Development of neurotransmitter enzyme activity in the rat gastrointestinal tract

Acetylcholine and norepinephrine play important roles in determining gastrointestinal (GI) tract motility and secretion. At this time, however, little is known concerning the postnatal developmental patterns of the enzymes that synthesize and degrade these two neurotransmitters within the GI tract. The present study examined the developmental activities, expressed per gram protein per minute, of the cholinergic enzymes choline acetyltransferase (ChAT) and acetylcholine esterase (AChE) and the adrenergic enzymes tyrosine hydroxylase (TH) and monoamine oxidase (MAO) in male rats between days 1 and 50. Seven anatomic segments of the GI tract were assayed for enzyme activities. In general, all four neurotransmitter enzymes were present throughout the length of the GI tract and increased during the early postnatal period. The synthesizing enzymes ChAT and TH displayed peak activity prior to day 21, while the degrading enzymes AChE and MAO continued to increase past day 21. Each enzyme exhibited segmental differences and unique postnatal developmental patterns. Such differences in enzyme activities may be related to developmental increases in neuronal density, hormonal factors, or direct stimulation of the GI tract by liquid and/or solid diet.