Cervical Vagal Trunks Research Articles

Respiratory effects of serotonin challenge to pulmonary and laryngeal circulation in anaesthetized cats.

Administration of serotonin (5-HT) to pulmonary circulation elicits prompt apnoea, followed by subsequent tachypnoea. The present study was designed to ascertain whether 5-HT challenge into the laryngeal artery will evoke the full constellation of this chemoreflex and to examine the role of laryngeal sensory input and importance of vagal afferents in the respiratory sequelae. The experiments were done on 10 anaesthetized, spontaneously breathing cats. Laryngeal artery injections of 5-HT, similarly to intravenous challenge, caused apnoeas, which were significantly diminished by the section of cervical vagal trunks. Breathing frequency increased in all conditions on intravenous injection but only prior to vagotomy, when administered into laryngeal artery. With resumed breathing, the peak inspiratory airflows were significantly increased in the neurally intact, those treated by bilateral section of the superior laryngeal nerves (SLNs-cut) and vagotomized cats, with no difference between them and independent of the route of injection. The results show that serotonin chemoreflex could evolve from the laryngeal vascular bed and that laryngeal afferents do not contribute to the respiratory arrest.

Depression of ventilation by dopamine in cats: effects of bilateral cervical sympathetic and vagal trunk section.

The contribution of sympathetic and vagal inputs to ventilatory depression induced by dopamine was studied in eighteen anaesthetized, spontaneously breathing, normoxic cats. Breathing was via a tracheostomy. Dopamine (20 micrograms (kg body wt)-1) was injected intravenously in the intact animal, then after section of the cervical sympathetic trunks, and finally after midcervical vagotomy. Dopamine, injected as a bolus, induced depression of ventilation, affecting predominantly the volume component of the breathing pattern at all experimental stages. The extent of volume reduction was larger and different from that in intact animals following section of sympathetic (P < 0.05) and vagal trunks (P < 0.01). The respiratory cycle was significantly prolonged (P < 0.01) prior to vagotomy, due entirely to the increase in the expiratory time (TE). Bilateral section of the carotid sinus nerves performed in six cats virtually abolished postdopamine ventilatory depression.

Influences of the sympathetic and parasympathetic nerve transection on cardiovascular reflexes induced by volleys in the IXth nerve fibers of rat

The effect of vagotomy and sympathectomy on cardio-acceleratory and arterial hypertensive reflexes evoked by electrical stimulation of the rat glossopharyngeal (IXth) nerve was studied in relation to changes in baseline heart rate and arterial blood pressure. Uni- and bi-lateral transection of the cervical vagal trunk brought about augmentation of baseline heart rate, accompanied by a depression in reflex tachycardia; the amount of depression being inversely related to that of an increase in baseline heart rate. The latter increased more after a right vagotomy than after a left vagotomy. No appreciable change in reflex hypertension as well as in baseline blood pressure was observed by different types of vagotomy. For unilateral sympathectomy, semilunar cordotomy caudal to the obex was performed. It was found that right semilunar cordotomy significantly depressed the magnitude of cardio-acceleratory and arterial hypertensive reflexes in association with a significant decrease in baseline heart rate, though there was a less pronounced decrease in baseline blood pressure. The result obtained by a left semilunar cordotomy was similar to that of a right semilunar cordotomy, except that the decrease in reflex tachycardia was very small and statistically insignificant. Thus, the efferent activities in vagus and sympathetic nerves were more effective on the right than on the left side, in modifying reflex tachycardia and baseline heart rate, whereas, right and left sympathetic efferent outflows were equally effective in depressing the reflex increase in blood pressure.

Corticotropin‐Releasing Factor Binding Sites Undergo Axonal Transport in the Rat Vagus Nerve

Corticotropin-releasing factor (CRF) binding sites were found to be present in the rat vagus nerve and underwent axonal transport. Binding sites accumulated on both sides of ligatures placed on the nerve and at similar rates following ligation of right or left cervical vagal trunks of either male or female rats. CRF binding sites also accumulated proximal and distal to ligatures on subdiaphragmatic vagal trunks. Binding was specific, reversible and inhibited by the CRF receptor antagonist α-helical-CRF(9-41). [(125) l]Tyr(0) -ovine-CRF binding to rat vagus nerve was not guanine nucleotide-sensitive. CRF and cholecystokinin binding sites were transported at a similar rate in the cervical vagus, although turnover of CRF binding sites was more rapid. No differences in CRF binding site transport were observed between Zucker rats of lean or obese genotype.

Effects of selective vagal stimulation on the gallbladder and sphincter of Oddi and peripheral vagal routes mediating bile evacuative responses induced by hypothalamic stimulation.

Peripheral routes of the vagus nerves to the biliary system were studied in anesthetized dogs using various selective vagal stimulation. Efferent stimulation of the gastric, hepatic, or celiac vagal branch as well as the cervical or thoracic vagal trunk induced gallbladder and Oddi's sphincter contractions, but those induced by hepatic vagal stimulation were rather small. The contraction responses in the gallbladder and sphincter of Oddi induced by thoracic vagal stimulation were greatly reduced after an external ligation around the pyloric sphincter. After administration of sympathetic blockers and atropine, vagally-induced gallbladder contractions were completely abolished and slight relaxation was seen in some animals. On the other hand, relaxation or transient relaxation followed by enhanced contractions was elicited in the sphincter of Oddi by vagal stimulation after atropine and sympathetic blockers. The relaxation response in the gallbladder after atropine and sympathetic blockers was abolished and that in the sphincter of Oddi was greatly reduced after the ligation around the pyloric sphincter. Stimulation of a ventral part of the anterior hypothalamic area induced gallbladder contraction and simultaneous relaxation of the sphincter of Oddi. These responses were completely abolished by the ligation around the pyloric sphincter in six dogs, while a slight relaxation response in the sphincter of Oddi remained in two dogs. These results suggest that the vagal fibers passing across the pyloric sphincter region are important for regulation of canine biliary motility and that extragastric vagal routes play a minor role in the nervous control of canine bile evacuation.

Vagal cooling blocks circulating neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) release

Neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) are regulatory peptides that constitute a new family of gastrointestinal and neural peptides. The influence of vagal integrity on NPY, PYY, and PP basal and postprandial release was evaluated using a new technique of reversible cryogenic cervical vagal blockade in an awake canine model. Cooling coils were placed around bilateral cervical vagal trunks in five dogs along with omocervical arterial catheters. Vagal transmission was monitored by pulse and arterial pressure monitoring. Cryogenic blockade of vagal nerves was performed by circulating a mixture of 0°C ethanol and water through the cooling coils. NPY, PYY, and PP were measured using standard radioimmunoassays. Vagal cooling decreased basal NPY and PYY levels ( P < 0.05) but not PP. After a standard meal, vagal cooling blocked the postprandial rise seen in circulating NPY and PP ( P < 0.05). These data demonstrate a technique of reversible vagal blockade to evaluate the role of cervical vagal integrity in gastrointestinal endocrinology. Cryogenic vagal blockade inhibits the postprandial rise of circulating PP into the circulation. Vagal pathways appear to contribute to fasting activity of PYY and NPY releasing cells. Inhibited meal-stimulated release of NPY supports a role for vagal modulation of postprandial NPY release into the circulation.

2‐Chloroadenosine induction of vagally‐mediated and atropine‐resistant bronchomotor responses in anaesthetized guinea‐pigs

1. The bronchoconstrictor effects of intravenous administration of adenosine derivatives in anaesthetized non-curarized guinea-pigs have been studied. 2. 2-Chloroadenosine (2-Cl-Ade), 5'-N-ethylcarboxamideadenosine (NECA) and L-N6-phenylisopropyl-adenosine (L-PIA) all produced dose-dependent, transient increases in tracheal insufflation pressure, with an order of potency (NECA greater than or equal to 2-Cl-Ade much greater than L-PIA) typical of A2-receptor mediated biological responses. 3. 2-Chloradenosine-induced bronchoconstrictor responses disappeared after vagotomy or topical application of tetrodotoxin (TTX) on cervical vagal trunks. 4. 2-Chloradenosine-induced bronchospasm was unaffected by atropine (1 mg kg-1 i.v.), physostigmine (50 micrograms kg-1 i.v.) and hexamethonium (30 mg kg-1 i.v.) but was significantly reduced by theophylline (25 mg kg-1 i.v.). 5. The magnitude of 2-Cl-Ade-induced bronchospasm was significantly reduced by acute (10 micrograms kg-1 i.v.) or chronic (55 mgkg-1 s.c. four days before the experiment) pretreatment with capsaicin. 6. Guanethidine (20 mg kg-1 s.c on two consecutive days), prazosin (10 micrograms kg-1 i.v.), diphenhydramine (1 mg kg-1 i.v.) and indomethacin (1 mg kg-1 i.v.) failed to block the bronchomotor response to 2-Cl-Ade. In contrast, cyproheptadine (1-5 mgkg-1 i.v.) markedly reduced, but did not abolish the bronchospasm elicited by the purine derivative. 7. We conclude that in anaesthetized non-curarized guinea-pigs, a transient vagally-mediated bronchospasm can be induced by stimulation of A2-purinoceptors. This effect is complex and involves, at least in part, stimulation of capsaicin-sensitive sensory nerves and 5-hydroxytryptamine release. This experimental model might be useful for the further study of the potential role of adenosine in asthma, and for the evaluation of new antiasthma drugs.

Frontolimbic disconnection (FLD) for relief of cancer pain suffering

The effect of vagotomy and sympathectomy on cardio-acceleratory and arterial hypertensive reflexes evoked by electrical stimulation of the rat glossopharyngeal (IXth) nerve was studied in relation to changes in baseline heart rate and arterial blood pressure. Uni- and bi-lateral transection of the cervical vagal trunk brought about augmentation of baseline heart rate, accompanied by a depression in reflex tachycardia; the amount of depression being inversely related to that of an increase in baseline heart rate. The latter increased more after a right vagotomy than after a left vagotomy. No appreciable change in reflex hypertension as well as in baseline blood pressure was observed by different types of vagotomy. For unilateral sympathectomy, semilunar cordotomy caudal to the obex was performed. It was found that right semilunar cordotomy significantly depressed the magnitude of cardio-acceleratory and arterial hypertensive reflexes in association with a significant decrease in baseline heart rate, though there was a less pronounced decrease in baseline blood pressure. The result obtained by a left semilunar cordotomy was similar to that of a right semilunar cordotomy, except that the decrease in reflex tachycardia was very small and statistically insignificant. Thus, the efferent activities in vagus and sympathetic nerves were more effective on the right than on the left side, in modifying reflex tachycardia and baseline heart rate, whereas, right and left sympathetic efferent outflows were equally effective in depressing the reflex increase in blood pressure.

Chapter 10 Electrophysiological analysis of chemosensitive neurons within the area postrema of the rat

Publisher Summary This chapter presents electrophysiological analysis of chemosensitive neurons within the area postrema of the rat. The chapter demonstrates chemosensitive neurons within the area postrema (AP) electrophysiologically. Two different techniques were employed for chemical stimulation of the AP neurons: (1) the floor of the exposed fourth ventricle was superfused with isotonic glucose solution, hypertonic or hypotonic Ringer solution, or LiCl Ringer solution, (2) these solutions were injected into the left carotid artery. To confirm vagal afferent influences on given AP neurons, single shock electrical stimulation was delivered to the cervical vagal trunks of both sides. Three types of chemosensitive neurons were identified: (1) glucose responsive neurons that may participate in the control of satiety, (2) sodium (osmotic pressure) responsive neurons that may contribute to salt preference or control of water balance, and (3) LiCl responsive neurons that may play a role in conditioned taste aversion. The glucose responsive neurons within the AP may play a role in the control of food intake.

Importance of vagal input in maintaining gastric tone in the dog.

1. Using a gastric barostat to quantify variations in gastric tone, we had previously demonstrated that food ingestion or intestinal nutrient perfusion induces gastric relaxation. These data suggested a basal tonic contraction of the stomach during fasting. 2. To determine the role of vagal input in maintaining fasting gastric tone, we prepared two chronic canine models, either isolating both cervical vagal trunks in a cutaneous tunnel or including the supradiaphragmatic vagi within an implanted cooling jacket. In the fasted conscious dogs, we then studied the effect, on gastric tone, of acute and reversible vagal blockade by cooling. 3. Cervical vagal cooling produced a reversible gastric relaxation and increased the heart rate. Supradiaphragmatic vagal cooling produced a similar gastric relaxation without the cardiac effect. 4. Adrenergic blockade did not change either the base-line gastric tone or the cooling-induced relaxation. Adrenaline decreased gastric tone, but vagal cooling still produced a significant relaxation. 5. Atropine alone or combined with adrenergic antagonists produced a gastric relaxation that was not further increased by vagal cooling. Bethanechol increased gastric tone, an effect unchanged by vagal cooling. 6. We conclude that gastric tone during fasting is maintained by a cholinergic input, which is vagally mediated at both the cervical and the supradiaphragmatic levels.

The upper esophageal sphincter in the cat: the role of central innervation assessed by transient vagal blockade.

Studies were performed on four cats to assess the role of extrinsic innervation via the cervical nerve trunks in the control of upper esophageal sphincter function. Transient vagal nerve blockade was accomplished by cooling the cervical vagosympathetic nerve trunks previously isolated in skin loops on each side of the neck. Upper esophageal sphincter pressure was measured using a multilumen oval manometry tube and a rapid pull-through technique. The upper esophageal sphincter response to cervical intraesophageal balloon distention and acid perfusion was assessed. The feline upper esophageal sphincter has a distinct asymmetric pressure profile, whereby anterior pressure greater than posterior pressure greater than left pressure greater than right pressure. Bilateral vagal nerve blockade lowered the mean upper esophageal sphincter pressure from 18.5 +/- 1.5 to 12.0 +/- 2.8 mmHg (1 mmHg = 133.3 Pa) (p less than 0.001), with a significant reduction in pressure in all four quadrants. Intraesophageal balloon distention and acid perfusion both produced a significant increase in upper esophageal sphincter pressure. Bilateral vagal nerve blockade completely abolished the response of the upper esophageal sphincter to balloon distention and acid perfusion. We conclude that normal upper esophageal sphincter tone in the cat is partially mediated by excitatory neural input via the cervical nerve trunks, presumably via the recurrent laryngeal nerves; and cervical intraesophageal balloon distention and acid perfusion produce reflex contraction of the upper esophageal sphincter, which is dependent on neural pathways via the cervical vagal nerve trunks, but the relative contribution of afferent and efferent pathways remains unknown.

Inhibition of vasopressin secreting neurons of the paraventricular nucleus by gastric distension in rats

The effects of gastric distension on the neural activity of vasopressin (AVP) secreting neurons of the paraventricular nucleus (PVN) were examined in rats anesthetized with urethane alpha - chloralose. Sixteen putative AVP neurons were identified on the basis of phasically firing patterns. About half of the putative AVP neurons (7/16) were inhibited by gastric distension, while distension of the intraperitoneal balloon had no effect. Severing of the left cervical vagus trunk greatly reduced the inhibitory response. In contrast, the gastric distension had no effect on most non-phasically firing neurons (55/66). These data indicate that sensory information originating from the gastric mechanoreceptors selectively inhibits the activity of PVN AVP secreting neurons and suggest that gastric afferent information is important in the rapid inhibition of AVP release after drinking.

Hepatic-vagal and gustatory afferent interactions in the brainstem of the rat

In a series of combined electrophysiological and peroxidase histochemical studies, we have established that first-order hepatic and gustatory afferents project to separate regions of the solitary nucleus (NST) and do not converge upon neurons within this structure. Additionally, we have found that hepatic vagal afferent fibers travel in the left cervical vagal trunk and project to the postero-medial division of the left NST. Very small (100–200 μm diameter) iontophoretic injections of horseradish peroxidase (HRP) into physiologically identified zones of the NST reveal that the immediately subjacent parvocellular reticular formation sends efferents to and receives afferents from both the hepatic and gustatory divisions of this nucleus. Further, hepatic and gustatory-NST regions send projections throughout the parabrachial nucleus (PBN). Axons from both the hepatic and gustatory regions of the NST terminate heavily in the posterior dorsomedial part of the PBN. At anterior levels, the gustatory and visceral NST projections are distinctly separate; the medial PBN receives input from gustatory-NST, while the lateral region received input from the hepatic-NST. These results provide anatomical support for our previous findings that single neurons within the PBN can be activated by both gustatory and hepatic afferent activation. Overlapping projections from hepatic (vagal) and gustatory regions of the NST within both the immediately subjacent parvocellular reticular formation as well as the postero-medial PBN may explain in part the decrebrate rat's ability to not only discriminate gustatory stimuli, but also switch its response to a constant stimulus dependent on its nutritive state.

A description of the upper thoracic autonomic nervous system in the rhesus monkey (Macaca mulatta).

The purpose of this study was to describe the autonomic innervation of the carotid sinus and heart in the rhesus monkey. Nine male rhesus monkeys (Macaca mulatta) and one male crab-eating macaque (M. fascicularis) were carefully dissected from the origin of the vagus nerves and superior cervical ganglia to the level of the fourth thoracic ganglion. The specimens were either freshly killed or obtained no later than 24 hours post mortem. The macaque monkeys were found to possess an innervation pattern that displayed features common to dog (connections between the vagus nerves and middle cervical ganglia), baboon (distinct cervical sympathetic and cervical vagal nerve trunks), and man (nerves projecting from the middle cervical and stellate ganglia to the heart). Distinct inferior cervical and first thoracic ganglia were never seen, but rather, large and well defined stellate ganglia were found. The macaque innervation pattern, when considered as a whole, most closely resembled the baboon.

The central distribution of the cervical vagus nerve and gastric afferent and efferent projections in the rat

The medullary distribution of afferent fibers and cells of origin of the cervical vagal trunk and of the vagal innervation of the stomach have been studied using the anterograde and retrograde transport of horseradish peroxidase (HRP). Injections of HRP were made into the cervical vagus nerve, the stomach wall, the proximal small intestine, or the peritoneal cavity. Two to four days following the injections, the rats were perfused and the medullae oblongatae and nodose ganglia were processed using the tetramethyl benzidine method. Cervical vagus nerve injections of HRP resulted in heavy anterograde labeling in the ipsilateral nucleus of the tractus solitarius (NTS) and the commissural nucleus. Lighter labeling was seen in these regions on the contralateral side, but did not extend as far rostrally in the NTS. Labeling was also seen in the area postrema. Retrogade labeling of somata was present in the ipsilateral side in the nodose ganglion, throughout the whole extent of the dorsal motor nucleus of the vagus, much of the nucleus ambiguus and in rostral levels of the cervical spinal cord. After stomach injections, labeling indicative of afferent fibers was observed bilaterally in the dorsomedial and medial portions of the NTS and in the commissural nucleus. Labeled efferent fibres arose from neurons in the dorsal motor nucleus of the vagus, nucleus ambiguus and the cervical spinal cord. Retrogradely labeled somata were found bilaterally, throughout the rostrocaudal length of the dorsal motor nucleus in all cases with stomach injections. In some, but not all cases, labeled somata were seen bilaterally in compact areas within the nucleus ambiguus, particularly rostrally. Control injections of HRP into the intestinal wall and peritoneal cavity indicated that the stomach was the primary source of afferent and efferent labeling in the medulla following subdiaphragmatic injections.

Hyperosmotic NaCl and severe hemorrhagic shock: role of the innervated lung.

Infusions of hyperosmotic NaCl (2,400 mosmol/l; 4 ml/kg) were given to dogs in severe hemorrhagic hypotension by intravenous injection (72 expts) or intra-aortic injection (25 expts). In 46 experiments intravenous infusions were given during bilateral blockage of the cervical vagal trunks (local anesthesia or cooling). Intravenous infusions (without vagal blockade) restore arterial pressure, cardiac output, and acid-base equilibrium to normal and cause mesenteric flow to overshoot prehemorrhage levels by 50%. These effects are stable, and indefinite survival was observed in every case. Intra-aortic infusions of hyperosmotic NaCl produce only a transient recovery of arterial pressure and cardiac output but no long-term survival. Intravenous infusions with vagal blockage produce only a transient recovery of cardiac output, with non long-term survival. Measurement of pulmonary artery blood osmolarity during and after the infusions shows that a different pattern is observed in each of these three groups and strongly indicates that the first passage of hyperosmotic blood through the pulmonary circulation at a time when vagal conduction is unimpaired is essential for the production of the full hemodynamic-metabolic response, which is needed for indefinite survival.

Neural factor in K homeostasis ureter-ligated dogs.

AbstractIn ureter ligated or nephrectomized dogs continuously infused with 2 mEq KCl/kg/hr, a nonrenal K homeostatic mechanism retards the development of hyperkalemia by transferring much of the K load from extracellular to intracellular fluid. But, the K transfer capacity of ureter-ligated dogs is significantly less than that of equally anuric nephrectomized animals. However, K transfer ability in ureter-ligated dogs can be raised to the nephrectomy level if the kidneys are denervated or if the animals are vagotomized by cutting both cervical vagus trunks; in ureter-ligated preparations with bilateral adrenalectomy, vagotomy is without effect. It has been shown that in anuric dogs activity of β-adrenergic receptors is importantly involved in transfer of a K load to intracellular fluid. Our findings suggest that ureter-ligated kidneys give rise to neural impulses that course in fibers of the cervical vagus trunk and diminish K transfer by suppressing the secretion of epinephrine, a powerful β receptor ago...

Effects of apomorphine on control of breathing in rats

This study was aimed at evaluating the effects of systemically-administered apomorphine (APO) on the control of breathing in rats. Animals were anesthetized with Dial-urethane, and the cervical vagal and sympathetic trunks were sectioned. This preparation eliminated several peripheral feedback mechanisms, and also produced qualitatively more reliable responses than in the intact animal. After APO administration, breathing frequency (f) and minute inspired ventilation (V 1) were reduced while inspired volumes (V 1), duration of inspiration (f 1) and peak inspiratory flow rates were increased. All of these effects were antagonized by the dopaminergic blocking agent haloperidol. In addition, the ratio of f 1 to duration of breaths ( f −1), t 1/ f 1, was typically decreased after APO, and the effect was most pronounced in animals showing the greatest increases in f −1 (reduction in f). Qualitatively similar responses to APO were obtained when animals breathed hyperoxic, hypoxic and hypercapnic test gases. Absolute reductions in/and increases in V 1 were comparable among groups, despite differences in initial breathing patterns (except for a smaller volume response during hypoxia). The reduction in t 1/ f −1 and relatively uniform decreases in f and increases in V 1 under differing conditions of chemical respiratory drive, suggest that APO may act primarily on central dopaminergic neurons affecting breathing pattern.

Mucosal receptors in the gastric antrum and small intestine of the rat with afferent fibres in the cervical vagus.

1. Electrical stimulation of the abdominal vagi revealed that abdominal vagal fibres are distributed throughout the cervical vagal trunk. Conduction velocities of the main group of abdominal fibres ranged from 0.4 to 1.5 m.sec-1. 2. Thirty-seven single afferent fibres, with endings in the gastric and intestinal mucosa, were isolated from the cervical vagus of adult rats. Conduction velocities of eighteen of these endings ranged from 0.5 to 2.5 m.sec-1. 3. Light mechanical stimulation, such as stroking the mucosa, evoked a rapidly adapting response from these endings. Sustained pressure or distension with fluid or air did not excite these endings although excessive stretching of the mucosa excited three units. Balloon distension usually evoked an 'on-off' response due to phasic stimulation of the mucosa by the balloon during inflation and deflation. 4. These same endings also functioned as non-specific, slowly adapting chemoreceptors responding to various organic and inorganic acids, tap water and distilled water, alcohol, hypertonic saline, NaOH, NH4Cl, CuSO4, casein hydrolysate, mustard powder and cayenne pepper. Hypertonic glucose and guinea-pig bile were ineffective as stimuli. 5. In the presence of an excess of chloride ions the effectiveness of acids in stimulating these endings was in part determined by the pK of the acid. However pH per se was not the basic determining factor but rather the molecular size of the acid.

Neuroinhibition in the regulation of emesis.

Elucidation of an inhibitory system in the regulation of emesis is presented in this report. Emesis preceded by retching, can be induced in the dog by appropriate electrical stimulation of abdominal vagus nerves at the supradiaphragmatic level. Failure to produce retching or emesis by electrical stimulation of the cervical vagus trunk suggests either that the abdominal vagal emetic afferent does not course in the cervical vagus or that fibers inhibitory to emesis are present. This report presents evidence for afferent fibers inhibitory to retching and emesis in the cervical vagus. Retching and emesis resulting from stimulation of the supradiaphragmatic vagus can be prevented by either transection of the cervical vagus or simultaneous stimulation of the cervical vagus trunk. In addition, retching and emesis occur with stimulation of a fine nerve bundle dissected from the cervical vagus trunk. That the afferent pathway inhibitory to retching and emesis involves pulmonary afferents is suggested by the observation that hyperventilation occurs with stimulation of the cervical vagus trunk.