Fluorescence histochemical demonstration of adrenergic nerve fibers in the vagus nerve of cats and dogs

Can a Sacrococcygeal Epidural of 0.25% Bupivacaine Prevent the Activation of the Sympathetic Nervous System during Feline Ovariectomy?

The ovariectomy (OVE) procedure can trigger somatosensory and visceral peritoneal nociception. Sacrococcygeal epidural (ScE) anesthesia may complement or replace systemic analgesia used for feline OVE, reducing opioid consumption and their related undesirable adverse effects and consequently reducing or completely blocking the sympathetic nervous system activation during this procedure. The present study aimed to evaluate the activation of the sympathetic nervous system resulting from adding an ScE injection of bupivacaine 0.25% (0.3 mL kg-1) in feline OVE and identify whether this translates to hemodynamic variables stability. A Parasympathetic Tone Activity (PTA) monitor was applied given that it performs analysis of heart rate variability (HRV) detecting changes in sympathetic and parasympathetic tone, making it a good tool for detecting activation of the sympathetic nervous system during the study. Two groups of animals were evaluated in five perioperative times, namely, the control group (CG) (n = 18) with systemic analgesia alone and the sacrococcygeal epidural group (ScEG) (n = 20) with 0.25% bupivacaine combined with systemic analgesia. Thirty-eight female cats were selected. All animals assigned to CG and ScEG were premedicated with dexmedetomidine (20 μg kg-1 IM) and methadone (0.2 mg kg-1 IM). General anesthesia was induced with propofol IV ad effectum and maintained with isoflurane in 100% oxygen. Heart rate, non-invasive systolic and median blood pressure, respiratory rate, and instantaneous parasympathetic tone activity were recorded. Compared to systemic analgesia alone (CG), sacrococcygeal epidural (ScEG) reduced the rise of common hemodynamic variables but did not prevent sympathetic nervous system activation.

Sympathetic components in left and right human cervical vagus nerve: implications for vagus nerve stimulation

Cervical vagus nerve stimulation is in a great variety of clinical situations indicated as a form of treatment. It is textbook knowledge that at the cervical level the vagus nerve contains many different fiber classes. Yet, recently, several reports have shown that this nerve also may contain an additional class of potentially noradrenergic fibers, suggested to denote efferent sympathetic fibers. As such, the nature and presence of these fibers should be considered when choosing a stimulation protocol. We have studied human vagus material extracted from dissection room cadavers in order to further confirm the presence of this class of fibers, to study their origin and direction within the nerve and to determine their distribution and variability between subjects and pairs of left and right nerves of the same individual. Sections were studied with immunohistochemical techniques using antibodies against tyrosine hydroxylase (TH: presumed to indicate noradrenergic fibers), myelin basic protein and neurofilament. Our results show that at least part of the TH-positive fibers derive from the superior cervical ganglion or sympathetic trunk, do not follow a cranial but take a peripheral course through the nerve. The portion of TH-positive fibers is highly variable between individuals but also between the left and right pairs of the same individual. TH-positive fibers can distribute and wander throughout the fascicles but maintain a generally clustered appearance. The fraction of TH-positive fibers generally diminishes in the left cervical vagus nerve when moving in a caudal direction but remains more constant in the right nerve. These results may help to determine optimal stimulation parameters for cervical vagus stimulation in clinical settings.

Organ- and function-specific anatomical organization of vagal fibers supports fascicular vagus nerve stimulation

Vagal fibers travel inside fascicles and form branches to innervate organs and regulate organ functions. Existing vagus nerve stimulation (VNS) therapies activate vagal fibers non-selectively, often resulting in reduced efficacy and side effects from non-targeted organs. The transverse and longitudinal arrangement of fibers inside the vagal trunk with respect to the functions they mediate and organs they innervate is unknown, however it is crucial for selective VNS. Using micro-computed tomography imaging, we tracked fascicular trajectories and found that, in swine, sensory and motor fascicles are spatially separated cephalad, close to the nodose ganglion, and merge caudad, towards the lower cervical and upper thoracic region; larynx-, heart- and lung-specific fascicles are separated caudad and progressively merge cephalad. Using quantified immunohistochemistry at single fiber level, we identified and characterized all vagal fibers and found that fibers of different morphological types are differentially distributed in fascicles: myelinated afferents and efferents occupy separate fascicles, myelinated and unmyelinated efferents also occupy separate fascicles, and small unmyelinated afferents are widely distributed within most fascicles. We developed a multi-contact cuff electrode to accommodate the fascicular structure of the vagal trunk and used it to deliver fascicle-selective cervical VNS in anesthetized and awake swine. Compound action potentials from distinct fiber types, and physiological responses from different organs, including laryngeal muscle, cough, breathing, and heart rate responses are elicited in a radially asymmetric manner, with consistent angular separations that agree with the documented fascicular organization. These results indicate that fibers in the trunk of the vagus nerve are anatomically organized according to functions they mediate and organs they innervate and can be asymmetrically activated by fascicular cervical VNS.

Anatomical and clinical implications of vagal modulation of the spleen

The vagus nerve coordinates most physiologic functions including the cardiovascular and immune systems. This mechanism has significant clinical implications because electrical stimulation of the vagus nerve can control inflammation and organ injury in infectious and inflammatory disorders. The complex mechanisms that mediate vagal modulation of systemic inflammation are mainly regulated via the spleen. More specifically, vagal stimulation prevents organ injury and systemic inflammation by inhibiting the production of cytokines in the spleen. However, the neuronal regulation of the spleen is controversial suggesting that it can be mediated by either monosynaptic innervation of the splenic parenchyma or secondary neurons from the celiac ganglion depending on the experimental conditions. Recent physiologic and anatomic studies suggest that inflammation is regulated by neuro-immune multi-synaptic interactions between the vagus and the splanchnic nerves to modulate the spleen. Here, we review the current knowledge on these interactions, and discuss their experimental and clinical implications in infectious and inflammatory disorders.

Innervation of the human spleen: A complete hilum-embedding approach

INTRODUCTION

The spleen is hypothesized to play a role in the autonomic nervous system (ANS)-mediated control of host defence, but the neuroanatomical evidence for this assumption rests on a sparse number of studies, which mutually disagree with respect to the existence of cholinergic or vagal innervation.

METHODS

We conducted an immuno- and enzyme-histochemical study of the innervation of the human spleen using a complete hilum-embedding approach to ensure that only nerves that entered or left the spleen were studied, and that all splenic nerves were included in the sampled area. Furthermore, a complete embedded spleen was serially sectioned to prepare a 3D reconstruction of the hilar nerve plexus.

RESULTS

All detected nerves entering the spleen arise from the nerve plexus that surrounds branches of the splenic artery and are catecholaminergic. Inside the spleen these nerves continue within the adventitia of the white pulpal central arteries and red pulpal arterioles. Staining for either choline acetyltransferase or acetylcholinesterase did not reveal any evidence for cholinergic innervation of the human spleen, irrespective of the type of fixation (regularly fixed, fresh-frozen post-fixed or fresh-frozen cryoslides). Furthermore, no positive VIP staining was observed (VIP is often co-expressed in postganglionic parasympathetic nerves).

CONCLUSION

Our comprehensive approach did not produce any evidence for a direct cholinergic (or VIP-ergic) innervation of the spleen. This finding does not rule out (indirect) vagal innervation via postganglionic non-cholinergic periarterial fibres.

The strange case of the ear and the heart: The auricular vagus nerve and its influence on cardiac control

The human ear seems an unlikely candidate for therapies aimed at improving cardiac function, but the ear and the heart share a common connection: the vagus nerve. In recent years there has been increasing interest in the auricular branch of the vagus nerve (ABVN), a unique cutaneous subdivision of the vagus distributed to the external ear. Non-invasive electrical stimulation of this nerve through the skin may offer a simple, cost-effective alternative to the established method of vagus nerve stimulation (VNS), which requires a surgical procedure and has generated mixed results in a number of clinical trials for heart failure. This review discusses the available evidence in support of modulating cardiac activity using this strange auricular nerve.

Morphology of the human cervical vagus nerve: implications for vagus nerve stimulation treatment

OBJECTIVES

The vagus nerve has gained a role in the treatment of certain diseases by the use of vagus nerve stimulation (VNS). This study provides detailed morphological information regarding the human cervical vagus nerve at the level of electrode implant.

RESULTS

Eleven pairs of cervical vagus nerves and four pairs of intracranial vagus nerves were analysed by the use of computer software. It was found that the right cervical vagus nerve has an 1.5 times larger effective surface area on average than the left nerve [1,089,492 ± 98,337 vs 753,915 ± 102,490 μm(2), respectively, (P < 0.05)] and that there is broad spreading within the individual nerves. At the right side, the mean effective surface area at the cervical level (1,089,492 ± 98,337 μm(2)) is larger than at the level inside the skull base (630,921 ± 105,422) (P < 0.05). This could imply that the vagus nerve receives anastomosing and 'hitchhiking' branches from areas other than the brainstem. Furthermore, abundant tyrosine hydroxylase (TH)- and dopamine ß-hydroxylase (DBH)-positive staining nerve fibres could be identified, indicating catecholaminergic neurotransmission. In two of the 22 cervical nerves, ganglion cells were found that also stained positive for TH and DBH. Stimulating the vagus nerve may therefore induce the release of dopamine and noradrenaline. A sympathetic activation could therefore be part of mechanism of action of VNS. Furthermore, it was shown that the right cervical vagus nerve contains on average two times more TH-positive nerve fibres than the left nerve (P < 0.05), a fact that could be of interest upon choosing stimulation side. We also suggest that the amount of epineurial tissue could be an important variable for determining individual effectiveness of VNS, because the absolute amount of epineurial tissue is widely spread between the individual nerves (ranging from 2,090,000 to 11,683,000 μm(2)).

CONCLUSIONS

We conclude by stating that one has to look at the vagus nerve as a morphological entity of the peripheral autonomic nervous system, a composite of different fibres and (anastomosing and hitchhiking) branches of different origin with different neurotransmitters, which can act both parasympathetic and sympathetic. Electrically stimulating the vagus nerve therefore is not the same as elevating the 'physiological parasympathetic tone', but may also implement catecholaminergic (sympathetic) effects.

Tyrosine hydroxylase-immunoreactive fibers in the human vagus nerve

Sympathetic catecholaminergic fibers in the vagus nerve were immunohistochemically examined in formalin-fixed human cadavers using an antibody against the noradrenalin-synthetic enzyme tyrosine hydroxylase (TH). TH-positive fibers were extensively distributed in the vagal nerve components, including the superior and inferior ganglia, the main trunk and the branches (superior and recurrent laryngeal, superior and inferior cardiac, and pulmonary branches). The inferior ganglion and its continuous cervical main trunk contained numerous TH-positive fibers with focal or diffuse distribution patterns in each nerve bundle. From these findings, we conclude that sympathetic fibers are consistently included in the human vagus nerve, a main source of parasympathetic preganglionic fibers to the cervical, thoracic and abdominal visceral organs.

The origin of catecholaminergic nerve fibers in the subdiaphragmatic vagus nerve of rat

It is known that the vagus nerve contains catecholaminergic fibers. However, the origin of these fibers has not been systematically examined. In this study, we addressed this issue using retrograde tracing from the subdiaphragmatic vagus nerve combined with immunocytochemistry. The cervical and thoracic sympathetic trunk ganglia, the nodose ganglia and the dorsal motor nucleus of the vagus nerve were examined following injection of Fluoro-Gold or cholera toxin horseradish peroxidase conjugate into the trunks of the subdiaphragmatic vagus nerve of rats. Numerous retrogradely labeled neurons were seen in the nodose ganglion and the dorsal motor nucleus of the vagus nerve. Very few labeled neurons were found in the sympathetic ganglia (less than 0.06% of the neurons in either superior cervical ganglion or cervicothoracic ganglion were retrogradely labeled). Double labeling with immunofluoresence for catecholamine synthesizing enzymes revealed that: (1) 92% of all Fluoro-Gold retrogradely labeled tyrosine hydroxylase immunoreactive neurons were found in parasympathetic sources (75% in the dorsal motor nucleus of the vagus nerve and 17% in the nodose ganglia), and only 8% in the cervicothoracic sympathetic ganglia; (2) 12% of the retrogradely labeled catecholaminergic neurons in the dorsal motor nucleus of the vagus nerve were also dopamine-beta-hydroxylase immunopositive neurons; (3) 70% of the retrogradely labeled neurons in the sympathetic ganglia were tyrosine hydroxylase immunopositive and 54% of these catecholaminergic neurons contained dopamine-beta-hydroxylase, while 30% of the retrogradely labeled neurons were non-catecholaminergic neurons. These results indicate that catecholaminergic fibers in the abdominal vagus nerve are primarily dopaminergic and of parasympathetic origin, and that only an extremely small number of these fibers, mostly noradrenergic in nature, arise from postganglionic sympathetic neurons.

Interaction between parasympathetic and sympathetic nerves in prevertebral ganglia: morphological evidence for vagal efferent innervation of ganglion cells in the rat

Vagal efferent preganglionic neurons were anterogradely labeled by injecting either DiI or DiA, fluorescent lipophilic carbocyanine dyes, into the dorsal motor nucleus of the vagus of the rat. All neurons of the peripheral nervous system (outside the blood-brain barrier) were then fluorescently counterstained in vivo by injecting Fluorogold (Fluorochrome, Inc., Englewood, CO) intraperitoneally. The upper abdominal prevertebral ganglia, including the numerous microganglia associated with the periarterial plexuses of the celiac and superior mesenteric arteries, were identified and dissected in formalin-fixed tissue under ultraviolet light and stereomicroscopic guidance. In 14 of 15 animals analyzed (93%), labeled vagal efferent fibers were found to penetrate into both the left and right celiac ganglia and the superior mesenteric ganglion, as well as into some of the associated microganglia. These projections formed varicose terminal-like structures, highly suggestive of synaptic contacts surrounding individual ganglion cells. In about half the animals, such vagal innervation was also seen in the left and right suprarenal ganglia. The specificity of vagal efferent labeling was confirmed by control experiments, which included injections in vagotomized animals and direct selective labeling of vagal afferents from the nodose ganglia. It is concluded that vagal efferent preganglionics innervate principal ganglion cells of prevertebral ganglia. These vagal contacts may either directly modulate the postganglionic outflow or else gate some or all of the potential modulatory inputs to these postganglionic neurons, thus allowing the vagal system to exert a more selective influence on sympathetic outflow. Finally, the use of laser scanning confocal microscopy and the in toto Fluorogold staining method for investigations of the peripheral nervous system are discussed.

The role of vagal adrenergic activity in the mechanism of gastric acid secretion after pylorus-ligation in the rat

The role of the vagus nerve and adrenoceptor stimulation in acid secretion after pylorus-ligation in the rat has been examined. All drugs were administered intraperitoneally. Atropine (5 mg kg-1) depressed the H+ output (111 mumols +/- 33.8 vs 412.5 mumols +/- 62.2, mean +/- s.e.m., n = 10, P less than 0.001); cimetidine (40 mg kg-1) did not enhance this action, while vagotomy was more effective than atropine (32.7 mumols +/- 4.9, mean +/- s.e.m., n = 10, P less than 0.05). Atropine (10 mg kg-1) produced a similar depression to the 5 mg kg-1 dose. Cimetidine (100 mg kg-1) depressed the H+ output (248.5 mumols +/- 46.8, mean +/- s.e.m., n = 10, P less than 0.05). Propranolol (5-20 mg kg-1) had no significant effect on the H+ output but dose-dependent inhibition was produced by phenoxybenzamine or phentolamine; an inhibition similar to that achieved by vagotomy was seen with the 20 mg kg-1 dose. Both these drugs (5 or 10 mg kg-1) had no significant effect on the H+ output when given with atropine (5 mg kg-1) but the H+ output was significantly lower than that produced by either drug at the same dose given alone. Atropine (5 mg kg-1) with phenoxybenzamine or phentolamine (20 mg kg-1) produced H+ output not significantly different from that with vagotomy or either alpha-adrenoceptor given alone at 20 mg kg-1, but the result was significantly (P less than 0.05) lower than the H+ output with atropine (5 mg kg-1) alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of vagal efferent fibers and putative target neurons in the enteric nervous system of the rat

The stomach and small intestine receive an efferent innervation from the dorsal motor nucleus of the vagus (DMX). The current experiments were undertaken as a partial test of the hypothesis that the CNS innervates only a small number of command neurons in a restricted number of enteric ganglia. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was injected into the DMX by iontophoresis, and 10-21 days later PHA-L was visualized in the bowel by immunofluorescence. Varicose vagal efferent fibers, labeled by PHA-L, were found in the myenteric plexus as far distally as the ileo-colic junction. PHA-L-labeled varicose axons were rare in comparison to nonlabeled fibers, entered a minority of myenteric ganglia, and contacted a small proportion of the neurons. Ganglia thus innervated by vagal efferent fibers were more numerous in the stomach than in the small intestine. Within the stomach, these ganglia were common in the antrum than in the corpus and none were found in the wall of the rumen. Innervated ganglia in the small intestine became progressively more sparse distally. No PHA-L-labeled axons were observed in the submucosal plexus, thus raising the possibility that vagal modulation of secretomotor responses involves an intermediate synapse in the myenteric plexus. Nonvaricose bundles of PHA-L-labeled fibers were also observed. These bundles appeared to utilize the connectives of the myenteric plexus as a pathway within which to descend within the bowel. Vagal efferent bundles were found to pass through the pyloric sphincter to enter the small intestine from the stomach; thus vagal fibers can reach the distal intestine by an intraenteric route that is not lesioned by crushing mesenteric nerves. The existence of this pathway affects the interpretation of experiments seeking to utilize such lesions to distinguish intrinsic from extrinsic neurites. Possible target neurons of the vagal efferent innervation were identified by simultaneously demonstrating the immunoreactivities of 5-hydroxytryptamine (5-HT), vasoactive intestinal polypeptide (VIP), enkephalin (ENK), galanin (GAL), and tyrosine hydroxylase (TH) along with that of PHA-L. Vagal terminals in the myenteric plexus appeared selectively to contact 5-HT- and, to a significantly lesser extent, VIP-, but not ENK- or GAL-immunoreactive neurons. Apparent vagal innervation of 5-HT-immunoreactive neurons was significantly more common in the duodenum, where a majority of the 5-HT-immunoreactive cells were encircled by varicose PHA-L-labeled axons, than in the stomach.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of adrenoceptors in the mechanism of reserpine-induced stimulation of gastric acid secretion in the rat

The role of alpha- and beta-adrenoceptors in the mechanism of reserpine-induced stimulation of gastric acid secretion in the rat has been examined. After 6 h reserpine (0.1 mg kg-1 i.p.) significantly stimulated acid secretion relative to control values (176 +/- 4 vs 60 +/- 3 mumol, mean +/- s.e.m., n = 10, P less than 0.001). Neither coeliac ganglionectomy nor propranolol (5-15 mg kg-1) influenced this action. Vagotomy prevented acid stimulation by reserpine and was associated with H+ output similar to that of vagotomy controls (13 +/- 1 vs 14 +/- 1 mumol, mean +/- s.e.m., n = 10). Dose-dependent inhibition of the reserpine-induced acid secretion was produced by phenoxybenzamine or phentolamine; an inhibition similar to that achieved by vagotomy was noted with the 15 mg kg-1 dose (13 +/- 1 and 15 +/- 1 mumol, respectively, vs 176 +/- 4 mumol, mean +/- s.e.m., n = 10, P less than 0.001). The similarity in action between vagotomy and large doses of phenoxybenzamine or phentolamine suggests that, in the rat, vagal alpha-adrenoceptor stimulation is directly involved in the mechanism of reserpine-induced stimulation of gastric acid secretion.

Effect of superior cervical ganglionectomy on insulin release by murine pancreas slices

The effect of superior cervical ganglionectomy (SCGx) on basal and glucose-stimulated insulin release in vitro was examined in pancreas slices of BALB/c mice subjected to surgery 14-96 h earlier. Fourteen or 20 h after SCGx a significant increase of insulin response to 11 mM glucose was detectable, while 96 h after SCGx a depression in response was found. Perifused pancreas slices obtained from mice subjected to SCGx 7 days earlier showed a decreased in vitro insulin response to glucose during both phases of insulin secretion. In sham-operated mice, injection of the beta-adrenoceptor blocker propranolol or of the cholinergic muscarinic antagonist atropine decreased basal and glucose-stimulated insulin release, while the alpha-adrenoceptor blocker phenoxybenzamine did not affect it significantly. In mice subjected to SCGx 14 h earlier, propranolol treatment decreased basal insulin release and impaired the release elicited by glucose to values similar to those found in controls, phenoxybenzamine injection increased the basal and amplified the enhanced glucose-stimulated insulin release, and atropine injection, although unable to affect basal insulin release, impaired partially the amplification of response detectable after surgery. Our results support the existence of significant effects of SCG neurons on insulin release in mice.

Vagal release of serotonin into gut lumen and portal circulation via separate control mechanisms

The mechanisms controlling vagally induced release of serotonin-like immunoreactivity (5-HTLI) into portal circulation and jejunal lumen were studied in individual cats. In control animals, electrical vagal nerve stimulation significantly enhanced both the endoluminal secretion rate of 5-HTLI and the release of 5-HTLI into the portal vein. The vagally induced release of 5-HTLI into portal circulation was blocked by pretreatment with propranolol or phenoxybenzamine, or by previous removal of the superior cervical ganglia, but was not blocked by atropine or hexamethonium. On the contrary, the luminal secretion of 5-HTLI after vagal stimulation was not blocked by adrenoceptor blocking agents or ganglionectomy, but instead was inhibited by cholinoceptor antagonists. Thus, in the same experimental animals it was shown that vagally induced release of 5-HTLI into portal circulation was mediated by adrenoceptor mechanisms, while endoluminal release of 5-HTLI was regulated via cholinoceptors. Based on indirect estimations, the apical release of 5-HT seems to be quantitatively small in comparison with the release into portal circulation.

The hypothalamus and gastric mucosal injuries: origin of stress-induced injury?

This paper reviews the role of the central nervous system in the genesis of gastrointestinal mucosal injuries. The discussion makes particular reference to the significance and mechanism of stress-induced injury of the gastroduodenal mucosa. It points out that in the rat, stress activates the hypothalamus, producing delivery of alpha-adrenergic stimulation to the stomach by the adrenergic hypothalamovagal pathway. This stimulation controls intragastric blood flow and 5-HT release. Low magnitude pharmacologically-induced stress enhances gastric acid secretion and, if this stress is maintained, it produces chronic duodenal ulceration. High magnitude pharmacologically-induced stress depresses acid secretion and injures the gastric mucosa. If such stress is maintained, it produces chronic gastric ulceration. The paper provides a detailed account of the mechanisms of these stress-induced gastroduodenal effects.

Reserpine, vagal adrenergic activity and stress-induced acute gastric mucosal injury in the rat

1. Stress activates the hypothalamus causing central adrenergic discharge and stimulation of the autonomic sympathetic system. Reserpine produces the same effect and, therefore, its acute gastric mucosal injury is stress-induced. This injury was employed in the gastric diversion rat, a model for determining gastric acid secretion under basal conditions, to examine the relationship of the vagus nerve to the autonomic sympathetic system in the mechanism of stress-induced acute gastric mucosal injury. 2. After 6 h of reserpine (5 mg/kg I.P.), all rats developed oval or round lesions confined to the glandular stomach and of no constant relationship to rugal crests (lesion score 29 +/- 2.7 mm2, mean +/- S.E., n = 10). Microscopically, these lesions were vascular in origin, developing as intramural foci of haemorrhage or necrosis and expanding to communicate with the lumen. Pre-treatment with potent antisecretory doses of the anticholinergic atropine (5 mg/kg I.P.) or the H2-receptor antagonist cimetidine (40 mg/kg I.P.) did not influence this reserpine action (28 +/- 3 mm2 and 27.5 +/- 2.3 mm2, respectively, mean +/- S.E., n = 10). Protection against the reserpine lesions by the alpha-adrenoceptor blocking drugs phenoxybenzamine or phentolamine given in a dose of 10 mg/kg I.P. was significantly (P less than 0.01) more than that afforded by the 5 mg/kg I.P. dose. However, the 15 mg/kg I.P. dose was completely protective against the lesions. Vagotomy had a similar protective effect. Interruption of autonomic sympathetic delivery to the stomach by coeliac ganglionectomy had no influence on the macroscopic or microscopic effects of reserpine on the stomach (30.5 +/- 3.4 mm2, mean +/- S.E., n = 10). 3. The H+ output associated with 6 h of gastric diversion (61 +/- 4.5 mumol, mean +/- S.E.) was significantly (P less than 0.001) depressed by reserpine alone (26 +/- 2 mumol) or with atropine (19 +/- 1.8 mumol) or cimetidine (21 +/- 2 mumol). Protection against the reserpine lesions by phenoxybenzamine or phentolamine was associated with dose-dependent increase of H+ output, which with the 15 mg/kg dose was similar to that of control values (58 +/- 4.1 mumol and 60.3 +/- 2.8 mumol vs. 61 +/- 4.5 mumol). Vagotomy protection was associated with an H+ output significantly (P less than 0.001) lower than that with reserpine alone (14 +/- 1.4 mumol). Coeliac ganglionectomy had no influence on the H+ output associated with reserpine treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Vagal release of serotonin into gut lumen and portal circulation via separate control mechanisms

The mechanisms controlling vagally induced serotonin-like immunoreactivity (5-HTLI) release into portal circulation and jejunal lumen were studied in individual cats. In control animals, electrical vagal nerve stimulation significantly enhanced both the endoluminal secretion rate of 5-HTLI and the release of 5-HTLI to the portal vein. The vagally induced release of 5-HTLI to the portal circulation was blocked by pretreatment with propranolol or phenoxybenzamine, or by prior removal of the superior cervical ganglia, but was not blocked by atropine or hexamethonium. On the contrary, the luminal secretion of 5-HTLI after vagal stimulation was not blocked by adrenoceptor blocking agents or ganglionectomy, but instead was inhibited by cholinoceptor antagonists. Thus, in the same experimental animal it was shown that vagally induced release of 5-HTLI to the portal circulation was mediated by adrenoceptor mechanisms, while the luminal release of 5-HTLI was regulated via cholinoceptors. Based on indirect estimations, the apical release of 5-HT seems to be qualitatively small in comparison with the release into the portal circulation.

Regulatory mechanisms in endoluminal release of serotonin and substance P from feline jejunum

The mechanisms controlling vagally induced 5-HT and SP release into the jejunal lumen were studied in the cat. In control animals, electrical vagal nerve stimulation doubled the rate of endoluminal secretion of 5-HT and SP. Propranolol pretreatment did not alter luminal secretion of these hormones. Atropine suppressed motor function and induced dose-related inhibition of vagal release of endoluminal 5-HT, but not of SP; the response to hexamethonium pretreatment was similar to that of atropine. In contrast, superior cervical ganglionectomy did not alter stimulated endoluminal 5-HT release but it completely abolished release into the portal vein. The portal 5-HT release was not affected by ganglionic blockade. The data suggest that vagally mediated 5-HT release into the lumen and the portal circulation are mediated by different neural mechanisms, the former cholinergic, the latter presumably adrenergic; and release of feline 5-HT and SP are independent, suggesting two intestinal sources, the EC cell for 5-HT and peptidergic neurons for SP.

Effect of total sympathectomy and of decentralization on migrating complexes in dogs

The effect of total sympathectomy and of decentralization on interdigestive myoelectric activity of the stomach and small intestine and on cycling levels of plasma motilin were studied in conscious dogs. In controls, 98.3% +/- 7.9% of the migrating myoelectric complexes (mean +/- SD) originated in the stomach. In sympathectomized dogs, 38.17% +/- 16.7% originated in the stomach, 35.8% +/- 12.3% in the duodenum, and 26.3% +/- 4.3% in the jejunum. In decentralized dogs, 5.3% +/- 1.4% of the migrating myoelectric complexes originated in the stomach, 71.0% +/- 16.5% in the duodenum, and 23.9% +/- 17.4% in the jejunum. Cycling of plasma motilin was not affected by long-term sympathectomy but coordination of peak levels of plasma motilin and initiation of gastric migrating myoelectric complexes was disrupted in decentralized dogs. These data suggest that central nervous input is required for initiation of migrating myoelectric complexes in the stomach and that central vagal but not central sympathectic input is essential for cycling of plasma motilin.

Vagal regulation of insulin, glucagon, and somatostatin secretion in vitro in the rat

Using a new in vitro procedure of the isolated perfused rat pancreas with vagal innervation, electrical vagal stimulation produced an increase in both insulin and glucagon secretion in proportion to the pulse frequency, but an inhibition in somatostatin release. When atropine was infused, both insulin and glucagon responses to vagal stimulation were partially suppressed, whereas somatostatin release was enhanced. In the presence of hexamethonium, vagal stimulation failed to affect insulin, glucagon, or somatostatin secretion. Propranolol partially blocked both insulin and glucagon responses but did not influence somatostatin response. Phentolamine had no significant effect on release of hormones. Simultaneous administration of propranolol and phentolamine tended to inhibit both insulin and glucagon responses to vagal stimulation. These findings suggest that not only a cholinergic but also a noncholinergic neuron may be involved in vagal regulation of pancreatic hormone secretion and that these neurons may be under the control of preganglionic vagal fibers via nicotinic receptors.

Vagotomy inhibits the effect of neurotensin on gastrointestinal transit in the rat

Neurotensin has previously been shown to delay gastric emptying, gastrointestinal transit and ileo-caecal emptying in the rat. To investigate the vagal influence on these effects of neurotensin, separate groups of rats were operated with combined vagotomy and pyloroplasty or with pyloroplasty alone and compared to a group of normal rats. All animals were supplied with a permanent gastrointestinal catheter and a venous catheter. After operation the rats were allowed to recover for 7 days, and were fasted for 24 h prior to the experiments. A radioactive marker of 1.0-0.5 ml Na2(51)CrO4 in isotonic polyethylene glycol 400 was instilled intraluminally in the stomach, proximal or distal the small intestine. Saline (control animals) or neurotensin (test animals) was given i.v. in each group studied. The animals were killed at 15, 30, 60, and 120 min after administration of the marker. The distribution of the marker in the gastrointestinal tract was registered with a scintillation detector and quantitative analysis of the amount of radioactivity retained in separate gastrointestinal segments was carried out. Gastric emptying was delayed by combined vagotomy and pyloroplasty (P less than 0.01) compared to pyloroplasty alone and normals. Neurotensin at doses of 6 (P less than 0.05) and 12 (P less than 0.01) pmol kg-1 min-1 retarded gastric emptying dose-dependently in normals and rats with pyloroplasty alone, but did not further slow the gastric emptying in rats with vagotomy and pyloroplasty. However, at a dose of 24 pmol kg-1 min-1 neurotensin delayed gastric emptying (P less than 0.01) compared to controls. Gastrointestinal transit was slowed down by neurotensin at a dose of 6 pmol kg-1 min-1 in normals (P less than 0.01) and rats with pyloroplasty alone (P less than 0.05). In rats with vagotomy and pyloroplasty, neurotensin at doses of 6 and 12 pmol kg-1 min-1 had no effect on gastrointestinal transit.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of tyrosine hydroxylase and neuropeptide Y-like immunoreactive neurons in rabbit medulla oblongata, with attention to colocalization studies, presumptive adrenaline-synthesizing perikarya, and vagal preganglionic cells

We studied the distribution, within the rabbit medulla oblongata, of neuronal cell bodies containing either tyrosine hydroxylase or neuropeptide Y-like immunoreactivity. Both avidin-biotin and immunofluorescence procedures were used. Because the two primary antibodies were raised in different species it was possible to perform simultaneous colocalization studies with the immunofluorescence procedure. Tyrosine hydroxylase-containing neurons in the rostral medulla were demonstrated to contain a catecholamine by the colchicine-enhanced FAGLU (formaldehyde-glutaraldehyde) fluorescence histochemical procedure. These neurons are presumably adrenergic, corresponding to the C1 and C2 groups described in the rat. No C3 group was found in the rabbit. The distribution of tyrosine hydroxylase-containing neurons in the caudal medulla was in accordance with previous descriptions of the A1 and A2 groups based on the unenhanced FAGLU procedure. Neuropeptide Y-like immunoreactivity was observed in cell groups corresponding to those already described in the rat, but additional groups were discovered in the rabbit. Some neurons containing neuropeptide Y-like immunoreactivity were observed in nucleus raphe pallidus and these also contained serotonin (5-HT). In the nearby nucleus reticularis gigantocellularis there were occasional neurons that contained neuropeptide Y-like immunoreactivity without any colocalized 5-HT. Neuropeptide Y-like immunoreactivity was also observed in the dorsal motor nucleus of the vagus, rostral to the obex, and these neurons were demonstrated to be true vagal preganglionic cells by colocalization of neuropeptide Y-like immunoreactivity and Fast Blue retrogradely transported from the cervical vagus. We found that neuropeptide Y-like immunoreactivity was colocalized in approximately 75% of the tyrosine hydroxylase-containing neurons in the rostral medulla (C1 and C2 cells). A smaller proportion of the A1 cells also contained this peptide but it was absent from both the most caudal A1 cells and from the A2 cells. Some tyrosine hydroxylase-containing neurons occur in direct apposition to vagal preganglionic cells in both the dorsal motor nucleus of the vagus and the nucleus ambiguous. However, colocalization studies revealed that none of these neurons contained Fast Blue when this dye was retrogradely transported from the cervical vagus. Medullary catecholamine-synthesizing neurons apparently do not contribute axons to the vagus nerve. This finding is consistent with our own studies in the rat but is in contrast to studies in this species published by other workers.

Evidence that catecholamine-synthesizing perikarya in rat medulla oblongata do not contribute axons to the vagus nerve

We attempted to confirm reports that medullary catecholamine-synthesizing neurons in the rat contribute axons to the vagus nerve. Vagal preganglionic neurons in the medulla were identified by the retrograde intra-axonal transport of Fast Blue from the cervical vagus. Catecholamine-synthesizing neurons were identified using a specific antibody against tyrosine hydroxylase. A rhodamine-labelled second antibody was used to ensure that Fast Blue and tyrosine hydroxylase could be viewed entirely independently. We did not find any medullary neurons which contained both tyrosine hydroxylase and Fast Blue. Although further investigations by other laboratories are necessary, we believe that previous studies, using punctate versus diffuse horseradish peroxidase staining to doubly label neurons may have produced false positive results.

An anomalous vagorenal reflex pathway in the cat

Although physiological investigations support the view that the innervation to the kidney is primarily sympathetic in origin, there is anatomic evidence suggesting direct vagal projections to the kidney. We examined electrophysiologically the possibility that neural connections exist between the cervical vagus and renal nerves. Electrical stimulation of the peripheral segment of the cut cervical vagus evoked electrical activity in the central segment of cut renal nerve of chloralose-anesthetized, paralyzed cats. The evoked potentials (vagorenal responses) displayed components with peak latencies of about 50, 120, and 500 ms. Another peak at about 175 ms was also seen in some cases. In addition, a period of postexcitatory depression occurred between approximately 180 and 400 ms after delivery of the stimulus. Evoked responses were recorded in the contralateral as well as the ipsilateral renal nerves. In contrast, stimulation of the central cut end of renal nerves did not elicit responses in the cervical vagus. Vagorenal responses were not altered by cutting the subdiaphragmatic vagus indicating that the abdominal vagus was not involved in this response. Electrical activity in renal nerves elicited by vagal stimulation could be eliminated by either ganglionic blockade or by cutting or cooling the splanchnic nerves. Finally, supraspinal ischemia abolished the vagorenal response. These data suggest that a vagorenal reflex pathway exists and that the potentials recorded in renal nerves are due to activation of aberrant sensory fibers traveling from the peripheral segment of the cut cervical vagus to the central nervous system, where they excite a sympathetic efferent pathway to the kidney.

Effect of extrinsic denervation on the rate of net water transport of the feline gall bladder

The influence on the concentrating ability of the gall bladder after extrinsic denervation was studied in anaesthetised cats, previously subjected to truncal vagotomy and/or coeliacectomy , and compared with sham operated controls. Net water absorption was studied by perfusion techniques. Acute experiments were performed under basal conditions and alpha-adrenoceptor stimulation (intra-arterial infusion of noradrenaline). Gall bladder biopsies were studied by fluorescence microscopy and cytofluorimetry to visualise and quantify catecholamines. Three weeks after coeliacectomy basal absorption had decreased significantly. In the short term vagotomy group no changes were shown. In the long term vagotomy group, however, there was a four-fold increase in absorptive capacity, which decreased to control levels after alpha-adrenoceptor blockade (phentolamine). Long term vagotomy with subsequent coeliacectomy caused no significant changes. Infusion of noradrenaline increased net water absorption by 60 +/- 11% in all experimental groups except in long term vagotomised animals, where the high basal absorption was not further augmented. One hour after noradrenaline infusion controls returned to basal absorption rate, while denervated cats remained at stimulated levels. In long term vagotomised gall bladders there were morphological signs of adrenergic proliferation (increased total number of nerve terminals, sprouting and raised levels of intraneuronal noradrenaline). These results suggest that the adrenergic nervous system is important for full absorptive capacity of the gall bladder. The increased absorption after long term vagotomy, abolished after alpha-adrenoceptor blockade, might well be explained by the parallel adrenergic proliferation. This hypothesis was further corroborated in animals with long term vagotomy, where subsequent surgical adrenergic denervation restored basal absorption to control levels.

Effects of extrinsic denervation on net water transport and motility of the feline gallbladder in vivo

The influence on the concentrating ability of the gallbladder after extrinsic denervation was studied in anesthetized cats, previously subjected to truncal vagotomy, and/or celiacectomy , and compared with sham-operated controls. Net water absorption was studied by perfusion techniques. Acute experiments were performed under basal conditions and alpha-adrenoceptor stimulation (iv infusion of norepinephrine (NE), 1 micrograms/kg X min). Gallbladder biopsies were studied by fluorescence microscopy to visualize and quantitate catecholamines. Three weeks after celiacectomy basal absorption had decreased significantly. In the short-term vagotomy group no changes were demonstrated. However, in the long-term vagotomy group there was a fourfold increase in absorptive capacity, which decreased to control levels after alpha-adrenoceptor blockade (phentolamine 1 mg/kg iv). Long-term vagotomy with subsequent celiacectomy caused no significant changes. Infusion of NE increased net water absorption by 70 +/- 16% in all experimental groups except in long-term vagotomized animals, where the high basal absorption was not further augmented. One hour after NE infusion controls returned to basal absorption rate, while denervated cats remained at stimulated levels. In long-term vagotomized gallbladders there were morphological signs of adrenergic proliferation (increased total number of nerve terminals, sprouting, and elevated levels of intraneuronal NE). In conclusion these results suggest that the adrenergic nervous system is important for full absorptive capacity of the gallbladder. The increased absorption after long-term vagotomy, abolished after alpha-adrenoceptor blockade, might well be explained by the parallel adrenergic proliferation. This hypothesis was further corroborated in animals with long-term vagotomy, where subsequent surgical adrenergic denervation restored basal absorption to control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Perspective on extra-gastric vagal fibers: should they be preserved when possible?

A number of discoveries have forced both basic scientists and practitioners of medicine to reinterpret their view of the relation of the autonomic nervous system, the brain, and the gastrointestinal tract. There is growing support for the concept of an autonomous enteric nervous system, one which has many participant and regulatory peptide neurotransmitters, but which can apparently function independently of certain afferent or efferent (vagal) connections to the central nervous system. Recognizing the possibility that extra-gastric vagus nerves may serve an essential role in physiologic functions, it is logical to support the concept that these nerves be preserved when possible. Whether operations which spare extra-gastric vagal nerves will pass the test of time remains to be seen.

Vagal mechanisms controlling serotonin release from the gastrointestinal tract and pyloric motor function

This chapter focuses on investigations of two mechanisms controlled by the vagal nerve; serotonin (5-HT) release from the small intestine and pyloric motor function. Morphological, physiological, pharmacological and biochemical methods were combined in these studies. 5-HT is mainly stored in enterochromaffin cells (EC), but is present also in mast cells and nerve terminals of the gut, as observed by immunocytochemistry. Vagal nerve stimulation causes a release of 5-HT from EC to the portal circulation and to the gut lumen. Morphological evidence for the endoluminal release of 5-HT was obtained by autoradiography and immunofluorescence. The 5-HT release from EC is mediated by a beta-adrenoceptor mechanism via sympathetic adrenergic fibers in the vagal nerve, originating from sympathetic ganglia, e.g. the superior cervical ganglion. This vagal adrenergic pathway was studied by fluorescence microscopy and retrograde tracing of horseradish peroxidase. The vagal peptidergic (nonadrenergic, noncholinergic) control of pyloric motor function was studied in chloralosed cats by means of an in vivo model, where changes of an applied flow of body-warm saline through the pylorus were recorded. Also, gastric volume changes were monitored. By means of immunofluorescence the presence of VIP-, enkephalin (ENK)- and substance P (SP)-like immunoreactivity was demonstrated in pyloric neurons and in the vagal nerve. Physiological evidence for a vagal VIPergic relaxatory mechanism was obtained, while ENK-neurons seem to mediate the vagally induced pyloric contraction, prevented by naloxone pretreatment. SP may mediate part of the vagally induced pyloric and gastric contraction, the latter probably via axon collaterals on final cholinergic neurons. ENKergic and SPergic vagal contractile mechanisms seem to be additive for the pylorus.

Evidence for non-cholinergic, non-adrenergic nervous control of mucus secretion into the cat trachea

We have investigated the effects of electrical stimulation of the vagus nerves on the output of mucus glycoproteins (mucins), radiolabelled with 3H and 35S, into the trachea of anaesthetized cats. In five control experiments, stimulation of the vagus nerves on four successive occasions, separated by 1 h, caused significant rises in the output of radiolabelled mucins. In these experiments repetition of stimulation did not appear to lessen the response. In a parallel series of five experiments the vagus nerves were again stimulated on four occasions, but atropine was administered in increasing doses between the stimuli. Large responses, not significantly less than those seen in the corresponding control stimulations, were seen even in the presence of the highest dose of atropine. In this series of experiments, however, the effect of the last vagal stimulation (with the highest dose of atropine) was significantly less then the first (no atropine). Administration of phentolamine and l-propranolol in addition to atropine failed to reduce the response to vagal stimulation significantly. We conclude that, while cholinergic nerves can probably explain part of the increase in mucin output which occurs with vagus nerve stimulation, there is a large response mediated by a non-cholinergic, non-adrenergic neurotransmitter. Possible neurotransmitters and the relationship of these findings to those of earlier studies are discussed.

Reinnervation of striated muscle by peripheral vagal fibres cut above or below the nodose ganglion in the cat and rabbit

In cats and rabbits, the peripheral stump of the vagus nerve cut above the nodose ganglion (supranodose anastomoses: s.n.) or below this ganglion (infranodose anastomoses: i.n.) was either sutured with epineurial sutures to the peripheral stump of the branch of the spinal accessory motor nerve innervating the sterno-cleido-mastoid (s.c.m.) muscle, or directly implanted in this muscle after resection of its motor nerve. After about six months, reinnervation of this muscle by vagal fibres was studied. By electromyographic recording during electrical stimulation of the cervical vagus nerve, it was shown that the vagal reinnervation of the s.c.m. muscle was established in 65% of the cats studied (57% s.n., 69% i.n.) and 33% of rabbits (37% s.n. and 31% i.n.). The average number of distinct potentials recorded in the reinnervated muscle, following vagal stimulation, was twenty-two in s.n. cats, thirteen in i.n. cats, eleven in s.n. rabbits and twelve in i.n. rabbits. Recorded potentials were monophasic (8%), biphasic (22.5%), triphasic (11.5%) or polyphasic (58%). These potentials were abolished by curare and alpha-bungarotoxin. The use of retrograde axonal transport of horseradish peroxidase showed labelled cells in the nodose ganglion, the cervical vagus and cranial thoracic vagus, and in the stellate ganglia. It is concluded that cholinergic vagal afferents reinnervated the s.c.m. muscle. Involvement of the sympathetic system is discussed.

Influence of electrical vagal stimulation and acetylcholine on the function of the feline gallbladder

The effects of electrical stimulation of the vagus nerves on the function of the feline gallbladder and hepatic bile outflow were studied with a perfusion technique in vivo. After elimination of the muscarinic receptors with atropine, efferent stimulation of the cut vagus nerve in the neck relaxed the gallbladder, reduced the net water absorption rate across its wall, and increased the bile outflow from the liver. The results imply that the concentrating function of the gallbladder and the bile formation in the liver are under regulatory control by noncholinergic, nonadrenergic nerve fibres in the vagus nerves.

Neurohumoral observations and the gastrointestinal tract

Vagal interrelationships with the gastric antrum have been studied in depth. A special experimental model, antroneurolysis, demonstrated that the function of the gastric mucosa is maintained after removal of central neural control, that is, vagotomy. A series of experiments are reported which demonstrate the importance of the sympathetic nervous system in the local control of gastrointestinal function. The concept of local neural control of the endocrine and secretory function of the epithelial cells of the intestinal mucosa (internal brain) is proposed.

The effect of phenoxybenzamine on the gastrin response to glycine stimulation

The nature of adrenergic mechanism involved in gastrin release in response to local stimuli and feeding is still unclear. In the present study, the effect of phenoxybenzamine, a potent alpha-blocking agent, on the gastrin release in response to glycine perfusion (pH 7.0) of an isolated canine antral pouch was examined. The experiment was repeated with truncal vagotomy performed before glycine perfusion. It was found that gastrin concentrations measured via right gastroepiploic vein were significantly increased during phenoxybenzamine infusion with and without truncal vagotomy. This finding indicates the presence of an alpha-adrenergic mechanism which inhibits gastrin release when the antrum is locally stimulated. After the drug was discontinued, though there was an enhancement in gastrin response in both saline and glycine perfused groups, the peak gastrin levels were reached earlier in the vagotomized dogs. This finding might indicate the influence of vagus nerve during the experiment.

The effect of propranolol on the serotonin concentration in the portal plasma after vagal nerve stimulation in the cat

Efferent cervical vagal nerve stimulation in the cat caused a marked increase of the portal plasma 5-HT concentration. This increase was more than two-fold within 15 min of stimulation. After cessation of stimulation portal plasma 5-HT returned to basal levels within 10 min. Treatment with the beta-adrenoceptor antagonist propranolol, in various doses (0.1-2 mg/kg b.wt.), did not abolish but significantly reduced the response to vagal stimulation, particularly during the final part of the stimulation period. The results confirm the existence of a beta-adrenoceptor-mediated release of 5-HT, but also suggest that other mechanisms for 5-HT release may be involved in the response on vagal nerve stimulation.

Origin of the adrenergic nerve fibers in the subdiaphragmatic vagus in the dog

The vagi at the subdiaphragmatic level were studied by the Hillarp-Falck technic in combination with a nerve crush procedure in three normal dogs and in eight dogs that had undergone previous surgical excision of the superior cervical ganglion and/or the stellate ganglia. Unilateral ganglionectomies were performed so that the contralateral vagus served as a control. Based on these results, it is concluded that: (1) the subdiaphragmatic canine vagus contains numerous adrenergic nerve fibers; (2) the main portion of these vagal adrenergic fibers arises from the stellate ganglia; and (3) removal of both the stellate and the superior cervical ganglia results in nearly complete adrenergic denervation of the abdominal vagus.

Efferent innervation of the small intestine by adrenergic neurons from the cervical sympathetic and stellate ganglia, studied by retrograde transport of peroxidase

The nervous pathways between the small intestine of cat and guinea pig and various sympathetic ganglia were investigated by the retrograde horse-radish peroxidase (HRP) technique. HRP was injected at multiple sites in the wall of the duodenum and the first third of the jejunum. At 1--5 days after the injections, the HRP reaction product was searched for in various sympathetic ganglia. Not only the coeliac and nodose ganglia, but also the superior cervical, medial cervical, stellate and thoracic ganglia contained HRP-positive nerve cells. Crushing the cervical vagal nerve prevented the occurrence of HRP-reaction in the cervical ganglia, indicating that the HRP was transported from the gut to the cervical ganglia via axons in the vagal nerve. The results demonstrate that the sympathetic ganglia in the neck (sup, and med. cerv. ganglia and stellate ggl.) send efferent fibres to the small intestine.

Comparative formaldehyde-induced and glyoxylic acid-induced fluorescence histochemical studies on the intrinsic adrenergic innervation of the intestine and the liver of normal and vagotomized cats

The inbuilt intrinsic adrenergic nervous apparatus of the intestine and liver of the cat was studied using 1. the formaldehyde-induced fluorescence histochemical method and 2. the glyoxylic acid-induced fluorescence histochemical method for serial microtome sections and whole mount tissue layers or smear preparations. In addition, the effect of I) total abdominal infra-diaphragmatic vagotomy with or without associated Finney-type gastro-duodenostomy and II) unilateral (left or right) and bilateral cervical vagotomy with or without tracheostomy on the intrinsic adrenergic innervation was tested. Fluorescing varicose axons, both "free" (i.e. unrelated to the blood vessels) and gathered to typical perivascular nerve plexuses were observed in all segments and all layers of the wall of the intestine. The density of the adrenergic innervation varied remarkably from an area to another, even in the same segment and tissue layer, which makes comparative estimations of the density of the innervation very difficult. However, the intrinsic adrenergic innervation of the circular muscle layer of the colon and the rectum seems to be consistently quite rich, and in the rectum, also the longitudinal muscle layer is relatively heavily innervated. It thus seems obvious that (in the cat) also the direct adrenergic innervation of the external smooth muscle layers is of considerable importance, specially in the rectum. In contrast, the results of the present study clearly indicate that the liver parenchyma (of the cat) is devoid of functional intrinsic adrenergic innervation. Vagotomies did not cause any changes in the intrinsic adrenergic innervation of the intestine and liver: even after complete vagotomy no reduction was observed in the number of fluorescing axons or in the intensity of the fluorescence. Consequently, the vagal contribution of adrenergic axons to the liver and the intestine must be negligible, at least in the cat. The use of the glyoxylic acid-induced fluorescence histochemical method and whole-mount tissue layers was found most suitable for mapping and comparative estimation of the density of the intrinsic adrenergic nerve net, and is therefore recommended for other similar or related studies.

Adrenergic innervation of the human gall bladder

Adrenergic innervation of the human gall bladder was studied using two specific fluorescence histochemical methods. Blue-green fluorescing varicose nerves were scarce and mostly followed the course of blood vessels as typical perivascular plexuses. However, some adrenergic nerves not associated with the vessels were occasionally seen, as well as structures suggestive of a pericellular arrangement of varicose adrenergic nerve terminals on non-fluorescing ganglion cells. A few enterochromaffin cells were seen in the epithelial lining, also in the deep invaginations obviously representing the Aschoff-Rokitansky sinuses. Occasionally, small rounded cells with a rounded, relatively large nucleus, and exhibiting a weak yellow-green to blue-green granular cytoplasmic fluorescence, were observed in the wall of the gall bladder. The possible functional and evolutionary significance of these neural and endocrine elements was discussed against the data on physiological and pharmacological studies obtained from the literature. It was concluded that their significance is, in all probability, secondary to the influence of the intestinal polypeptide hormones, vagal innervation and circulating catecholamines upon the normal function of the gall bladder. The glyoxylic acid-induced fluorescence histochemical method was found to be superior to the conventional formaldehyde technique in studies on human tissue.

Uptake of serotonin by intrinsic neurons of the myenteric plexus grown in organotypic tissue culture

The myenteric plexus contains axons, not found elsewhere in the peripheral nervous system, which are distinguished by a specific, high affinity transport system for serotinin (5-HT). This study was undertaken to determine the location of the cell bodies of origin of these axons. Vagotomy decreased uptake of [3H]5-HT and tritiated norepinephrine ([3H]NE) by the myenteric plexus. However, while examination by histofluorescence revealed the presence of descending vagal adrenergic fibers, no evidence was found for the presence or accumulation of 5-HT above a vagal ligature. Vagus nerves thus contain adrenergic but not serotonergic axons. The gut was also denervated of all extrinsic axons by growth of intestinal explants in organotypic tissue culture for 3 weeks. Uptake of [3H]5-HT persisted while uptake of [3H]NE was lost. Light and quantitative electron microscopic radioautography revealed that, as in intact gut, the elements of the cultures responsible for uptake of [3H]5-HT were axons distinguished by varicosities containing large dense cored vesicles. In conclusion, these experiments establish that the mammalian gut contains intrinsic neurons which selectively take up 5-HT. The capacity of these neurons for 5-HT uptake may be influenced by the vagus nerves.

A possible vagal adrenergic release of serotonin from enterochromaffin cells in the cat

The intracellular concentrations of serotonin (5-HT) in enterochromaffin cells (EC) in the cat small intestine have been studied by a cytofluorimetric method before and after long-lasting efferent vagal nerve stimulation in the neck. Such stimulation induces a decrease of 5-HT in EC of the gut as observed previously. Pretreatment with atropine could not block this decrease, suggesting a noncholinergic mechanism. Pretreatment with a beta-blocking agent, propranolol, or bilateral removal of the superior cervical ganglia could, however, block this 5-HT decrease. Pretreatment with an alpha-blocking agent, phenoxybenzamine, caused an increase in the 5-HT content of EC both with and without nerve stimulation; the reason for this is obscure. The results indicate, that vagal nerve stimulation induces a neurogenic 5-HT release from EC in the gut, and that adrenergic fibres, originating in the superior cervical ganglia, mediate this release probably via a beta-receptor mechanism. Whether or not an alpha-receptor mechanism is also involved cannot be judged at present.

Vagal influence on serotonin concentration in enterochromaffin cells in the cat

The intracellular concentrations of 5-HT in enterochromaffin cells of the jejunum, midgut and ileum of the cat have been estimated by a cytofluorimetric method before and after various periods of peripheral vagal nerve stimulation. The fluorescence intensities in randomized cell samples were measured photometrically after a standard illumination time before and after nerve stimulation. A significant decrease in 5-HT concentration in the enterochromaffin cells all through the small intestine could be demonstrated, which is in support of the hypothesis of a neurogenic release of 5-HT from enterochromaffin cells, possibly caused by vagal adrenergic fibres.

The vagal control of the ileo-cecal sphincter in the cat

In acute experiments on chloralosed cats the effect of efferent cervical vagal stimulation on a flow through the ileo-cecal sphincter (ICS) was studied. The motor activity of the jejunum, ileum and large intestine adjacent to the sphincter was recorded simultaneously. Vagal stimulation caused a decrease in the transphincteric flow and increased motor activity in the ileum. Increased motor activity in the proximal colon was recorded only occasionally. When the vagal nerves were stimulated during continuous splachine stimulation the transsphincteric flow was decreased although the tone and motility of the ileum was suppressed. Furthermore, guanethidine (1-3 mg/kg b.w.) blocked or suppressed the effect of vagal stimulation on the transsphincteric flow while the excitatory response of the proximal colon was greatly enhanced. This indicates that the reduction of the transsphinctteric flow following vagal stimulation was at least partly due to a direct effect of the vagal nerves on the sphincteric muscle and not to a squeezing effect of that part of the colonic wall that surrounds the sphincter. Atropine (0.1 and 1 mg/kg b.w.) blocked all responses to vagal stimulation. Thus, both guanethidine and atropine blocked the vagally induced contraction of the ICS. Relaxation to the ICS was never obtained by vagal stimulation even when the tone of the sphincter had been increased by infusion of noradrenaline.