The effect of culture on the neuronotrophic activity of avian smooth muscle

Abstract

The expansor secundariorum is a smooth muscle of the chicken wing which receives a dense noradrenergic innervation and contains high concentrations of trophic activity for sympathetic neurons. Expansor cells were dissociated in trypsin and grown to confluency in standard nutrient medium. Medium that had been conditioned by expansor cells contained trophic activity for chick sympathetic nerves which differed from the activity which is found within the muscle prior to culture, in that it was effective on a different neuronal subpopulation. Furthermore, unlike the factor(s) found in vivo, the trophic activity of the conditioned medium was not enhanced by NGF and could be partially inhibited by mouse NGF antibodies. Both the production of total trophic activity in the conditioned medium and the activity which differed from that in the muscle extract, increased rapidly and to the same extent between 24 and 48 h culture. Greater concentrations of trophic activity were present in medium conditioned by smooth muscle cells than by skin cells. The conditioned medium was able to support more neurons from 11 and 18 day incubated embryos than a saturating dose of NGF. Neither this effect nor the additive effect of conditioned medium with expansor muscle extract could be attributed to the presence of neurite promoting factors. We conclude that the cultured muscle produces neuronotrophic activity that is similar to the activity found in denervated but not innervated muscle.