Localization of choline acetyltransferase within identified motoneurons of the nematode Ascaris

Choline acetyltransferase (CAT) activity has been measured in the nematode Ascaris lumbricoides. Strips of hypodermal tissue which contained branches of single identified motoneurons (Stretton, A.O.W., R.M. Fishpool, E. Southgate, J.E. Donmoyer, J.P. Walrond, and I.S. Kass (1978) Proc. Natl. Acad. Sci. U.S.A. 75: 3493-3497) as well as control strips containing no neural tissue were assayed. In strips of hypodermis which contained branches of excitatory motoneurons (classes DE1, DE2, and DE3), CAT activity was elevated 5 to 10 times compared to control levels. Branches of inhibitory motoneurons (classes D1 and V1) did not add to the level of CAT observed in the controls. These data provide additional support for the suggestion (e.g., del Castillo, J., W.C. deMello, and T. Morales (1963) Experientia 20: 141) that acetylcholine is an excitatory neurotransmitter at nematode neuromuscular junctions. The function of the low level of CAT observed throughout the hypodermis is unknown.