Nitrergic innervation and nitrergic cells in arteriovenous anastomoses

Nitrergic innervation and nitrergic epithelioid cells were studied in arteriovenous anastomoses of the tongue, ear, eye, and glomus organ of the finger in different species (rat, rabbit, dog, and man), by means of immunohistochemistry for nitric oxide synthase and enzyme histochemistry utilizing the catalytic activity of this enzyme (the NADPH-diaphorase reaction). Nitrergic perivascular fibers of the tongue were concentrated along the arterial tree and were maximal at the arteriovenous anastomoses in all species. Generally, fewer fibers were located around comparable segments of the episcleral eye vasculature. Only a few nitrergic fibers were found in the canine and rabbit ear, and in the glomus organ of the human finger; however, epithelioid cells in the tunica media of arteriovenous anastomoses of these organs were NADPH-diaphorase-positive and were moderately immunoreactive for nitric oxide synthase. In the epithelioid cells, the reaction product of the NADPH-diaphorase could also be demonstrated by transmission electron microscopy. The epithelioid cells were negative for the panneural and neuroendocrine marker PGP 9.5 confirming the myocytotic nature of these nitrergic cells. Thus, nitric oxide might play a role in mediating the vessel tone of arteriovenous anastomoses via nitrergic nerves or epithelioid cells.     

Innervation of the arteriovenous anastomoses in the dog tongue

Summary Profiles of nerve plexuses in the arteriovenous anastomoses of the dog tongue were investigated by both transmission and scanning electron microscopy. Three-dimensional morphology of the vascular nerves was examined after removal of the connective tissue components by the HCl-hydrolysis method. Tight bending and a rich nerve supply were the most characteristic features of the anastomosing channels. The tunica media consisted of an outer circular layer of typical smooth-muscle cells and an inner region containing longitudinal plicae of ramified smoothmuscle cells. The tunica adventitia was exclusively occupied by nerve bundles; fibroblasts were poorly developed. Numerous nerve bundles of variable size were coiled around the anastomosing channels, and occasional bundles ran crosswise over the U-shaped bent vessels.     

Autonomic innervation of the arteriovenous anastomoses in the dog tongue

Summary The innervation of the arteriovenous anastomoses in the dog tongue has been investigated. At the lightmicroscopic level, the vessels were found to be densely supplied with adrenergic and AChE-positive nerve plexuses and less densely with the quinacrine-binding nerve plexus. At the electron-microscopic level, at least two apparently different types of axon profiles were identified: 1) Small vesicle-containing axons, characterized by many small granular vesicles, variable numbers of small clear vesicles and large granular vesicles. Storage of endogenous amines and uptake of exogenous amines into most small granular vesicles and many large granular vesicles was demonstrated. These axons stained only lightly with reaction products for AChE activity and thus seemed to be adrenergic in nature. Some axons contained numerous large granular vesicles, whose cores occasionally stained with uranyl ions; this suggests a co-localization of ATP or peptides as neurotransmitters. 2) Small granular vesicle-free axons, containing small clear vesicles and large granular vesicles in variable ratio. Most cores of these large granular vesicles were heavily stained with uranyl ions. No storage or uptake of amine into the synaptic vesicles was detected. Some axons appeared to be typically cholinergic, some, typically non-adrenergic, noncholinergic, and the rest, intermediate between the two. All axons stained heavily with reaction products for AChE activity, suggesting their cholinergic nature.     

Three-dimensional cytoarchitecture of the media of arteriovenous anastomoses in the rabbit ear

Arteriovenous anastomoses in the rabbit ear were examined with scanning electron microscopy to elucidate the structural differentiation of the media of the shunt. Arterial, intermediate, and venous segments in the shunt and two layers of the media in the intermediate segment were differentiated based on cell shape and cell organization. In the arterial segment, smooth muscle cells were spindle-shaped, either elongated or short, with a few branches, and were arranged circularly or diagonally with respect to the vessel's long axis. There were also stellate muscle cells with radiating processes. In the intermediate segment, the smooth muscle cells of the outer layer of the media were also arranged circularly and resembled the elongated cells in the arterial segments, but they were more irregular in shape and had more processes than those of the arterial segment. The epithelioid cells of the inner layer of the media were oval or polygonal and oriented irregularly with respect to the vessel's long axis, clustering to form longitudinal plicae. The smooth muscle cells of the venous segment were flat with many lateral processes and formed a thin, discontinuous layer. The smooth muscle cells in the arterial segment and those of the outer layer of the intermediate segment exhibited a highly rugged surface texture, indicating their strong contractility; the epithelioid cells and the smooth muscle cells in the venous segment exhibited a generally smooth surface, indicating less contractility. The intermediate segments were supplied with a dense nerve plexus. The intermediate segments, therefore, may be actively involved in the regulation of blood flow under neuronal influence.     

Changes in the diameter of organ arteriovenous anastomoses during pressor reflexes]

In acute experiments on cats, the diameter changes of the arterio-venous anastomoses in a number of vascular zones and their shunting coefficient were studied under the pressor reflexes; the method of injections of the microspheres was used. In these experiments the shunting capacity of the arterio-venous anastomoses was shown to be decreased in the small intestine, the spleen, the kidney and the gastrocnemius muscle under the pressor synocarotid reflex and the electrical stimulation of the somatic afferents.     

Innervation of arteriovenous anastomoses in the brood patch of the domestic fowl

Summary The innervation of blood vessels in the brood patch (thoracic skin) of the domestic fowl was studied by use of the catecholamine fluorescence technique, acetylcholinesterase staining, and the immunoperoxidase technique for demonstration of vasoactive intestinal polypeptide (VIP). Large arteries and veins were sparsely innervated, whereas arteriovenous anastomoses (AVAs) were densely innervated by adrenergic, acetylcholinesterase-positive, and VIP-immunoreactive nerve fibres. The rich supply of different vasomotor nerves to AVAs emphasizes the importance of these vascular shunts in regulating blood flow and, in turn, the transport of heat to the brood patch. Furthermore, the presence of VIP-immunoreactive nerve fibres in the vasculature of the brood patch suggests that VIP might be the mediator of the previously reported cold-induced vasodilatation.