An histological study of the nerves associated with the ductus arteriosus

The study from which this paper is taken was initiated as an attempt to consider in detail the fate of the nervous elements in the wall of the ductus arteriosus as that structure, following birth, is converted into the fibrous ligamentum arteriosum. The study was based upon the premise, apparently amply supported by a number of gross and histological observations (Boyd, ’38 and ’41; Muratori, ’37; Nonidez, ’37; Takino and Watanabe, ’37; Kennedy and Clark, ’41; Allan, ’55; and Holmes, ’ 5 8 ) , that the mammalian ductus arteriosus is associated with a plexus of nerve fibers having terminals on its smooth muscle. These nerves are visible grossly and are intimately associated with the ductus as demonstrated by histological methods. Agreement regarding the distribution and characteristics of the nerve fibers associated with the presumed pressor receptors found in the ductus arteriosus has followed the histological studies noted. However, description of the smaller, finely myelinated fibers thought to be motor to the musculature of the ductus has been superficial and incomplete. Nevertheless, statements by Boyd (’40), Kennedy and Clark (’41), and Holmes (’58) imply that these elements do indeed exist. In the papers cited above, Takino and Watanabe, (’37) and Boyd, (’40) demonstrated that sensory (receptor) endings were seen in the ligamentum arteriosum of the adult. Boyd noted, however, that none of the finer fibers were observed in the adult material. The studies cited above included tissues from man, rabbits, cats, dogs, rats, guinea pigs, and pigs. In general, the findings are comparable throughout the forms studied with the exception that no “sensory” terminations were found in the ductus arteriosus of the newborn pig (Boyd, ’40; Takino and Watanabe, ’37). Although the aortic pressor receptors in the chick have been analyzed and described by Nonidez ( ’ 3 5 ) , only incidental mention of the “arterial ducts” (ductus arteriosus) is made. Insofar as it has been possible examination of the literature has failed to uncover a definitive paper on the innervation or, for that matter, the histology of the ductus arteriosus in birds. Therefore certain aspects of this study dealing with the chick attempt to provide information in this area. Since findings to be reported in this paper contradict earlier reports regarding the nature of the motor innervation of the mammalian ductus arteriosus, additional background concerning this portion of the innervation will be outlined here. In his consideration of the ductus arteriosus of the rabbit, Boyd (’40) states that in addition to the thick (sensory) fibers, finer fibers “terminate in relation to the muscle fibres in the wall of the ductus by simple endings which resemble the endings of vaso-motor fibres in other blood vessels. They appear, then to be motor fibres. ” Kennedy and Clark (’41) stated that “In other regions of the ductus as on the ventral surface or near the junction with the pulmonary artery a few fibers of fine caliber suggesting unmyelinated postganglionic efferents were found. There were not enough of these to consider them sufficient for innervation of the smooth muscle of the ductus wall, perhaps. ” In a note on the ductus arteriosus, Holmes (’57) concluded from the negative cholinesterase reaction displayed by the media of the ductus that “most of the ductus muscle is not in intimate contact with nervous elements. ” In a paper on the same subject published a year later ____ 1 Supported in part by U.S.P.H. S. grant H-2335.