Comparative effects of nerve growth factor and ganglionic nonneuronal cells on purified mouse ganglionic neurons in culture

Purified neuronal fractions from dissociated mouse dorsal root ganglia were cultured in the presence of variable amounts of homologous ganglionic nonneuronal cells, and with or without addition of variable amounts of exogenous Nerve Growth Factor in the culture medium. The ability of the nonneurons to support long‐term neuronal survival in the absence of exogenous Nerve Growth Factor increased linearly with their numbers and maximal neuronal performance was achieved with a 4:1 ratio of non‐neurons to neurons; however, neuronal attachment was elicited maximally as soon as that ratio reached or slightly exceeded a value of one. Besides this Nerve Growth Factor‐like function, the nonneurons were also involved in determining whether and to what extent the factor was capable of supporting neuronal performance. In the absence of non‐neurons, even high concentrations of the factor failed to elicit neuronal attachment. As more nonneuronal cells were made available, Nerve Growth Factor progressively raised neuronal performance and did so at sharply declining requirement levels: with 12,000 nonneurons/dish maximal performance required only 10−2 biological unit/ml of the factor. Further increases of the nonneurons reduced the scope of a neuronal response to Nerve Growth Factor between the maximal performance of the culture system and the increasing performance elicited without the factor. The results indicate that, given a minimal level of nonneurons, the performance in culture of these ganglionic neurons could be promoted in very similar patterns by either increasing the exogenous Nerve Growth Factor in the medium or increasing the ganglionic nonneurons on the culture floors, with an approximate and fixed ratio of 10−7 biological unit per nonneuron. Possibilities are discussed of a common mechanism underlying the supportive properties of the two agents.