Postganglionic Cholinergic Nerves Research Articles

6. A potential biomarker to differentiate degenerative from acquired peripheral autonomic neuropathy

This study aimed to test whether peripheral α-synuclein staining might be useful for pure autonomic failure (PAF) diagnosis helping to differentiate degenerative from acquired peripheral autonomic neuropathy. We studied 21 patients with chronic peripheral autonomic neuropathy. Twelve patients showed a specific cause of neuropathy (acquired autonomic neuropathy – AAN) whereas nine had no specific acquired causes fulfilling the diagnostic criteria for PAF. Fifteen matched healthy subjects served as controls. Subjects underwent skin biopsy from thigh and leg to study skin innervation and phosphorylated α-synuclein deposits in the peripheral axons. Somatic and autonomic skin innervations were significantly decreased in peripheral autonomic neuropathy patients compared to controls. No differences were found between AAN and PAF. The deposits of α-synuclein were not found in controls but served to distinguish acquired from degenerative autonomic peripheral neuropathy: all pure autonomic failure patients showed α-synuclein deposits in the postganglionic sympathetic adrenergic and cholinergic nerve fibers which were absent in acquired autonomic neuropathy patients. Our study demonstrated that a search for neuritic inclusions of phosphorylated α-synuclein in the skin sympathetic nerve fibers could provide a sensitive in vivo biomarker for degenerative peripheral autonomic neuropathy and may shed more light on the PAF pathogenesis.

Ross syndrome

Ross syndrome is a rare autonomic disorder described by Ross in 19581 and characterized by tonic pupil, hyporeflexia, and segmental anhidrosis. A postganglionic cholinergic nerve degeneration of unknown cause underlies this condition2 although erratic association with Sjogren3 and antinuclear antibody4 positivity has led some authors to hypothesize immunologic causes. Familial cases have not been reported.

An investigation of the effects of angiotensin on the release of neurohumoral transmitters at motor, adrenergic and cholinergic nerve terminals.

Abstract On the sciatic nerve-gastrocnemius-soleus muscle preparation of the cat, angiotensin (1–5 μg/kg, i.v.) potentiated the twitch response to maximal and submaximal stimulation of the sciatic nerve and produced partial reversal of an incomplete tubocurarine blockade. These actions could not be explained in terms of increased acetylcholine release since they were not seen in isolated motor nerve-striated muscle preparations and were probably secondary to the cardiovascular actions of angiotensin. Blockade of conduction in the postganglionic cholinergic nerves in the guinea-pig isolated ileum preparation by cooling or anoxia antagonized the response of this tissue to angiotensin. These procedures left the response to exogenous acetylcholine unchanged though they removed the cholinergic component of the response to angiotensin which is known to be present in this tissue. No evidence of increase in catecholamine output could be found in preparations of guinea-pig and rabbit vasa deferentia or rabbit duodenum responding to submaximal stimulation of their adrenergic nerves. It is concluded that angiotensin has no direct action on the stores of neurohumoral transmitter at motor, postganglionic cholinergic or postganglionic adrenergic nerves and that its known acetylcholine releasing action in the isolated ileum results from stimulation of the ganglia.

Mechanism of mesaconitine-induced contractile response in guinea-pig ileum.

Mesaconitine (MA) caused contractions of the guinea-pig isolated ileum in a dose-dependent manner (10-8-10-5 g ml-1), slightly potentiated the contractile response to acetylcholine (ACh) and histamine and enhanced responses to electrical stimulation. Repeated application of MA (10-5 g ml-1) produced tachyphylaxis. Atropine blocked contractions to MA (3 X 10-M g ml-1), but only partially those to MA (10-5 G ML-1). Morphine, strychnine and hemicholinium-3, but not hexamethonium, also inhibited MA-induced contractions. Contractions produced by both doses of MA were abolished by cocaine, tetrodotoxin, or noradrenaline, or by previous cooling of the ileum. The atropine-resistant contractions produced by MA (10-5 g ml-1) were blocked by indomethacin. MA (3 X 10-7-10-5 g ml-1) elicited a dose-dependent release of ACh from the isolated ileum which was blocked by treatment with tetrodotoxin or cocaine, or exclusion of calcium ions from the bath. It is concluded that the contractions induced by lower doses of MA are brought about by the release of ACh from the postganglionic cholinergic nerve and that the contractions by higher doses could also be mediated by release of prostaglandins from the ileum.

Excitatory P1-purinoceptors on pre- and post-ganglionic cholinergic nerve terminals in the chick oesophagus.

The mechanism of action of ATP and the purinoceptors involved have been investigated on the chick oesophagus. The susceptibility of the excitatory responses to ATP/adenosine to tetrodotoxin indicates that their action is neurally mediated. Blockade of ATP/adenosine responses by atropine suggests the involvement of endogenous acetylcholine. ATP action depends on breakdown to AMP/adenosine, since theophylline blocks ATP/adenosine responses. The inhibition of ATP responses by pentolinium implies the involvement of preganglionic fibres.

Reflex regulation of airway smooth muscle tone

Autonomic nerves in most mammalian species mediate both contractions and relaxations of airway smooth muscle. Cholinergic-parasympathetic nerves mediate contractions, whereas adrenergic-sympathetic and/or noncholinergic parasympathetic nerves mediate relaxations. Sympathetic-adrenergic innervation of human airway smooth muscle is sparse or nonexistent based on histological analyses and plays little or no role in regulating airway caliber. Rather, in humans and in many other species, postganglionic noncholinergic parasympathetic nerves provide the only relaxant innervation of airway smooth muscle. These noncholinergic nerves are anatomically and physiologically distinct from the postganglionic cholinergic parasympathetic nerves and differentially regulated by reflexes. Although bronchopulmonary vagal afferent nerves provide the primary afferent input regulating airway autonomic nerve activity, extrapulmonary afferent nerves, both vagal and nonvagal, can also reflexively regulate autonomic tone in airway smooth muscle. Reflexes result in either an enhanced activity in one or more of the autonomic efferent pathways, or a withdrawal of baseline cholinergic tone. These parallel excitatory and inhibitory afferent and efferent pathways add complexity to autonomic control of airway caliber. Dysfunction or dysregulation of these afferent and efferent nerves likely contributes to the pathogenesis of obstructive airways diseases and may account for the pulmonary symptoms associated with extrapulmonary disorders, including gastroesophageal reflux disease, cardiovascular disease, and rhinosinusitis.

Urinary dysfunction and autonomic control in amyloid neuropathy

Uro-neurological assessment was performed in four patients with small-fiber neuropathy due to amyloidosis (2 transthyretin-type/2 immunoglobulin light-chain-type). Voiding difficulties were due to detrusor weakness and impaired bladder sensation. In two patients cholinesterase inhibition treatment caused urge incontinence, indicating detrusor denervation supersensitivity. The underlying mechanisms of urinary dysfunction seem to involve postganglionic cholinergic and afferent somatic nerves.

The role of neuroeffector mechanisms in the pathogenesis of asthma

Neural regulation of the airways consists of cholinergic excitatory, adrenergic inhibitory nerves and nonadrenergic, noncholinergic (NANC) nerves. NANC nerves can be either inhibitory or excitatory. Cholinergic nerves form the predominant bronchoconstrictor neural pathway in human airways. Acetylcholine controls neuronal and nonneuronal target cells via a short-lived action at nicotinic and muscarinic receptors. The most important control over acetylcholine release from postganglionic cholinergic nerves is exerted by acetylcholine itself. The M2 autoreceptor is located prejunctionally on postganglionic nerves. Its stimulation limits the further release of acetylcholine. A loss of function in the neuronal muscarinic M2 autoreceptor occurs after exposure to allergen, ozone, or viruses. In human airways, inhibitory NANC (i-NANC) mechanisms are the only neural bronchodilatory mechanisms. The presumed neurotransmitters of the i-NANC system are vasoactive intestinal peptide and nitric oxide. Substance P and neurokinin A have been implicated as the neurotransmitters mediating the excitatory part of the NANC nervous system. NK2 receptors are present on smooth muscle of both large and small airways and mediate part of the bronchoconstrictor effect of tachykinins. Most of the proinflammatory effects of substance P are mediated by the NK1 receptor. Tachykinin receptor antagonists are currently being developed as a possible anti-asthma treatment. An extensive cross-talk exists between nerves and the immune system. The complexity of the picture has increased further as it has become clear that classical neurotransmitters, such as acetylcholine and neuropeptides, are produced by nonneuronal cells.

Evidence for nitroxidergic innervation in monkey ophthalmic arteries in vivo and in vitro

In anesthetized monkeys, electrical stimulation (ES) of the pterygopalatine or geniculate ganglion dilated the ipsilateral ophthalmic artery (OA). The induced vasodilatation was unaffected by phentolamine but potentiated by atropine. Intravenous N(G)-nitro-L-arginine (L-NNA) abolished the response, which was restored by L-arginine. Hexamethonium-abolished vasodilator responses induced solely by geniculate ganglionic stimulation. The L-NNA constricted OA; L-arginine reversed the effect. Destruction of the pterygopalatine ganglion constricted the ipsilateral artery. Helical strips of OA isolated under deep anesthesia from monkeys, denuded of endothelium, responded to transmural ES with relaxations, which were abolished by tetrodotoxin and L-NNA but were potentiated by atropine. It is concluded that neurogenic vasodilatation of monkey OA is mediated by nerve-derived nitric oxide (NO), and the nerve is originated from the ipsilateral pterygopalatine ganglion that is innervated by cholinergic neurons from the brain stem via the geniculate ganglion. The OA appears to be dilated by mediation of NO continuously liberated from nerves that receive tonic discharges from the vasomotor center. Acetylcholine liberated from postganglionic cholinergic nerves would impair the release of neurogenic NO.

Eosinophils and airway nerves in asthma.

In the lungs, neuronal M2 muscarinic receptors limit the release of acetylcholine from postganglionic cholinergic nerves. However, these receptors are not functional under certain circumstances in animal models of hyperreactivity such as occurs after exposure of sensitised animals to an allergen or during a respiratory tract virus infection. This loss of M2 receptor function leads to an increase in acetylcholine release from cholinergic nerves and thus is a mechanism for the vagally mediated hyperreactivity seen in these animals. Studies in animal models of hyperreactivity have shown that eosinophils localise to the airway nerves of sensitised animals after antigen challenge. Inhibiting this localisation of eosinophils either with an antibody to the eosinophil survival cytokine IL-5 or the eosinophil adhesion molecule VLA-4 prevents loss of M2 muscarinic receptor function. It is likely that eosinophil MBP is responsible for the loss of M2 receptor function, since inhibiting eosinophil MBP with an antibody or neutralising MBP with heparin prevents this loss of function. These data are also supported by ligand binding studies where it has been shown that eosinophil MBP is an allosteric antagonist at neuronal M2 muscarinic receptors. Loss of function of lung neuronal M2 muscarinic receptors may also occur under certain circumstances in patients with asthma, although the mechanisms are not yet established.

Function of the neuronal M2muscarinic receptor in asthmatic patients

Background The dominant innervation of airway smooth muscle is parasympathetic fibers which are carried in the vagus nerve. Activation of these cholinergic nerves releases acetylcholine which binds to M3 muscarinic receptors on the smooth muscle causing bronchocontraction. Acetylcholine also feeds back onto neuronal M2 muscarinic receptors located on the postganglionic cholinergic nerves. Stimulation of these receptors further inhibits acetylcholine release, so these M2 muscarinic receptors act as autoreceptors. Loss of function of these M2 receptors, as it occres in animal models of hyperresponsiveness, leads to an increase in vagally mediated hyperresponsiveness. However, there are limited data pertaining to whether there are dysfunctions of these receptors in patients with asthma. The aim of this study is to determine whether there are dysfunction of M2 muscarinic receptors in asthmatic patients and difference of function of these receptors according to severity of asthma. Methods We studied twenty-seven patients with asthma who were registered at Pulmonology Division of Korea University Hospital. They all met asthma criteria of ATS. Of these patients, eleven patients were categorized as having mild asthma, eight patients moderate asthma and eight patients severe asthma according to severity by NAEPP Expert Panel Report 2(1997). All subjects were free of recent upper respiratory tract infection within 2 weeks and showed positive methacholine challenge test(PC 20<16mg/ml). Methacholine provocation tests performed twice on separate days allowing for an interval of one week. In the second test, pre-treatment with the M2 muscarinic receptor agonist pilocarpine(180µg) through inhalation was performed before the routine procedures. Results Eleven subjects with mild asthma and eight aubjects with moderate asthma showed significant increase of PC20 from 5.30±5.23mg/ml(mean±SD) to 20.82±22.56mg/ml(p=0.004) and from 2.79±1.5mg/ml to 4.67±3.53mg/ml(p=0.012) after pilocarpine inhalation, respectively. However, in the eight subjects with severe asthma significant increase of PC20 from 1.76±1.50mg/ml to 3.18±4.03mg/ml(p=0.161) after pilocarpine inhalation was not found. Conclusion In subjects with mild and moderate asthma, function of M2 muscarinic receptors was normal, but there was a dysfunction of these receptors in subjects with severe asthma. These results suggest that function of M2 muscarinic receptors is different according to severity of asthma.

Epinastine (WAL 801CL) inhibits the electrical field stimulation-induced cholinergic contraction in guinea pig and human airways in vitro.

Epinastine is an antihistamine drug with binding affinities at 5-hydroxytryptamine (5-HT) receptors. The current study was performed to investigate whether epinastine could modulate the cholinergic contraction in guinea pig and human airways in vitro. Isolated guinea pig and human airway preparations were suspended in organ baths containing modified Krebs-Henseleit solution. Electrical field stimulation was applied to elicit cholinergic contractions. Epinastine produced a concentration-dependent inhibition of the cholinergic contraction in guinea pig airways and pretreatment with methysergide (5-HT1/2/7 antagonist) significantly attenuated these inhibitory effects of epinastine. Pretreatment with tropisetron (5-HT3/4 antagonist), ketanserin (5-HT2 antagonist), SDZ216-525 (5-HT1A antagonist) or phentolamine (alpha-adrenergic antagonist) had no effect. Epinastine did not displace the concentration-response curve to acetylcholine. These results suggest that epinastine inhibits the cholinergic contraction in guinea pig airways through stimulation of prejunctional 5-hydroxytryptamine receptors, located to postganglionic cholinergic nerves. Inhibitory effects of epinastine on the cholinergic contraction in human airways in vitro were also demonstrated, which suggests that a similar mechanism might be present in human airways. The pharmacological profile of epinastine, which shows binding affinity at the 5-hydroxytryptamine7 receptor but not at the 5-hydroxytryptamine1 receptor subtypes corroborates the hypothesis that the inhibitory prejunctional 5-hydroxytryptamine receptor on cholinergic nerves is of the 5-hydroxytryptamine7 subtype.

The effects of 8-hydroxy-2-(di-n-propylamino)tetralin on the cholinergic contraction in guinea pig and human airways in vitro.

Electrical field stimulation of guinea pig tracheal strips and human bronchial rings, in vitro, evokes a cholinergic contraction mediated by the release of acetylcholine. 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) is a 5-HT1A and 5-HT7 agonist. In this study, we have investigated whether 8-OH-DPAT could modulate the cholinergic contraction in guinea pig and human airways in vitro. 8-OH-DPAT (1 to 30 microM) produced a concentration-dependent inhibition of the cholinergic contraction in guinea pig tracheal strips with a maximal inhibition of 75.8% +/- 4. 7% (30 microM, 0.5 Hz). Pretreatment of the tissues with the 5- HT1/2/7 antagonist methysergide (10 to 30 microM) significantly attenuated the inhibitory effects of 8-OH-DPAT (10 to 30 microM) on the cholinergic contraction. Pretreatment with ketanserin (10 microM), a 5-HT2 antagonist, tropisetron (1 microM), a 5-HT3/4 antagonist, SDZ 216-525 (1 to 10 microM) and pindobind (10 microM), both selective 5-HT1A antagonists, or capsaicin (10 microM), which depletes sensory nerves from neuropeptides, had no effect on the inhibition of the cholinergic contraction by 8-OH-DPAT (10 to 30 microM). 5-carboxamidotryptamine (5-CT) (10 to 100 microM), a 5-HT1/2/7 agonist, partially mimicked the inhibitory effects of 8-OH-DPAT on the cholinergic contraction. 8-OH-DPAT (10 to 30 microM) also inhibited the cholinergic contraction in human bronchial rings in vitro with a maximal inhibition of 46.2% +/- 7.2% (30 microM, 1 Hz). SDZ 216-525 (10 microM) had no effect, whereas methysergide (30 microM) partially prevented the effect of 8-OH-DPAT in human airways. 8-OH-DPAT (30 microM) did not displace the concentration-response curve to acetylcholine (10 nM-30 mM) in guinea pig and human airways in vitro. These results suggest that 8-OH-DPAT inhibits the cholinergic contraction in guinea pig and human airways in vitro through stimulation of prejunctional atypical 5-HT receptors, possibly of the 5-HT7 subtype, located on postganglionic cholinergic nerves.

Pulmonary neuronal M2 muscarinic receptor function in asthma and animal models of hyperreactivity.

In the lungs neuronal M2 muscarinic receptors limit acetylcholine release from postganglionic cholinergic nerves. These inhibitory M2 receptors are dysfunctional in antigen challenged guinea pigs and in humans with asthma which leads to an increase in vagally mediated hyperreactivity. In vitro, eosinophil products act as allosteric antagonists at neuronal M2 muscarinic receptors. In vivo, displacing or neutralising MBP preserves neuronal M2 muscarinic receptor function and prevents hyperreactivity. Thus, there is good evidence from animal studies that after antigen challenge pulmonary M2 muscarinic receptors become dysfunctional because MBP inhibits their function. Loss of function of pulmonary neuronal M2 muscarinic receptors has also been reported in patients with asthma, although the clinical significance of this dysfunction and the mechanisms underlying it are not yet established.

Muscarinic receptor subtypes in airways

Muscarinic receptor subtypes in the airways appear to subserve different physiological functions. M1-receptors facilitate neurotransmission through parasympathetic ganglia and enhance cholinergic reflexes, but are also localized to alveolar walls. M2-receptors act as autoreceptors on post-ganglionic cholinergic nerves and inhibit acetylcholine release. There is some evidence that they may be defective in asthma (as a consequence of airway inflammation?) and this may enhance cholinergic reflexes and account for beta-blocker-induced asthma. M2-receptors in airway smooth muscle may also counteract the bronchodilator action of beta-agonists. M3-receptors mediate contractile responses in airway smooth muscle via phosphoinositide hydrolysis, and are the predominant receptors on submucosal glands and airway vascular endothelium. M4- and M5-receptors have not been identified in human airways, but in rabbit lung M4-receptors are expressed on alveolar walls and smooth muscle. Anticholinergic drugs which selectively block M3 and M1-receptors may have an advantage over currently used non-selective antagonists in the treatment of airway obstruction.

Insulin secretion by gastrin-releasing peptide in mice: ganglionic versus direct islet effect.

Gastrin-releasing peptide (GRP) stimulates insulin secretion by a direct islet effect. In this study, we initially demonstrated, by immunocytochemistry of the mouse pancreas, GRP immunoreactive nerve fibers within exocrine tissue, islets, and intrapancreatic ganglia. A more pronounced GRP innervation was found in ganglia compared with in islets. We therefore studied whether indirect cholinergic mechanisms contribute to the insulinotropic action of GRP. In mice, the insulinotropic response to GRP (4.25 nmol/kg i.v.) was inhibited by the m3-selective, muscarinic receptor antagonist 4-diphenylacetoxy-N-methyl piperidine methobromide (4-DAMP, 0.21 mol/kg; by 68%, P < 0.05) and by the ganglionic blocker hexamethonium (28 mol/kg; by 98%, P < 0.05). In contrast, in isolated islets, 4-DAMP or hexamethonium (10 or 100 microM) did not inhibit GRP (100 nM)-induced insulin secretion. Furthermore, afferent denervation by neonatal capsaicin did not affect the insulin response to GRP. We conclude that the insulinotropic effect of GRP in the mouse is mediated by both direct islet effects and through activation, at the ganglionic level, of postganglionic cholinergic nerves. In vivo, the indirect cholinergic mechanism predominates.

Possible functional modulation by acetylcholine of nitric oxide on guinea pig isolated trachea

The aim of this study was to evaluate whether acetylcholine induces NO release. We determined the responses on the cholinergic component of the response to electrical field stimulation (EFS) the effects of L-nitro-arginine-methyl-ester (L-NAME; 1 mM), an inhibitor of NO synthase, of L-Arginine (L-ARG; 1 mM), a precursor of NO synthesis, and methoctramine (0.01-0.1-1 μM), an antagonist of M 2 receptors, alone or associated with L-NAME. The experiments were performed on guinea pig isolated intact- or denuded-epithelium tracheal rings contracted in a frequency-dependent manner to EFS. At the maximum frequency tested (30 Hz), the contractile response elicited was 60.36 ± 0.61 % of acetylcholine (100 μM) contraction, while the maximal relaxant effect induced by EFS was −28.40 ± 0.61% in epithelium intact preparations. A pretreatment with L-NAME significantly (P < 0.05) increased the contraction (76.08 ± 1.39 %) and reduced the relaxation elicited by EFS. L-NAME effect on both EFS induced responses were statistically (P < 0.05) reversed by the association L-NAME + L-ARG. Methoctramine (1 μM) enhanced contractile (P < 0.05) (79.20 ± 2.21 %), as well as relaxant responses (−38.73 ± 0.99 %) elicited by EFS in guinea pig epithelium-intact tracheal rings; in a separate series of experiments, performed on guinea pig epithelium-intact rings, L-NAME increased the contractile responses to methoctramine (82.6 ± 2.31), but reduced the relaxant ones (26.38 ± 1.29). In contrast, at the maximum frequency tested, it increased only the contractile response, but not modify the relaxant one, in epithelium denuded rings. In conclusion, the present data showed that the release of acetylcholine from postganglionic cholinergic nerves plays an important role on NO formation and this effect may be modulate by epithelium.

Maturation of porcine tracheal cholinergic and inhibitory non-adrenergic, non-cholinergic innervation.

It is known that both excitatory cholinergic neural activity and nitric oxide (NO) release from inhibitory non-adrenergic, non-cholinergic (iNANC) nerves are important determinants of adult human airway smooth muscle tone. However, the level of cholinergic and iNANC activity in the newborn is unknown. Therefore, isolated trachealis muscle strips were obtained from neonatal, 10-day-old, and adult pigs. To quantify cholinergic nerve activity, isometric contractions were elicited by stimulating the nicotinic receptors of the cholinergic intramural ganglia with dimethyl-phenyl-piperazinium (DMPP). After ganglionic blockade with hexamethonium, the post-ganglionic cholinergic nerves were subjected to electrical field stimulation (EFS). To assess whether DMPP and EFS were also stimulating nitric oxide release from iNANC nerves, the stimulations were repeated after NO-synthase inhibition with 3 x 10(-5) M NG-monomethyl-L-arginine acetate (LNMMA). All responses were expressed as a percentage of maximal response to 10(-4) M acetylcholine. Although no significant age-related differences in the contractile responses to DMPP were demonstrated between the three age groups, the EFS responses were significantly different. At EFS frequencies of 1 and 2 Hz the responses of all three groups were different (P < 0.05, unpaired t-test). At frequencies of 0.125 and 0.5 Hz the contractile responses in the neonatal and 10-day-old groups were less than in the adult animal tissues (P < 0.05, unpaired t-test). At 4 Hz and above, the responses of the 10-day-old and adult groups became greater than the neonatal (P < 0.05, unpaired t-test). LNMMA did not significantly increase the contractile responses to DMPP at any age. Only in the neonatal rat and 10-day-old groups was a significant increase of the EFS frequency responses by LNMMA demonstrated (140.4 +/- 38.2% and 144.2 +/- 41.2%, respectively, at 0.5 Hz, ANOVA, P < 0.001). In conclusion, the DMPP responses suggest that the neonatal porcine cholinergic innervation is mature at birth. This contrasts with a frequency-dependent increase in EFS responses from birth. This may be due in part to a relative increase in iNANC modulation of post-ganglionic cholinergic activity at birth. This mechanism is not responsible for the increase in higher EFS frequency responses with post-natal maturation. Inhibitory iNANC activity may serve a protective role in the newborn, given the reported hyper-responsiveness of airway smooth muscle, small airway caliber, and high chest wall compliance at this age.

Parasympathetic innervation of the salivary glands

The autonomic nervous system (ANS) is a mixed nervous system. There are two divisions of the ANS: the parasympathetic autonomous nervous system (PANS), and the sympathetic autonomic nervous system (SANS). The PANS plays a role in the conservation and homeostasis of bodily functions. The cells giving rise to parasympathetic fibers are situated at three different levels of the central nervous system: the midbrain, the medulla oblongata, and the sacral region of the spinal cord. The parasympathetic fibers leave the brain in the facial (VII CN), glossopharyngeal (IX CN), and vagus (X CN) nerves. The postganglionic parasympathetic fibers of the VII CN enter the sublingual and submanidublar glands and the minor salivary glands of the mucous membrane of the mouth, pharynx and nasopharynx, and those of the IX CN converge into the parotid gland. Parasympathetic postganglionic cholinergic nerve fibers supply cells of both the secretory end-piece and ducts and stimulate the rate of salivary secretion, inducing the formation of large amounts of a low-protein, serous saliva. Parasympathetic denervation of the major salivary glands leads to an immediate reduction of salivary secretion.

A simple method for measuring the effects of drugs on intestinal longitudinal and circular muscle

A tissue preparation is described which makes it possible to examine the effect of drugs on the nerves that control both longitudinal and circular muscles of the small intestine. The preparation consists of a segment of rat ileum set up to measure the tension developed in the longitudinal muscle and intraluminal pressure developed by the circular muscle in response to transmural electrical stimulation. The method showed that both muscles differed in their patterns of responses to transmural stimulation from the threshold of 2.5–60 Hz. All responses were tetrodotoxin-sensitive, the fast longitudinal muscle contraction and the intraluminal pressure response being caused by both pre- and postganglionic cholinergic nerves. The responses differedd in their sensitivities to the α 2-adrenoceptor agonists clonidine and UK 14,304, whereby the cholinergic responses of the circular but not longitudinal muscle were inhibited by the agonists. Comparison of results with the guinea-pig ileum set up in the same way revealed a marked species variation in responses, in that the intraluminal pressure response of the guinea-pig ileum was not sensitive to α 2-adrenoceptor agonists. This clear species difference makes it possible to use the circular muscle of the rat ileum, as measured indirectly via intraluminal pressure, to assess compounds for activity at α 2-adrenoceptors over a wide range of frequencies.