Nerve growth factor stimulates neurite outgrowth from goldfish retinal explants: the influence of a prior lesion

Goldfish (Carassius auratus) retinal explants, whose ganglion cells were 'primed' in vivo by an optic nerve crush at varying intervals prior to culture, were found to respond by enhanced neurite outgrowth to low (ng/ml) concentrations of nerve growth factor (NGF). This in vitro response was dose-dependent and specific for NGF. The spontaneous fiber outgrowth which normally occurs in vitro in response to optic nerve lesion without exogenous NGF in the medium could be reduced by approximately 80% with administration of NGF antiserum. These observations strongly indicate the formation of an NGF-like molecule in the goldfish retina. The magnitude and sensitivity of the NGF response was dependent on the post-crush interval, referred to as days post-axotomy (DPA). Without a prior crush there was no response unless explants remained in culture 1-2 weeks before NGF treatment. NGF elicited the greatest increase in neurite outgrowth when administered to 7 DPA explants. With increasing intervals after axotomy the response decreased until by 35 DPA none could be elicited.