Storage, uptake and synthesis of catecholamines in the intrinsic adrenergic neurones in the proximal colon of the guinea-pig

In the present work, the effects of drugs on the storage, uptake and synthesis of catecholamines in intrinsic and extrinsic adrenergic neurones of the guinea-pig intestine are compared, using the fluorescence histochemical technique for localising catecholamines. In respect to the properties examined in this work, the intrinsic adrenergic neurones of the proximal colon of the guinea-pig were found to be qualitatively similar to adrenergic neurones of the sympathetic chains: the intrinsic cells and their terminals are depleted by reserpine or guanethidine; they concentrate and retain catecholamines and this uptake is blocked by desmethylimipramine or phenoxybenzamine; after depletion by reserpine, the fluorescence can be restored by the dopamine and noradrenaline precursor, dopa and this restoration is prevented by blocking the decarboxylation of dopa to dopamine. However, there are clear quantitative differences: the terminals of intrinsic neurones are less susceptible than are extrinsic neurones to depletion by reserpine, guanethidine or 6-hydroxydopamine; the intrinsic neurones more readily retain noradrenaline after reserpinisation. It is suggested that quantitative differences between extrinsic and intrinsic neurones of the intestine could involve a difference in the activity of monoamine oxidase.