The Golgi apparatus of satellite cells associated with spinal ganglion neurons: changes with age in the rabbit.

We studied the Golgi apparatus in the satellite cell sheaths enveloping spinal ganglion neurons of rabbits aged 12, 42, and 79 months. We found neither structural changes nor indications of peripheral displacement of this organelle with advancing age. The mean percentage of cytoplasmic volume occupied by the Golgi apparatus decreased significantly passing from young adult to old rabbits. 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. The mean cytoplasmic volume of perineuronal satellite cell sheaths did not change significantly with increasing age, whereas the total volume of the Golgi apparatus within these sheaths decreased significantly with age. This decrease strongly suggests that the activity of satellite cells diminishes in old age, further suggesting that these cells are unable to compensate for the decrease in the neuronal metabolism that a number of authors have described in old age.

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.

Decrease in the nucleo-cytoplasmic volume ratio of rabbit spinal ganglion neurons with age.

Nuclear and perikaryal volumes, as well as the mean percentage of perikaryal volume occupied by lipofuscin, were estimated in spinal ganglion neurons of 12, 42 and 79 month-old rabbits. The volume ratio between nucleus and perikaryal cytoplasm (N/C volume ratio) decreased progressively and significantly with increasing age. This was not a consequence of the perikaryal enlargement due to the age-related lipofuscin accumulation since the same result was obtained when the volume occupied by lipofuscin was subtracted from the perikaryal volume. The decrease in the N/C volume ratio may depend on an age-related loss of DNA, a cytoplasmic influence on nuclear size, or other unknown causes.

Amount and distribution of lipofuscin in nerve and satellite cells from spinal ganglia of young adult and aged rabbits.

The quantitative aspects of the age-related accumulation of lipofuscin were studied in the rabbit spinal ganglia by stereological methods using the electron microscope. Both neurons and their associated satellite cells were examined. In neurons, the shape and structure of lipofuscin bodies differed in young adults (12-months-old) compared to aged rabbits (79-months-old), whereas substantial changes were not observed in satellite cells. Both in nerve and satellite cells, lipofuscin bodies were scattered singly in young adults, but were often clustered in old animals. Lipofuscin occupied an average of 0.36% of neuronal perikaryal volume in the young adults and 2.55% in the aged rabbits; these percentages are much lower than those observed in the same neurons of other species. In the satellite cells, the corresponding values were 0.29% and 2.02%. In the young adults, the mean size of lipofuscin bodies was significantly greater in neurons than in satellite cells; the size of these bodies increased with age by about 2.7 times in neurons and by about 1.7 times in satellite cells. Consequently, in the old rabbits the mean size of lipofuscin bodies was about 2.2 times greater in neurons than in satellite cells. It has been suggested that lipofuscin bodies are transferred from the neuronal perikaryon to the surrounding satellite cells and then removed via the capillaries. However, the present findings suggest that lipofuscin located in satellite cells represents pigment formed by these cells rather than being transferred from neuronal perikaryon. It would appear that the age-related accumulation of lipofuscin in the rabbit spinal ganglia has little effect on neuronal metabolism.

Cell body volume of spinal ganglion neurons: estimation by three different methods.

We estimated the mean volumes of two series of nerve cell bodies, one from rabbit and one from rat spinal ganglia by three different methods: a procedure we devised 25 years ago (the circle-fitting method), one of the new stereological methods (the nucleator method) and the method of serial sectioning--the most direct and accurate procedure presently available for estimating cell size. In the case of the rabbit, in which most spinal ganglion neurons have a single nucleolus, the mean volumes estimated by the first two methods are closely similar and deviate by less than 2% from the mean obtained by serial sectioning. In the case of the rat, in which approximately half of the spinal ganglion neurons have more than one nucleolus, the mean volumes estimated by the first two methods are again closely similar, but deviate by about 12% from the mean obtained by serial sectioning. These findings show that: a) both the nucleator method and the circle-fitting procedure are more accurate when applied to neurons with a single nucleolus; b) if certain conditions are respected, not all the methods previously used to estimate cell size give biased results. However, the new stereological procedures are easier and quicker to use than the earlier methods. These findings also show that our previous results obtained by the circle-fitting method are to be considered valid.