LEVELS OF NGF PROTEIN DO NOT CORRELATE WITH CHANGES IN INNERVATION OFTHE RAT IRIS IN OLD-AGE

WE have examined the hypothesis that alterations in target levels of N GF protein lead to selective changes in peripheral nerve fibres in mat urity and old age. NGF levels were assayed using 2-site ELISA in iris of young and old rats. NGF levels in the iris showed no significant ch ange in old age and did not correlate with age-related changes in the density of NGF-sensitive irideal sympathetic and sensory nerve fibres, Following sympathectomy, NGF levels increased substantially in old hu t not in young irises, possibly because the lower density of aged sens ory nerves resulted in reduced capacity for NGF uptake. Content and up take of NGF in sympathetic (SCG) neurones was shown to he reduced in o ld age, while NGF content of the sensory (trigeminal) ganglion increas ed in old age. Thus NGF levels in neurones, as well as targets, fail t o correlate with peripheral nerve fibre growth or atrophy.