Plasticity of substance P in mature and aged sympathetic neurons in culture.

The effect of age on the plasticity of the putative peptide neurotransmitter substance P (SP) was examined in the rat superior cervical sympathetic ganglion. Explantation of ganglia from 6-month-old rats to serum-supplemented culture resulted in a tenfold increase in SP concentration, reproducing results previously obtained for ganglia from neonatal rats. Veratridine prevented the increase in SP concentration in adult ganglia, and tetrodotoxin blocked the veratridine effect, suggesting that membrane depolarization and sodium influx prevented the rise in the SP content of adult ganglia as well as of neonatal ganglia. However, the time courses of the increase in the amount of the peptide differed in neonatal and mature ganglia, suggesting that some aspects of regulation may differ in the two. The effects of aging on neural plasticity were further analyzed by explanting ganglia from 2-year-old rats. No significant increase in SP concentration was observed in these ganglia. Remarkable plasticity thus seems to persist in mature neurons but may be deficient in aged sympathetic neurons.