Ultrastructural and histochemical observations on innervation of developing human urinary bladder

Abstract

Urinary bladder innervation in human foetuses of 13 to 25 weeks has been studied by electron microscopy and glyoxylic acid and acetylcholinesterase histochemical methods. Cholinergic fibers appear as a faintly stained dense plexus at 13 weeks. An increase in thickness and intensity of staining of the cholinergic nerve bundles occurs over the foetal age period under study. At 25 weeks, the finer cholinergic plexuses are demonstrable on the muscle fibers. Adrenergic innervation, on the other hand, becomes apparent at 16 weeks as faintly stained plexuses along the blood vessels in the trigone and is also sparsely seen in the wall of the fundus. By 25 weeks the intensity of staining increases. Plexuses appear around the ganglionic clusters in the adventitia and in the wall of the urinary bladder; intensely fluorescent neurons and individual adrenergic fibers in the muscle layers are also seen. Ultrastructurally the muscle fibers undergo maturation by 19 weeks with the development of myofibrils and increasing number of intercellular contacts. The axonal profiles in all the layers of the bladder wall of foetuses from 13 to 19 weeks contain large numbers of small granulated vesicles and some have large vesicles with a halo around them. Neuromuscular synaptic zones seen by 16 weeks do not show the typical structure and generally contain clear vesicles in the presynaptic varicosities.