Chick heart peptidergic innervation: localization and development.

Localization and development of chick heart peptidergic innervation (Substance P, VIP and Somatostatin) were investigated by means of immunofluorescence technique. The peptidergic component of the heart innervation was observed, for the first time, in older than 11 day chick embryos, i.e., subsequently to the appearance of the cholinergic component. The peptidergic structures achieve nearly full development in about 16-17 day embryos. Substance P is the most represented of the three peptides. It is localized both in nerve bundle fibers and in isolated fibers within the myocardium, the pericardium, the vessel walls; it is also present in fibers of some heart base ganglia. VIP is mostly contained in some thick single fibers travelling along the vessel walls of the heart base, the myocardium and the pericardium. Some VIP immunoreactive cells were also observed in the base ganglia. Somatostatin is mostly contained in some ganglia cells, whilst thin Somatostatin-immunoreactive fibers form a rich plexus among the atrial and ventricular myofibers, without contacting the vessel walls.