DECREASED CHOLINE-ACETYLTRANSFERASE ACTIVITY IN NERVE GROWTH FACTOR-TRANSGENIC MICE DURING BRAIN-DEVELOPMENT

Activity of the synthetic enzyme for acetylcholine, choline acetyltransferase was investigated during development and in adult nerve growth factor-transgenic mice. A conspicuous reduction of choline acetyltransferase activity was observed in the anterior brain of nerve growth factor-transgenic embryos from embryonic days 13 to 16 (E13 to E16). Choline acetyltransferase activity levels subsequently resumed to normal levels, with the exception of a 15% increase in the adult hippocampus. Nerve growth factor contents followed a similar time-course and regional distribution in normal and nerve growth factor-transgenic animals and displayed significantly higher values from E14 to the early postnatal period. Nerve growth factor contents were normal in the adult brain. In vitro experiments confirmed the involvement of nerve growth factor in the decrease of choline acetyltransferase activity levels observed in transgenic neurons during development. These results suggest a role for nerve growth factor in the initial phase of the phenotypic differentiation of cholinergic neurons. They show that nerve growth factor may, under specific developmental conditions, lead to a paradoxical down-regulation of choline acetyltransferase activity.