Abnormalities in the vagus nerve in canine acrylamide neuropathy

Docking Proteins Upregulate IL-1β Expression in Lower Esophageal Sphincter Muscle in Esophageal Achalasia

Background/Objectives: Esophageal achalasia is an archetypal esophageal motility disorder characterized by abnormal peristalsis of the esophageal body and impaired lower esophageal sphincter (LES) relaxation. Methods: In this study, the mRNA expression of docking proteins 1 and 2 (DOK1 and DOK2, respectively) were analyzed and the mechanisms underlying achalasia onset were investigated. Results:DOK1 and DOK2 mRNA levels significantly increased in the LES of patients with achalasia. Moreover, significant correlations were observed between IL-1β and DOK1, IL-1β and DOK2, ATG16L1 and DOK1, and HSV1-miR-H1-3p and DOK2 expression levels. However, a correlation between ATG16L1 and DOK2 or between HSV-miR-H1-3p and DOK1 expression was not observed. In addition, a positive correlation was observed between patient age and DOK1 expression. Microarray analysis revealed a significant decrease in the expression of hsa-miR-377-3p and miR-376a-3p in the LES muscle of patients with achalasia. Conclusions: These miRNAs possessed sequences targeting DOK. The upregulation of DOK1 and DOK2 expression induces IL-1β expression in the LES of achalasia patients, which may contribute to the development of esophageal motility disorder.

Spontaneous Axonal Dystrophy in the Brain and Spinal Cord in Naïve Beagle Dogs

Axonal dystrophy (AD) is a common age-related neurohistological finding in vertebrates that can be congenital or induced by xenobiotics, vitamin E deficiency, or trauma/compression. To understand the incidence and location of AD as a background finding in Beagle dogs used in routine toxicity studies, we examined central nervous system (CNS) and selected peripheral nervous system (PNS) tissues in twenty 18- to 24-month-old and ten 4- to 5-year-old control males and females. Both sexes were equally affected. The cuneate, gracile, and cochlear nuclei and the cerebellar white matter (rostral vermis) were the most common locations for AD. Incidence of AD increased with age in the cuneate nucleus, cerebellar white matter (rostral vermis), trigeminal nuclei/tracts, and lumbar spinal cord. Axonal dystrophy in the CNS was not accompanied by neuronal degeneration/necrosis, nerve fiber degeneration, and/or glial reaction. Axonal dystrophy was not observed in the PNS (sciatic nerve, vagus nerve branches, or gastrointestinal mural autonomic plexuses).

Use of Nerve Conduction Assessments to Evaluate Drug-Induced Peripheral Neuropathy in Nonclinical Species—A Brief Review

The peripheral nervous system (PNS) is subject to a wide range of structural and functional insults including direct damage to axons, loss of myelin, and progressive deficits in saltatory conduction. Drugs that damage the PNS often result in neuropathies that impact the structure and function of targeted nerves. In most cases, both sensory and motor neurons are affected with damage initially evident in the distal extremities. Drug-induced neuropathies are potentially reversible following cessation of treatment, but early stages of neuropathy can be subclinical and asymptomatic making diagnosis difficult. Nerve biopsy is highly validated and provides definitive evidence of nerve injury and corresponding severity; however, it is limited in some respects and electrophysiological measures can complement histopathological assessments and provide a functional measure of potential toxicity. In a drug development setting, nerve conduction assessments are valuable to monitor nerve function longitudinally if nerve damage is suspected or confirmed, and importantly, can be used to monitor progression and/or recovery of a drug-induced neuropathy. This review will summarize the methodology used in nerve conduction assessments as well as discuss data interpretation and considerations for use in nonclinical species. Finally, the use of nerve conduction assessments in nonclinical drug development is discussed.

Modulation of heart rate by temporally patterned vagus nerve stimulation in the anesthetized dog

Despite current knowledge of the myriad physiological effects of vagus nerve stimulation (VNS) in various mammalian species (including humans), the impact of varying stimulation parameters on nerve recruitment and physiological responses is not well understood. We investigated nerve recruitment, cardiovascular responses, and skeletal muscle responses to different temporal patterns of VNS across 39 combinations of stimulation amplitude, frequency, and number of pulses per burst. Anesthetized dogs were implanted with stimulating and recording cuff electrodes around the cervical vagus nerve, whereas laryngeal electromyogram (EMG) and heart rate were recorded. In seven of eight dogs, VNS‐evoked bradycardia (defined as ≥10% decrease in heart rate) was achieved by applying stimuli at amplitudes equal to or greater than the threshold for activating slow B‐fibers. Temporally patterned VNS (minimum 5 pulses per burst) was sufficient to elicit bradycardia while reducing the concomitant activation of laryngeal muscles by more than 50%. Temporal patterns of VNS can be used to modulate heart rate while minimizing laryngeal motor fiber activation, and this is a novel approach to reduce the side effects produced by VNS.

High-resolution measurement of electrically-evoked vagus nerve activity in the anesthetized dog

OBJECTIVE

Not fully understanding the type of axons activated during vagus nerve stimulation (VNS) is one of several factors that limit the clinical efficacy of VNS therapies. The main goal of this study was to characterize the electrical recruitment of both myelinated and unmyelinated fibers within the cervical vagus nerve.

APPROACH

In anesthetized dogs, recording nerve cuff electrodes were implanted on the vagus nerve following surgical excision of the epineurium. Both the vagal electroneurogram (ENG) and laryngeal muscle activity were recorded in response to stimulation of the right vagus nerve.

MAIN RESULTS

Desheathing the nerve significantly increased the signal-to-noise ratio of the ENG by 1.2 to 9.9 dB, depending on the nerve fiber type. Repeated VNS following nerve transection or neuromuscular block (1) enabled the characterization of A-fibers, two sub-types of B-fibers, and unmyelinated C-fibers, (2) confirmed the absence of stimulation-evoked reflex compound nerve action potentials in both the ipsilateral and contralateral vagus nerves, and (3) provided evidence of stimulus spillover into muscle tissue surrounding the stimulating electrode.

SIGNIFICANCE

Given the anatomical similarities between the canine and human vagus nerves, the results of this study provide a template for better understanding the nerve fiber recruitment patterns associated with VNS therapies.

Selective control of physiological responses by temporally-patterned electrical stimulation of the canine vagus nerve

Vagus nerve stimulation (VNS) is effective for treating epilepsy and depression, and has emerging indications for anxiety and heart failure. However, stimulation-evoked side effects remain a challenge for long-term compliance. We investigated the feasibility of reducing VNS side effects by using a temporally-modified stimulation pattern. In 4 anesthetized canines, we measured changes in both the heart rate and evoked laryngeal muscle activity. Compared to baseline, we found that a 5% duty cycle (measured by the number of pulses per second of stimulation) could still evoke a 21% reduction in heart rate; whereas compared to continuous stimulation (3 mA, 300 μs pulsewidth, 20 Hz) the same 5% duty cycle reduced the evoked laryngeal muscle activity by 90%. The results of this study indicate that temporally-patterned stimulation may provide an effective tool for optimizing VNS therapy.

Excitation properties of the right cervical vagus nerve in adult dogs

Vagus nerve stimulation (VNS) is an approved treatment for epilepsy and depression, and it is currently under investigation for applications in Alzheimer's disease, anxiety, heart failure, and obesity. However, the mechanism(s) by which VNS has its effects are not clear, and the stimulation parameters for obtaining therapeutic outcomes appear highly variable. The purpose of this study was to quantify the excitation properties of the right cervical vagus nerve in adult dogs anesthetized with propofol and fentanyl. Input-output curves of the right cervical vagus nerve compound action potential and laryngeal muscle electromyogram were measured in response to VNS across a range of stimulation parameters: amplitudes of 0.02-50mA, pulsewidths of 10, 50, 100, 200, 300, 500, and 1,000μs, frequencies of 1-2Hz, and train lengths of 20 pulses with 3 different electrode configurations: monopolar cathode, proximal anode/distal cathode, and proximal cathode/distal anode. Electrode configuration and stimulation waveform (monophasic vs. asymmetric charge-balanced biphasic) did not affect the threshold or recruitment of the vagal nerve fibers that were activated. The rheobase currents of A- and B-fibers were 0.4mA and 0.7mA, respectively, and the chronaxie of both components was 180μs. Pulsewidth had little effect on the normalized threshold difference between activation of A- and B-fibers. The results provide insight into the complement of nerve fibers activated by VNS and guidance to clinicians for the selection of optimal stimulation parameters.

Use of radiographic measurements in distinguishing myasthenia gravis from other causes of canine megaoesophagus

OBJECTIVES

To evaluate whether dogs with megaoesophagus due to myasthenia gravis display less oesophageal dilatation radiographically than dogs with other causes of megaoesophagus.

METHODS

Thoracic radiographs of 66 dogs with megaoesophagus in which concurrent acetylcholine receptor antibody titre was known were analysed retrospectively. Maximum oesophageal diameter was transformed to a "relative oesophageal diameter" using a ratio with thoracic inlet diameter. Dogs were divided into two groups according to "MG" or "non-MG" antibody status and median relative oesophageal diameter values were compared between groups and with age, weight and sex. A receiver operating characteristic plot was used to evaluate a suitable relative oesophageal diameter cut-off.

RESULTS

Twenty dogs were diagnosed with myasthenia gravis and 46 with other causes of megaoesophagus. Thoracic inlet size correlated significantly with bodyweight and surface area (r(2)=0.627 and 0.669, respectively). Median values of relative oesophageal diameter for the MG group and non-MG group were 0.58 and 0.66, respectively, and these showed a small, but significant, difference (P=0.029), although there was complete overlap in the range of relative oesophageal diameter values between groups. There was no significant association between relative oesophageal diameter and sex, age or weight or significant difference in age, sex or weight between the two groups. An increased odds ratio for myasthenia gravis existed in golden retrievers and German shepherd dogs.

CLINICAL SIGNIFICANCE

Relative oesophageal diameter appears to be of limited diagnostic utility in distinguishing dogs with megaoesophagus due to myasthenia gravis from those with megaoesophagus due to other causes.

Achalasia: a vagal disease

BACKGROUND

Achalasia is considered to be a primary motor disorder of the oesophagus. However, there is increasing evidence to suggest extra-oesophageal involvement in this disease. Vagal disturbances at different levels and extra-oesophageal dysmotility have been reported in several studies. The aim of this study was to examine cardiovascular reflexes in patients with achalasia further to evaluate the involvement of the autonomic nervous system outside the oesophagus in this entity.

METHODS

Five patients (age range 38-58 years, median 45 years) diagnosed with achalasia were assessed for the autonomic nerve function by the heart rate reaction to deep breathing (E/I ratio) and to tilt (acceleration and brake index). The blood pressure reaction to tilt was also assessed. The results were compared with a control group comprising 56 healthy individuals (age range 16-59 years, median 40 years).

RESULTS

Patients with achalasia had a significantly decreased E/I ratio compared with controls (absolute values 1.13 (0.23) (median value (interquartile range)) versus 1.38 (0.14): P=0.0309, age corrected values -1.39 (1.49) versus -0.25 (1.20): P=0.0457). This reflects impairment of the vagus nerve. In contrast, sympathetic nerves were not affected, as the acceleration index and brake index and postural blood pressure reaction were not disturbed in patients.

CONCLUSION

Patients with achalasia have autonomic nerve dysfunction in the vagal nerve outside the oesophagus.

Selective vagal afferent dysfunction in dogs with congenital idiopathic megaoesophagus

Congenital idiopathic megaoesophagus (CIM) is a rare, naturally occurring disorder of the dog that is characterised by deficient motility and dilatation of the oesophagus. Recent studies indicate that the vagal sensory system mediating reflexes induced by oesophageal distension is defective in, and may underlie the pathomechanism of this disorder. We sought to establish whether other distension sensitive vagal afferent systems were impaired in CIM, or whether the vagal afferent dysfunction was selective. Thus, we examined the Hering-Breuer lung inflation reflex (HBR), which is subserved by a contiguous and physiologically similar vagal afferent system, in five dogs with CIM in which oesophageal vagal afferent dysfunction had been demonstrated. At varying levels of lung inflation, we found the HBR to be normally graded and of normal strength in affected dogs and that this result was unlikely to be influenced by other factors known to alter the strength of the reflex. These observations provide evidence for an organ specific, selective vagal afferent dysfunction in dogs with CIM. It is possible that similar processes may be active in disorders of visceral organ systems subserved by vagal afferents in other species, including man.

Fast axonal transport: a site of acrylamide neurotoxicity?

The cellular and molecular site and mode of action of acrylamide (ACR) leading to neurotoxicity has been investigated for four decades, without resolution. Although fast axonal transport compromise has been the central theme for several hypotheses, the results of many studies appear contradictory. Our analysis of the literature suggests that differing experimental designs and parameters of measurement are responsible for these discrepancies. Further investigation has demonstrated consistent inhibition of the quantity of bi-directional fast transport following single ACR exposures. Repeated compromise in fast anterograde transport occurs with each exposure. Modification of neurofilaments, microtubules, energy-generating metabolic enzymes and motor proteins are evaluated as potential sites of action causing the changes in fast transport. Supportive and contradictory data to the hypothesis that deficient delivery of fast-transported proteins to the axon causes, or contributes to, neurotoxicity are critically summarized. A hypothesis of ACR action is presented as a framework for future investigations.

Acrylamide-induced neuropathic changes in rat enteric nerves: similarities with effects of streptozotocin-diabetes

The effect of acrylamide intoxication (a widely used model for autonomic neuropathy) on the fluorescence intensity and density of catecholamine- and peptide-containing nerve fibres and tissue content of noradrenaline and the peptides vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P and neuropeptide Y in the enteric nerves of rat ileum was examined. Histochemical and immunohistochemical techniques were used to localize catecholamine- and peptide-containing nerve fibres. The tissue content of noradrenaline was measured using high-performance liquid chromatography, and an enzyme-linked immunosorbent assay technique was used to determine the tissue content of the peptides investigated. Acrylamide intoxication caused a significant decrease in the density of catecholamine-containing nerve fibres and tissue content of noradrenaline in the myenteric plexus of rat ileum. A decrease in tissue content and immunoreactivity of calcitonin gene-related peptide and an increase in vasoactive intestinal polypeptide was seen in the myenteric plexus of ileum from acrylamide-intoxicated rats. In the submucous plexus, the acrylamide treatment caused a decrease in calcitonin gene-related peptide immunoreactivity and an increase in vasoactive intestinal polypeptide and neuropeptide Y immunoreactivity. There was no change in either tissue content or immunoreactivity of substance P in both myenteric and submucous plexuses of the treated rat ileum. These changes have a striking similarity with those found in the enteric nerves of streptozotocin-diabetic rat ileum, suggesting the possible presence of an underlying common mechanism(s) in the development of neuropathic changes in the autonomic nerves of acrylamide-intoxicated and streptozotocin-diabetic rats.

Effects of acrylamide on cotransmission in perivascular sympathetic and sensory nerves

The effects of chronic administration of acrylamide on sympathetic and sensory nerves were examined in the mesenteric artery of rabbits. The noradrenaline (NA) content of the artery was significantly decreased and the total contractile response to electrical field stimulation (4-64 Hz) markedly reduced in the acrylamide group. This was not due to an impairment of the contractility of the smooth muscle or to alterations in the postjunctional receptors. At 16 Hz, only the purinergic component of sympathetic cotransmission was significantly reduced by acrylamide. At 64 Hz, both the purinergic and the adrenergic components were significantly decreased. Field stimulation of the artery pretreated with guanethidine and precontracted with NA produced a frequency-dependent relaxation which was prevented by capsaicin and thus mediated by perivascular sensory nerves. In contrast to its effects on sympathetic cotransmission, acrylamide resulted in a trend, although not significant, towards increased responses at each frequency studied (2-16 Hz). 2-Methylthio-ATP (2Me-S-ATP) caused significantly greater relaxation following acrylamide treatment while vasodilator responses to calcitonin gene-related peptide and substance P were unchanged. It is concluded that, in addition to its known action in producing neuropathy in myelinated somatic motor and sensory nerves, acrylamide causes damage to unmyelinated perivascular sympathetic fibres. Purinergic mechanisms may be particularly susceptible to acrylamide since both the purinergic component of sympathetic vasoconstriction and the relaxation in response to 2Me-S-ATP were affected by acrylamide treatment.

Abnormalities of sympathetic sudomotor function in experimental acrylamide neuropathy

The possible involvement of sympathetic sudomotor function by acrylamide intoxication was investigated in the mouse, and compared with nerve conduction studies and global motor tests. Acrylamide (40 mg/kg, 3 days per week, 8 weeks) was given per os to a group of mice (A1). Their motor ability to stand on the rotarod was impaired from day 11, reaching a minimum between 46 and 60 days. The number of pilocarpine reactive sweat glands (SG), evaluated by the silicone mold technique, was similar to controls at 40 days and slightly decreased at 54 days. Another group of mice (A2), given acrylamide at a higher dose (50 mg/kg, 5 days per week, 5 weeks), showed abnormalities on the rotarod by 11 days, a progressive decrease of muscle action potential (CMAP) amplitude, and significantly decreased number of reactive SG from 15 days, with respect to controls. Comparatively, sudomotor dysfunction was milder and appeared later in time than alphamotor involvement, being noticeable only after severe poisoning. The decrease in SG response is attributable to damage by acrylamide intoxication of postganglionic sudomotor nerve fibers, which are unmyelinated sympathetic efferents.

Acrylamide-induced autonomic neuropathy of rat mesenteric vessels: histological and pharmacological studies

The effects of chronic acrylamide treatment on the autonomic nervous system were investigated by histochemical and pharmacological studies. Histochemical studies showed that acrylamide caused different degrees of damage to different nerve fibre types: calcitonin gene-related peptide (CGRP)-immunoreactive (IR) nerves showed the greatest reduction in intensity and number; noradrenaline (NA)-containing nerves were somewhat less affected; substance P (SP)-IR nerves were reduced in number, but this was not significant. The profiles of SP- and particularly of CGRP-IR nerves from treated animals were noticeably different to those from the control group, being flattened and irregular. Periarterial nerve stimulation (4-32 Hz) of the isolated rat mesenteric arterial bed preparation at basal tone elicited frequency-dependent vasoconstrictor responses. The magnitude of these responses was significantly reduced at higher frequencies in acrylamide-treated animals. In preparations with tone raised by the addition of methoxamine (10(-5) M), and in the presence of guanethidine (5 x 10(-6) M), periarterial nerve stimulation elicited vasodilator responses. These responses, which result from stimulation of sensory nerves, were greatly reduced in acrylamide-treated animals. There was a tendency for mesenteric beds from acrylamide-treated animals to show increased vasoconstrictor responses to doses of exogenous NA, although this was not significant. Responses to exogenous adenosine 5'-triphosphate (a cotransmitter with NA from sympathetic nerves) were not affected. In the raised-tone preparation, vasodilator responses to exogenous CGRP (the principal vasodilator sensory transmitter of rat mesenteric arteries) were not affected by acrylamide treatment. Hence, it is unlikely that the reduced responses to nerve stimulation were due to defects in the postjunctional receptors for the principal transmitters of sympathetic and sensory-motor nerves. There was no difference in the ability of mesenteric beds from control and treated animals to vasodilate in response to acetylcholine or sodium nitroprusside, or to vasoconstrict in response to potassium chloride, indicating normal smooth muscle and endothelial responses. These results suggest that chronic acrylamide treatment produces peripheral autonomic neuropathy of rat mesenteric vessels, manifested as a dysfunction of sympathetic and sensory-motor nerves. Furthermore, the graded destruction of nerve types, such that damage occurred in the order: CGRP-IR greater than NA greater than SP-IR, indicated a differential sensitivity of different nerves to this toxin.

Abnormalities of sympathetic vasomotor tone in distal axonal neuropathy

Microneurographic studies have shown that sympathetic vasomotor nerve activity is observed less frequently in patients with peripheral neuropathy than in controls, but when detected its pattern and the baroreflex latencies appear to be normal. Vasomotor nerve function was examined in chloralose-urethane anaesthetised dogs by comparing the discharge of renal sympathetic nerves in control animals and animals with acrylamide neuropathy. There was a normal pattern of pulse related inhibition of sympathetic nerve activity as well as normal amplitude spontaneous compound nerve action potentials in the animals with neuropathy. When vasomotor tone was altered abruptly by raising pressure in a bilateral isolated carotid sinus preparation, the baroreflex latencies were normal in the affected animals. However, when carotid sinus pressure was kept constant, pulse-related sympathetic inhibition, normally mediated by vagal cardiopulmonary baroreceptors, was absent in animals with neuropathy. It is likely that the vagal nerve fibres to cardiopulmonary baroreceptors as well as the receptors themselves are damaged while shorter carotid sinus nerve fibres are relatively spared in axonal neuropathies. As long as these shorter nerves are intact patients with axonal neuropathy should have relatively normal baroreflexes and normal sympathetic vasomotor tone when measured microneurographically.

Esophageal achalasia syndromes

Esophageal achalasia, characterized by failure of the lower esophageal sphincter to relax normally with swallowing and esophageal aperistalsis, may be primary or secondary to another disorder (in the United States most often cancer). Primary achalasia is of unclear etiology but almost certainly is a disorder of the innervation of the smooth muscle portion of the esophagus. This article reviews the classification and clinical features of achalasia syndromes, as well as current concepts of pathogenesis, diagnosis, complications, and therapy of this group of disorders.

Pathological changes in the vagus nerve in diabetes and chronic alcoholism

The pathological changes in the vagus nerve removed at necropsy have been studied in patients with chronic alcoholism and diabetes. Morphometric studies on myelinated fibres were performed on the nerve at mid-cervical, lung hilum and diaphragmatic levels. In two insulin-dependent diabetics the density of myelinated fibres was below the lower limit of the control range at all levels. In all the diabetic and chronic alcoholic subjects there was significant reduction in the density of myelinated fibres at the most distal level in the nerve. The degenerative changes in the nerve are consistent with the findings of abnormal vagal function in diabetics and chronic alcoholics.

Reversible abnormalities of the Hering Breuer reflex in acrylamide neuropathy

The sensitivity of the Hering Breuer reflex was compared in anaesthetised rabbits before, during and after the induction of acrylamide neuropathy, and was measured as the tracheal pressure which produced 30 seconds of apnoea. After four weeks of acrylamide (400 mg/kg total dose) there was ataxia and the conduction velocity of hindlimb motor nerves was significantly reduced. At this time there was a marked and reproducible reduction in the sensitivity of the Hering Breuer reflex. The ataxia resolved within a month of stopping acrylamide administration. Three months after the cessation of acrylamide the sensitivity of the Hering Breuer reflex had increased significantly but had not returned to normal.

Abnormalities of oesophageal mechanoreceptors in canine acrylamide neuropathy

Dogs exposed to acrylamide develop peripheral neuropathy and megaoesophagus. The properties of slowly adapting oesophageal mechanoreceptors were studied in six control and five acrylamide affected greyhounds in which the oesophagus had been surgically isolated under anaesthesia and oesophageal pressure was controlled while monitoring impulses in oesophageal afferent fibres in the cervical vagus. In the acrylamide affected animals oesophageal afferent units had elevated thresholds and significantly reduced firing rates during ramp increases in oesophageal pressure. It is concluded that abnormalities of oesophageal mechanoreceptors may be important in the pathogenesis of certain oesophageal motility disorders in man and animals.

Acrylamide-induced remodelling of perikarya in rat superior cervical ganglia

To extend investigations on how acrylamide affects neuronal perikarya, we studied post-ganglionic cell bodies in the superior cervical ganglia of control and intoxicated rats (50 mg/kg/day for 9-10 days) with light and electron microscopy and with stereology. By light microscopy, perikarya of intoxicated rats showed peripheral Nissl bodies and nuclear eccentricity. Ultrastructurally, many experimental neurons showed augmented Nissl bodies, often extending from nucleus to plasma membrane; cisternae of granula endoplasmic bodies often appeared in orderly stacked configurations. Intoxicated neurons had increased numbers of normal-appearing mitochondria; some mitochondrial profiles appeared in clumps and others were hypertrophied. Compared to control neurons where Golgi complex most often aligned in a circumnuclear position, experimentals showed reductions in amount and loss of orientation. In some perikarya the pattern of eccentricity of nucleus, peripheral mantle of Nissl, and increased mitochondria gave a distinctive chromatolysis-like appearance. Ultrastructural stereologic analysis showed significantly increased volume fractions of Nissl (P less than 0.001) and mitochondria (P less than 0.002), a trend towards decreased Golgi, and no change in lysosomes, confirming the ultrastructural findings. These data indicate that cell body remodelling is a widespread phenomenon, specific for different neuronal types, and that it probably acts importantly in the pathogenesis of disease.

Circulatory control in canine acrylamide neuropathy

The baroreflex regulation of arterial blood pressure and heart rate was examined in dogs with acrylamide-induced peripheral neuropathy. In anaesthetized animals the carotid sinuses were isolated from the systemic circulation and perfused. The carotid sinus and vagus nerves were kept intact. The maximum baroreflex gain (the ratio of the change in systemic pressure to a change in sinus pressure) was significantly greater in the treated animals. A step increase in carotid sinus pressure produced long periods of asystole and sustained bradycardia in the animals with neuropathy. The alterations in the baroreceptor reflex responses were consistent with dysfunction of baroreceptor fibres in the vagus.