Development of the autonomic ground plexus in the atrioventricular valves of the rat

The development of the adrenergic and cholinergic innervation of the rat atrioventricular valves was studied in whole mount stretch preparations. Specimens obtained from rats ageing 2-30 days were processed for the histofluorescence and enzyme histochemical demonstration of monoamines and acetylcholinesterase (AChE) activity, respectively. Adrenergic and AChE-positive nerve fibres could be detected from the 9-10th postnatal days onwards. Fluorescence microscopy showed the presence of many brightly fluorescent mast cells in the close vicinity of the ingrowing terminals. The presence of mast cells during early stages of development of the ground plexus may be related either to the preneural state of the tissue or the structural and/or functional maturation of the autonomic nerve terminals.