Muscle metaboreflex increases ventricular performance in conscious dogs

Ischemia of active skeletal muscle stimulates neuronal afferents within the muscle, which elicits a reflex increase in systemic arterial pressure (SAP), heart rate (HR), and cardiac output (CO) termed the muscle metaboreflex. We investigated whether activation of the muscle metaboreflex elicits increases in ventricular performance using conscious, chronically instrumented dogs trained to run on a treadmill (3.2 km/h, 0% grade). The muscle metaboreflex was activated via progressive partial vascular occlusion of the terminal aorta during control experiments and with HR maintained constant via a pacemaker connected to ventricular electrodes (225 beats/min). In control experiments, hindlimb ischemia elicited substantial increases in SAP, HR, and CO (+53.9 +/- 4.3 mmHg, +32.4 +/- 4.5 beats/min, and +1.57 +/- 0.22 l/min, respectively; all changes P < 0.05), whereas stroke volume (SV) remained unchanged with reflex activation (control 45.9 +/- 2.3 vs. 46.1 +/- 2.4 ml, P > 0.05). During metaboreflex activation at constant HR, SV significantly increased such that the increases in CO and SAP were not significantly different from control experiments (+1.77 +/- 0.56 l/min and +57.4 +/- 3.8 mmHg, P > 0.05 vs. control experiments). No significant change in central venous pressure occurred in either experiment, indicating no Frank-Starling effect on SV. We conclude that muscle metaboreflex-induced increases in ventricular contractility act to sustain SV despite decreases in ventricular filling time due to the tachycardia such that the sustained SV coupled with the tachycardia elicits substantial increases in CO that contribute importantly to the reflex increase in SAP.

Muscle afferent block for the treatment of oromandibular dystonia

Oromandibular dystonia is a focal dystonia involving the masticatory and tongue muscles, causing difficulties in speech or mastication. We treated 13 patients with this condition by injecting diluted lidocaine and alcohol intramuscularly. This method is aimed at reducing muscle spindle afferent activity. The symptoms had been resistant to other therapies such as pharmacotherapy or dental treatment. All patients showed clinical improvement after this therapy with reduced EMG activities in the affected muscles, whereas control injection of normal saline gave no changes in EMG activities. The overall subjective improvement was 57.7 +/- 25.1% (mean +/- standard deviation) in a self-rating scale. The mean response of the jaw elevator muscles (70 +/- 13.1%) was significantly higher (p < 0.02, t test) than that of the depressor muscles (38 +/- 28.4%). Despite the precise mechanism being unknown, this difference might be related to the smaller number of muscle spindles in the depressor than the elevator muscles. This therapy is useful for the treatment of drug-resistant oromandibular dystonia.

Dysfunction of Ib (autogenic) spinal inhibition in patients with progressive supranuclear palsy

We compared the activity of Ib spinal interneurons in five patients with progressive supranuclear palsy (PSP) with six age-matched control subjects. Stimulation of the medial gastrocnemius nerve at motor threshold intensity activated Ib afferents that in turn inhibit H reflexes from the soleus muscle. Maximum inhibition occurred at interstimulus intervals of 6 and 8 ms for both control subjects and PSP patients and was significantly greater in the PSP patients. Increased Ib activity of PSP patients may be caused by loss of inhibition of Ib interneurons through degeneration of the medullary reticulospinal pathway. The corticospinal pathways, unopposed by the medullary reticulospinal tract, may excessively activate Ib interneurons.

Prognostic predictors of acute transverse myelitis

INTRODUCTION

The role of clinical, MRI and neurophysiological parameters in predicting the outcome of acute transverse myelitis (ATM) is reported.

MATERIALS AND METHODS

Thirty-one patients with ATM were subjected to clinical, MRI, somatosensory and motor evoked potential studies in both upper and lower limbs and concentric needle electromyography. The outcome was defined at the end of 6 months into poor (Barthel Index score <12) and good (> or =12). The relationship of various prognostic variables was evaluated by biserial correlation coefficient and stepwise discriminant analysis.

RESULTS

The mean age of the patients was 30.4 years and 7 were females. Fifteen patients had good and 16 had poor outcome. The variables significantly related to the outcome included severity of weakness, denervation on EMG and unrecordable central motor conduction time to tibialis anterior (CMCT-TA) and tibial somatosensory evoked potentials (SEPs). Combination of severity of weakness and EMG had 90.3% predicting power. Addition of central sensory conduction time (CSCT) or central motor conduction time (CMCT) did not offer further advantage.

CONCLUSION

Severity of weakness and denervation on EMG are most useful for predicting the outcome of ATM at 6 months although in early stage motor and somatosensory evoked potentials may be used instead of EMG.

Attenuation of ischemia-induced activation of cardiac sympathetic afferents following brief myocardial ischemia in cats

OBJECTIVE

We have previously shown that brief myocardial ischemia impairs neural conduction in cardiac sympathetic efferent fibers. However, attenuation of the activity of afferent sympathetic nerves, which may contribute to impaired ischemic nociception and reflex hemodynamic responses, is not well understood. Therefore, we studied the electrophysiological effects of brief myocardial ischemia on the mechano-, chemo- and ischemia-sensitive properties of cardiac sympathetic afferent fibers.

METHODS

Single unit activity of sympathetic afferent A delta and C fibers innervating the left ventricle (LV) was recorded from the thoracic chain or rami communicantes in 16 anesthetized cats. We tested the response of impulse activity to (1) mechanical LV probing, (2) epicardial application of bradykinin (10 microg), H2O2 (1.5%) or adenosine (500 microg), and (3) 1 min of coronary occlusion. Repeat tests were performed in 11 of 16 fibers after 15 min of coronary occlusion and 15 min of reperfusion. Control responses were measured in five fibers before and after a 30-min interval without ischemia.

RESULTS

Afferent fibers responded with increased activity to LV probing (16/16 fibers), bradykinin (13/16 fibers), H2O2 (7/11 fibers), adenosine (1/11 fibers), and to a 60 s period of coronary occlusion (11/16 fibers). The unit impulse activity to 1 min of coronary occlusion was markedly attenuated after 15 min of myocardial ischemia and 15 min of reperfusion (P < 0.05). This attenuation was associated with reduced sensitivity to mechanical and chemical stimuli, while in separate time-control studies (n = 5) no attenuation was observed in absence of ischemia.

CONCLUSION

A brief period of myocardial ischemia is capable of attenuating mechano-, chemo- and ischemia-sensitive activity of cardiac afferent sympathetic nerves. This may have important implications for the mechanism of silent myocardial ischemia.

[Lesions of ponto-cerebellar and olivo-cerebellar afferents demonstrated by neurophysiologic analysis]

We describe a 52-year-old woman presenting a 2-year history of limb clumsiness and gait difficulties, characterized by progressive worsening. Neurological examination revealed cerebellar intention tremor, cerebellar dysmetria of all 4 limbs and ataxic gait. However, brain MRI was normal. Analysis of fast wrist flexion movements demonstrated hypometric movements, with decreased intensities of agonist EMG activities and increased durations of antagonist EMG activities. Such EMG abnormalities have been demonstrated in patients presenting lesions of the middle cerebellar peduncle, affecting the crossed cerebellopontine projections. Moreover, adaptation motor learning during a pinch task (isometric force) showed a severe inability to adapt motor programming, indicating a disruption of cerebellolivary and cerebellopontine afferent systems. We suggest that our patient presented an exceptional brainstem syndrome involving the function of cerebellar inflow tracts. Such electrophysiological findings are not encountered in patients presenting a cerebellar cortical degeneration or cerebellovlivopontine atrophy, and might have important implications in the treatment of cerebellar ataxia in the future.

Ice-water test in the urodynamic evaluation of spinal cord injured patients

The purpose of this study was to determine the clinical utility of the ice-water test (IWT) during urodynamic evaluation in spinal cord injured (SCI) patients. Thirty-two suprasacral SCI patients with documented detrusor hyperreflexia (DH) underwent urodynamic study and IWT. Fifteen patients had repeated testing 2 weeks later. The IWT was performed with the patient in the supine position; 100 mL of sterile saline water at 4-8 degrees C was injected manually. If cystometric capacity was <200 mL, a volume of about 50% of the individual cystometric bladder capacity was used. The cold fluid was left within the bladder for 3 minutes. The test was considered positive if an involuntary bladder contraction > or =15 cm H2O was registered. All patients with cervical or thoracic level SCI had DH, which had 100% test-retest reproducibility on urodynamics. Seventy-two percent of patients with DH had a positive IWT and 28% had a negative IWT. IWT (same volume, 2 weeks later) in 4 (27%) of the 15 repeated tests gave different responses. Autonomic hyperreflexia, manifested as systolic blood pressure increase > or =50 mm Hg within 3 minutes of ice-water instillation, occurred in 16 (57%) of 28 patients with lesions above T7. In SCI patients, the IWT did not contribute to their management because of the insensitivity and nonspecificity. Autonomic hyperreflexia can occur during evaluation. The IWT did not influence clinical management in this group of SCI patients.

[Neurophysiologic diagnosis in proctology]

Functional diagnostic exploration in proctology is ever-expanding and becoming more differentiating. Neurophysiologic examinations can take over an essential share. They have in part already been introduced into routine diagnostic workup. Both afference and efference, as well as the muscular system can be investigated in functional neurologic disorders of the pelvic floor. The electromyogram using concentric needle electrodes constitutes the most significant tool. It provides us with a better verification of the neurogenic lesion, and enables us to discriminate between acute and chronic and comment on severity and prognosis. The diagnostic program is additionally supplemented by motor and sensory evoked potentials, electroneurography of the pudendal nerve, and measurements of vegetative nerve paths.

[Interdisciplinary diagnosis and therapy of traumatic optic nerve damage]

Traumatic optic nerve lesions (TONL) still pose a large clinical problem concerning early detection and treatment. Neuro-ophthalmology provides reliable tests to detect afferent lesions but these methods are limited to just 30% of the severely injured patients. Especially in the patient with multiple injuries, optic nerve injuries are hardly predictable. In the latter group we established well-known neurophysiological methods for early detection of afferent disorders of the visual pathway, i.e. flash-VEP ERG. Apart from these diagnostic problems of TONL, controversy still surrounds the appropriate treatment of TONL--whether conservative or surgical or even combined treatment should be advocated. Our aim was to establish a reliable diagnostic schedule, based on the combination of neuro-ophthalmological, spiral-CT and clinical findings, and a treatment plan, so that in any patient there is a distinct guideline as to whether there is a need for early treatment of the peripheral visual pathway or not. In 52 patients who were assessed by the above-mentioned schedule, we could detect any of the 20 afferent disorders of the peripheral visual pathway. Although it is difficult to prove therapeutic effects on the injured optic nerve, immediate combined conservative treatment plus optic nerve decompression helped in three patients, who reported unilaterally no light-perception at admission, to regain at least partial recovery of afferent function of the visual pathway. Most of the trauma units still handle the problem of optic nerve trauma with a 'wait and see' policy. This is not regarded as an up-to-date option, since there are alternatives, and these will be outlined.

Neurophysiologic evaluation of long-term desferrioxamine therapy in beta-thalassemia patients

Forty patients with beta-thalassemia major (BTM), between 11 and 19 years of age and maintained on long-term desferrioxamine (DFO) treatment, were examined by evoked potential and nerve conduction velocity studies to investigate a possible involvement of the auditory, visual, somatosensory, or peripheral nervous pathways. Pathologic findings in brainstem auditory-, visual-, and somatosensory-evoked potentials, and nerve conduction velocity studies were demonstrated in 25%, 15%, 7.5%, and 25% of the patients, respectively, whereas 15% demonstrated involvement of multiple neural pathways. Subclinical involvement of the auditory pathway was statistically associated with higher mean daily DFO dose and longer duration of DFO therapy, whereas abnormalities regarding the somatosensory pathways were related to older age, longer mean duration of DFO therapy, and lower serum copper levels. Involvement of the peripheral nervous system was related to lower serum copper levels. Multiple involvement of neural pathways was related to longer mean duration of DFO therapy. We conclude that risk factors related to long-term DFO treatment are only partly responsible for the subclinical involvement of neural pathways demonstrated in beta-thalassemia major patients.

Calcitonin gene-related peptide and spinal afferents partly mediate postoperative colonic ileus in the rat

BACKGROUND

Calcitonin gene-related peptide (CGRP) is a widely distributed neuropeptide contained in intrinsic and extrinsic neurons of the gastrointestinal wall that has been shown to be released by noxious stimulation, to be involved in nociception, to inhibit gastrointestinal motility, and to partly mediate postoperative gastric ileus. We hypothesized that abdominal surgery-induced release of CGRP might inhibit postoperative colonic motility and food intake.

METHODS

Colonic transit, stool pellet number, stool pellet weight, and food intake were measured for 48 hours after induction of postoperative ileus in rats. CGRP was immunoneutralized by preoperative injection of CGRP monoclonal antibody, or visceral afferent nerve fibers containing CGRP were functionally ablated by topical capsaicin treatment of the vagus nerves or of the celiac/superior mesenteric ganglia before abdominal surgery.

RESULTS

Abdominal surgery increased colonic transit time and decreased 24-hour cumulative stool pellet number, stool pellet weight, and food intake. CGRP immunoneutralization reversed postoperative inhibition of colonic transit, 24-hour cumulative stool pellet number, stool pellet weight, and food intake by 77%, 82%, 80%, and 52%, respectively. Whereas ablation of vagal afferent nerve fibers had no effect, spinal afferent nerve fiber ablation reversed postoperative inhibition of 24-hour cumulative stool pellet number, stool pellet weight, and food intake by 41%, 38%, and 19%, respectively.

CONCLUSIONS

CGRP and spinal afferent nerve fibers partly mediate postoperative colonic ileus and inhibition of food intake in the rat. By the magnitude of reversal of postoperative ileus, CGRP seems to be an important mediator of postoperative colonic ileus. Our results for the first time show involvement of a neuropeptide and spinal afferents in the mediation of postoperative colonic ileus and postoperative inhibition of food intake in rats.

Roles of ascending inhibition during two rhythmic motor patterns in Xenopus tadpoles

We have investigated the effects of ascending inhibitory pathways on two centrally generated rhythmic motor patterns in a simple vertebrate model, the young Xenopus tadpole. Tadpoles swim when touched, but when grasped respond with slower, stronger struggling movements during which the longitudinal pattern of motor activity is reversed. Surgical spinal cord transection to remove all ascending connections originating caudal to the transection (in tadpoles immobilized in alpha-bungarotoxin) did not affect "fictive" swimming generated more rostrally. In contrast, cycle period and burst duration both significantly increased during fictive struggling. Increases were progressively larger with more rostral transection. Blocking caudal activity with the anesthetic MS222 (pharmacological transection) produced equivalent but reversible effects. Reducing crossed-ascending inhibition selectively, either by midsagittal spinal cord division or rostral cord hemisection (1-sided transection) mimicked the effects of transection. Like transection, both operations increased cycle period and burst duration during struggling but did not affect swimming. The changes during struggling were larger with more rostral hemisection. Reducing crossed-ascending inhibition by spinal hemisection also increased the rostrocaudal longitudinal delay during swimming, and the caudorostral delay during struggling. Weakening inhibition globally with low concentrations of the glycine antagonist strychnine (10-100 nM) did not alter swimming cycle period, burst duration, or longitudinal delay. However, strychnine at 10-60 nM decreased cycle period during struggling. It also increased burst duration in some cases, although burst duration increased as a proportion of cycle period in all cases. Strychnine reduced longitudinal delay during struggling, making rostral and caudal activity more synchronous. At 100 nM, struggling was totally disrupted. By combining our results with a detailed knowledge of tadpole spinal cord anatomy, we conclude that inhibition mediated by the crossed-ascending axons of characterized, glycinergic, commissural interneurons has a major influence on the struggling motor pattern compared with swimming. We suggest that this difference is a consequence of the larger, reversed longitudinal delay and the extended burst duration during struggling compared with swimming.

Generators of short latency human somatosensory-evoked potentials recorded over the spine and scalp

Somatosensory evoked potentials (SEPs) are most commonly obtained after stimulation of the median nerve and the posterior tibial nerve. SEPs reflect conduction of the afferent volley along the peripheral nerve, dorsal columns, and medial lemniscal pathways to the primary somatosensory cortex. Short-latency SEPs are recorded over the spine and scalp. After posterior tibial nerve stimulation, the following waveforms are recorded: N22, W3, the dorsal column volley, N29, P31, N34, and P37. After median nerve stimulation, the brachial plexus volley, dorsal column volley (N11), N13, P14, N18, N20, and P22 potentials are recorded. We discuss the current state of knowledge about the generators of these SEPs. Such information is crucial for proper interpretation of SEP abnormalities.

Dysafferentation: a novel term to describe the neuropathophysiological effects of joint complex dysfunction. A look at likely mechanisms of symptom generation

BACKGROUND AND OBJECTIVES

Since the founding of the chiropractic profession, very few efforts have been made to thoroughly explain the mechanism(s) by which joint complex dysfunction generates symptoms. Save for a few papers, only vague and physiologically inconsistent descriptions have been offered. The purpose of this article is to propose a precise and physiologically sound mechanism by which symptoms may be generated by joint complex dysfunction.

DATA SOURCES

The data was accumulated over a period of years by reviewing contemporary articles and books, and subsequently retrieving relevant papers. Articles were also selected from volumes 1-4 of the Chiropractic Research Archives Collection. The Nexus, published by the David D. Palmer Health Sciences Library, and In Touch, published by Logan College of Chiropractic Library, were reviewed and relevant articles were retrieved. Medline searches were found to be ineffective because appropriate key indexing terms were difficult to identify.

DATA SYNTHESIS

The symptoms generated by joint complex dysfunction, such as pain, nausea and vertigo, are probably caused by increased nociceptive input and/or reduced mechanoreceptive input.

CONCLUSIONS

Joint complex dysfunction should be included in the differential diagnosis of pain and visceral symptoms because joint complex dysfunction can often generate symptoms which are similar to those produced by true visceral disease.

Hereditarily elongated carotid sinus nerve in a rat colony

A specific colony of Wistar rats was found in which the common carotid artery bifurcates at an unusually caudal position, thereby the carotid sinus nerve that originates from the bifurcation is elongated. The present study was done to determine whether this elongated nerve carries baro- and chemosensations in the same manner as the carotid sinus nerve of conventional rats or of other species. In chloralose-urethane anesthetized rats of this specific colony, the afferent discharges were recorded from the elongated carotid sinus nerve in response to a phenylephrine-induced rise in blood pressure and a fall in oxygen tension, as well as an increase in carbon dioxide tension in the respiratory gas. Reflex effects of electrical stimulation of the nerve were also examined. In nerve recording, the afferent discharges of the elongated carotid sinus nerve were increased by any of the perturbations, hypertensive, hypoxic or hypercapnic. Electrical stimulation of the elongated carotid sinus nerve caused an initial rise and a subsequent fall in blood pressure, bradycardia, and an increase of respiratory volume and rate. These results confirmed that the elongated carotid sinus nerve of rats in this colony contains both baroreceptor and chemoreceptor afferent fibers. It seems that this colony of rats proffers a beneficial material which will facilitate the studies to analyze the features and reflex functions of carotid body chemoreceptors and/or carotid sinus baroreceptors.

Assessment of afferent gut--brain function using cerebral evoked responses to esophageal stimulation

Increasing awareness is attributed to altered sensory perception in the pathogenesis of gastrointestinal disorders. Evoked potentials (EP), which represent the brain's electrical response to peripheral stimulation, have recently been used to investigate where and how (GI) afferent information is processed along the brain-gut axis. EP can be obtained with electrical stimulation or balloon distention in the esophagus in humans. Stimulation of afferent neural pathways in the esophagus produces cerebral evoked responses allowing assessment of the peripheral afferent neural pathways involved, and of the function of integrative neural centers within the brain. Recent studies using esophageal EP indicate that the cerebral response to either mode of stimulation depends on the perception of the stimuli. Using electrical stimulation, a clear dose-response relationship is found. The EP response obtained with electrical stimulation is in keeping with those recorded using direct cervical stimulation of the vagus nerve, supporting evidence that esophageal EP are produced by activation of afferent vagal pathways. From the conduction velocity of the autonomic (vagal) nerves conveying information from esophagus to brain, it was concluded that non-painful electrical stimuli predominantly activate fast conducting myelinated afferent sensory fibers (A-fibers), while EP to balloon distention are largely due to activation of unmyelinated C-fibers. Techniques, however, vary widely amongst different investigators, and some electrophysiological parameters remain controversial, as there is no standard approach. Using balloon distention, EP waveforms vary widely between laboratories, suggesting that EP are substantially influenced by the stimulator devices (pump, respirator). EP to balloon distention are hampered by a relatively low signal-to-noise ratio (SNR), which is probably due to long inflation-deflation time (> 200 ms). With electrical stimulation, there is much less variability between different groups, and SNR is distinctly higher. This method appears to be most attractive for studies of afferent esophageal function. Standardization of the techniques is important, before esophageal EP can be regarded as a useful diagnostic approach in patient groups.

Masseter reflex potentials in olivo-ponto-cerebellar atrophy

We recorded masseter reflex potentials to examine the correlation between the masseter reflex and the muscle stretch reflexes of limbs in 19 patients with olivo-ponto-cerebellar atrophy (OPCA). The patients were subdivided into hyper- (n = 5), normo- (n = 7) and hypo- (n = 7) reflexia groups according to the degrees of the conventional deep tendon jerks in the upper limbs. The masseter reflex potentials, elicited by tapping the chin with a reflex hammer, were recorded from the bilateral masseters using a pair of surface electrodes. The latency of the potentials in the hyporeflexia was significantly longer than in the other groups, while the amplitude of those in the hyperreflexia group was significantly higher than in the other groups. These results indicate that in patients with OPCA the magnitude and latency of the masseter reflex correlates with the status of the muscle stretch reflexes of the limbs in contrast with Friedreich's ataxia where the masseter reflex has been reported to be normal or hyperactive despite hyporeflexia in the limbs.

[Value of magnetic stimulation and F-wave determination in diagnosis of proximal demyelinating lesions. Follow-up of acute Guillain-Barré polyradiculitis]

A 47-year-old woman developed acute Guillain-Barré-syndrome (GBS) within one day, presenting tetraparesis (muscle strength 1/5 for the upper and 2/5 for the lower extremities) and respiratory failure. On day 5 a cardiac pacemaker was necessary due to severe bradycardia. Electrophysiological studies were performed on days 2, 3, 5, 6, 8, 12, 15, 30 and 40. Our initial findings revealed normal motor conduction velocities and normal spinal motor evoked potentials. However, neither F-waves nor cortical motor evoked potentials could be registered from the upper or lower extremities. The motor conduction of the median nerve remained normal until day 6. The compound motor action potential declined thereafter and disappeared by day 12, indicating axonal degeneration. No axonal degeneration occurred in the lower extremities. The cervical or lumbar magnetic stimulation excites nerve roots at the level of the foramen intervertebrale. Thus, our findings suggest a conduction block between the foramen intervertebrale and the point where the nerve roots enter the spinal cord.

Review article: heart rate and blood pressure control in vasovagal syncope

Vasovagal syncope is characterized by transient failure of usually reliable physiologic mechanisms responsible for maintaining both systemic arterial pressure and cerebral blood flow. Two circulatory phenomena are almost universally present: systemic arterial vasodilation and bradycardia. A third phenomenon, cerebrovascular constriction, has also been described but its contribution to the faint is less well established. The neural reflex pathways responsible for triggering the circulatory changes in the vasovagal faint are incompletely understood, but have recently been the subject of renewed interest. In part, this interest probably stems from the frequency with which vasovagal symptoms are now recognized to be the cause of fainting spells. Additionally, however, there is an increasingly recognized need to develop treatment strategies for those affected patients in whom recurrent vasovagal symptoms are particularly troublesome. It is the goal of this discussion to focus on those aspects of circulatory control, and in particular on potential interactions among certain neural and humoral systems, which may contribute to the inappropriate physiologic responses associated with the vasovagal faint.

Impaired hypothalamus-pituitary-adrenal axis in men with spinal cord injuries

Twenty-five men with spinal cord injuries were studied for evaluation of the hypothalamus-pituitary-adrenal axis, using corticotropin-releasing hormone and insulin-induced hypoglycemia. Twenty-five age-matched healthy male volunteers served as controls. Three spinal cord-injured subjects had hyperprolactinemia, three had elevated basal follicle-stimulating hormone levels, one had an elevated basal luteinizing hormone level, and four had hypotestosteronemia. The mean plasma adrenocorticotropin response to corticotropin-releasing hormone of spinal cord-injured subjects was smaller than that of the healthy controls but did not reach a statistical significance. The cortisol response to corticotropin-releasing hormone of the spinal cord-injured subjects was significantly lower than that of healthy controls. However, the difference disappeared if a correction was made for baseline values. Six spinal cord-injured subjects did not have a cortisol response to insulin-induced hypoglycemia, and they had either a minimal or no adrenocorticotropin response. Another 11 spinal cord-injured subjects had a maximal cortisol response to insulin-induced hypoglycemia below the lowest limit of normal, i.e., 0.5 micromol/l. Among these spinal cord-injured subjects, three had a less than 50% increase of plasma adrenocorticotropin after insulin-induced hypoglycemia. These findings are consistent with the notion that spinal cord-injured subjects have an altered central neurotransmitter tone and substantiate the hypothesis that an afferent neural pathway exists between the adrenal and hypothalamus and may modulate stress-induced secretion of adrenocorticotropin. Long-term abnormal adrenocorticotropin secretion may cause mild adrenocortical atrophy and, thereby, a reduced cortisol response.

[Anatomic-physiologic principles of pain]

Pain, particularly chronic pain, arises from the interaction of multiple simultaneously operating physiologic processes. The current understanding of the anatomy and physiology of pain is limited to a characterization of pathways and does not explain why a particular stimulus is felt as pain of a particular kind and intensity. In this article, we trace the afferent pain pathways from periphery (reception) to center (perception), i.e., from peripheral nerve, through the spinal cord and brain stem, to the thalamus and cerebral cortex. A number of neurosurgical procedures for the treatment of pain are discussed, and their anatomic basis is explained.

Suppression of autotomy by N-methyl-D-aspartate receptor antagonist (MK-801) in the rat

The effects of different doses and time of administration of the N-methyl-D-aspartate (NMDA) receptor antagonist (MK-801) on the development of the autotomy (self-mutilation) were studied in the rats receiving dorsal root ganglionectomy (DRGn). The rats without any treatment and those treated with normal saline immediately after DRGn were the control groups. Three groups of rats were treated with 0.1, 0.5 or 1.0 mg/kg of MK-801 immediately after DRGn, and another three were treated with 1.0 mg/kg of MK-801 2, 4, or 7 days after DRGn. The behavioral observations of these rats were quantified using an autotomy grading scale ranging from 0 to 19, and the scores were compared among these groups. The rats in the control groups manifested autotomy from 5 to 17 days after DRGn and all of them (100%) attained the highest autotomy score. Lower doses (0.1 or 0.5 mg/kg) of MK-801 had no effect on the development of the autotomy. In contrast, higher dose (1.0 mg/kg) of MK-801 administered immediately after DRGn significantly suppressed the autotomy as compared to the control groups (P < 0.01) and only 17% of the rats in this group attained the highest score. The antagonistic effect was retained when the treatment of MK-801 was delayed to 2 days after DRGn, however, it disappeared when the treatment was delayed to 4 or 7 days after DRGn. Thus, the antagonistic effect of MK-801 on the autotomy induced by DRGn was dose-related and time-dependent. The main role of the NMDA receptor in the development of the autotomy was within several days after DRGn.

A neuronal correlate of secondary hyperalgesia in the rat spinal dorsal horn is submodality selective and facilitated by supraspinal influence

Tissue injury produces hyperalgesia not only in the injured area (primary hyperalgesia) but also outside of it (secondary hyperalgesia). In the present investigation, the submodality selectivity and the contribution of supraspinal influence to a neural correlate of the secondary hyperalgesia induced by neurogenic inflammation was studied in the presumed pain relay neurons of the rat spinal dorsal horn. Mechanically and thermally evoked responses to wide-dynamic range (WDR) neurons of the spinal dorsal horn were recorded under sodium pentobarbital anesthesia in rats. Neurogenic inflammation was induced by application of mustard oil outside of the receptive fields of WDR neurons. To study the contribution of supraspinal influence to mustard oil-induced changes in neuronal responses, the spinal cord was transected at a midthoracic level or lidocaine was microinjected into the rostroventromedial medulla (RVM). Furthermore, the antidromically evoked compound volley in the sural nerve was determined to reveal excitability changes in the central terminals of primary afferent A-fibers induced by mustard oil. The results indicate that mustard oil adjacent to the receptive fields of spinal WDR neurons significantly enhanced their responses to mechanical but not to noxious heat stimuli, without a significant influence on their spontaneous activity. Both high- and low-threshold mechanoreceptive input to WDR neurons was equally facilitated, whereas mechanoreceptive input to spinal dorsal horn neurons mediating innocuous messages (low-threshold mechanoreceptive neurons) was not changed. Mustard oil in a remote site (forepaw) did not produce any hyperexcitability to responses evoked by hindpaw stimulation. Spinal transection or lidocaine block of the RVM significantly attenuated the mustard oil-induced mechanical hyperexcitability in spinal dorsal horn neurons. Mustard oil had no significant effect on a compound volley in the sural nerve induced by intraspinal stimulation of sural nerve terminals at a submaximal intensity. The selective mechanical hyperexcitability in spinal WDR neurons, without a change in their spontaneous activity, can be explained by a heterosynaptic facilitatory action on presynaptic terminals mediating mechanical signals to these nociceptive spinal neurons. These findings indicate that brain stem-spinal pathways, involving the RVM, do not only suppress nociception but under some pathophysiological conditions concurrent facilitatory influence may predominate and lead to enhancement of mechanical hyperexcitability. The descending facilitatory feed-back loop to nociceptive spinal neurons may help to protect the wounded tissue and thus promote healing.

Cochleovestibular afferent pathways of trapezius muscle responses to clicks in human

Brief intense clicks cause short-latency cervical muscles microcontractions which are supposed to be of vestibular origin. Averaging these microcontractions allows myogenic vestibular evoked potentials (MVEP) to be obtained. MVEP from the trapezius muscles were investigated in normal subjects, cochleovestibular nerve-damaged patients and patients with a vestibular or a cochlear lesion. Muscular responses were recorded on right and left trapezius by averaging from surface electrodes following right and left monaural 100 dB hearing level click stimulation. In normal subjects, responses to monaural stimuli were bilateral, of equal amplitude and latency in left and right trapezia. Normal response consisted of four consecutive waves, labelled p13, n23, p32 and n40 according to their polarity (p, positive; n, negative) and mean peak latency in msec. In total unilateral cochleovestibular damaged patients, auditory stimulation of the affected side gave no MVEP either ipsilateral or contralateral to the stimulation. In the case of selective cochlear lesion, stimulation of the affected side gave MVEP which was present on ipsilateral and contralateral trapezius muscles. The four successive waves were present with a normal latency; however, amplitude was lower than that obtained after stimulation of the healthy ear. In the case of selective vestibular lesion, the four waves of MVEP were again present with normal latency but with reduced amplitude. Responses were present on both the ipsilateral and contralateral trapezius muscle. It is concluded that normal MVEP recorded on the trapezius muscles are bilateral and consist of four waves, the amplitude of which could depend on the simultaneous stimulation of both cochlear and vestibular afferents. In the case of unilateral cochlear and/or vestibular impairments responses were present on both ipsilateral and contralateral trapezius muscles. Latencies had normal values but amplitudes were reduced. MEVP recorded on trapezius muscles were absent in the case of total cochleovestibular damage.