The effect of sympathectomy on the occurrence of microliths in salivary glands of cat as studied by light and electron microscopy

Parasympathectomy is followed by a greatly increased occurrence of microliths in the feline submandibular gland, which appears to be because of secretory inactivity. The sympathetic nerves are also important in secretory processes, and so feline submandibular, sublingual and parotid glands subjected to postganglionic sympathectomy for periods from 1 day to 1 yr have now been investigated. Microliths were detected in two out of 28 sympathectomized submandibular glands and four out of 27 untreated glands, and in 10 out of 22 sympathectomized sublingual glands and seven out of 19 untreated glands. There were no significant differences between the occurrence of microliths in sympathectomized and untreated glands. Microliths were not detected in any of 29 sympathectomized and 30 untreated parotid glands. The appearance of the sympathectomized glands was similar to that of the untreated glands. The failure of sympathectomy to affect the occurrence of microliths or the appearance of the glands is possibly because of parasympathetic nerve impulses, which produce continuing secretory activity, and also the spontaneous secretion of the sublingual gland. The results support the concept that secretory inactivity is an aetiological factor of microlithiasis.

Substance P and neurokinin A immunoreactive nerve fibres in the developing salivary glands of the rat

The time of appearance and distribution of substance P (SP) and neurokinin A (NKA) immunoreactive nerve fibres in developing salivary glands of the rat were studied by the use of indirect immunohistochemical methods. The glands were examined at daily intervals from the 15th day in utero (i.u.) until birth, and subsequently on the 2nd, 5th, 7th, 12th, 16th and 30th postnatal day. The findings were compared to samples from adult. The first SP- and NKA-immunoreactive (IR) nerve fibres appeared on the 19th day i.u. in the parotid and submandibular glands and were abundantly distributed around developing ductal branches. In the mesenchyme around the developing ductal branches of the parotid gland the fibres appeared on the 20th day i.u. In the submandibular gland NKA-IR fibres appeared in the mesenchyme surrounding the developing ductal branches on the 19th day i.u. and SP-IR fibres on the 21st day i.u. Around blood vessels of both glands, SP- and NKA-IR fibres made their appearance only much later, on the second postnatal day. The number of SP- and NKA-IR nerve fibres in the developing salivary glands was already high on the 19th day i.u. when they were first detected. From this point up to the 16th postnatal day the glands were richly innervated by the fibres, but later the numbers slowly decreased to adult levels. The abundance of SP- and NKA-IR nerve fibres especially around the ductal branches and secretory structures in the developing salivary glands suggests a role in the functional maturation of salivary glands.

[Peptidergic innervation of human salivary glands (parotid gland and submandibular gland)]

Immunocytochemistry and a radioimmunoassay were used to investigate the existence and distributions of various regulatory peptide immunoreactivities (ir) in human submandibular and parotid glands. Numerous nerve fibers containing vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM), or neuropeptide tyrosine (NPY) and C-flanking peptide of NPY (CPON)-ir were found in close proximity to acini, ducts and blood vessels. Only a few calcitonin gene-related peptide (CGRP)- and substance P (SP)-ir nerve fibers could be demonstrated and were mainly localized around blood vessels and ducts. Galanin and the recently discovered peptides helospectin and pituitary adenylate cyclase activating peptide were unable to be detected in the salivary glands studied. Preliminary quantitative investigations of four human submandibular glands using radioimmunoassay showed that VIP-ir had the highest concentration, followed by NPY-ir and CGRP-ir; SP-concentrations were below the detection limit. The possible physiological significance of these peptides for salivary secretion is discussed.

Endothelium-derived vasodilator responses to sympathetic stimulation of the submandibular gland in the cat

1. The extent to which vasodilator responses to electrical stimulation of the sympathetic innervation, in the submandibular gland of the cat, depend upon release of endothelium-derived relaxing factor (EDRF) within the gland has been investigated in anaesthetized cats given N-nitro-L-arginine methyl ester (L-NAME) which specifically blocks the synthesis of EDRF from arginine. 2. Close intra-arterial infusions of L-NAME (> or = 100 mg kg-1) produced a steady and significant rise in mean aortic pressure together with a steady increase in basal submandibular vascular resistance over the next 20-30 min. It also reduced, but failed to abolish, the vasodilatation which occurs during intermittent stimulation of the sympathetic innervation (20 Hz for 1 s at 10 s intervals) together with the after-dilatation which occurs immediately after a period of continuous stimulation of these nerve fibres (2 Hz). 3. In cats pretreated with the beta-blocker propranolol (> or = 1.0 mg kg-1) both vasodilator responses were reduced, but persisted until L-NAME was administered, whereupon both were abolished. 4. It is concluded that release of EDRF within the submandibular gland of the cat contributes to the basal tone of the vasculature and is responsible for the alpha-adrenergic vasodilator responses to stimulation of the sympathetic innervation, but not for the beta-adrenergic vasodilator responses.

The intraglandular submandibular ganglion of postnatal and adult rats. II. A morphometric and quantitative study

A morphometric study was undertaken on the submandibular ganglion cells in rats of different ages. This showed a direct proportional increase with age in all the variables measured. Mean cross-sectional cell area showed the most dramatic growth, an increase of more than 5-fold between birth and young adulthood. Mean cell diameter and cell perimeter doubled over the same period. The growth of the nucleus, expressed as diameter, was slower when compared with that of the ganglion cells as a whole. The number of intraglandular ganglion cells remained relatively unchanged from birth to young adulthood, ranging from about 3000 to 5000 cells. They were mainly distributed at the hilar region of the submandibular salivary gland, contributing 1/2 to 2/3 of the total ganglion cell population. The second largest cell population was in the intralobular region, which made up about one-third of the population. The least populated region was in the connective tissue of the sublingual salivary gland, which contained only about 5-7% of the total cell number. Cell counts based on the fluorogold labelling method were generally lower than those made after haematoxylin and eosin staining. In the 2-d-old animals, counts of fluorogold-labelled cells were only about half the H & E counts. The discrepancy may be due to the thicker sections used in the fluorogold method, superimposition of cells leading to an underestimation of cell numbers. Nevertheless, the fluorogold labelling method provided rapid and reproducible results. Its main advantage is that the labelled ganglion cells emit a bright yellow fluorescence which is readily identified; the other is the simplicity of the procedure, as labelling of ganglion cells can be achieved by the intraperitoneal route.

Characterization of superior cervical ganglion neurons that project to the submandibular glands, the eyes, and the pineal gland in rats

These studies sought to determine whether the cell bodies of rat superior cervical ganglion neurons projecting to three very different target organs differ in terms of their size, number, location within the ganglion and/or neuropeptide content, and whether these features are altered in response to neonatal deafferentiation of the ganglion. A series of retrograde tracer, immunocytochemical, and double-labeling studies revealed differences in the size, number, location and neuropeptide content of superior cervical ganglion neurons that project to the submandibular salivary glands, eyes, or pineal gland. The mean areas of the cell bodies of neurons projecting to the submandibular gland are largest, those projecting to the eye are smallest, and those projecting to the pineal are intermediate in size. Submandibular gland projecting neurons are found throughout the ganglion, while the eye and pineal projecting populations are localized to the rostral quadrants. The different subpopulations of target organ specific superior cervical ganglion neurons are heterogeneous in their content of vasoactive intestinal peptide-, neuropeptide Y- and somatostatin-like immunoreactivity. A greater percentage of submandibular gland than of pineal projecting neurons display vasoactive intestinal peptide-like immunoreactivity, but there are no differences in the percentage of neurons displaying neuropeptide Y- or somatostatin-like immunoreactivity between the target organ specific groups. Neonatal deafferentiation does not result in changes in the size, number or distribution of target organ specific neurons, or in the percentage of immunoreactive neurons in these populations. In conclusion, these studies provide evidence that the size and distribution of neurons and percentage of peptide-containing neurons in the superior cervical ganglion is related to the target organ innervated, but provides no evidence of exclusive target organ-peptide relationships.

Increase of microliths in inactive salivary glands of cat

Secretory inactivity could be a factor in the formation of microliths, and so their occurrence in feline salivary glands after the secretory inactivity produced by parasympathectomy was investigated. Parasympathectomy was followed by a greatly increased occurrence of microliths in the submandibular salivary gland, but not in the parotid and sublingual, which may relate to residual secretory activity in these glands. This discovery suggests that secretory inactivity may indeed be a factor in the production of microliths in human salivary glands, and consequently of chronic sialadenitis and sialothiasis.

Histochemistry of NADPH-diaphorase, a marker for neuronal nitric oxide synthase, in the peripheral autonomic nervous system of the mouse

In order to identify possible sites of synthesis of nitric oxide in the peripheral nervous system, several mouse organs were investigated for the presence of NADPH-diaphorase activity. Diaphorase-positive neurons and fibers were localized in the tongue, submandibular salivary glands, gastrointestinal and biliary duct systems, lower urinary tract and pelvic ganglia. By thionin counterstaining it was found that a distinct subpopulation of neurons was labeled. The present study indicates that nitric oxide synthase may be present in intrinsic neurons of various organs, suggesting a widespread function of nitric oxide in the peripheral autonomic nervous system.

The intraglandular submandibular ganglion of postnatal and adult rats. I. A light and electron microscope study

The structure of the intraglandular submandibular ganglion is described in both postnatal and adult rats. The ganglion is localised mainly at the hilum where the majority of the cell bodies are observed. Ganglia are also present in the intralobular septa of both the submandibular and the sublingual glands. Often they are found along the main salivary ducts with the larger ganglia being encapsulated by connective tissue. On electron microscopy, the submandibular ganglion cells show the usual features of autonomic neurons. The cells contain a prominent round nucleus. Numerous short processes project from the soma together with a few long dendrites. The organelles are randomly distributed throughout the soma. Most of the synapses observed were on the short processes with occasional axosomatic synapses. Nonsynaptic desmosome-like contacts are a common feature among the ganglion cells. Especially noteworthy are contacts made by the dendrites which deeply invaginate the soma of an adjacent nerve cell. The ganglion cells of the postnatal and adult submandibular ganglia show minor differences. Ultrastructurally, the postnatal cells show signs of immaturity such as abundant free ribosomes, well developed Golgi complexes and disorganised rough endoplasmic reticulum. Mitotic satellite cells were observed associated with the postnatal ganglion cells. The study has confirmed that all the submandibular ganglion cells show a positive reaction for acetylcholinesterase. Enzyme activity is localised in the cisternae of rough endoplasmic reticulum, the Golgi complex, plasma membrane and nuclear envelope.

Galanin-like innervation of rat submandibular and sublingual salivary glands: origin and effect on acinar cell membranes

The distribution and source of a galanin-like innervation of rat salivary glands has been examined. Additionally, submandibular and sublingual acinar cell membrane responses to galanin or a cholinergic agonist were studied. Galanin-immunoreactive fibers were observed throughout the submandibular and sublingual glands in association with ducts and acini. A subset of submandibular ganglion cells expresses galanin immunoreactivity. Parasympathectomy resulted in a marked decrease in galanin immunoreactivity in the glands. Sympathectomy resulted in marked reduction of dopamine beta-hydroxylase immunoreactivity with no appreciable change in galanin immunoreactivity. Retrograde labeling experiments demonstrated that galanin-immunoreactive sensory neurons in the trigeminal ganglion do not innervate the submandibular or sublingual gland. These results indicate that the galanin-like innervation of rat salivary glands is derived from parasympathetic nerves to the glands. Since rat sublingual glands contain largely mucous acini while rat submandibular gland acini are seromucous, electrophysiological responses to galanin and the muscarinic agonist, bethanechol, were compared. Agonist-induced voltage shifts varied between the two glands. The galanin-induced response at the level of the resting membrane potential in submandibular acinar cells was a hyperpolarization, while that in sublingual acinar cells was a depolarization. There was also a greater voltage dependence to the galanin-induced submandibular response than to the sublingual response. Differences were also noted in the acinar cell response to cholinergic stimulation between these glands. These results demonstrate the existence of a galanin-like innervation to salivary glands that may be functionally relevant. Moreover, the results challenge the idea that agonist-induced membrane responses are similar among acinar cells of different glands.

CNS cell groups projecting to the submandibular parasympathetic preganglionic neurons in the rat: a retrograde transneuronal viral cell body labeling study

The retrograde transneuronal viral tracing method was used to study the CNS nuclei that innervate the parasympathetic preganglionic neurons controlling the submandibular gland in the rat. A genetically engineered beta-galactosidase expressing Bartha strain of pseudorabies virus (PRV) was injected into the submandibular gland of rats. After 4 days, PRV infected tissues were reacted with the Bluo-Gal substrate (halogenated indolyl-beta-D-galactoside) and labeled cell bodies were identified throughout the brain. In the medulla oblongata, cell body labeling was seen in the superior salivatory nucleus, and throughout the medullary reticular formation as well as in the nucleus of the solitary tract, spinal trigeminal nucleus, and deep cerebellar nuclei. In the pons, PRV labeled neurons were found bilaterally in the locus ceruleus, subceruleus region, and parabrachial complex. In the mesencephalon, labeled cells were found in the Edinger-Westphal nucleus, deep mesencephalic nucleus, and central grey matter. Several hypothalamic regions were labeled including the lateral, perifornical and paraventricular hypothalamic nuclei. In the telencephalon, PRV-positive cell bodies were observed in the substantia innominata, bed nucleus of the stria terminalis and central nucleus of the amygdala. The results suggest that widespread areas of the CNS are involved in control of salivation.

Labelling and recording from dissociated target-specific rat superior cervical ganglion neurons

A population of neurons was retrogradely labelled in the superior cervical ganglia (SCG) of the adult rat following the injection of the fluorescent dye Fast blue into the submandibular salivary glands (SMG). The neurons retained the fluorescent label following dissociation and culture. Electrical and chemosensitive properties of the labelled neurons were studied with the whole-cell patch-clamp technique.

Bilateral irradiation of head and neck induces an enhanced expression of substance P in the parasympathetic innervation of the submandibular gland

Substance P and calcitonin gene-related peptide (CGRP) are present in nerve fibers innervating the submandibular gland. Radiotherapy of tumors in the head and neck region usually embraces the salivary glands in the irradiated field and consequently a dramatic decrease in salivary function is seen. In this study, the submandibular glands and ganglia of rats subjected to fractionated irradiation were examined by use of immunohistochemical techniques for demonstration of substance P and CGRP. Irradiation was given on five consecutive days (daily doses of 6-9 Gray) with unilateral or bilateral irradiation techniques. Specimens of control and experimental animals were processed in parallel. A marked increase in the expression of substance P in the ganglionic cells--presumably parasympathetic--and in the number of fibers showing substance P-like immunoreactivity in association with acini and small ducts was seen in response to bilateral irradiation. (Surprisingly, unilateral irradiation of the parotid area had no effect on peptide distribution in the irradiated gland and ganglion). No changes in the pattern of CGRP immunoreactivity occurred. In the trigeminal ganglion, which supplies the submandibular gland with the majority of the sensory substance P- and CGRP-containing nerve fibers, no changes in the expression of substance P or CGRP immunoreactivity were seen. The results suggest that bilateral irradiation leads to an increase in the synthesis of substance P-like substance in the parasympathetic ganglionic cells supplying the submandibular gland with secretory nerves, and can thus be an additional factor in explaining the altered secretory capacity of salivary glands.

Neuropeptides in human salivary (submandibular and parotid) glands

The existence, distribution and density of various neuropeptides in human submandibular and parotid glands were investigated using immunocytochemistry and radioimmunoassay. Numerous nerve fibers containing vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM), or neuropeptide Y (NPY) and C-flanking peptide of NPY (CPON) immunoreactivities (ir) were found in close association to acini, ducts and blood vessels. Only few calcitonin gene-related peptide (CGRP)- and substance P (SP)-ir nerve fibers could be demonstrated, mainly localized around blood vessels and ducts. Galanin and the newly discovered peptides helospectin and pituitary adenylate cyclase activating peptide (PACAP) could not be detected in human salivary glands.

Beta-adrenergic signal transduction in aging parotid and submandibular salivary glands

This study assessed agonist- and post-receptor-stimulated adenylate cyclase (AC) activity in parotid and submandibular salivary glands from female F-344 rats of 3, 12, and 24 months of age. Isoproterenol-stimulated dose-response activation of adenylate cyclase was unchanged between 3 and 12 months but decreased at 24 months (p less than .05). Forskolin-stimulated AC activity, representing catalytic unit activity, was decreased at 24 months in the parotid (p less than .05) and at 12 months (p less than .05) and 24 months (p less than .01) in the submandibular gland. Beta-adrenergic signal transduction in salivary glands stimulates the secretion of salivary proteins that have important functions in the maintenance of oral health.

Morphological evidence for the maintenance of the cervical sympathetic system in aged rats

Elements of the cervical part of the sympathetic nervous system have been examined quantitatively in four and twenty-four month Wistar rats. The number of unmyelinated axons in the cervical trunk had significantly (P less than 0.002) increased in the old animals and the number of myelinated axons comprised less than 4% of the total number at both ages. The number of neurons in the superior cervical ganglion and the density of noradrenergic innervation of two of its target organs, the iris and the submandibular gland, were insignificantly different at the two ages. These results are consistent with other evidence which suggests that the cervical sympathetic system is maintained throughout the adult lifespan in rats.

Topography of functional subpopulations of neurons in the superior cervical ganglion of the rat

This study describes the distribution patterns of neurons in the rat SCG that project to a number of spatially separated and functionally different target tissues. Fluorescent dyes were used to label retrogradely neurons that project to the pineal gland, iris, nictitating membrane, Müller's smooth muscle of the eyelid, submaxillary gland, thyroid gland, tongue, buccal mucosa, and skin in several areas of head and neck. The numbers of neurons in the various subpopulations were quantified and, in several instances, postganglionic nerve transection was used to correlate the topography of subpopulations with the exit site/s of their projections from the ganglion. Individual neurons were found to have very limited projection fields and contralateral innervation of bilateral targets appeared to be minimal. Neurons with specific functions or projection fields were not highly localised within the SCG, but there was a general rostrocaudal organisation of neurons with respect to the position of their targets along the rostrocaudal axis of the body and this was correlated with the exist sites of the neurons from the ganglion.

Neuronal metabolism and DOPA decarboxylase immunoreactivity in terminal noradrenergic sympathetic axons of rat

This study was undertaken to determine whether immuno-histochemical staining for DOPA decarboxylase (DDC) is present in axons of rat noradrenergic sympathetic neurons. A sparse plexus of varicose axons exhibiting DDC-like immunoreactivity (DDC-IR) was associated with blood vessels and acini in the submandibular gland, but this was much less extensive than the population that exhibited tyrosine hydroxylase-like immunoreactivity (TH-IR). The varicose terminal TH-IR axons in atrium, spleen, and vas deferens were devoid of DDC-IR both in grown rats and during the post-natal period of axon growth, although weak DDC-IR was seen in large pre-terminal nerve bundles. Similar patterns of staining were seen with paraffin-embedded and with frozen, formaldehyde-fixed material. No enhancement of DDC-IR was seen in any tissue after chronic alteration of catecholamine turnover with reserpine or alpha-methyl-para-tyrosine, and the numbers of submandibular DDC-IR axons were not increased by disruption of axonal transport with colchicine or by decentralization of the superior cervical ganglion. We conclude that terminal noradrenergic axons contain insufficient DDC-IR for microscopic visualization, regardless of their metabolic state, reinforcing previous evidence that DDC-IR can be used as a histochemical marker for dopaminergic axons. By this criterion, the rat submandibular gland may receive a sparse dopaminergic innervation.

The role of substance P in parasympathetic nerve-induced secretion in the rat submandibular gland

Fluid secretion from rat submandibular saliva evoked by electrical stimulation of the chorda tympani (parasympathetic secretory stimulation) was greatly reduced in the presence of atropine. However, some secretion was always evident at frequencies of 5 Hz and higher. The substance P-antagonist ([D-Arg1, D-Pro2, D-Trp7,9, Leu11]-substance P) also reduced the chorda-evoked saliva. Salivary secretion induced by the electrical stimulation of the superior cervical ganglion (sympathetic secretory nerve) was not affected by either atropine or substance P-antagonist. Continuous chordal stimulation reduced the glandular content of substance P to approximately 50% after 60 min, but similar stimulation of the superior cervical ganglion failed to produce such a reduction. Electron histochemical observation showed that the chordal stimulation caused depletion of substance P from the appropriate nerve fibers within the gland. The reduced secretory capability after continuous stimulation of the chorda at high frequency (20 Hz) was reversed by infusion of a subthreshold dose of exogenous substance P. Histological examination of granular duct cells revealed no degranulation in either chorda-stimulated or substance P-infused rats. The summation of findings suggests that endogenous substance P plays a complementary role in the regulation of parasympathetic nerve-induced fluid secretion in the acinus but is minimally involved in degranulation from granular duct cells.

Secretory responses in granular ducts and acini of submandibular glands in vivo to parasympathetic or sympathetic nerve stimulation in rats

The roles of sympathetic and parasympathetic nerves in the secretion of saliva from submandibular glands of rats have been tested by electrical stimulation of either nerve for 1 h unilaterally in separate animals. The flows of saliva thereby induced and their protein content were monitored. Structural changes in each gland were assessed by light- and electron microscopy and compared with the unstimulated contralateral control gland, and the extent of the changes was determined morphometrically. Sympathetic nerve stimulation induced a relatively low flow of saliva that was rich in protein and was accompanied by extensive degranulation from both acinar and granular duct cells. In contrast parasympathetic nerve stimulation induced a considerable flow of saliva that had a low protein content and no detectable degranulation occurred from the secretory cells. It is possible, therefore, that some protein in parasympathetic saliva may have arisen from a non-granular pathway.

Yohimbine increases submaxillary kallikrein release into the saliva in dogs: evidence for alpha 2-adrenoceptor-mediated inhibition of cholinergic pathways

1. The effects of the alpha 2-adrenoceptor antagonist, yohimbine (0.5 mg kg-1, i.v.) on basal, sympathetic and parasympathetic stimulation-induced submaxillary kallikrein release were investigated in the anaesthetized dog. Kallikrein was measured by its kininogenase activity before and after trypsin activation which also allowed a study of the proportion of active to total enzyme. 2. Yohimbine induced a rapid, three fold increase in basal kallikrein release correlated with an increase in salivary flow rate which lasted for 60 min following injection. 3. Sectioning the chorda tympani did not affect basal kallikrein release but abolished yohimbine-induced rise in salivary kallikrein secretion. 4. Parasympathetic stimulation alone induced a 3 to 4 fold increase in basal kallikrein release correlated with an increase in salivary flow rate. Yohimbine induced a significant additional increase in parasympathetic-stimulated kallikrein release. 5. When the cervical sympathetic nerve was sectioned the basal kallikrein release decreased by 30 to 40%. 6. Sympathetic stimulation alone also induced a 3 to 4 fold increase in basal kallikrein. This was not correlated with the salivary flow and unaffected by yohimbine. 7. The results indicate that yohimbine increases submaxillary kallikrein release into the saliva by inhibition of presynaptic alpha 2-adrenoceptors located on the chorda tympani nerve endings.

Pattern of ongoing activity in rat superior cervical ganglion neurons projecting to a specific target

The ongoing activity of superior cervical ganglion neurons projecting to the rat submandibular gland was investigated with intracellular techniques. The relevant cells were identified by retrograde labeling with the fluorescent dye DiI placed in the submandibular gland 7-10 days earlier. The majority of labeled cells (89%) were 'silent' during a standard 5-min period of recording. In contrast, only 15% of cells projecting to targets other than the submandibular gland were silent during the standard period of observation. Evidently, ganglion cells innervating different targets have different patterns of activity.

Immunohistochemical localization of [Met5]enkephalin and [Met5]enkephalin-Arg6-Gly7-Leu8 in sympathetic and parasympathetic neurons and nerve fibers projecting to the rat submandibular gland

The localization of [Met5]enkephalin, [Met5]enkephalin-Arg6-Gly7-Leu8, vasoactive intestinal polypeptide and tyrosine hydroxylase immunoreactivities was studied in the submandibular gland of adult Sprague-Dawley and Wistar rats using the indirect immunofluorescence technique. Immunoreactivities for [Met5]enkephalin and [Met5]enkephalin-Arg6-Gly7-Leu8, a proenkephalin A-derived octapeptide, showed identical distributions. A large number of enkephalin-immunoreactive nerve fibers were detected around secretory acini, along intercalated ducts, convoluted granular tubules, intra- and interlobular ducts, as well as in close contact with blood vessels. The submandibular ganglia contained several enkephalin-immunoreactive neurons and nerve fibers. In the superior cervical ganglion numerous enkephalin-immunoreactive neurons and nerve fibers were also detected. Immunohistochemical co-localization studies indicated that [Met5]enkephalin and [Met5]enkephalin-Arg6-Gly7-Leu8 immunoreactivities co-exist with vasoactive intestinal polypeptide in a subpopulation of neurons of the rat submandibular ganglia, in nerve trunks along the salivary ducts of the gland, and in nerve fibers around the acini. Uni- or bilateral superior cervical ganglionectomies for 1-4 weeks resulted in a complete disappearance of tyrosine hydroxylase immunoreactivity in the glandular parenchyma, while moderate tyrosine hydroxylase immunoreactivity was seen in some neurons of the submandibular ganglia. Abundant [Met5]enkephalin-Arg6-Gly7-Leu8-immunoreactive nerve fibers were still seen around the acini and blood vessels, as well as close to salivary ducts. These operations did not affect the [Met5]enkephalin-Arg6-Gly7-Leu8-immunoreactive neurons in the submandibular ganglia. Many principal neurons in the superior cervical ganglion contained both [Met5]enkephalin-Arg6-Gly7-Leu8 and tyrosine hydroxylase immunoreactivity. Nerve ligation experiments indicated that [Met5]enkephalin-Arg6-Gly7-Leu8-immunoreactive sympathetic fibers project along the external carotid nerve. Accordingly, nerve fibers were found around the acini and blood vessels as well as in nerve trunks along the salivary ducts of the submandibular gland, showing co-localization of [Met5]enkephalin-Arg6-Gly7-Leu8 and tyrosine hydroxylase. Taken together, these observations suggest that the nerve fibers of the rat submandibular gland containing proenkephalin A-derived peptides are of both sympathetic and parasympathetic origin.

VIP-containing nerve fibres in the submandibular gland of the dog and protein secretion in vitro in response to VIP

Previously, administration of VIP has been shown to elicit no flow of saliva from the submandibular gland of the dog. However, in the present study we found VIP to cause release of protein in vitro from canine submandibular gland tissue. Furthermore, VIP-containing nerve fibres were demonstrated in large numbers in association with acini. Thus, VIP may be involved in the nervous regulation of salivary protein secretion in the dog.

Endogenous levels of nerve growth factor (NGF) are altered in experimental diabetes mellitus: a possible role for NGF in the pathogenesis of diabetic neuropathy

Sympathetic and neural-crest derived sensory neurons consisting of unmyelinated and small myelinated fibers are known to be affected at an early stage in diabetes mellitus (DM). Since these peripheral neurons need nerve growth factor (NGF) for their development and maintenance of function in adulthood, changes in endogenous NGF levels could be of relevance for the pathogenesis of diabetic neuropathy (DNP). Using an improved two-site enzyme immunoassay for NGF, we have investigated whether endogenous NGF levels are altered in Sprague-Dawley rats with DM induced by a single injection of streptozotocin (STZ). STZ-treated rats are known to develop in many respects equivalents to neuropathic complications observed in human DM. We found in some sympathetically innervated target organs decreased NGF contents by maximally 56%: transiently in the iris 2 weeks and in the ventricle 12-24 weeks after DM induction and permanently in the submandibular gland already 3 days after DM induction. Several weeks after onset of DM, NGF content was increased by maximally 145-300% in most peripheral targets investigated, such as in iris, cardiac atrium and ventricle, spleen, prostate gland, and vas deferens. This is suggestive for an impaired NGF removal by NGF-sensitive neurons in diabetic rats. Moreover, NGF levels were decreased to minimally 42.6 +/- 4% of control in the NGF-transporting sciatic nerve. NGF levels began to decrease not before 3 weeks after DM induction and remained decreased with 54.0 +/- 5% of control even after 6 months duration of DM. About the same time (i.e., 2 weeks after induction of DM) NGF levels began to decrease in the superior cervical ganglion (where the sympathetic perikarya are located) to minimally 53.2 +/- 4% of control 12 weeks after DM induction. No altered NGF levels were observed during a 3-month duration of DM in the terminal ileum and sensory trigeminal ganglion. Since NGF exerts its neurotrophic action in the perikarya after its retrograde transport from the NGF-producing periphery, our results are consistent with the hypothesis that an alteration in NGF levels may play a role in the pathogenesis of DNP as far as sympathetic neurons are concerned. Thus, our results suggest that DM influences the production and/or transport of endogenous NGF and consequently, that a deprivation of this neurotrophic factor may account for some of the functional deficits known to occur in DNP, such as impaired catecholaminergic transmitter synthesis. This hypothesis possibly opens the way for new concepts in the therapy of DNP.

Target size regulates calibre and myelination of sympathetic axons

Axons in vertebrate peripheral nerves are ensheathed by Schwann cells. For some axons, this sheath consists of a single layer of glial cell cytoplasm and plasma membranes; for other axons, Schwann cells form multilayered myelin. Whether or not a Schwann cell makes myelin is determined by a signal from the axon, but the nature of this signal is not known. Here I show that sympathetic postganglionic axons, which are normally not myelinated, become myelinated when their calibre is increased as a result of increasing the size of the peripheral target they innervate. This result implies that axon calibre, which is known to be correlated with myelination, is in fact the crucial determinant of whether an axon becomes myelinated. Furthermore, the finding that increasing or decreasing target size causes corresponding increases or decreases in axon size indicates that axon calibre is itself regulated by retrograde signals from peripheral target tissues.

Effects of atropine injection on food-associated drinking in rats with superior salivatory nucleus lesions

The neuropharmacological mechanisms involved in the prandial drinking pattern seen in rats with superior salivatory nucleus lesions + parotidectomy were investigated with behavioral methods. Results showed that the administration of low doses (0.1 mg/kg body wt) of atropine in lesioned rats potentiated previously established prandial drinking. Higher doses of atropine (1.0 mg/kg), however, were required to induce a similar degree of prandiality in control rats (parotidectomy alone). These findings suggest that the salivatory nucleus lesions affected a cholinergic brainstem-salivary gland system involved in the neural control of food-associated drinking.

Experimental American trypanomiasis in rats: sympathetic denervation, parasitism and inflammatory process

Tissue parasitism, inflammatory process (histologic methods) and sympathetic denervation (glyoxylic acid-induced histofluorescence for demonstration of catecholamines) were studied in the heart (atrium and ventricle) and the submandibular gland of rats infected with the Y strain of Trypanosoma cruzi. In the heart paralleling intense parasitism and inflammatory process, the sympathetic denervation started at day-6 of infection and at the end of the acute phase (day 20) practically no varicose nerve terminals were found in both myocardium and vessels. In the submandibular gland, in spite of the rarity of amastigote pseudocysts and the scarcity of inflammatory foci, slight to moderate (days 13-15 of infection) or moderate to severe denervation (day 20) was found. At day 120 of infection both organs exhibited normal pattern of sympathetic innervation and only the heart showed some inflammatory foci and rare pseudocysts (ventricle). Our data suggest the involvement of circulating factors in the sympathetic denervation phenomena but indicate that local inflammatory process is, at least, an aggravating factor.

Rectification of synaptic and acetylcholine currents in the mouse submandibular ganglion cells

1. Synaptic currents and responses to acetylcholine (ACh) were recorded from mouse submandibular ganglion (SMG) cells under whole-cell voltage clamp. 2. The peak amplitude of excitatory synaptic currents (ESCs) as well as the currents evoked by the ionophoretic application of ACh followed a unique non-linear current-voltage (I-V) relation. The chord conductance of the whole-cell currents decreased with depolarization of the membrane potential and became virtually 0 at 50 mV. 3. The decay of ESCs was described by two exponential functions. Both the fast (tau f) and slow (tau s) time constants were sharply decreased at depolarizing potentials beyond -40 mV, being insensitive to hyperpolarizing potentials more than -50 mV. 4. Single ACh receptor channels were characterized by the whole-cell current noise analysis. The single-channel currents followed Ohm's law at negative membrane potentials but tended to reach a plateau at positive membrane potentials. The mean slope conductance measured between -40 and -20 mV was 28.5 pS. 5. The product of the number of functional channels (N) and the probability of a channel being open (p) showed a steep voltage dependence. The value of Np at 20 mV was only 31% of that at -20 mV. 6. The noise power spectrum was best fitted by a double-Lorentzian function. Both the fast (tau f) and slow (tau s) time constants were sharply decreased by depolarizations beyond -20 mV. being less sensitive to membrane potentials more negative than -30 mV. 7. The non-linear I-V relation of ESCs was attributed in part to the voltage dependence of p and in part to the voltage dependence of the single-channel conductance (gamma) of ACh receptor channels.

Secretion of protein from salivary glands in the ferret in response to vasoactive intestinal peptide

1. Secretory responses of ferret parotid and submandibular glands were investigated in the presence of muscarinic, alpha- and beta-adrenoceptor blocking agents. 2. In pentobarbitone-anaesthetized animals I.V. doses of vasoactive intestinal peptide (VIP) failed to elicit overt secretion of saliva from either gland. 3. However, an occult secretion of protein occurred in response to VIP from both types of gland. This was revealed by means of a subsequent I.V. wash-out injection of substance P, which is a potent secretagogue in ferrets. This effect of VIP was much more marked in the submandibular than in the parotid gland. 4. Electrical stimulation of the chorda-lingual nerve gave rise to protein secretion in the submandibular gland at subthreshold frequencies for overt non-cholinergic, non-adrenergic secretion of saliva, as revealed by subsequent wash-out I.V. injection of substance P. 5. Protein secretion in response to VIP was also demonstrated in vitro by perifusing small pieces of the two glands. The sensitivity of submandibular tissue to VIP greatly exceeded that of the parotid tissue. 6. It is concluded that VIP, or a structurally related peptide, may be involved in the non-cholinergic, non-adrenergic secretory response of ferret salivary glands evoked by parasympathetic nerve stimulation.

Peripheral target regulation of dendritic geometry in the rat superior cervical ganglion

Dendritic arborizations of neurons in the adult rat superior cervical ganglion were measured in control ganglia and in ganglia innervating peripheral targets that were relatively larger or smaller than normal. The relative size of the target--the submandibular gland in these experiments--was manipulated during development by changing the ratio between the amount of target tissue and the number of innervating ganglion cells. Thus, ligating the submandibular salivary duct reduced the size of the gland, whereas partially denervating the gland produced a relatively larger target by making a smaller number of ganglion cells innervate a gland of normal size. Neurons innervating targets that were smaller than normal had significantly smaller dendritic arborizations and cell bodies than control cells. Conversely, neurons projecting to relatively larger than normal targets had larger dendritic arborizations and cell bodies, and more primary dendritic branches. Such cells were also innervated by a larger than normal number of preganglionic inputs. A similar change in dendritic geometry was observed when relative target size was increased after cutting the cervical sympathetic trunk, showing that target regulation of dendritic geometry is not dependent on ganglion cell activity or the presence of presynaptic innervation. Dendrites in the superior cervical ganglion normally grow in parallel with body size throughout life (Purves et al., 1986a; Voyvodic, 1987a). The present results imply that an important aspect of dendritic growth is an ongoing responsiveness of ganglion cells to feedback signals arising from the peripheral targets they innervate.

Morphological changes in salivary glands after treatment with sialagogues. An electronmicroscopical study

A dual innervation in salivary glands has been discussed. It is unclear how alpha-adrenergic and cholinergic agents stimulate the secretory cells. Different effects on serous and mucous cells are reported after stimulating with carbachol, clonidine, noradrenaline, cyclocytidine and pilocarpine, respectively. In the rat, carbachol and clonidine predominantly affect the mucous cells, however, with different morphological effects. Cyclocytidine exclusively degranulates the serous cells. Noradrenaline stimulates both serous and mucous cells and gives rise to vast cytoplasmic changes. Pilocarpine only shows effect on the mucous cells with formation of intracytoplasmic vacuoles. The effects reported are discussed with regard to experiments on salivary gland radiosensitivity.

Gustatory-salivary reflex: neural activity of sympathetic and parasympathetic fibers innervating the submandibular gland of the hamster

Electrophysiological experiments were performed to clarify the neural control mechanisms subserving gustatory-salivary reflex in anesthetized and decerebrate hamsters. Efferent neural activities of postganglionic sympathetic and preganglionic parasympathetic fibers, innervating the submandibular gland, were recorded when taste stimuli were infused into the oral cavity. Neural activities of primary gustatory afferents were also recorded from the chorda tympani (innervating the anterior part of the tongue) and the glossopharyngeal nerve (innervating the posterior part of the tongue). The parasympathetic fibers showed a low rate of spontaneous discharges (about 0.3 Hz), and responded tonically in an excitatory manner to taste stimulation. The magnitude of parasympathetic activity was highly correlated with the magnitude of gustatory afferent responses of the chorda tympani rather than that of the glossopharyngeal nerve. On the other hand, the sympathetic fibers showed irregular burst discharges (1.5 burst/s), and the rate of burst discharges was increased in response to high concentrations of HCl (0.03 M) or NaCl (1 M) solutions. Deafferentation experiments suggest that the parasympathetic activity is mainly influenced by gustatory information via the chorda tympani, while the sympathetic activity can be evoked by both the chorda tympani and glossopharyngeal nerve.

Acute amitriptyline effects on parasympathetic-evoked rat saliva

The present study was undertaken to investigate the acute effects of amitriptyline on salivary secretion evoked by electrical stimulation of the parasympathetic innervations of rat salivary glands. Single intravenous injections of amitriptyline (0.1-1 mg/kg) caused a dose-related decrease in flow and Na concentration of saliva from both parotid and submandibular glands. However, the only effect on K concentration was a slight increase when the salivary flow was almost completely inhibited. Amitriptyline increased the Ca concentration of nerve-evoked submandibular saliva, but had no effect on the Ca concentration of similarly evoked parotid saliva. However, amitriptyline (0.5 and 1 mg/kg) increased the protein concentration of both kinds of saliva. Amylase activity of parotid saliva was also moderately increased by amitriptyline. These effects were similar to those observed with atropine, a known cholinergic receptor antagonist. These results suggest that amitriptyline, like atropine, reduces parasympathetic-evoked salivary secretion by blocking cholinergic receptors.

CGRP-immunoreactive sensory nerve fibers in the submandibular gland of the rat

Indirect immunofluorescence technique was used to study the occurrence and distribution of CGRP immunoreactivity in the submandibular gland of normal rats and after unilateral sensory and sympathetic denervations. In normal rats, CGRP-immunoreactive nerve fibers and nerve trunks were seen around or in close contact with interlobular salivary ducts as well as around small blood vessels of the gland. Occasionally, CGRP-immunoreactive nerve fibers were also detected between or around the acini of the gland. The submandibular ganglia contained CGRP-immunoreactive nerve fibers, but the ganglion cells were not immunoreactive for CGRP. The trigeminal ganglion contained a population of CGRP-immunoreactive, mainly small sized ganglion cells and nerve fibers distributed throughout the ganglion. Unilateral electrocoagulation of the trigeminal nerve caused a significant reduction in the number of immunoreactive nerve fibers in the gland, although some fibers still were present in the ipsilateral glandular tissue. Unilateral superior cervical ganglionectomy caused no detectable effect on the number of CGRP-immunoreactive nerve fibers in the gland. The present results suggest that the rat submandibular gland contains CGRP-immunoreactive nerve fibers both around blood vessels and in glandular secretory elements. Denervation experiments support the view that the majority, but perhaps not all of them originate from the trigeminal ganglion.

Neural substrates for reflex salivation induced by taste, mechanical, and thermal stimulation of the oral region in decerebrate rats

In order to investigate the neural mechanisms of reflex salivary secretion, experiments were carried out on anesthetized, decerebrate rats from which the volumes of submandibular salivary secretion and the efferent discharges in the preganglionic parasymapathetic fibers innervating the submandibular gland were recorded. Salivary secretion was induced by either infusing a taste solution, or an aliquot of hot water (45-55 degrees C) into the oral cavity, or by pinching the frontal parts of the oral region with a pair of forceps. The reflex salivation induced by noxious thermal and mechanical stimuli was markedly reduced by lesioning either the caudal (VC), or the interpolar (VI) trigeminal sensory nuclei. Taste-elicited salivary secretion was significantly reduced by lesioning the nucleus of the tractus solitarius (NTS). Of 43 preganglionic parasympathetic fibers sampled, 27 responded to both noxious mechanical and thermal stimulation of the oral region, and to electrical stimulation of the VC. Ten fibers responded only to taste stimulation and to electrical stimulation of the NTS. The remaining 6 fibers responded to both taste and noxious thermal stimulation of the oral region. These fibers responded well to NTS stimulation, but gave only a slight response to VC stimulation. These results suggest that two distinct neural pathways exist which mediate reflex salivation in the lower brain stem of the rat, i.e., the taste pathway via the NTS and the nociceptive pathway via the trigeminal sensory nuclei.

Morphometric and histological analysis of the superior cervical ganglion in experimental Chagas' disease in rats

Histological methods were used for studying the left superior cervical ganglia of control and T. cruzi infected female rats killed 13, 20, and 34 days after inoculation. Concomitantly, the sympathetic innervation of the heart auricular appendages and of the submandibular gland was studied by a glyoxylic acid-induced fluorescence method for catecholamines. At day 34 of infection, the superior cervical ganglia of an additional group of control and infected animals were studied morphometrically through the determination of ganglion volume, total number, and nuclear diameter of the principal neurons. No amastigote pseudocyst could be detected inside the ganglia at any time during infection. Inflammatory reactions were very discrete or absent at day 13 of infection, but were clearly present at day 20 as periganglionitis (in all infected animals) or ganglionitis (in 62.5% of the infected animals). These reactions again became very discrete at day 34 of infection. None of the morphometric parameters analyzed were altered by Chagas' disease. Histochemical studies on the sympathetic innervation of the heart and submandibular gland showed disappearance or rarefaction of fluorescent nerve fibers, starting around the 13th day of infection. The involvement of sympathetic nerve terminals in Chagas' disease is a local phenomenon rather than a consequence of parasitism or destruction.

The effect of a bradykinin antagonist on vasodilator responses with particular reference to the submandibular gland of the cat

A bradykinin analogue, D-Arg[Hyp3, Thi5,8, D-Phe7]-Bk, antagonized the vasodilator effect of bradykinin injected close-arterially in the submandibular salivary gland of the cat, without affecting that due to acetylcholine or nerve stimulation. The same analogue also antagonized the hypotensive response to bradykinin injected intravenously in cats and rabbits. We conclude that functional hyperaemia in the submandibular gland of the cat is not due to the release of bradykinin by salivary kallikrein.

Ability of developing epithelia to attract neurite outgrowth in culture is not correlated with the appearance of laminin

Using a new technique for organ explants that facilitates the visualization of developing epithelia, we tested the abilities of salivary gland and lung rudiments to support de novo axonal outgrowth from the embryonic submandibular ganglion. We confirmed that salivary gland epithelia, but not lung epithelia, are able to support axonal outgrowth. This neurite outgrowth is also supported by salivary gland epithelia that have been lightly fixed with paraformaldehyde. When given a choice of both salivary gland and lung epithelia as a substrate for axonal outgrowth, the submandibular ganglion neurons showed an absolute preference for the salivary gland. Immunohistochemical localization of laminin was performed on whole mounts of developing epithelia after growing neurites were localized with a histochemical stain for esterase. Areas of lung epithelium devoid of any neurite outgrowth contained substantial immunoreactivity for laminin. In addition, Western blot analyses of extracts of embryonic lung and salivary gland indicate that the same amount of laminin or more is present on a per protein basis in the lung as in the salivary gland. An antiserum directed against laminin and a monoclonal antibody that blocks axonal regeneration on basal laminae in vitro (INO) were unable to block the outgrowth of axons over fixed epithelia. This suggests that molecules other than laminin are responsible for the preferential growth of axons over the salivary gland epithelia.

Transient involvement of enkephalins in both the sympathetic and parasympathetic innervations of the submandibular gland of rats. Light- and electron-microscopic immunocytochemical study

A time course study with enkephalin (Enk)-like immunoreactivity has revealed that nerve fibers intensely immunoreactive for Enk-8 appeared transiently only during the postnatal week 2 and 4 within the acini as well as in the inter- and intralobular connective tissues of the submandibular gland of rats. At these stages numerous nerve fibers immunoreactive for tyrosine hydroxylase (TH) appeared also in the inter- and intralobular connective tissues and within the acini. Coincidently with these postnatal stages, abundant Enk-immunoreactive principal ganglion cells appeared in the superior cervical ganglion. These were not immunoreactive for neuropeptide tyrosine (NPY). A substantial number of Enk-immunoreactive ganglion cells were also present in the submandibular ganglia at these younger postnatal stages. Superior cervical ganglionectomy at these stages resulted in a marked decrease in number of the inter- and intralobular Enk-immunoreactive nerve fibers, a slight decrease in number of the intraacinar Enk-immunoreactive nerve fibers, and almost complete disappearance of intraglandular TH-immunoreactive nerve fibers. Immuno-electron-microscopic analysis revealed that Enk-immunoreactive nerve fibers in the submandibular gland were identified as electron-dense neuronal profiles enclosed by Schwann cells in the inter- and intralobular connective tissues and those directly apposed to secretory cells within the acini. They contained small clear vesicles mixed with some large granular vesicles. After postnatal week 6, no Enk-immunoreactive nerve fibers were detected in the submandibular gland, and no TH-immunoreactive nerve fibers were seen within the acini, while TH-immunoreactive nerve fibers remained numerous in the inter- and intralobular connective tissues. These findings indicate that both sympathetic and parasympathetic nerve fibers exhibit Enk-like immunoreactivity transiently during postnatal weeks 2 and 4.(ABSTRACT TRUNCATED AT 250 WORDS)

"Paralytic' secretion after parasympathectomy of rabbit submandibular glands includes a cholinergic component

Chronic parasympathetic decentralization of submandibular glands in rabbits has been studied after 3 weeks, in acute experiments under urethane anaesthesia. A "paralytic' secretion occurred from the supersensitive denervated glands and it was not attributable to an increase in the "spontaneous' flow, that is present in normal glands. The "paralytic' secretion was completely inhibited by atropine, after which a "spontaneous' flow, that was similar to the contralateral glands, persisted. The alpha-adrenergic blocker dihydroergotamine, when given before atropine, reduced the "paralytic' secretion by 50-75% but when this drug was given after atropine it had no additional effect. The beta-adrenergic blocker propanolol did not cause a reduction in the "paralytic' secretion. Superior cervical ganglionectomy, in contrast, did not give rise to a significant "paralytic' flow. The results suggest that acetylcholine, released spontaneously from terminals of postganglionic parasympathetic nerves, plays an essential part in the "paralytic' secretion that occurs from rabbit submandibular glands after preganglionic denervation. Circulating catecholamines make a secondary contribution, acting synergistically with the acetylcholine on the supersensitive secretory cells.

Tachykinin involvement in parasympathetic nerve-evoked salivation of the ferret

1. The tachykinin antagonist (D-Arg1, D-Cl2Phe5, Asn6, D-Trp7.9, Nle11)-substance P, injected intravenously, blocked salivary secretion from the ferret parotid and submandibular glands in response to subsequent i.v. injections of the tachykinins, substance P and neurokinin A. 2. The tachykinin antagonist reduced the parasympathetic nerve-evoked secretion of parotid and submandibular saliva by 15-20% and 35-40%, respectively. Atropine abolished the remaining secretory response. 3. The 'atropine-resistant' parasympathetic nerve-evoked secretion of saliva from the parotid and submandibular glands (about 5 and 30%, respectively, of that before administration of atropine) was abolished by the tachykinin antagonist. 4. The tachykinin antagonist was without effect on the protein concentration of parotid and submandibular saliva secreted in response to parasympathetic nerve stimulation. Parotid and submandibular saliva lacked amylase. 5. Atropine reduced the protein concentration of the submandibular saliva secreted in response to parasympathetic nerve stimulation by 50%; this was the protein concentration of substance P-evoked saliva. 6. The secretory response to methacholine and to stimulation of preganglionic sympathetic nerve fibres, tested in rats, was unaffected by the tachykinin antagonist, contra-indicating an unspecific action of the antagonist. 7. The results suggest that the neuronal release of tachykinins is probably important in the nerve-evoked secretory response of the parotid and submandibular glands.