Cytological localization of noradrenaline, monoamine oxidase and acetylcholinesterase in salivary glands of dog

Interlobular excretory ducts of mammalian salivary glands: structural and histochemical review

In the major salivary glands of mammals, excretory ducts (EDs) succeed striated ducts. They are for the most part interlobular in position, although their proximal portions sometimes are on the periphery of a lobule, where they occasionally retain some of the structural features of striated ducts. Based on a survey of a broad range of mammalian species and glands, the predominant tissue type that composes EDs is pseudostratified epithelium. In some species, there is a progression of epithelial types: the proximal EDs are composed of simple cuboidal or columnar epithelium that, in the excurrent direction, usually gives way to the pseudostratified variety. Secretory granules are visible in the apical cytoplasm of the principal cells of the EDs of only a few species, but histochemistry has shown the presence of a variety of glycoproteins in these cells in a spectrum of species. Moreover, the latter methodology has revealed the presence of a variety of oxidative, acid hydrolytic, and transport enzymes in the EDs, showing that, rather than simply acting as a conduit for saliva, these ducts play a metabolically active role in gland function. It is difficult to describe a "typical" mammalian ED because it can vary along its length and interspecific variation does not follow a phylogenetic pattern. Moreover, in contrast to intercalated and striated ducts, ED cellular features do not exhibit a relationship to diet.

Parasympathetic innervation of cutaneous blood vessels by vasoactive intestinal polypeptide-immunoreactive and acetylcholinesterase-positive nerves: histochemical and experimental study on rat lower lip

The distribution and origin of perivascular acetylcholinesterase-active and vasoactive intestinal polypeptide-immunoreactive nerve fibers were studied in the rat lower lip by means of acetylcholinesterase histochemistry and vasoactive intestinal polypeptide immunohistochemistry. The perivascular nerve fibers stained intensely with both histochemical techniques and were widely distributed on small arteries and arterioles of the lower lip, especially in the transitional zone between the hairy skin and the mucous membrane. The distributions of the two types of fibers were very similar and most of them showed overlapping coloration, on consecutive staining for vasoactive intestinal polypeptide and acetylcholinesterase. Both acetylcholinesterase-positive and vasoactive intestinal polypeptide-immunoreactive fibers were completely lost on removal of the otic ganglion, while they were not affected by sympathetic ganglion removal or sensory nerve sectioning. In the otic ganglion, most cells exhibited acetylcholinesterase activity, and about 60% of the cells showed light to heavy vasoactive intestinal polypeptide immunoreactivity. These findings indicate that vessels in the rat lip are innervated by parasympathetic fibers originating from the otic ganglion and support the view that vasoactive intestinal polypeptide is present in cholinergic neurons. This may suggest the possible control by the parasympathetic nervous system of cutaneous blood vessels through vasoactive intestinal polypeptide-containing cholinergic neurons, in general or at least in the facial area.

Autonomic innervation of salivary glands in the armadillo, anteater, and sloth (Edentata)

The intraglandular distribution of adrenergic and cholinergic nerve fibers was studied histochemically in the parotid, mandibular, and sublingual glands of six species of edentates belonging to the three families that comprise the order; namely the Dasypodidae (armadillos), the Myrmecophagidae (anteaters), and the Bradipodidae (sloths). The following histochemical techniques were used: (a) acetylcholinesterase reaction for the demonstration of cholinergic fibers; (b) formaldehyde- and glyoxylic acid-induced fluorescence for the demonstration of adrenergic fibers. In addition, norepinephrine (NE) was assayed fluorimetrically in the mandibular and parotid glands of the armadillo. A network of acetylcholinesterase-positive nerve fibers surrounds the intra- and interlobular ducts and endpieces of all glands; it is of low density in the mandibular and sublingual gland of the sloth, of high density in the sublingual gland of the anteater and of moderate density in the remaining glands. A vascular cholinergic innervation occurs in all salivary glands. Although present around the vessels, adrenergic new fibers were virtually absent from the parenchyma of all glands, even after in vitro incubation of glandular tissue with NE or after administration of NE to armadillos previously treated with a monoamine oxidase (MAO) inhibitor. Consistent with this fact, the amount of NE present in the parotid and mandibular gland of the armadillo was extremely low. These findings may indicate that the salivary secretion in the edentates is regulated by the parasympathetic rather than by the sympathetic nervous system.

A histochemical study of catecholamines and cholinesterases in the autonomic nerves of the human minor salivary glands

The cholinergic and adrenergic innervation of human minor sublingual, buccal and labial salivary glands has been studied with histochemical techniques for localizing acetylcholinesterase and catecholamines. A rich cholinergic innervation was observed around the acini, blood vessels and some ducts of the three glands. The adrenergic innervation, however, was virtually absent from the parenchyma although present around the blood vessels, in marked contrast to the dense parenchymal adrenergic innervation observed in the human parotid and submandibular glands. These results suggest that the autonomic nervous mechanism which regulates salivary secretion is more elaborate in the major than in the minor salivary glands.

Effects of sympathetic nerve stimulation in the presence of a slow parasympathetic secretion in the parotid and submaxillary glands of the rabbit

Sympathetic secretory responses from the parotid and the submaxillary glands of the rabbit were studied; sympathetic excitation occurred either alone or during a slow parasympathetic background secretion, imitating the resting secretion normally present. The fairly rapid sympathetically evoked flow of saliva from the parotid gland was, in the background secretion, further increased and obtained at low frequencies, which at sympathetic stimulation alone were subthreshold. The effects, which could be repeated with sympathomimetic drugs in a pilocarpine induced secretion, were abolished by alpha and beta-adrenoceptor blockade in combination. The submaxillary gland gave a very scanty secretion on sympathetic excitation, the effects being mediated via beta-adrenoceptors. The responses were not increased in a background secretion but the main effect of sympathetic activation was to retard the salivary flow. The retardation was attributed to vasoconstriction accompanying sympathetic excitation. Eliminating the vasoconstrictor responses, while retaining the sympathetic secretory effects, did not reveal any increase of the sympathetic salivary responses in the submaxillary gland.

Innervation of the rat Harderian gland by adrenergic and cholinergic nerve fibres

The innervation of the rat Harderian gland was studied using histochemical methods for catecholamines and acetylcholinesterase (AChE). Selective denervations were performed to investigate the neural connections of this gland with various ganglia. Light microscopically the AChE-positive nerves seemed to run as thick bundles in the intertubular connective tissue. These bundles sent finer branches around the acini. The blood vessels, localized in the connective tissue septa, were surrounded by a dense plexus of AChE-containing fibres. By electron microscopy, the AChE-positive fibres were seen to terminate near the myoepithelial cells surrounding secretory cells. These fibres were also observed in contact with the blood vessels and occasionally close to the secretory cells. Fluorescent adrenergic nerves surrounded the blood vessels. Some fibres were also observed in the interlobular tissue. All the AChE-containing nerves degenerated after cutting the zygomatic nerve. On the other hand, removal of the ciliary ganglion or the superior cervical ganglion, or stereotactic coagulation of the ophthalmic nerve did not affect these nerves. The fluorescent adrenergic fibres disappeared following both removal of the superior cervical ganglion and coagulation of the ophthalmic nerve. These fibres were intact after removal of the ciliary ganglion.

Changes in monoamine oxidase and catechol-0-methyl transferase activities after denervation of the nictitating membrane of the cat

1. The question of cellular localizations of monoamine oxidase and catechol-o-methyl transferase, enzymes involved in the metabolism of noradrenaline, has been investigated by following the changes in the enzyme activity of the smooth muscle of the cat nictitating membrane after sympathetic denervation. Any falls in enzyme activity coinciding with the time course for degeneration of the sympathetic nerve endings (2-3 days) can reasonably be ascribed to a former localization of the enzyme within the sympathetic nerve.2. Monoamine oxidase activity of the inferior and medial smooth muscle was significantly reduced 3 days after sympathectomy and remained reduced 14 days after sympathectomy.3. A correlation was found between the fall in monoamine oxidase activity and the endogenous noradrenaline concentration of the contralateral normal muscle, indicating that the higher the endogenous noradrenaline concentration, the greater the fall in monoamine oxidase activity after denervation.4. It was concluded that the fall in monoamine oxidase activity after denervation indicated a former localization of the enzyme within the sympathetic nerve endings.5. The fall in monoamine oxidase activity of the denervated muscle was significantly less measured with benzylamine as a substrate than with tyramine. This suggested that the neuronal monoamine oxidase may have different properties than the extraneuronal enzyme.6. A small fall in the catechol-o-methyl transferase activity of denervated smooth muscle was found and a correlation between the fall in enzyme activity and endogenous noradrenaline indicated that in this smooth muscle a proportion of the catechol-o-methyl transferase activity may be of presynaptic origin.

The role of monoamine oxidase in the response of the isolated central artery of the rabbit ear to tyramine

1. Monoamine oxidase activity was demonstrated histochemically throughout the media of the rabbit ear artery but not in the adventitia at its border with the media where the sympathetic nerve terminals are concentrated. Neither intensity nor distribution of enzyme activity was perceptibly altered up to 60 days after sympathetic denervation.2. Iproniazid and nialamide increased the sensitivity of the artery to intraluminal tyramine much more than that to extraluminal tyramine, so that the difference between the potencies for the two routes of administration became less marked.3. The results indicate that inactivation by monoamine oxidase in the media is a factor contributing to the relatively low potency of intraluminal tyramine on the artery.

Ulcerogenic effect of 5-hydroxytryptamine (serotonin) in the stomach: histochemical study by fluorescent method

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