apparatus did not differ between large light and small dark neurons.

Age-related decrease in the overall extent of perikaryal projections in rabbit spinal ganglion neurons

The overall extent of the perikaryal projections of sensory neurons from spinal ganglia of young adult and aged rabbits was estimated by a stereological method using the electron microscope. The extent of perikaryal projections was significantly smaller in the aged animals. This age-related decrease did not seem to depend on factors intrinsic to the neuron, but on the absence of a satellite cell covering over extensive portions of the nerve cell body surface. This decrease may influence the organization of the subplasmalemmal cytoskeleton, metabolic exchange between the nerve cell body and its environment and perhaps also neuronal metabolism.

Neurons and microvessels of the nodose (vagal sensory) ganglion in young adult and aged rats: morphometric and enzyme histochemical studies

The neuron cell bodies and microvessels in sections of the nodose (vagal sensory) ganglion (NG) of Wistar rats of 4- and 24-months of age have been examined morphometrically and by quantitative enzyme histochemistry. The range of neuronal somata areas was similar at the two ages and distributed unimodally, ranging approximately from 200-1500 microns 2 with the largest somata occurring in the older age group. The range of microvessel diameters was also comparable but the largest microvessels were seen in the older animals. The histological arrangement of the ganglion permitted analyses to be made of 'neuronal' and 'axonal' areas independently. The number of microvessels per unit area was less in regions of the ganglion occupied by axons at both ages. Random transects indicated that the percentage area occupied by neuron somata decreases and that of axons increases with age. Overall, however, the results suggest that the histological organization, the size of vagal sensory neurons, the ganglionic microvessels, and the relationship between them, does not change greatly in Wistar rats of up to 2 years of age. Ultrastructural features of the aged sensory neurons included the presence of secondary lysosomes, disrupted rough endoplasmic reticulum, swollen Golgi cisternae, and the presence of much filamentous material in the perikaryon similar to that seen in chromatolytic neurons. However, analysis of electron micrographs did not reveal significant changes in the numbers of mitochondria or Golgi bodies. There was an overall increased thickness in the microvascular wall in the older animals with the endothelium and pericyte covering being significantly increased, but the thickness of the basal lamina was unchanged. The activities of neuronal NADH tetrazolium reductase, succinate dehydrogenase and cytochrome oxidase were all increased with age. The results suggest that vagal sensory neurons are not greatly affected by age in the rat.

The microenvironment of the spinal ganglion neuron in the rat during aging

The environment and particularly the glial sheath of the spinal ganglion neurons was systematically studied by light and electron microscopy in the young and senescent rat. Experiments using radioactive tracers tested the consequences of the functional perturbations associated with structural impairments. The results suggested the possibility that the glial sheath and the neuron aged differently. Whereas the glial sheath maintained its functional capacity relatively intact, neuronal performance was markedly and more rapidly impeded. The morphology and volume of the extracellular space were unchanged. Therefore, impairment of the glioneuronal units in the spinal ganglion during aging cannot be assigned to environmental and vascular phenomena.

Selective uptake of [3H]glutamine and [3H]glutamate into neurons and satellite cells of dorsal root ganglia in vitro

The uptake of [3H]glutamate and [3H]glutamine into rat dorsal root ganglia has been examined by autoradiography and thin-layer chromatography. [3H]glutamate was selectively accumulated by satellite glial cells and after 10 min, 53% of this had been converted to [3H]glutamine. [3H]glutamine, on the other hand, entered neuronal perikarya and 40% was converted to [3H]glutamate. It is suggested that these selective uptake processes provide supporting evidence for the existence of a neuronal-glial glutamine cycle in dorsal root ganglia. Small dark (B) cells accumulated 6 times as much [3H]glutamine as did large light (A) cells. The reasons for this marked difference in the metabolism of the two main types of dorsal root ganglion neurone are discussed.