Neuronotrophic activity for ciliary ganglion neurons. Induction following injury to the brain of neonatal, adult, and aged rats.

The induction of neuronotrophic activity following injury to the brain of neonatal, adult, and aged Sprague-Dawley rats was compared using an improved in vitro assay. The maximal levels of activity in tissue surrounding the wound were reached at 3, 10-15, and about 15 days postlesion in neonatal, adult, and aged animals, respectively. Tissue neuronotrophic levels were always much lower in neonatal animals relative to the older animals. Accumulation of neuronotrophic activity in the gelfoam placed into the wound cavities in neonatal and adult animals lagged behind the levels in tissue by 4-5 days, suggesting that either the neuronotrophic factor itself or the cells which produce it are transferred from the tissue into the gelfoam. Relatively little activity accumulated in the gelfoam taken from aged Sprague-Dawley rats, and this observation was confirmed in aged Fischer rats. Aged animals seem to be unable to produce or release one of a number of neuronotrophic factors in response to injury.