Monoamine-storing cells in the avian aortic wall.

Using the Falck-Hillarp method, monoamine-storing cells were demonstrated in the avian thoracic aorta just above the openings of the ductus arteriosus. By electron microscopy, numerous dense-cored vesicles, 90-220 nm in diameter, were seen in the cytoplasm. The electron opacity of these dense-cored vesicles was reduced when reserpine (5 mg/kg) was administered. These monoamine-storing cells formed typical synapses with the Schwann cell-enclosed nerve terminals. The monoamine-storing cells first appeared in the aortic wall at 9 days in ovo but it remained obscure whether they originated from the neuroectoderm.