Adrenergic nerves to the rat parotid gland originating in the contralateral sympathetic chain

Neuropeptide Y in salivary glands of the rat: origin, release and secretory effects

In the parotid gland, double immunostaining showed the perivascular and most of the periductal neuropeptide Y (NPY)-immunoreactive nerve fibres to contain dopamine beta-hydroxylase, while the majority of periacinar NPY-fibres contained vasoactive intestinal peptide. Sympathectomy caused a marked depletion of perivascular and periductal NPY-fibres, leaving periacinar NPY-fibres less affected. Following combined sympathectomy and parasympathectomy, only a few NPY-fibres persisted. The parasympathetic auriculotemporal nerve contributed most (75%) and the cervical sympathetic nerve least (15%) to the parotid gland content of NPY as judged by radioimmunoassay. The sensory neurotoxin capsaicin was without effect on the occurrence and gland content of NPY. Upon long-lasting electrical stimulation of the auriculo-temporal nerve at a high frequency, the gland content of NPY was reduced (by 55%), a depletion thought to indicate release of the peptide from parasympathetic nerve terminals. In vitro, tissues of parotid, submandibular and sublingual glands released concentration-dependently protein (and as to the parotid gland amylase also) in response to NPY; the protein response was largest from sublingual tissue (per unit weight). A concentration-dependent in vitro release of potassium from tissues of parotid and submandibular glands in response to NPY occurred and here, submandibular gland tissue was the most sensitive. Comparisons between the action of some secretagogues (at 10(-6) M) showed NPY to be less effective than vasoactive intestinal peptide and adrenaline, but as effective as bethanechol and substance P, in releasing protein (and amylase) in parotid and submandibular gland tissues; in sublingual gland tissue NPY was less effective than vasoactive intestinal peptide, in the range of adrenaline and more effective than bethanechol and substance P. As to potassium release (at agonist concentration of 10(-6) M) from tissues of parotid and submandibular glands NPY was less effective than substance P and vasoactive intestinal peptide. The fluid response to NPY upon i.v. administration was scanty from parotid and submandibular glands. NPY is likely to play a complementary role in mediating parasympathetic secretory responses in salivary glands of the rat. It seems preferentially involved in the control of protein secretion.

Modification of the beta-adrenergic sensitivity of rat submandibular gland by constant light

Rats exposed for 2, 5, 10, 20, 35 and 50 days to constant light (CL) showed beta-adrenergic desensitization of the submandibular gland as indicated by dose-response curves to 1.5, 2.0, 3.0, 10.0, 30.0 and 50.0 micrograms/kg isoproterenol. The phenomenon, evident with 1.5, 2.0 and 50.0 micrograms/kg after 2 days at CL, was more intense as time of exposure increased to reach values of about 50% those for controls after 20 days. After 35 and 50 days, desensitization showed some reversion, but the secretory responses were still lower than for controls maintained under a typical photoperiod. In the groups of rats exposed to CL for 20 days, gland wet and dry weights were higher (10%) than those of controls. These changes probably indicate an adaptation of the sympathetic control of salivary secretion induced by environmental illumination.

The sympathetic and parasympathetic nature of neuropeptide Y-immunoreactive nerve fibres in the major salivary glands of the rat

The distribution and origin of neuropeptide Y in the major salivary glands of the rat was studied by indirect immunofluorescence technique. Numerous nerve fibres immunoreactive for the peptide were seen in the parotid and sublingual glands. Most of the fibres were located around blood vessels and salivary acini. In the submandibular gland the number of immunoreactive nerve fibres around the acini was lower in comparison with that in the parotid and sublingual glands. Some immunoreactive nerve fibres were also found around or along intra- and interlobular ducts in all major salivary glands. A large number of the neuropeptide-containing neuronal cell bodies and nerve fibres were detected in the sympathetic superior cervical ganglion. Sympathetic postganglionic nerve trunks of this ganglion contained numerous immunoreactive nerve fibres as well. A subpopulation of the neuronal cell bodies in the submandibular ganglion were immunoreactive to neuropeptide Y. Both uni- and bilateral superior cervical ganglionectomies caused a significant decrease in the number of immunoreactive nerve fibres around the blood vessels in all the major salivary glands. However, these denervations did not affect the density of nerve fibres around the acini and ducts. On the contrary, unilateral parasympathetic denervation by sectioning the auriculotemporal nerve reduced the fibres around the secretory acini in the parotid gland remarkably, while only a minor reduction in the density of immunoreactive fibres associated with the blood vessels of the gland was detected. Unilateral electrocoagulation of the trigeminal nerve branches caused no detectable change in the density of immunoreactive nerve fibres in any of the major salivary glands.(ABSTRACT TRUNCATED AT 250 WORDS)

The innervation of salivary glands as revealed by morphological methods

Salivary secretion is nerve mediated. The salivary glands are supplied by parasympathetic and sympathetic efferent nerves which travel to the glands by separate routes. Once in the glands the axons from each type of nerve intermingle and travel together in association with Schwann cells, forming Schwann-axon bundles. Two types of neuro-effector relationships exist with salivary parenchymal and myoepithelial cells: epilemmal (outside the parenchymal basement membrane) and hypolemmal (within the parenchymal basement membrane). Their relative frequencies with either type of nerve differ greatly between glands and species. Salivary blood vessels receive epilemmal innervations by both sympathetic and parasympathetic axons. The classical transmitters--acetylcholine in parasympathetic and noradrenaline in sympathetic axons--are stored in small vesicles. A variety of non-conventional neuropeptide transmitters have also been found in salivary nerves by immunohistochemistry, and they occur in large dense-cored vesicles. Prolonged high frequency stimulation has been found to cause depletion of large dense-cored vesicles from glandular nerves. In recent years afferent nerves have started to be identified and are found in greatest numbers around the main salivary ducts, where they may form a hypolemmal association with the epithelial cells. Functional studies demonstrate complex interactions between parasympathetic and sympathetic nerves. Morphological assessments of changes in the parenchymal cells after nerve stimulations or denervations add greatly to our understanding of the nerve functions. At least four types of influence can be exerted on salivary parenchymal cells by the nerves: hydrokinetic (water mobilizing), proteokinetic (protein secreting), synthetic (inducing synthesis), and trophic (maintaining normal functional size and state). In respect to each role, wide glandular and species differences exist between the relative contributions made by each type of nerve.

Appearance of retrogradely labeled neurons in the rat superior cervical ganglion after injection of wheat-germ agglutinin-horseradish peroxidase conjugate into the contralateral ganglion

Injection of wheat-germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) into the superior cervical ganglion (SCG) of the rat results in accumulation of WGA-HRP in sympathetic postganglionic neurons in the contralateral SCG. The sympathetic pathways involved and the mechanism underlying the labeling were investigated. The labeling in neurons in the contralateral SCG was apparent 6 h after injection and increased in intensity with longer survival times. The number of labeled neurons reached 1300 at 72 h after the injection. Transection of the external (ECN) or internal carotid nerves (ICN) resulted in considerable reduction in the number of labeled neurons. Combined transection of both ECN and ICN virtually eliminated labeling in the contralateral SCG. This provides strong evidence that these two nerves are the major pathways for WGA-HRP transport out of the SCG. No labeling was observed in the contralateral SCG following injection of horseradish peroxidase (HRP). Therefore, it seems unlikely that a direct nerve connection exists between the bilateral ganglia. Instead, the labeling of contralateral SCG neurons appears to depend on the transneuronal transport capacity of WGA-HRP, which conveys the marker in an anterograde direction along the postganglionic fibers to terminals in sympathetic target organs, and then delivers it transneuronally to contralateral SCG neurons. We suggest that the sympathetic nerve fibers originating in the bilateral SCGs run intermingled and are in close contact in their peripheral target organs.

Effects of beta-adrenergic agonists in the parotid gland of the rat--an electrophysiological study

The effects of some beta-adrenergic agonists were studied in the parotid gland of the rat by electrophysiological techniques. In the unoperated gland, isoprenaline caused depolarizations which were slowly developing, long-lasting and of low amplitude. The same response was seen when noradrenaline was combined with alpha-adrenoceptor blocking drugs. A greater number of cells responded to this combination than to isoprenaline. After either parasympathetic or sympathetic denervation 1-3 weeks in advance, to induce supersensitivity, the number of cells responding to beta-adrenoceptor stimulating drugs was significantly increased. In the latter case the threshold dose required to evoke a response was also significantly lowered. Atropine did not have any effect on the isoprenaline-evoked response. The combined parasympathetic and sympathetic denervation did not further increase the responsiveness. It is concluded that beta-adrenoceptor stimulation in the parotid gland of the rat may cause membrane depolarizations. The response is mediated by beta 1-adrenoceptors. The responsiveness is increased in the denervated gland. Secretory studies have demonstrated a supersensitivity to beta-adrenergic agonists as a result of denervation. On the other hand, beta-adrenoceptor stimulation is believed mainly to activate the adenylate cyclase/cyclic AMP system independent of membrane potential changes. It is thus not known if the present 'supersensitivity' is correlated to the increased secretory response earlier demonstrated in this gland.

Dopamine actions in vitro on enzyme and electrolyte secretion from normal and sympathectomized rat parotid glands

1. Adult rats were denervated unilaterally by removal of the left superior cervical ganglion or chemically denervated with 6-hydroxydopamine or reserpine. Two weeks later the parotid glands were used for in vitro secretory studies and their catecholamines and major metabolites were measured. 2. Noradrenaline concentrations were reduced 2 weeks after surgical sympathectomy and reserpine pre-treatment 18 h previously, whereas 6-hydroxydopamine pre-treatment for 3 days reduced both noradrenaline and dopamine concentrations. 3. Dopamine caused a prominent amylase release from incubated control glands. However, a subsensitivity for dopamine-induced amylase release was recorded on the denervated side. 4. Dopamine caused a prominent potassium efflux measured as 86Rb+ efflux from control glands, but was without effect in denervated glands. This is in contrast to noradrenaline-induced 86Rb+ efflux which was equally effective in both denervated and control glands. 5. Dopamine caused [3H]noradrenaline efflux in control glands, but was without effect in surgically denervated glands and in glands pre-treated with reserpine or 6-hydroxydopamine. 6. It is concluded that dopamine-induced potassium release is caused by a presynaptic action on noradrenergic nerves, whereas dopamine-induced amylase release has a presynaptic and a postsynaptic component. The results suggest a specific action of dopamine in salivary glands, with different effects on enzyme release and ionic fluxes.

The effects of atropine and chronic sympathectomy on maximal parasympathetic stimulation of parotid saliva in rats

1. The effects of stimulating the postganglionic parasympathetic nerve to the parotid gland, the auriculo-temporal nerve, continuously at 40 Hz for 80 min have been assessed on the flow of saliva and its amylase content during each 10 min period and on the glandular morphology at the end of the stimulation, in female Sprague-Dawley rats under chloralose anaesthesia. Adrenergic responses were blocked by prior administration of dihydroergotamine (1 mg/kg I.P.) and propranolol (1 mg/kg I.P.). The contralateral unstimulated parotid gland from each animal was used for morphological control purposes. 2. In normal animals there was a copious flow of saliva reaching 3 ml or more in 80 min. It was well maintained after a gradual small decline and the flow in the last 10 min period was still 60% of that in the initial period. Amylase output was relatively high in the initial period but then declined more rapidly than the flow. The acini were densely packed with granules on the control side and showed a moderate amount of degranulation on the parasympathetically stimulated side. 3. After atropine (2 mg/kg I.V.), normal animals initially showed a moderate flow of saliva, being 41% of the non-atropinized animals, but there was a rapid decline and the total flow over 80 min was only 15% of that in the non-atropinized animals. The amylase secreted was also high initially and showed a rapid decline; the total amount secreted was similar to that in non-atropinized animals. The morphology was similar to that in non-atropinized animals and showed a similar loss of acinar granules on the stimulated side. 4. Chronic bilateral postganglionic sympathectomy (4-6 weeks duration) caused a drastic reduction in the capacity of the gland to secrete saliva in response to parasympathetic stimulation, reaching only one-third of that from normal animals. The initial output of amylase was greater than in normal animals but the total output was similar. The control unstimulated sympathectomized glands appeared similar morphologically to normal resting glands. However, on the parasympathetically stimulated side, besides the usual amount of acinar degranulation, there was also a conspicuous development of acinar vacuolation, not seen in the other groups of animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Non-specific secretory supersensitivity in rat parotid gland following neonatal sympathetic denervation

Newborn rats were surgically sympathectomized by extirpation of the left superior cervical ganglion. After 9 weeks the parotid glands of both sides were used for secretory studies. Isoprenaline, dopamine, and the dibutyryl analogue of cAMP (DBcAMP) caused an increase in amylase release, which was significantly higher in the denervated glands. Also carbamylcholine was more effective in the denervated gland; the concentration-response curve was shifted to the left, and the maximal output of amylase was increased. Neonatal sympathetic denervation induces supersensitivity for both adrenergic and cholinergic agonists as well as for DBcAMP. This may be due to compensatory mechanisms involving both up-regulation of receptors as well as amplification of the intracellular mediation.

Amylase-secretory responses to sympathetic nerve impulses in the rat parotid gland following partial sympathetic ganglionectomy

Some sympathetic axons reach the parotid gland from the contralateral sympathetic chain. Such contralateral nerves were stimulated and saliva secreted after intravenous injections of methacholine was collected from the parotid duct at various times after removal of the ipsilateral superior cervical ganglion. The secretion of amylase caused by sympathetic nerve stimulation was greatly increased three days after the sympathectomy and even more after ten weeks. This effect is attributed to denervation supersensitivity, prejunctional after three days and, in addition, postjunctional later.

Amylase in parotid saliva of rats after sympathetic nervous decentralization

The marked increase in the amylase secretion that occurs in parasympathetic saliva some days after sympathetic ganglionectomy occurred after decentralization also; hence, it results from lack of impulses from the central nervous system. It occurred whether salivation was evoked by activating muscarinic receptors with methacholine, peptidergic receptors with substance P or physalaemin, or alpha-adrenoceptors with phenylephrine. Unilateral operation affected to some degree the contralateral gland also.