Age-related increase in c-fos expression in the sympathetic neurons of the rat superior cervical ganglion.

C-fos expression was studied immunocytochemically in sympathetic neurons of the rat superior cervical ganglion (SCG). Fos-like immunoreactivity was confined to the principal neurons of the ganglion and was exclusively localized within their nuclei. In 2-month-old rats, the immunoreactivity was detected in 1.2% of the principal neurons with a density of 4.95 Fos-positive cells/mm2 of ganglion area. This proportion increased with age and reached a value which was 6.5-fold higher in the 26-month-old rats than that in the young adult. A density of 24.5 Fos-positive cells/mm2 of ganglion area was seen in the 26-month-old animals. The age-enhanced c-fos expression suggests that Fos may be involved in regulation of the genetic events associated with the adaptive changes in neuronal activity of the sympathetic ganglion during aging.