INFLUENCE OF AGE AND ANTI-NERVE GROWTH-FACTOR TREATMENT ON THE SYMPATHETIC AND SENSORY INNERVATION OF THE RAT IRIS

We have investigated alterations in the nerve supply to the iris of ag ed rats and the role of endogenous nerve growth factor in these change s. The overall density of nerve fibres, and the density of calcitonin gene-related peptide containing sensory nerves, were decreased by over 20% on the aged iris, as measured by computerized image analysis on i mmunostained preparations, while the density of sympathetic innervatio n was maintained. Whilst the majority of nerves supplying the iris (sy mpathetic, sensory and parasympathetic) are known to respond to exogen ous nerve growth factor during development and in adulthood, the role of endogenous, target-derived nerve growth factor in nerve maintenance in maturity and old age awaits confirmation. Our results showed that localized treatment with anti-nerve growth factor of iridial nerve ter minals did not affect sympathetic or sensory neurons in young rats, bu t caused a dramatic reduction of sympathetic nerve density on irides o f old rats. The effect of anti-nerve growth factor treatment on the se nsory innervation of old irides was less obvious. We conclude that age d sympathetic nerves are more susceptible to nerve growth factor depri vation than young ones, or than young or aged sensory neurons, perhaps as a result of reduced responsiveness to nerve growth factor with age . Since sympathetic innervation is maintained, whilst sensory innervat ion is decreased in the aged iris, age-related changes in innervation are unlikely to be due to altered availability of endogenous nerve gro wth factor. Copyright (C) 1996 IBRO. Published by Elsevier Science Ltd .