THE classical concept of the innervation of the urinary tract pretends that the ureter is supplied by sympathetic nerves while the bladder receives essentially parasympathetic nerves.Morphological studies of the intrinsic innervation of the urinary tract have been limited for decades by classical microscopic techniques (such as intravital methylene blue or silver impregnation) which could not establish the difference between sympathetic (adrenergic) and parasympathetic (cholinergic) nerves.The application of new and highly specific histochemical methods for the demonstration of adrenergic (norepinephrine) and cholinergic (acetylcholinesterase) nerve elements has thrown new light on the organisation and dynamics of the autonomic innervation of the mammalian ureter and bladder.Material and Methods.-Specimens were taken from the ureters and bladders of 25 mongrel dogs and 5 rabbits. The tissues studied were excised under light intravenous nembutal anaesthesia and specimens were obtained from all levels of the ureter and bladder. The tissues were quickly frozen in liquid nitrogen and sectioned in a cryostat at -30°C. Transverse and sagittal serial sections of 10 to 20 p were selected every 100 to 200 p. At the level of the ureterovesical junction, serial sections were taken each 40 p. The sections were mounted on a frosted slide and subsequently stained after the different histochemical methods.Clzolinergic nerve elements were studied by the technique of Karnovsky and Roots (1964) as modified by El-Badawi and Schenk (1967) for the demonstration of acetylcholinesterase (AChE). AChE activity is characterised by a fine granular reddish-brown precipitate. The sections were studied under a Zeiss photomicroscope by ordinary light, phase contrast microscopy and Nomarski differential phase microscopy. Adrenergic nerves were demonstrated by the formaldehyde-induced fluorescence of catecholamines following the method of Falck et a/. (1962) as modified by Spriggs et a/. (1966). The sections were examined under a Zeiss fluorescent photomicroscope using a high-pressure mercury lamp, a BG 12 excitation filter and a 470 p barrier filter. Under these conditions the specific fluorescence of norepinephrine (NE) is identified by a yellowish-green fluorescence localised in varicosities along the sympathetic nerve fibres and in granular formations in the cytoplasm of adrenergic neurons (for details see Corrodi et al., 1967).The distribution of monoamine oxidase (MAO) activity was studied histochemically by the method of Glenner et a/. (1957). The sites of M A 0 activity are identified by deposits of a bluishpurple formazan pigment developed when tryptamine is oxidised by M A 0 following the reduction of nitroblue tetrazolium. RESULTSThis paper is limited to the description of the essential features of the ureteral and vesical

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