During the development of the acetylcholine system of the Xenopus brain a distinct increase in neurotransmitter content was found which is interpreted as an expression of increased activity of cholinergic neurons. The acetylcholine content in the whole brain increases markedly from hatching to metamorphosis. During this period regional differences of transmitter distribution can be observed. 2. The ChAT activity of the whole brain remains constant during total larval life, whereas the AChE activity increases with the beginning of metamorphosis. Comparing the different brain parts, both enzymes show a regional decrease in activity from caudal to rostral, whereas in adult animals the enzyme activity of the midbrain is dominant.
