Effects of haemin on neurones derived from the neural crest.

Haemin at high concentrations promoted the survival and neuritic outgrowth in vitro of dissociated sensory and parasympathetic neurones from 8-day-old chick embryos. Similar concentrations of haemin increased the activities of the neurotransmitter biosynthetic enzymes, tyrosine hydroxylase and choline acetyltransferase, in explant cultures of neonatal rat sympathetic ganglia, and in explant and dissociated 14-day-old embryonic chick parasympathethic ganglia, respectively. Enzyme activities of both dissociated neonatal rat sympathetic ganglia and explant and dissociated 8-day-old embryonic chick parasympathetic ganglia were not affected by haemin. Since the neurotrophic effects of haemin were small compared to those of tissue extracts, and were seen mainly at concentrations approaching the limits of its solubility, it is concluded that haemin resulting from the breakdown of haem proteins in tissue extracts is unlikely to contribute significantly to their effects.