[Enzyme histochemical investigations of the nucleus nervi oculomotorii of Salmo irideus (Gibbons 1855) during biomorphosis. I. Transmitter enzymes].

1. The activities of the transmitter enzymes acetylcholine esterase (AChE), monoamine oxidase (MAO) and gamma-aminobutyrate transaminase (GABA-TR) were investigated in the nucleus nervi oculomotorii of Salmo irideus (Teleostei) during biomorphosis. 2. AChE as well as MAO-activity could be demonstrated already before the time of hatching, whereas GABA-TR occured from the 10th day post hatching. 3. In earliest stages the AChE activity was found in the neuronal pericarya of the nucleus n. III, but later on a strong increase occured in vestibular presynaptic terminals establishing synaptic contacts with the lateral surface of the large pericarya, especially in the medial part of the dorsal subnucleus and the ventral subnucleus. In adults the enzyme activity was localized in vestibular nerve fiber terminals exclusively due to the loss of enzyme activity in the pericarya. 4. The activity of MAO was found surrounding the neurons of the nucleus nervi oculomotorii with stronger deposits of reaction product at the medial surface that is not occupied by cholinergic terminals. 5. Besides non reacting neurons in all parts of the nucleus some cells in the transition zone between the medial and lateral area of the dorsal subnucleus, exhibited high cytoplasmatic GABA-TR activity. 6. The different ways of chemical transmission between nerve terminals and the neurons of the nucleus nervi oculomotorii are discussed.