Aging is associated with an increase in dye coupling and in gap junction number in satellite glial cells of murine dorsal root ganglia

Glial cells in both central and peripheral nervous systems are connected by gap junctions, which allow electrical and metabolic coupling between them. In spite of the great current interest in aging of the nervous system, the effect of aging on glial cell coupling received little attention. We examined coupling between satellite glial cells in murine dorsal root ganglia using the dye coupling technique and electron microscopy. We studied mice at ages of postnatal 90-730 days. Dye coupling incidence between satellite glial cells associated with a single neuron increased from 24.2% at postnatal day 90 to 50.5% at postnatal day 730. Dye coupling between satellite glial cells that are in contact with two or more neurons increased from 2.7% at postnatal day 90 to 18.6% at postnatal day 730 (P < 0.05). Examination of the ganglia with the electron microscope showed that the number of gap junctions per 100 mu m(2) of surface area of satellite glial cells increased from 0.22 at postnatal day 90 to 1.56 at postnatal day 730 (P < 0.01). The mean length of individual gap junctions did not change with age. These results provide strong evidence for an increase of functional coupling between satellite glial cells during life. This increase is apparently due to an increase in the total area of the system of gap junctions connecting these cells.