Choline acetyltransferase activity in mouse cerebellar cultures

The finding of the acetylcholine synthetic enzyme, choline acetyltransferase, has been reported in mouse cerebellar cultures, and it has been used as an index of neuronal survival and maturation. These results are curious in light of immunocytochemical studies which show that this enzyme is localized within mossy fiber terminals in glomerular structures of the cerebellar cortex. Since most mossy fibers are of extracerebellar origin, a significant population of mossy fiber terminals would not be expected to be present in cerebellar cultures. The origin of this acetylcholine synthetic activity has been examined in mouse cerebellar cultures. Two groups of explants, one with and the other without incorporated dorsal pontine tissue, were cultivated. Only cultures that included pons showed well developed glomerular structures with mossy fiber rosettes. Homogenates of the cultures were assayed for their ability to synthesize acetylcholine, and the synthesis was shown to be due to choline acetyltransferase by use of the specific inhibitor, (naphthylvinyl)pyridine. Cultures lacking dorsal pontine tissue had only low levels of enzyme activity, whereas those which included pons had 20-60 times greater synthetic activity. These results indicate that the choline acetyltransferase activity arises from pontine tissue in cerebellar cultures and are consistent with mossy fibers being the source of this enzyme.