Light and electron microscopic demonstration of neuropeptide Y-like immunoreactive nerves in human cardiac muscle.

Neuropeptide Y (NPY)-like immunoreactive nerves were demonstrated in human cardiac muscle. The atrial specimens were obtained from open-heart surgery. The PAP method was applied for immunocytochemistry for light and electron microscopy. A dense, extensive network of NPY-like immunoreactive nerve fibres was seen between cardiac muscle cells and around blood vessels. In electron microscope PAP precipitates were localized in large dense-cored vesicles of 80-120 nm in size in separate nerve terminals or in the terminals situated in the nerve bundles. Close contacts were observed between NPY nerves and muscle cells and blood vessels. The possible functional role of NPY innervation in the human heart is discussed.