Functional and structural studies concerning the control of activity in zygomatic glands of cats

The zygomatic gland of the cat consists of at least two parts, separated by a septum, and each drains by a separate duct opening on a mucosal ridge postero-medial to the parotid orifice. It is composed on thin-walled ducts and tubulo-acini, containing mainly mucous cells, but scattered cap cells are also present. In cats under chloralose anaesthesia there is a spontaneous flow of extremely viscous saliva and often, in addition, there is a reflexly elicited component to the secretion. In fact, in contrast to the other major salivary glands, the zygomatic gland is easily made to secrete reflexly even in deep] anaesthesia, e.g. by pinching ipsilateral parts of the tongue, by stimulation of the oesophagus mimicking swallowing, or by afferent excitation of ipsilateral lingual, glossopharyngeal or vagal nerves. The efferent link of the reflex arc is contained in the buccal branch of the mandibular nerve. Section of this nerve abolishes these reflexes, and two weeks later a great loss of acetylcholinesterase positive nerves can be demonstrated in the gland. Efferent stimulation of the buccal nerve evokes a lively secretion that is not affected by hexamethonium but is abolished by atropine. Histochemically, adrenergic nerves are also found surrounding the acini and these nerves disappear after excision of the superior cervical ganglion. Electrical stimulation of the cervical sympathetic trunk causes some secretion, mainly by way of beta 1-adrenoreceptors. Myoepithelial cells are present around the tubulo-acini, and indications of the effect caused by their contraction on the flow from the glands have been observed. Such activity can be induced reflexly and it is then abolished by cutting the buccal nerve or by injecting atropine.

Localisation of esteroproteases in 'resting' salivary glands from different species and the effects of the organophosphorus inhibitor E600

The distribution of reaction sites for esteroproteases has been assessed in 'resting' salivary glands from rats, guinea-pigs, cats, dogs and rabbits using the new substrate N-acetyl-L-methionine alpha-naphthyl ester (Lexow et al. 1979). Two main types of activity were observed in the parenchyma. 1) Condensed staining was present on the luminal sides of certain ducts in some, but not all, glands, and this type of staining was always most conspicuous in the submandibular glands of each species. It is likely that this periluminal esteroprotease activity arises from secretory enzymes that will pass into the saliva. Their greater presence in submandibular glands may have association with specialised licking activities. 2) Variable diffuse cytoplasmic staining was present in certain acinar cells from some, but not all, glands. This was most pronounced in the mucous cells of zygomatic glands from dogs. It is considered that the enzymes demonstrated in acinar cells are involved in processing secretory products rather than in being secretory themselves. The possibility that this includes 'signal peptidase' is discussed. Ductal activity in rats, cats and guinea-pigs had some relationship with sites of tryptophan staining but not in rabbits or dogs. Any relationship with acinar staining was less evident. Mast cells, showing strong esteroprotease staining, were present in variable numbers in the different glands. Preliminary attempts to qualify the enzymes being demonstrated were made by using the inhibitor E600. This substance inhibited all activity in acinar cells from each species, and in rabbits and dogs it also inhibited the ductal activity as well. However, in rats and guinea-pigs it had little or no effect on the ductal activity and in cats it had only a small inhibitory effect on the ductal activity. E600 had no obvious inhibitory effects on mast cell activity.

New observations on the innervation of striated ducts in submandibular glands of cats, including possible peptidergic nerves

The presence of hypolemmal axons between striated duct cells in submandibular glands of cats has been established electron microscopically. Axons were found between "light" cells, between "light" and "dark" cells and between "light" and basal cells. Hypolemmal axons were observed most frequently in the junctional region between striated and intercalary ducts. They were often more common in younger animals. "Dark" cells with numerous processes sometimes appeared to have a special relationship with hypolemmal axons. Most of the hypolemmal axons in striated ducts contained characteristic agranular vesicles of the cholinergic type, about 40 nm in diameter; many of these axons also contained large dense cored vesicles of the peptidergic type, about 100 nm in diameter and possessing a more clear outer halo. No adrenergic axons have been observed beneath the basal lamina of striated ducts, even after use of 5-OHDA. The possibility that some of the hypolemmal axons in striated ducts are peptidergic and their possible functions are discussed. Apart from other activities these axons may have a role in supplying special trophic factors to the cells, helping them in their developmental specialisation and maintaining them in normal condition. An absence of such factors after parasympathetic decentralisation may be responsible for the dramatic atrophic changes in striated duct cells, especially since the atrophy in the gland is not solely due to an absence of acetylcholine activation.

Activities of salivary myoepithelial cells: a review

Historical developments concerning salivary myoepithelial cells have been outlined and structural features of the cells have been described. Evidence from structural and functional studies supports the belief that myoepithelial cells usually have a dual innervation by parasympathetic as well as sympathetic nerves, and impulses from both types of nerve cause the cells to contract. Functional assessment using salivary flow phenomena and intraluminal pressure changes have been used to determine, so far as is possible, the effects of myoepithelial contractions. In some instances tissues have been examined structurally after such experimental procedures. These investigations indicate that salivary myoepithelial activity 1. Speeds up the outflow of saliva 2. Reduces luminal volume 3. Contributes to the secretory pressure 4. Supports the underlying parenchyma 5. Helps salivary flow to overcome increases in peripheral resistance. However, beyond a certain point, this may lead to sialectatic damage of striated ducts with increase in glandular permeability. Myoepithelial activity may also help to expel parenchymal cell contents in certain instances.

Effect of botulinum toxin on the choline acetyltransferase activity in salivary glands of cats

The choline acetyltransferase activity of submandibular glands that had previously received a retrograde injection of botulinum toxin via their ducts was found to be markedly lower than in the untreated contralateral glands. In the parotid glands exposed to the same treatment the activity of this enzyme was less affected.

Movement of horseradish peroxidase in submandibular glands of dogs after ductal injection

Small volumes of solutions of a tracer enzyme, horseradish peroxidase (HRP), have been injected retrogradely via the main duct of submandibular glands in dogs, and the distribution of the peroxidase reaction product within the glands has been studied light microscopically and electron microscopically at different times after the injection. Tissue taken immediately after injections of 0.25 ml, given over 10 sec, showed that HRP had penetrated into the interstitial spaces of the gland. It was usually irregularly distributed and appeared to have reached the interstices of the gland by passing through the intercellular junctions of adjacent acinar cells. In time the tracer gradually disappeared from the interstices of the gland. Most of this removal was probably via lymphatic and blood vessels, into both of which peroxidase rapidly passed after ductal injection. At 5 hours after the HRP injection only very weak interstitial staining was present and at later times none was detected. An inflammatory reaction occurred in the gland, starting within minutes after the injection of this foreign protein and reaching a peak after about 12 hours. The events in dogs and those occurring in rabbits under similar experimental conditions have been compared. This study has given some indication how foreign substances may be distributed after retrograde injection into salivary glands.

The adrenergic innervation of the submandibular gland of the cat and the effects of various surgical denervations on these nerves. A histochemical and ultrastructural study including the use of 5-hydroxydopamine

Images

Effects of secretory nerve stimulation on acid phosphatase and peroxidase in submandibular saliva and acini in cats

The effects of parasympathetic or sympathetic nerve stimulation either alone, or in combination, on the acid phosphatase-containing central acinar cells and the peroxidase-containing demilunar cells of the cat submandibular salivary gland have been investigated by histochemical and cytochemical techniques. The results obtained with these techniques were correlated with biochemical assays for both enzymes in the saliva secreted. The results indicate that, although both sets of nerves probably affect both sets of cells, the predominant secretory effect of parasympathetic stimulation is on the central cells and, conversely, the predominant secretory effect of sympathetic stimulation is on the demilunes. Sympathetic stimulation appeared also to have initiated synthesis of peroxidase in the demilunar cells, especially when it was superimposed upon parasympathetic stimulation.

Adrenergic influences on the permeability of rabbit submandibular salivary glands to blood-borne horseradish peroxidase

Horseradish peroxidase (HRP) administered close-arterially, has been found to enter rabbit submandibular saliva elicited by parasympathetic nerve stimulation. Adrenalin, superimposed on parasympathetic nerve stimulation, increased the passage of HRP into the saliva. Use of alpha- and beta-adrenoceptor agonists, either separately or together, and use of alpha- or beta-adrenoceptor antagonists together with adrenalin indicate that both alpha- and beta-receptor stimulation is necessary for this increase in glandular permeability to occur. Histochemical assessment showed that HRP had permeated the interstitial spaces of the gland and entered the spaces between adjacent parenchymal cells. However, in unstimulated glands it had only reached the lumina of striated ducts, but after adrenalin administration, peroxidase was also observed within acinar lumina. This work indicates that the predominant pathway taken by the HRP was via intercellular spaces and it is suggested that the permeability between junctional complexes of parenchymal cells is capable of being modified in vivo.

Supporting effects of myoepithelial cells in submandibular glands of dogs when acting against increased intraluminal pressure

1. In dogs under chloralose-urethane anaesthesia secretion from the submandibular gland was recorded with the outflow at gland level and at heights of up to 50 cm above the gland.2. With the outflow level increased, secretion elicited by sympathetic nerve stimulation was far better maintained before than after injection of the alpha-adrenoceptor blocking agent dihydroergotamine.3. When the outflow level was raised while no secretion occurred, fluid flowed into the gland. Part of this amount was returned on lowering the outflow to gland level. This volume was assumed to have been accommodated in the distended luminal system, whereas some fluid was obviously lost into the gland tissues.4. Both these fractions of the fluid flowing into the gland when the outflow level was high could be reduced by injecting the alpha-receptor agonist phenylephrine. Bradykinin, which like phenylephrine is known to contract salivary myoepithelial cells, had the same effect on the two inflow volumes.5. It is concluded that myoepithelial contraction reduced the distensibility of the luminal system and in addition supported the acini, thereby diminishing backflow into the glandular tissues and enabling the gland to discharge saliva against a high pressure.6. Morphologically it was found that in resting glands PAS-positive saliva was displaced from the ductal system when the outflow cannula was raised, but it was preserved in the lumina under similar conditions when the myoepithelial cells were being stimulated by phenylephrine or bradykinin.7. Although sympathetic secretion could be maintained against a head of pressure, so long as it was accompanied by myoepithelial contraction, the increased force caused by the secretion led to disruptive damage of striated ducts which are the first part of the luminal system not supported by myoepithelial cells.8. The morphological findings reinforce the belief that contraction of myoepithelial cells gives active support to the underlying parenchyma.

The autonomic innervation of rabbit salivary glands studied electron microscopically after 5-hydroxydopamine administration

In submandibular glands of rabbits both adrenergic and cholinergic axons are intimately associated with parenchymal cells of the intercalary ducts and the granular tubules, lying beneath the basement membrane and often in the space between the parenchymal cell and an associated myoepithelial cell. The submandibular acini receive a less intimate and less plentiful innervation by adrenergic and cholinergic axons which remain outside the basement membrane and are still associated with Schwann cells. Occasional axons of both adrenergic and cholinergic type occur beneath the basement membrane of submandibular striated ducts in intimate association with basal parts of the cells. In the parotid glands numerous adrenergic and cholinergic axons are found beneath the basement membrane of acini and intercalary ducts in intimate association with the cells.

Myoepithelial activity and the appearances of sialograms: a possible role in the formation of sialectasis

In experimental studies on dogs it has been shown that the sialographic filling of the ductal system may be severely restricted if the myoepithelial cells are contracting and it seems likely that myoepithelial activity in man will also influence sialographic appearances. It has also been found that when secretory forces were accompanied by myoepithelial contraction against a sialographic pressure the ersuing damage to striated ducts produced appearances of sialectasis. IT IS WONDERED WHETHER SIMILAR EVENTS MAY SOMETIMES BE RESPONSIBLE FOR SIALECTATIC APPEARANCES IN MAN.

Analytical ultrastructural studies on implanted dental amalgam in guinea-pigs

Implantation of amalgam induced a cellular reaction, and a rapid loss of copper and zinc and a more gradual loss of tin and mercury occurred. The silver remaining was generally associated with sulphur and was present either as a diffuse fuzz around remaining masses or in a finely particulate form.

Inflammatory cells in duct-ligated salivary glands of the cat: a histochemical study

Inflammatory cells were studied in submandibular, sublingual and parotid glands of cat following ductal ligation. Macrophages were seen within the parenchyma and associated with extravasated mucin, and were possibly of importance in removing secretory material. Neutrophils were seen interstitially and within the parenchyma. Eosinophils were involved in an initial inflammatory response in interstitial tissue. Fibrous connective tissue was more apparent.

Acid phosphatase and peroxidase in "resting" acinar cells of the major salivary glands of cats and their possible movement into secretory granules

After fixation of perarterial perfusion using an aldehyde mixture, salivary tissues were prepared for ultrastructural cytochemistry of acid phosphatase or peroxidase. Great variations in the distributions of the reaction product occurred, often within the same cell. Acid phosphatase staining occurred not only in lysosomes and sometimes in a GERL system, but a diffuse cytoplasmic component was also found in submandibular central acinar cells and to a lesser extent in parotid acini and variable staining occurred in the secretory granules of these cells. Peroxidase was variably associated with rough endoplasmic reticulum in submandibular demilunar cells, parotid acini, and more strongly in some sublingual cells. The secretory granules of the latter were darkly stained, but in parotid granules there was variable staining and least staining occurred in the granules of submandibular demilunes. These results are thought to indicate that not all enzymes present in secretory granules have reached there by an elective secretory process. Sometimes they appear to have entered the granules haphazardly, possibly having been enzymes associated with intracellular cisternal channels for transport or metabolism of other secretory substances and ultimately to have passed into the cisternal channels by chance or as part of a natural removal of redundant material.

Histological effects of ductal ligation of salivary glands of the cat

Forty-two submandibular, 32 sublingual and 31 parotid glands have been examined microscopically after ductal ligation avoiding the nerves for periods from 1 day to 1 yr. After an initial increase in size, there was over-all atrophy in all three glands. In the parotid gland the response was uniform and there was progressive atrophy until most of the acini were extremely atrophic. However, in the submandibular and sublingual glands the response was very variable, and although in some glands most of the acini were extremely atrophic, in other glands there was far less atrophy and most of the remaining acini appeared more or less similar to normal despite prolonged ligation. These results contrast with those of earlier experimental studies on ductal ligation, but have similarities with observations on the behaviour of human salivary glands.

Effects of heterologous cross-suture between the postganglionic sympathetic and the preganglionic parasympathetic nerve trunks of submandibular glands in cats

After sectioning the postganglionic adrenergic sympathetic nerve trunk for the submandibular gland, as close to the submandibular artery as practicable, its central end was sutured to the peripheral end of the preganglionic cholinergic parasympathetic nerve trunk for the gland, the chorda, which had been sectioned where it left the lingual nerve. The effects of this heterologous cross-sature were studied at different times, up to 1 year afterwards, by assessing the physiological and pharmacological responses of the glands and the neuro-histochemical changes in the nerve trunks and in the nerves within the glands. In all cases adrenergic sympathetic nerves grew across the site of suture and down the erstwhile cholinergic parasympathetic trunk, eventually to develop connections in the gland. In some cases the functional adrenergic reinnervation of the submandibular gland appeared to result exclusively or predominantly from the direct downgrowth of adrenergic axons to the gland, via the crossed nerves. In other cases however, in addition to a direct glandular reinnervation, there was some physiological and morphological evidence which suggested that possible heterogneous synaptic contracts may have been created between postganglionic sympathetic axons and cholinergic ganglion cells in the chorda nerve.

Movement of horseradish peroxidase in rabbit submandibular glands after ductal injection

Horseradish peroxidase (HRP) has been used as a tracer to study movements of solutions injected retrogradely via the duct of submandibular glands in rabbits. 0.1 ml of solution was injected either manually or by a constant hydrostatic pressure, and the subsequent distribution of HRP in the gland and duct at different times after injection has been examined histochemically at light and electron microscopical levels. Shortly after the injections, strong interstitial staining for peroxidase resulted from passage between acinar cells. Some sites of cellular uptake were observed and staining occurred in some ductal cells even when the duct had been cut at the hilum to minimize pressure effects. It is not known whether this diffuse uptake represents a physiological or pathological phenomenon. Some interstitial activity still remained 24 hr after injection but had disappeared by 48 hr. Inflammatory cells first appeared in the gland about 4hr after the injection and slowly increased up to about 24 hr after injection. The results indiate that the HRP reaches the interstices of the gland principally by penetration between acinar cells, and that the junctional complexes between striated duct cells appear to be more resistant to disruption by luminal pressures.

Secretory and structural effects of 6-hydroxy-dopamine on normal parotid glands of rats, and at different times after surgical sympathectomy

The effects of i.v. 6-hydroxydopamine (6-OHDA), 100 mg/kg, have been studied on parotid glands of rats at 12, 24, 48, 72 hr and 3 weeks after avulsion of the right superior cervical sympathetic ganglion. The salivary flow from normal left control glands and from right glands 12 hr after ganglionectomy were similar, but at longer times after ganglionectomy the secretory response from the test glands was greatly reduced. Morphological assessment showed that 6-OHDA induced a massive depletion of secretory granules from all control glands and also at 12 hr after ganglionectomy but at 48 and 72 hr there was considerably less depletion of granules on the ganglionectomized side. It is thought that at the longer times after ganglionectomy the secretion from the test glands is caused by circulating catecholamines released by the action of 6-OHDS on adrenergic nerves elsewhere, plus a possible small direct secretogogue effect oomy are thought to be attributable to the release of catecholamines from adrenergic nerves within the gland.

The effects of ductal ligation on the parenchyma of salivary glands of cat studied by enzyme histochemical methods

Submandibular, sublingual and parotid glands of cat have been studied following periods of ductal ligation ranging from 1 day to 1 year. An increased prominence of granules of acid phosphatase, beta-glucuronidase and E600-resistant esterase reaction products was sometimes seen in acinar cells and atropic striated ductal cells, and probably represents increased lysosomal enzymic activity, which may be of importance in the adapation of the parenchyma to the altered environment. Other reaction products often appeared to be at normal levels in parenchymal structures that were not very atrophic, and at reduced levels in those that were very atrophic, suggesting a reduction of functional activity in these structures.

Experimental salivary mucoceles in cat. A histochemical study

Ductal ligation of the sublingual gland induced mucocele formation in a high percentage of cats. Extravasated mucus was associated with all sublingual glands up to 20 days after ligation, and extravasation mucoceles were associated with 12 out of 27 sublingual glands between 7 and 365 days after ligation. Enzyme-histochemic examination revealed that the extravasated mucus induced a migration of macrophages and a fibroblastic reaction. It is thought that if these reactions are sufficiently intense in the early days after ligation, then continued spread of extravasated mucus and mucocele formation does not occur; however, if the extravasation is too great to be contained, a mucocele forms in which a balance develops between extravasation of mucus and its removal. Possibly the numerous macrophages in the mucoceles are involved in degrading mucus and facilitating its removal.

Structural changes associated with parotid "degeneration secretion" after post-ganglionic sympathectomy in rats

Parotid glands of rat have been examined 12, 24 and 48 hours after avulsion of the cervical sympathetic ganglion and compared with normally innervated left glands. Formaldehyde-induced fluorescence showed a relatively normal complement of adrenergic nerves at 12 hours but most of the nerves had lost their noradrenaline content by 24 hours and no fluorescent nerves were detected at 48 hours. Ultrastructural degenerative changes in axons were rare at 12 hours, common at 24 hours, and the degenerating axons appeared to have disappeared by 48 hours. The glands looked whitish and pale and similar to the controls at 12 and 48 hours but were pinkish and oedematous on the sympathectomised side at 24 hours. Correspondingly the acini were loaded with secretory granules at 12 and 48 hours but were extensively depleted of granules at 24 hours. This loss of granules is considered to be due to sympathetic "degeneration secretion" caused by the release of noradrenaline from the degenerating adrenergic nerves between 12 and 24 hours after ganglionectomy. This is thought to be the first example of morphological change resulting from "degeneration activation" to be recorded microscopically.

Changing attitudes on salivary secretion - a short history on spit

Images

Effects of nerve stimulation and denervation on secretory material in submandibular striated duct cells of cats, and the possible role of these cells in the secretion of salivary kallikrein

Striated ducts in cats after 24 hours starvation normally contained glycogen, especially in the basal regions. They also contained neutral mucin and tryptophan in apical parts of "light" cells and small irregular "secretory" granules were found in a similar distribution by electron microscopy.--Parasympathetic nerve stimulation caused a loss of glycogen but no apparent change in the apical secretory material, despite a copious secretion.--Sympathetic stimulation caused a loss of glycogen and an extensive depletion of apical secretory material, although the salivary flow was small.--Parasympathetic denervation caused progressive atrophy of striated ducts and oedematous degeneration of some cells occurred. Persisting "light" cells tended to contain few basal infoldings, few mitochondria and little apical secretory material.--Sympathetic denervation caused a loss of apical secretory material between 2-4 days, which may have been due to "degeneration activation". Thereafter little change was evident but some ductal atrophy had occurred by 32 days.--These changes in ductal secretory material correspond more closely than acinar changes to the alterations in glandular and salivary kallikrein resulting from similar experiments by other workers. It therefore seems likely that submandibular salivary kallikrein in the cat is present in the secretory material of striated ducts.

Changes in parotid acinar cells accompanying salivary secretion in rats on sympathetic or parasympathetic nerve stimulation

Morphological and secretory effects of stimulating autonomic nerves have been studied in parotid glands of rats. Sympathetic stimulation evoked a slow flow of saliva which had a high concentration of amylase. After long term sympathetic stimulation secretory granules were heavily depleted from the parotid acinar cells. Parasympathetic stimulation evoked a copious flow of saliva with a low concentration of amylase. However, at high frequency stimulation the total amount of amylase secreted on parasympathetic stimulation was as great or even greater than on symphatetic stimulation, nevertheless, any loss of secretory granules from the acinar cells was very small. It is concluded that secretion of parotid acinar granules in the rat is prinicipally a sympathetic function. Secretion of fluid is more effectively produced by parasympathetic stimulation and much of the amylase in such saliva appears to have arisen from sources other than the secretory granules.

The internal anal sphincter in the cat: a study of nervous mechanisms affecting tone and reflex activity

1. Smooth muscle activities in rectum and internal anal sphincter have been recorded using intraluminal balloons.2. Reflex activation of the sphincter, caused by distension of the rectum, has been assessed before and after various combinations of blocking drugs.3. Responses to stimulation of hypogastric or sacral nerves, or to the administration of drugs with autonomic actions have been tested before and after various combinations of blocking drugs.4. Results indicate that the tone of the internal anal sphincter is influenced by a number of neural mechanisms. These include motor pathways involving both alpha-adrenergic and cholinergic mechanisms and inhibitory pathways involving both beta-adrenergic and non-adrenergic non-cholinergic mechanisms.5. Cholinergic contractions of the sphincter were converted to relaxations after alpha-adrenergic blockade. This indicates that the contractions are an indirect effect operating through an adrenergic reflex. Cholinergic relaxations may also be indirect and operate through reflex inhibition secondary to rectal contractions.6. Sphincteric motor activity is controlled largely through alpha-adrenergic mechanisms by adrenergic nerves acting directly on the muscle. beta-Adrenergic inhibitory mechanisms are thought to operate indirectly via ganglia.7. The over-all control of the sphincter is by complex reflex mechanisms involving numerous pathways and the activity of the sphincter at any one time is determined by the net balance between motor and inhibitory influences.8. Sacral nerve stimulation indicated that it contains cholinergic nerves to the rectum, non-adrenergic non-cholinergic inhibitory axons to the sphincter and variable numbers of adrenergic axons to the sphincter.9. Responses of the sphincter to drugs and nerve stimulation were often variable, as has been described many times in the literature. It is considered that this is due to complex combinations of indirect reflex effects, secondary to activation of structures outside the sphincter, operating with or against direct effects on the sphincter itself.