Indices of neurotransmitter synthesis and release in aging sympathetic nervous system

Activities of tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and choline acetyltransferase (ChAT) were assayed in sympathetic ganglia and adrenal glands of young and aged Fischer-344 rats. The recovery of reserpine-depleted catecholamine stores and catecholamine loss following inhibition of synthesis and intraneuronal degradation also were assessed in sympathetic ganglia of young and aged rats. No age differences were observed in DBH activity of any tissues examined or in the activities of any enzymes in the coeliac-mesenteric ganglion complex. However, TH and ChAT activities were significantly higher in the superior cervical ganglia and adrenal glands of aged rats. In the hypogastric ganglion, only TH activity was higher in the old rats. Recoveries of reserpine-depleted catecholamine stores in the superior cervical and hypogastric ganglia of aged rats were slower than in young rats. Catecholamine loss following inhibition of synthesis and intraneuronal degradation was faster in the superior cervical ganglia but not in the hypogastric ganglia of old rats as compared with young rats. These findings suggest that neurotransmitter synthesis and release are enhanced with age in the superior cervical ganglion. The lack of age-related changes in the hypogastric ganglion might reflect the different cellular composition as well as the physiological role of this ganglion.