Ultrastructural and histochemical studies on the innervation of the heart of a teleost, Pleuronectes platessa L.

Abstract

The innervation of the heart of the plaice has been studied ultrastructurally and histochemically in order to describe the anatomy, and the nature of the neuro-transmitters involved in the regulation of the heart. A single cardiac branch of the vagus runs over the Duct of Cuvier and sinus venosus where it forms a plexus extending into the sinoatrial region. Many ganglion cells are scattered throughout this plexus upon which are seen cholinergic-type terminals at which AChE can be localised. It is therefore concluded that this is the parasympathetic cardiac ganglion. The innervation of the atrium is dense at the sinoatrial end but decreases towards the ventricle. The ventricle is probably aneural, possibly a consequence of the lack of a coronary blood supply to act as a pathway for an innervation of this chamber. Most of the intramural axon profiles contain large numbers of small agranular vesicles and are cholinergic, AChE being localised at their membranes. Other profiles contain small numbers of larger granular vesicles amongst the agranular vesicles but these are not adrenergic since these vesicles are not depleted by reserpine, do not load with 6-OHDA, and AChE can be localised at the membranes of the profiles. No adrenergic-type profiles were seen in any part of the heart, nor were any fluorescent, catecholamine-containing fibres observed.