Pain and hyperalgesia following tissue injury: new mechanisms and new treatments

KIF2A characterization after spinal cord injury

Axons in the central nervous system (CNS) typically fail to regenerate after injury. This failure is multi-factorial and caused in part by disruption of the axonal cytoskeleton. The cytoskeleton, in particular microtubules (MT), plays a critical role in axonal transport and axon growth during development. In this regard, members of the kinesin superfamily of proteins (KIFs) regulate the extension of primary axons toward their targets and control the growth of collateral branches. KIF2A negatively regulates axon growth through MT depolymerization. Using three different injury models to induce SCI in adult rats, we examined the temporal and cellular expression of KIF2A in the injured spinal cord. We observed a progressive increase of KIF2A expression with maximal levels at 10 days to 8 weeks post-injury as determined by Western blot analysis. KIF2A immunoreactivity was present in axons, spinal neurons and mature oligodendrocytes adjacent to the injury site. Results from the present study suggest that KIF2A at the injured axonal tips may contribute to neurite outgrowth inhibition after injury, and that its increased expression in inhibitory spinal neurons adjacent to the injury site might contribute to an intrinsic wiring-control mechanism associated with neuropathic pain. Further studies will determine whether KIF2A may be a potential target for the development of regeneration-promoting or pain-preventing therapies.

The Different Types of Algodystrophy after Fracture of the Distal Radius

A prospective study of algodystrophy after fracture of the distal radius was carried out to search for early diagnostic and prognostic criteria. One hundred consecutive patients were assessed by a radiographic score and by a semi-quantitative clinical score at 1, 6 and 12 weeks and 1 year after fracture. The reactive disorders observed could be classified in four groups, each with a different course. There was a close link between patient satisfaction at 1 year and the group to which the patient belonged. Algodystrophy was diagnosed in 26% of cases. Of these, 58% were active and left sequelae at 1 year. A clinical score greater than 7 at 6 weeks predicted 96% of these cases of active algodystrophy. Active algodystrophy was more likely after a severe initial injury and if there was pain at the distal radioulnar joint.

Management of Chronic Postthoracotomy Pain

Postthoracotomy pain management is essential imme diately after surgery and crucial for the patient suffering from this problem for a long duration. Understanding the causative and pathophysiological basis for this condition requires frequent assessment and a multidi mensional approach. Inadequate pain control has detri mental effects on the routine activities of patients as well as on their physical and emotional well-being. During the last 2 decades, the understanding of various pain-related issues has been strengthened resulting in early intervention and pain management. Various phar macological modalities including the role of nonopiates, opiates, and adjuvant drugs are helpful in combating postthoracotomy pain. A selective group of patients will benefit from interventional techniques. The treat ment decision requires a clear understanding of the disease and its impact on the patient. There must also be an understanding of risk and benefits as well as cost and benefits for various drugs and techniques before selecting the appropriate therapy.

Contact lenses, migraine, and allodynia

Clinical trials and electrophysiologic studies demonstrated increased perceptual sensitivity in patients suffering from migraines. At least, one triggering factor is described in 85% of migraine patients. The aim of this report was to investigate the relationship between contact lens (CL) usage and migraine attacks in two cases. Two patients who were diagnosed with migraine reported that the frequency of migraine attacks increased after they switched to using CL with different base curves (BCs). These two patients, who began using CL with different BCs experienced discomfort and dryness of the eye. The ocular complaints were followed by migraine attacks. CL intolerance was also developed during migraine attack in one of the cases. The frequency of migraine attacks decreased and allodynia relieved significantly when flatter BCs were selected. CL related stimulus could have triggered the migraine attack. CLs should be well fitted in migraine patients with allodynia.

Management of acute pain in patients on treatment with opioids

The use of opioids for both benign and cancer-related chronic pain has increased exponentially over the last few years. For this reason, increasing numbers of such patients are presenting for surgery. It is known that continuous use of opioids is associated with an increase in postoperative analgesic requirements. This is believed to be mediated by the development of tolerance and opioid-induced hyperalgesia. Patients treated with opioids have special needs in the perioperative setting and it is the anesthesiologist's responsibility to manage these needs optimally. The aim of the present paper is to briefly orient the reader in the management of postoperative pain in patients chronically treated with licit opioids.

Perioperative management of the opioid tolerant patient for orthopedic surgery

The prevalence of opioid use in the North America and some countries of the European Union has resulted in an increase in the number of patients who may exhibit opioid tolerance when requiring postoperative pain management. The approach to postoperative pain control in these patients is different from the strategies used in opioid-naïve patients. Better understanding of the cellular mechanisms of opioid tolerance in animals has resulted in the transfer of these concepts from the basic research to the clinical arena. This article presents new developments in opioid tolerance and how this knowledge can be applied to clinical practice.

The role of descending inhibitory pathways on chronic pain modulation and clinical implications

The treatment and management of chronic pain is a major challenge for clinicians. Chronic pain is often underdiagnosed and undertreated, and there is a lack of awareness of the pathophysiologic mechanisms that contribute to chronic pain. Chronic pain involves peripheral and central sensitization, as well as the alteration of the pain modulatory pathways. Imbalance between the descending facilitatory systems and the descending inhibitory systems is believed to be involved in chronic pain in pathological conditions. A pharmacological treatment that could restore the balance between these 2 pathways by diminishing the descending facilitatory pain pathways and enhancing the descending inhibitory pain pathways would be a valuable therapeutic option for patients with chronic pain. Due to the lack of evidence for pharmacological options that act on descending facilitation pathways, in this review we summarize the role of the descending inhibitory pain pathways in pain perception. This review will focus primarily on monoaminergic descending inhibitory pain pathways and their contribution to the mechanism of chronic pain and several pharmacological treatment options that enhance these pathways to reduce chronic pain. We describe anatomical structures and neurotransmitters of the descending inhibitory pain pathways that are activated in response to nociceptive pain and altered in response to sustained and persistent pain which leads to chronic pain in various pathological conditions.

Neuron-immune interactions in the sensitized thalamus induced by mustard oil application to rat molar pulp

We have reported that mustard oil application to the rat dental pulp induces neuronal activation in the thalamus. To address the mechanisms involved in the thalamic changes, we performed neuronal responsiveness recording, immunohistochemistry, and molecular biological analysis. After mustard oil application, neuronal responsiveness was increased in the mediodorsal nucleus. When MK801 (an N-methyl-D-aspartate receptor antagonist) was applied to the mediodorsal nucleus, the enhanced responsiveness was decreased. N-methyl-D-aspartate receptor 2D, glial fibrillary acidic protein, and antigen-presenting cell-related gene mRNAs in the contralateral thalamus were up-regulated at 10 minutes after mustard oil application, but were down-regulated within 10 minutes after the antagonist application. OX6-expressing microglia and glial fibrillary acidic protein-expressing astrocytes did not increase until 60 minutes after mustard oil application. These results suggested that the thalamic neurons play some roles in regulating the glial cell activation in the mediodorsal nucleus via N-methyl-D-aspartate receptor 2D during pulp inflammation-induced central sensitization.

Role of the spinal cord NR2B-containing NMDA receptors in the development of neuropathic pain

Activation of N-methyl-d-aspartate (NMDA) receptors in the spinal dorsal horn has been shown to be essential for the initiation of central sensitization and the hyperexcitability of dorsal horn neurons in chronic pain. However, whether the spinal NR2B-containing NMDA (NMDA-2B) receptors are involved still remains largely unclear. Using behavioral test and in vivo extracellular electrophysiological recording in L5 spinal nerve-ligated (SNL) neuropathic rats, we investigate the roles of spinal cord NMDA-2B receptors in the development of neuropathic pain. Our study showed that intrathecal (i.t.) injection of Ro 25-6981, a selective NMDA-2B receptor antagonist, had a dose-dependent anti-allodynic effect without causing motor dysfunction. Furthermore, i.t. application of another NMDA-2B receptor antagonist ifenprodil prior to SNL also significantly inhibited the mechanical allodynia but not the thermal hyperalgesia. These data suggest that NMDA-2B receptors at the spinal cord level play an important role in the development of neuropathic pain, especially at the early stage following nerve injury. In addition, spinal administration of Ro 25-6981 not only had a dose-dependent inhibitory effect on the C-fiber responses of dorsal horn wide dynamic range (WDR) neurons in both normal and SNL rats, but also significantly inhibited the long-term potentiation (LTP) in the C-fiber responses of WDR neurons induced by high-frequency stimulation (HFS) applied to the sciatic nerve. These results indicate that activation of the dorsal horn NMDA-2B receptors may be crucial for the spinal nociceptive synaptic transmission and for the development of long-lasting spinal hyperexcitability following nerve injury. In conclusion, the spinal cord NMDA-2B receptors play a role in the development of central sensitization and neuropathic pain via the induction of LTP in dorsal horn nociceptive synaptic transmission. Therefore, the spinal cord NMDA-2B receptor is likely to be a target for clinical pain therapy.

Long-term synaptic plasticity in the spinal dorsal horn and its modulation by electroacupuncture in rats with neuropathic pain

Our previous study has reported that electroacupuncture (EA) at low frequency of 2 Hz had greater and more prolonged analgesic effects on mechanical allodynia and thermal hyperalgesia than that EA at high frequency of 100 Hz in rats with neuropathic pain. However, how EA at different frequencies produces distinct analgesic effects on neuropathic pain is unclear. Neuronal plastic changes in spinal cord might contribute to the development and maintenance of neuropathic pain. In the present study, we investigated changes of spinal synaptic plasticity in the development of neuropathic pain and its modulation by EA in rats with neuropathic pain. Field potentials of spinal dorsal horn neurons were recorded extracellularly in sham-operated rats and in rats with spinal nerve ligation (SNL). We found for the first time that the threshold for inducing long-term potentiation (LTP) of C-fiber-evoked potentials in dorsal horn was significantly lower in SNL rats than that in sham-operated rats. The threshold for evoking the C-fiber-evoked field potentials was also significantly lower, and the amplitude of the field potentials was higher in SNL rats as compared with those in the control rats. EA at low frequency of 2 Hz applied on acupoints ST 36 and SP 6, which was effective in treatment of neuropathic pain, induced long-term depression (LTD) of the C-fiber-evoked potentials in SNL rats. This effect could be blocked by N-methyl-d-aspartic acid (NMDA) receptor antagonist MK-801 and by opioid receptor antagonist naloxone. In contrast, EA at high frequency of 100 Hz, which was not effective in treatment of neuropathic pain, induced LTP in SNL rats but LTD in sham-operated rats. Unlike the 2 Hz EA-induced LTD in SNL rats, the 100 Hz EA-induced LTD in sham-operated rats was dependent on the endogenous GABAergic and serotonergic inhibitory system. Results from our present study suggest that (1) hyperexcitability in the spinal nociceptive synaptic transmission may occur after nerve injury, which may contribute to the development of neuropathic pain; (2) EA at low or high frequency has a different effect on modulating spinal synaptic plasticities in rats with neuropathic pain. The different modulation on spinal LTD or LTP by low- or high-frequency EA may be a potential mechanism of different analgesic effects of EA on neuropathic pain. LTD of synaptic strength in the spinal dorsal horn in SNL rats may contribute to the long-lasting analgesic effects of EA at 2 Hz.

Chronic neuropathic pain: mechanisms, drug targets and measurement

Neuropathic pain is common in many diseases or injuries of the peripheral or central nervous system, and has a substantial impact on quality of life and mood. Lesions of the nervous system may lead to potentially irreversible changes and imbalance between excitatory and inhibitory systems. Preclinical research provides several promising targets for treatment such as sodium and calcium channels, glutamate receptors, monoamines and neurotrophic factors; however, treatment is often insufficient. A mechanism-based treatment approach is suggested to improve treatment. Valid and reliable tools to assess various symptoms and signs in neuropathic pain and knowledge of drug mechanisms are prerequisites for pursuing this approach. The present review summarizes mechanisms of neuropathic pain, targets of currently used drugs, and measures used in neuropathic pain trials.

Intercostal muscle flap reduces the pain of thoracotomy: A prospective randomized trial

BACKGROUND

Thoracotomy is associated with significant pain and morbidity.

METHODS

We performed a prospective randomized trial over 4 months. Patients were randomized to a standard posterior-lateral thoracotomy or an identical procedure, except an intercostal muscle was harvested from the lower rib (to protect the intercostal nerve) before chest retraction. To ensure an equal distribution among both groups, patients were stratified by race, sex, and type of pulmonary resection. All patients received similar pain management. Pain was assessed by using multiple pain scores during hospitalization and after discharge. Outcomes assessed were pain scores, spirometric values, analgesic use, and activity level.

RESULTS

There were 114 patients. The median time for intercostal muscle harvesting was 3.7 minutes. The numeric pain scores were lower for the intercostal muscle group on postoperative days 1 and 2 and at weeks 1, 2, 3, 4, 8, and 12 (P < .05 for all). In addition, patients in the intercostal muscle group had a smaller decrease in spirometric values, were less likely to be using analgesics, and were more likely to have returned to normal activity.

CONCLUSIONS

The harvesting of an intercostal muscle flap before chest retraction decreases the pain of thoracotomy and leads to a lower decrease in spirometry. In addition, patients have less pain at 1, 2, 3, 4, 8, and 12 weeks postoperatively and are less likely to be using narcotics. Finally, it offers a pedicled muscle flap that takes little time to harvest and is able to buttress all bronchi after lobectomy.

Effects of the N-Methyl-D-Aspartate Receptor Antagonist Dextromethorphan on Temporal Summation of Pain are Similar in Fibromyalgia Patients and Normal Control Subjects

Temporal summation of second pain at least partly reflects temporal summation of dorsal horn neuronal responses, and both have been termed windup (WU), a form of nociception-dependent central sensitization. Animal and human experiments have shown that both forms of WU depend on N-methyl-D-aspartate (NMDA) and substance P receptor systems. WU of second pain (WU(SP)) in patients with fibromyalgia (FM) is enhanced compared with normal control (NC) subjects and is followed by exaggerated WU(SP) aftersensations and prolonged WU(SP) maintenance at low stimulus frequencies. Because the enhanced WU(SP) of FM patients could be related to abnormal endogenous modulation of NDMA receptors, we tested the effects of the NMDA receptor antagonist dextromethorphan (DEX) on WU(SP) in FM and NC subjects in a double-blind, placebo-controlled, crossover study. WU(SP) was elicited by trains of 0.7-second duration thermal pulses applied to the glabrous surface of the hands or by 1-second mechanical stimuli to the adductor pollicis muscle of the hands at a frequency of 0.33 Hz. In comparison to baseline and placebo conditions, single oral doses of DEX 60 and 90 mg reduced thermal and mechanical WU(SP) in NC and FM subjects, with DEX 90 mg being most effective. These effects did not differ for male and female NC subjects. FM subjects required less thermal and mechanical stimulus intensity than NC to achieve maximal WU(SP), but the extent of WU(SP) reduction by DEX did not statistically differ between NC and FM subjects for all study conditions. Thus, central pain processing of FM subjects is not different from NC in at least one important aspect, namely their NMDA receptor system responsiveness to pharmacologic inhibition by DEX.

PERSPECTIVE

Results of this study demonstrate that FM patients show abnormal WU(SP) during thermal and mechanical stimulation compared with NC. Because oral doses of the NMDA receptor antagonist DEX attenuated thermal and mechanical WU(SP) similarly in FM patients and NC, other mechanisms than WU(SP) need to be considered for the widespread pain of FM patients. These mechanisms might include tonic nociceptive input from peripheral tissues and/or enhanced descending facilitation.

Electrophysiological characterization of facilitated spinal withdrawal reflex to repetitive electrical stimuli and its modulation by central glutamate receptor in spinal anesthetized rats

The present study is aimed to systematically investigate wind-up and after-discharge of the spinal withdrawal reflex assessed by recording single motor unit (SMU) electromyographic (EMG) response to different intensities [0.5-1.5xreflex threshold (T)] of repetitive [frequencies (0.5-200 Hz)] transcutaneous electrical stimuli for 5 s. The role of central glutamate receptors in modulation of the withdrawal reflex facilitation was observed and evaluated in order to explore the potential central mechanism. Stimulus intensities below reflex threshold, such as 0.8xT, but not 0.5xT, could by repetition elicit and facilitate withdrawal reflex. The facilitation (wind-up and after-discharge) of the withdrawal reflex is a result of central integration and is increased significantly for increasing stimulus intensity and frequency. Electrical stimuli at 3-5 Hz for 5 s are appropriate to elicit wind-up. In contrast, 10-20 Hz frequencies of electrical stimuli are adequate to evoke the after-discharge. For pharmacological intervention, suprathreshold (1.5xT) repeated (5 Hz) electrically evoked facilitated reflex (wind-up) were apparently depressed by intrathecal (i.t.) administration of MK-801 as well as CNQX (40 nmol/10 microl, respectively). However, wind-up of spinal reflexes evoked by subthreshold (0.8xT) electrical stimuli could only be depressed by the treatment with CNQX, not MK-801. The after-discharge of the withdrawal reflex elicited by 20 Hz electrical stimulation with either 0.8xT or 1.5xT intensity was depressed by i.t. treatment with CNQX. I.t. application of MK-801 only depressed 0.8xT the intensity of electrically evoked after-discharge. In conclusion, for the first time, the present study clearly demonstrates that, following the wind-up phase, the spinal withdrawal reflex pathways continue to fire spontaneously in a stimulus frequency- and intensity-dependent way (temporal and/or spatial summation). This inherited memory and the central non-N-methyl-d-aspartate (non-NMDA) receptor, but not the NMDA receptor, mainly involving pharmacological mechanisms, may play an important role in pathological conditions with spontaneous nociceptive firing. Furthermore, the after-discharge of the spinal reflex may be an important indicator for studies on central sensitization in many pathological pain conditions.

P300-amplitudes in upper limb amputees with and without phantom limb pain in a visual oddball paradigm

The aim of the study was to investigate to what extent cortical hyper-reactivity to visual stimuli is present in upper limb amputees. Five amputees with phantom limb pain (PLP), five amputees without PLP (Non-PLP) and 10 healthy controls (HC) were investigated using a visual oddball paradigm. Two hundred visual stimuli were presented with target stimuli occurring at a probability of 25% and standard stimuli at a probability of 75%. Event-related potentials were recorded from nine scalp positions (F3, F4, Fz, C3, C4, Cz, P3, P4, Pz). The PLP-patients had significantly higher P300-amplitudes to both types of stimuli compared to the non-PLP-patients. The HC were not significantly different from both amputee groups. P300-amplitude to targets at frontal sites in the hemisphere contralateral to the amputation was higher in the PLP patients. P300-latencies to target stimuli differed only at frontal sites with PLP-patients showing significantly longer latencies than non-PLP-patients. To standard stimuli, however, they showed significantly shorter latencies at central and parietal scalp positions. The HC had significantly shorter latencies than both amputee groups. The size of the P300-amplitude was positively correlated with the intensity of PLP. These findings suggest a higher magnitude of non-specific cortical excitability in amputees with PLP and a reduced excitability in amputees without PLP. This extends previous findings of differences in cortical excitability in PLP and non-PLP patients in the sensorimotor domain.

Pain in a Balance: Noxious Events Engage Opposing Processes That Concurrently Modulate Nociceptive Reactivity

Studies have shown that noxious cutaneous stimulation engages physiologically different antinociceptive systems to inhibit a spinal reflex, tail withdrawal from radiant heat. Two experiments are reported that examine the relationship between the inhibition of the tail-flick response and brain-mediated responses to nociception. The induction of a spinally mediated antinociception was accompanied by an increase in latency to vocalize to a noxious thermal stimulus, suggesting pain inhibition. Physiological manipulations that eliminated the inhibition of the tail-flick reflex restored vocalization to thermal stimulation and revealed a concurrent sensitization that generally heightened behavioral reactivity. The results suggest that net pain is regulated by 2 opposing processes, a selective inhibition of nociceptive signals within the spinal cord and a general sensitization that heightens stimulus processing.

Perioperative nursing and acute pain management

This article explores the broader aspects and opportunities available to perioperative nurses in the field of pain management. It will help to develop nurses' insight into how perioperative nurses can develop their role in pain management. In turn this will benefit patients' service provision and enhance nurses' career pathways.

Cellular mechanisms of opioid tolerance and the clinical approach to the opioid tolerant patient in the post-operative period

The high prevalence of opioid use for recreational purposes in the USA and the European Union, as well as the use of opioids for the treatment of chronic non-malignant pain, has resulted in an increase in the number of patients with opioid tolerance who undergo surgery and require post-operative pain management. The approach to post-operative pain control in these patients is significantly different to the strategies used in opioid naïve patients. Fortunately, better understanding of the cellular mechanisms of opioid tolerance in animals has resulted in the transfer of concepts from the 'bench' to the clinical arena. This chapter describes the new developments in opioid tolerance and how this knowledge can be applied to clinical practice.

Time-dependent plasticity of synaptic transmission produced by long-term potentiation of C-fiber evoked field potentials in rat spinal dorsal horn

Our previous work has shown that repetitive stimulation of Adelta-fibers depresses long-term potentiation (LTP) of C-fiber evoked field potentials in spinal dorsal horn. Here, we tested the effects of the Adelta stimulation on the spinal LTP at different time points following LTP induction. Fifteen minutes after LTP induction Adelta stimulation depressed LTP by 44.1+/-4.2% (mean+/-SEM, n=7) for 69.3+/-18.5 min and 1 h after LTP the same Adelta stimulation depressed spinal LTP by only 16.9+/-3.1% for 21.9+/-2.0 min (n=7). Three hours after LTP, however, the Adelta stimulation produced a further potentiation (31.9+/-6.3%, n=7) lasting for all the recording periods (1-3 h). These data indicate that the effects of repetitive stimulation of Adelta-fibers on established spinal LTP of C-fiber evoked field potentials is time-dependent.

Pathophysiology of opioid tolerance and clinical approach to the opioid-tolerant patient

The physiologic basis for opioid tolerance has been elucidated, resulting in a better understanding of this problem. As a result of this ongoing effort, patients exhibiting opioid tolerance can now expect better pain management both in the postoperative period and during the course of their treatment. This article outlines the pathophysiology of opioid tolerance and a practical clinical approach to this problem.

Effects of performance feedback on patient pain outcomes

The purpose of this study was to examine the effects of an individual feedback intervention provided to nurses on selected patient outcomes related to postoperative pain management Individual performance feedback served as the intervention. Thirty orthopedic staff nurses received feedback information on their past performance of recommended pain management practices. Data were collected preintervention and postintervention on selected patient pain outcomes from the medical records of 240 patients who had undergone total knee arthroplasty. The patient outcome measures were mean 4-hour pain intensity ratings, mean highest pain intensity ratings, mean number of times pain ratings exceeded patients' acceptable level of pain, mean administered morphine equivalents, and mean pain ratings on reassessment following analgesia administration. An improvement was noted in all pain outcomes following the feedback intervention. Results indicate that providing nurses with feedback on their past performance of pain management practices may contribute to decreased postoperative pain.

An experimental pain model based on electric stimulations of the colon mucosa

BACKGROUND

Pain intensity and distribution related to diseases of the gut are important diagnostic indicators in gastroenterology. Experimental pain models provide a unique possibility for standardized activation of the nociceptive system, but only few human models exist.

METHODS

An experimental pain model based on electric stimuli in the human colon was developed and applied. Eleven patients who were referred for surveillance colonoscopy due to earlier polyps in the colon were included. None had any abdominal pain complaints. The following areas were stimulated with 'single', 'repeated', or 'continuous' electric current: the cecum, the hepatic and splenic flexures, and the rectosigmoid junction.

RESULTS

All subjects felt deep, diffuse pain during the stimulation, with referral to localized somatic structures. The pain detection thresholds after repeated stimuli were similar in the four areas. The threshold for single stimulation was higher than the threshold for repeated stimulation. Most reported pain in the lower and left site of the abdominal wall during stimuli at the splenic flexure and rectosigmoid junction. Stimuli at the right colon, however, resulted mostly in pain at the contralateral site of the abdomen.

CONCLUSIONS

The presented model was robust and suitable for eliciting pain in different regions of the large intestine. The importance of temporal summation in visceral pain was shown. Mapping of the referred pain areas mimics clinical observations and has ontogenetic and anatomic consistency. The model may therefore improve the evaluation of pain in patients with diseases of the colon.

Experimental human muscle pain induced by intramuscular injections of bradykinin, serotonin, and substance P

After intramuscular (m. tibialis anterior) injection of three different algogenic substances, the pain intensity was continuously scored on a visual analogue scale (VAS) in eight volunteers. The subject drew the distribution of the local and referred pain areas on a map. Four times within the first hour after injection, the pressure pain-thresholds (PPTs) and supra pressure-pain thresholds were assessed at the injection point, 2 cm distal from the injection site, at the arm, and at the contralateral leg. Measurements were done before and after injection of 0.5 ml of the algogenic substance [bradykinin (BKN), serotonin (5-HT), substance P (SP)], and isotonic saline as control. Cutaneous sensitivity to mechanical stimuli was assessed with a Von Frey hair at the same location as PPT determinations.The pain intensity (VAS-peak) after BKN (2, 4, and 10 nmol) and 5-HT (2, 4, and 20 nmol) was significantly higher (p< 0.05) than after SP (0.2, 0.4, and 0.8 nmol) and isotonic saline. The VAS-peak after infusions of hypertonic saline was significantly higher (p< 0.05) compared with VAS-peaks after all other substances. A significantly larger (p< 0.05) local pain area was found after BKN compared with isotonic saline. After injections of hypertonic saline, the offsets of evoked pain were significantly longer (p< 0.05) and the local and referred pain areas were significantly larger (p< 0.05) compared with all other substances. There was no dose-response relation between the pain intensity and the different doses of BKN, 5-HT, and SP. PPTs and skin sensitivity were not affected by any of the injections.We conclude that under the present experimental conditions, BKN and 5-HT can produce low levels of muscle pain after intramuscular injection. In the used concentrations, however, BKN, 5-HT, and SP did not generate cutaneous or muscular hyperalgesia. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.

Activation of spinal N-methyl-D-aspartate or neurokinin receptors induces long-term potentiation of spinal C-fibre-evoked potentials

The use-dependent increase in synaptic strength between primary afferent C-fibres and second-order neurons in superficial spinal dorsal horn may be an important cellular mechanism underlying central hyperalgesia. This long-term potentiation can be blocked by antagonists of the N-methyl-D-aspartate subtype of glutamate receptor, the neurokinin 1 or the neurokinin 2 receptor. We have tested here whether activation of these receptors by superfusion of the spinal cord with corresponding agonists in the absence of presynaptic activity is sufficient to induce long-term potentiation. In urethane anaesthetized rats C-fibre-evoked field potentials were elicited in superficial laminae of lumbar spinal cord by electrical stimulation of the sciatic nerve. In rats with intact spinal cord, controlled superfusion of the spinal cord at recording segments for 60 min with N-methyl-D-aspartate, substance P or neurokinin A never induced long-term potentiation. Spinal superfusion with a mixture of N-methyl-D-aspartate, substance P and neurokinin A also failed to induce long-term potentiation in four rats tested. In spinalized rats, however, long-term potentiation was induced by either N-methyl-D-aspartate (at 10 microM, to 173 +/- 16% of control) substance P (at 10 microM, to 176 +/- 13% of control) or by neurokinin A (at 1 microM, to 198 +/- .20% of control). The induction of long-term potentiation by N-methyl-D-aspartate, substance P or neurokinin A was blocked by intravenous application of the receptor antagonists dizocilpine maleate (0.5 mg/kg), RP67580 (2 mg/kg) or SR48968 (0.2 mg/kg), respectively. Thus, activation of N-methyl-D-aspartate or neurokinin receptors may induce long-lasting plastic changes in synaptic transmission in afferent C-fibres and this effect may be prevented by tonic descending inhibition.

The management of postsurgical pain in the elderly population

It is likely that the trend towards ever more aggressive surgery in elderly and possibly frail patients will continue, with the lifting of traditional age limits. Recent evidence has show that surgical trauma induces processes of nervous system sensitisation that contributes to and enhances postoperative pain and leads to chronic pain. This knowledge provides a rational basis for pro-active, pre-operative and post-operative analgesic strategies which can reduce the neuronal barrage associated with tissue damage. As well as a reduction or elimination of post-operative pain, an improvement in physiological variables, such as neuroendocrine stress responses and post-operative pulmonary function can be expected. Complete pain control cannot be achieved with a single agent or technique without significant serious adverse effects, a problem which is compounded in the elderly patient due to a combination of slower drug metabolism, decreased organ function and physiological changes in cardiovascular and respiratory reserves. A balanced analgesic regimen that includes an effective afferent block (regional analgesia) is more appropriate. By preventing postoperative pain and its associated neuroendocrine sequelae, major surgical procedures in traditionally unsuitable patients can be seriously considered.

Temporal summation in muscles and referred pain areas: an experimental human study

The aim of the present study was to assess temporal summation within saline-induced, localized and referred muscle pain areas. The sensibility to single and repeated electrical stimuli were assessed in the muscle by means of needle electrodes and in the referred pain area by surface stimulation. The study demonstrates that temporal summation of nociceptive input from muscles exists and that the responses to single and repeated nociceptive stimuli of the referred pain area are facilitated.

Characterization of long-term potentiation of C-fiber-evoked potentials in spinal dorsal horn of adult rat: essential role of NK1 and NK2 receptors

Impulses in afferent C fibers, e.g., during peripheral trauma, may induce plastic changes in the spinal dorsal horn that are believed to contribute to some forms of hyperalgesia. The nature of lasting changes in spinal nociception are still not well understood. Here we characterized the long-term potentiation (LTP) of spinal field potentials with a negative focus in superficial spinal dorsal horn evoked by supramaximal electrical stimulation of the sciatic nerve in urethan-anesthetized adult rats. The field potentials studied in this work had high thresholds (>/=7 V, 0.5 ms), long latencies (90-130 ms), and long chronaxy (1.1 ms) and were not abolished by muscle relaxation and spinalization. Thus they were evoked by afferent C fibers. In response to 1-Hz stimulation of afferent C fibers, amplitudes of C-fiber-evoked field potentials remained constant, whereas number of action potentials of some dorsal horn neurons increased progressively (wind-up). In all 25 rats tested, high-frequency, high-intensity stimulation (100 Hz, 30-40 V, 0.5 ms, 400 pulses given in 4 trains of 1-s duration at 10-s intervals) always induced LTP (to approximately 200% of control), which consistently lasted until the end of recording periods (4-9 h). This tetanic stimulation also significantly decreased mean threshold of C-fiber-evoked field potentials. The C-fiber volley, which was recorded simultaneously in sural nerve, was, however, not affected by the same tetanic stimulation. High-frequency, low-intensity stimulation (100 Hz, 3 V, 0.5 ms) never induced LTP in six rats tested. At an intermediate frequency, high-intensity stimulation (20 Hz, 40 V, 0.5 ms, 400 pulses given in 4 trains of 5 s at 10-s intervals) induced LTP in four out of six rats, which lasted until end of recording periods (3-6 h). In the remaining two rats, no LTP was induced. Low-frequency, high-intensity stimulation (2 Hz, 30-40 V, 0.5 ms, 400 pulses) induced LTP that lasted for 2-8 h in four out of five rats. Intravenous application of neurokinin 1 (NK1) or neurokinin 2 (NK2) receptor antagonist RP 67580 (2 mg/kg, n = 5) or SR 48968 (0.3 mg/kg, n = 5) 30 min before high-frequency, high-intensity stimulation blocked the induction of LTP in all rats tested. In contrast, the same dose of their inactive enantiomers RP 68651 (n = 5) or SR 48965 (n = 5) did not affect the induction of LTP. Spinal superfusion with RP 67580 (1 microM) from 30 min before to 30 min after high-frequency, high-intensity stimulation blocked induction of LTP in all five rats tested. Spinal application of SR 48968 (10 nM) prevented LTP in five out of seven rats. However, when spinal superfusions with RP 67580 (1 microM, n = 3) or SR 48968 (10 nM, n = 3) were started 1 h after high-frequency, high-intensity stimulation, established LTP was not affected. Thus the activation of neurokinin receptors is necessary for the induction but not for the maintenance of LTP of C-fiber-evoked field potentials in spinal dorsal horn. This model may be useful to study plastic changes in spinal cord induced by peripheral C-fiber stimulation. The LTP of C-fiber-evoked field potentials may be a mechanism underlying some forms of hyperalgesia.

The hypoalgesic effect of tramadol in relation to CYP2D6

Tramadol inhibits norepinephrine reuptake, stimulates serotonin release, and acts with mu-opioid receptors by way of its metabolite (+)-M1. Formation of M1 seems to depend on the genetic polymorphic CYP2D6. The analgesic effect of 2 mg/kg tramadol was evaluated in 15 extensive and 12 poor metabolizers of sparteine in two parallel, randomized, double-blind, placebo-controlled crossover studies that used experimental pain models. In extensive metabolizers, tramadol increased pressure pain detection (p = 0.03) and tolerance (p = 0.06) thresholds, as well as thresholds for eliciting nociceptive reflexes, after single (p = 0.0002) and repeated (p = 0.06) stimulation of the sural nerve. Peak pain and pain area in the cold pressor test were reduced (p = 0.0006 and 0.0009). In poor metabolizers, only thresholds to pressure pain tolerance (p = 0.02) and nociceptive reflexes after single stimulation (p = 0.04) were increased and the reflex threshold was less increased in poor metabolizers than in extensive metabolizers (p = 0.02). The serum concentration of (+)-M1 2 to 10 hours after tramadol ranged from 10 to 100 ng/L in extensive metabolizers, whereas in poor metabolizers serum concentrations of (+)-M1 were below or around the detection limit of 3 ng/ml. It is concluded that formation of (+)-M1 by way of CYP2D6 is important for the effect of tramadol on experimental pain.

Preoperative wound infiltration with bupivacaine reduces early and late opioid requirement after hysterectomy

We conducted a randomized, double-blind trial to evaluate the early and late analgesic effect of preoperative wound infiltration with bupivacaine 0.25% (40 mL) compared to placebo (NaCl 0.9%, 40 mL) in patients undergoing major surgery. Forty-one patients scheduled for elective hysterectomy during general anesthesia were included. The pain management focused on pain prevention, including preoperative administration of nonsteroidal antiinflammatory drugs (NSAIDs), and peroperative administration of opioids. Postoperatively patients received buprenorphine and/or acetaminophen on demand. A significant difference between treatments was evident in the 3-day postoperative trial period. With identical pain scores in the two groups, the requested total amount of buprenorphine was greater in the placebo group (2.0 [0-5.1] mg) (median and [range]) than in the bupivacaine group (0.8 [0-2.8] mg) (P < 0.05). The demand for analgesics occurred earlier in those who received placebo (225 min) than in those who received bupivacaine (345 min), but did not reach the level of significance. In conclusion, preoperative wound infiltration with bupivacaine improved immediate and late postoperative pain management after hysterectomy compared to placebo.

The massive expression of c-fos protein in spinal dorsal horn neurons is not followed by long-term changes in spinal nociception

It has been suggested that the expression of c-fos and other immediate early genes in spinal dorsal horn neurons would trigger changes in the phenotype of nociceptive neurons which may lead to long-term changes in spinal nociception. To test this hypothesis, we have used a minimally invasive intrathecal stimulation and injection technique which can be applied to adult Sprague-Dawley rats under brief ether anesthesia to induce massive c-fos expression in spinal neurons without affecting peripheral nociceptors. Electrical intrathecal stimulation (0.5 ms pulses, 15 V, 3 Hz for 15 min) or intrathecal injection of N-methyl-D-aspartate (25 nmol) produced massive c-Fos immunoreactivity in neurons throughout the sacral spinal cord and the dorsal horn of the lumber spinal cord. Immunoreactivity declined to control values at mid-thoracic levels. To assess effects of these intrathecal stimuli on nociception, hot-plate and tail-flick latencies and mechanical thresholds of hindlimb withdrawal reflexes were measured once every day for 14 days before and up to 14 days after conditioning stimulation. Spontaneous locomotion of each animal was video-taped daily for 5 min and analysed off-line. On the day of the intrathecal stimulation the tests were performed 1 h before and also 6 h after conditioning stimulation. Thermal and mechanical nociceptive thresholds were temporarily enhanced 6 h after intrathecal stimulation but they were not different from controls one to 14 days later. Thus, the massive expression of c-fos in spinal neurons is not, as previously suggested, a sufficient condition for the induction of long-term changes in spinal nociception.

Pain perception and brain evoked potentials in patients with angina despite normal coronary angiograms

OBJECTIVE

To evaluate the role of nociception in patients with angina despite normal coronary angiograms and to investigate whether any abnormality is confined to visceral or somatosensory perception.

METHODS

Perception, pain threshold, and brain evoked potentials to nociceptive electrical stimuli of the oesophageal mucosa and the sternal skin were investigated in 10 patients who had angina but normal coronary angiograms, no other signs of cardiac disease, and normal upper endoscopy. Controls were 10 healthy volunteers. The peaks of the evoked potential signal were designated N for negative deflections and P for positive. Numbers were given to the peaks in order of appearance after the stimulus. The peak to peak amplitudes (P1/N1, N1/P2) were measured in microV.

RESULTS

(1) Angina pectoris was provoked in seven patients following continuous oesophageal stimulation. (2) Distant projection of pain occurred after continuous electrical stimulation of the oesophagus in four patients and in no controls. (3) Patients had higher oesophageal pain thresholds (median 16.3 mA v 7.3 mA, P = 0.02) to repeated stimuli than controls, whereas the values did not differ with respect to the skin. There were no intergroup differences in thresholds to single stimuli. (4) Patients had substantially reduced brain evoked potential amplitudes after both single oesophageal (P1/N1, median values: 7.2 microV, controls: 29.0 microV; N1/P2: 16.5 microV, controls: 66.0 microV; P < 0.001 for both) and skin (N1/P2: 13.5 microV; controls: 76.0 microV; P < 0.001) stimuli despite the similar pain thresholds.

CONCLUSION

Central nervous system responses to visceral and somatosensory nociceptive input are altered in patients who have angina despite normal coronary angiograms.

Intact nociception-induced neuroplasticity in transgenic mice deficient in neuronal nitric oxide synthase

Nitric oxide is thought to play an important role in multiple forms of use-dependent synaptic plasticity, including that which follows noxious peripheral stimulation. This suggests that development of nociception-induced neuroplasticity should be impaired in transgenic animals lacking the neuronal form of nitric oxide synthase. We used the formalin model of nociception to test this hypothesis in wild-type and nitric oxide synthase knockout mice. Formalin-induced nociceptive behavior was intact in the knockout mice. Furthermore, administration of a nitric oxide synthase inhibitor blocked nociception-induced neuroplasticity in wild-type mice but had no effect in the knockouts, whereas inhalation of the gaseous analgesic nitrous oxide attenuated development of neuroplastic changes in both phenotypes. These data indicate that nitric oxide is sufficient but not essential for development of nociception-induced neuroplasticity.

The effect of N-methyl-D-aspartate antagonist (ketamine) on single and repeated nociceptive stimuli: a placebo-controlled experimental human study

Ketamine is a noncompetitive N-methyl-D-aspartate (NMDA) receptor channel blocker known to inhibit "wind-up" and hence central hyperexcitability of dorsal horn neurons. We sought to assess the effect of ketamine on single and repeated nociceptive stimuli. A placebo-controlled, human (12 volunteers) experimental study was conducted in which several psychophysical (pain detection and tolerance thresholds, magnitude ratings) and electrophysiologic (withdrawal reflex) techniques were used 1) to investigate whether a ketamine (0.5 mg/kg) bolus followed by a 20-min infusion (9 micrograms.kg-1.min-1) inhibits central temporal summation to repeated nociceptive electrical stimuli, and 2) to assess quantitatively the hypoalgesic potency using several experimental nociceptive stimuli (argon laser, pressure, electrical). Facilitation of the withdrawal reflex to and pain rating of repeated electrical stimuli (five pulses at 2 Hz) were inhibited by ketamine. Reflex and pain rating to a single stimulus did not change. The pressure pain detection and tolerance thresholds were increased significantly by ketamine, whereas the laser heat pain and tolerance thresholds remained stable compared with placebo. The stimulus response function showed that ketamine reduced the responses to the highest electrical stimulus intensities (1.4, 1.6, and 1.8 times the reflex threshold). We conclude that ketamine inhibits central temporal summation in humans and has a marked hypoalgesic effect on high intensity nociceptive stimuli.

Long-term potentiation of C-fiber-evoked potentials in the rat spinal dorsal horn is prevented by spinal N-methyl-D-aspartic acid receptor blockage

Long-term potentiation (LTP) of synaptic potentials is a fundamental mechanism of memory formation in the hippocampus. Here, we have characterized long-term changes of field potentials which were evoked in the lumbar spinal dorsal horn by supramaximal electrical stimulation of the sciatic nerve in urethane anesthetized rats. The field potentials had high thresholds (> or = 7 V), long latencies (90-130 ms, corresponding to conduction velocities between 1.2 and 0.85 m/s) and were not affected by spinalization (at C5-C6) or muscle relaxation (with pancuronium), i.e. the potentials were probably evoked by afferent C-fibers. Tetanic electrical stimulation (0.5 ms pulses, 30-40 V, 100 Hz, given in 4 trains of 1 s duration at 10 s intervals) of sciatic nerve induced in all 9 rats tested a LTP of amplitude of the C-fiber-evoked potential throughout recording periods which lasted between 4 and 9 h. Mean potentiation ranged from +71% to +174%. Superfusion of spinal cord with N-methyl-D-aspartic acid (NMDA) receptor antagonist D-(-)-4-(3-phosphonopropyl)piperazine-2-carboxylic (500 nM), which has little effect on the amplitude of C-fiber-evoked potentials, completely blocked LTP induced by tetanic stimulation in all five rats tested. Superfusion of spinal cord with NMDA (1 microM, 10 microM or 50 microM) induced LTP in only 2 out of 8 rats. This is the first report showing that LTP of C-fiber-evoked field potentials in the spinal dorsal horn in vivo may last for more than 8 h. This LTP in the spinal dorsal horn may underlie plastic changes of spinal nociception.

Beneficial effects of ketamine in a chronic pain state with allodynia, possibly due to central sensitization

Allodynia is a well-known component of neuropathic pain resulting from injury to the nervous system. Clinical pain states with allodynia in connection with longstanding superficial wounds have, however, not been reported in the literature. In this case a chronic pain state developed in a previously healthy 17-year-old girl in and around a persistently suppurating appendectomy wound. There was no spontaneous pain but pronounced allodynia in the wound and in the surrounding skin. Quantitative thermal tests showed abnormal thresholds for several sensory modalities confirming abnormal processing of sensory input from the involved area. The pattern of sensory abnormalities evaluated with thermal testing changed transiently and the allodynia diminished during a phentolamine block. Since the pain responded poorly to opioids and ketamine has been reported to reduce allodynia, it was administered in a sub-dissociative bolus dose during wound dressing. The wound was essentially unchanged after treatment for 3 months but the allodynia and sensory aberrations had decreased significantly. We interpret these results as a de-sensitizing effect in the long term of repeated NMDA-receptor blockade by ketamine in a chronic pain state, with indications of central sensitization, partially maintained by sympathetic activity.

The experience of chronic nonmalignant pain

This article reports the results of a survey of 204 persons with chronic nonmalignant pain who were members of a national self-help organization. The survey evaluated the organization, explored the perceived effect of pain on quality of life, and assessed experiences with and perceptions of health-care providers. Response rate was 40%. Of survey respondents, 50% reported inadequate pain relief. Respondents identified depression as one of the worst problems caused by their chronic pain: 50% reported that they had considered suicide due to feelings of hopelessness associated with their pain, 51% reported taking only as much medication as prescribed, and 44% reported taking less medication than prescribed. Further investigation is needed to describe the personal impact of chronic nonmalignant pain.

The effects of the clinically tested NMDA receptor antagonist memantine on carrageenan-induced thermal hyperalgesia in rats

This study tested the prophylactic and the therapeutic efficacy of memantine (1-amino-3,5-dimethyl-amandate), a clinically tested N-methyl-D-aspartate (NMDA) receptor antagonist, in suppressing carrageenan-induced thermal hyperalgesia in rats. Rats were injected with 0.1 ml of 1% carrageenan solution s.c. into the right hindpaw, and exhibited hyperalgesia in the injected paw as evidenced by a significant reduction of withdrawal latencies from baseline 1, 3, 5, and 24 h following carrageenan. Prophylactic injection of memantine, 10 and 15 mg/kg, significantly suppressed the hyperalgesia 1, 3, and 5 h post-carrageenan, with maximal effects of 70% (10 mg/kg) and 90% (15 mg/kg) at 1 h post-carrageenan. Therapeutic injection of 10 mg/kg of memantine (2.5 h post-carrageenan) had no effect. The 15 mg/kg dose produced a small effect (peak of 44%) at 3.5 h but not at a statistically significant level, and had no effect 5 h post-carrageenan. This study provides evidence that memantine produces primarily a prophylactic effect (and has only a tendency to produce a therapeutic effect) on carrageenan-induced hyperalgesia at doses that do not significantly alter other motor behaviors.

NMDA causes release of nitric oxide from rat spinal cord in vitro

Anatomic studies have localized nitric oxide synthase (NOS) activity in the rat spinal cord dorsal horn and intermediolateral cell column. Behavioral and electrophysiologic studies suggest that N-methyl-D-aspartate (NMDA) stimulates nitric oxide synthesis in the dorsal horn. This report describes a novel bioassay to determine directly in vitro whether NMDA causes release of nitric oxide from rat spinal cord. Modified Krebs-Henseleit solution at 26 degrees C was perfused over spinal cord slices from adult male rats, then dropped onto a ring of endothelium-denuded rat aorta. Following preconstriction with phenylephrine, NMDA (10(-10) to 10(-3) M) alone or with other drugs was added to the perfusion solution and vascular tension measured. NMDA-containing solutions applied directly on the preconstricted vessels without exposure to spinal cord tissue had no effect on vessel tone. In contrast, NMDA via the spinal cord perfusion caused concentration-dependent vascular relaxation, which was blocked by MK-801, hemoglobin, methylene blue, and several arginine analogues which inhibit NOS. [14C]citrulline assay suggested NOS in rat spinal cord was non-endothelial in nature. NMDA perfusion of spinal cord slices in vitro causes vascular relaxation in this bioassay due to actions on NMDA receptors and which is consistent with release of nitric oxide. These results support previous anatomical, behavioral, and electrophysiologic studies in rat spinal cord and describe a novel, sensitive, and simple bioassay for nitric oxide release from neural tissue in vitro.

Evidence for an inhibitory role of central histamine on carrageenin-induced hyperalgesia

The effects of intracerebroventricular (i.c.v.) injection of histamine, the H1 agonist 2-methyl-histamine and the H2 agonist dimaprit were tested on carrageenin induced hyperalgesia by the Randall-Selitto paw pressure test in the rat. Treatment with histamine (0.1, 0.2, 0.4 mumol/rat, i.c.v.) 150 min after intraplantar carrageenin (0.1 ml of 1% solution) caused a significant increase of paw pressure thresholds in inflamed (but not in non-inflamed) paws. The magnitude and the duration of the antinociceptive effects of histamine were dose-dependent. Administration of 2-methyl-histamine (0.2, 0.4, 0.8, 1.0 mumol/rat, i.c.v.) and dimaprit (0.1, 0.2, 0.4, 0.8 mumol/rat, i.c.v.) also displayed dose-dependent blockade of carrageenin-induced hyperalgesia. Antinociceptive ED50 values calculated 30 min after drug treatments were: histamine 0.18 mumol/rat; 2-methyl-histamine 0.65 mumol/rat; dimaprit 0.33 mumol/rat. These data indicate that histamine through central H1 and H2 receptors exerts an inhibitory role in the control of nociception in pain resulting from inflammation.

Pre treatment with MK-801, a non-competitive NMDA antagonist, prevents development of mechanical hyperalgesia in a rat model of chronic neuropathy, but not in a model of chronic inflammation

In the rat, loose ligation of the sciatic nerve results in behavioural signs of hyperalgesia reminiscent of neuropathy in man. A further rat model, of chronic inflammatory hyperalgesia, is produced by intraplantar administration of Freund's complete adjuvant (FCA). We report here that preemptive administration of a non-competitive antagonist of the glutamate N-methyl-D-aspartate (NMDA) receptor, MK-801 (0.3 mg kg-1, s.c.) 30 min prior to and twice daily for a further 8 days following loose ligation of the sciatic nerve, blocks the development of mechanical hyperalgesia measured 27 days later. In contrast, MK-801 administration using the same dosing regimen did not significantly inhibit the hyperalgesia apparent 15 days following i.pl. administration of FCA. Our results suggest that the mechanisms responsible for the development of mechanical hyperalgesia associated with chronic nerve injury and chronic inflammation differ.

Systemic or intracerebroventricular injection of NMDA receptor antagonists attenuates the antinociceptive activity of intrathecally administered NMDA receptor antagonists

We have previously reported that the response latency in the mouse hot-plate test is affected differently by spinal intrathecal (i.t.) injection of competitive and non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, in that only the former produces an antinociceptive effect. Since the lipophilic non-competitive antagonists will redistribute rapidly from the spinal injection site, it is conceivable that they reach sites where they counteract the spinal antinociceptive effect. In the present study, we have tested this hypothesis by comparing the antinociceptive effect of the competitive NMDA receptor antagonist CGS 19755 and the non-competitive NMDA receptor antagonist MK-801 after i.t., intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administration as well as after combinations thereof. CGS 19755 injected i.p. or i.c.v. and MK-801 injected i.p. or i.t. attenuated the antinociceptive effect of i.t. injected CGS 19755. Both i.p. and i.c.v. administration of either CGS 19755 or MK-801 dose-dependently impaired motor function without producing antinociceptive effects. Thus, the effect of CGS 19755 and MK-801 on the motor system was found to be separate from their antinociceptive effect. In a separate experiment, changes in hind-paw skin temperature were excluded as a possible confounding factor. These findings demonstrate that supraspinal systems can limit the spinal antinociceptive effect of NMDA receptor antagonists.

[Perioperative analgesia in adults : The concept of balanced analgesia.]

The spectrum of perioperative pain treatment is discussed in the present review. The analgesic efficacy of various drugs and the dosage methods of administration and side effects reported for them in such reference works as the practical guide on the management of acute pain recently published by the International Association for the Study of Pain (IASP) are described. Effective postoperative analgesia can diminish stress reactions following surgery. Recovery and physical mobilization are improved as the result of adequate treatment. Results obtained in recent studies have demonstrated that primary adaptive hyperalgesia in the peripheral nociceptive area may develop into secondary maladaptive hypersensibility with a high degree of nociceptive excitability and pain. Chronic pain can develop following acute alterations. Increasing nociceptive activity of primary afferents induces alterations in the dorsal horn of the spinal cord. These alterations imply an increase in the excitability of nociceptive neurons, which has been described as neuronal plasticity. Clinical results have demonstrated prevention or delay of acute postoperative pain after injection of local anaesthetics, analgesic premedication or epidural injection of opioids just before the start of surgery. Continuous perioperative spinal analgesia has contributed significantly to the prevention of phantom limb pain in patients undergoing amputation of extremities. The development of pain memory may be prevented as a result of effective acute pain treatment. Several changes to the terminology of acute pain treatment for animal and clinical studies have recently been proposed, including such new terms as preemptive analgesia and pain prevention, which indicate new strategies in the treatment of postoperative pain. The concept of balanced analgesia refers to a strategy for the improvement of analgesic efficacy as a result of a combination of drugs with different local actions on nociception. The combination of systemic analgesics (opioids in low dosages) with nonsteroidal analgesics (e.g. diclofenac or ketorolac) and the combination of regional analgesic procedures with opioids have been shown to be very effective. The peripheral action of morphine offers new options in pain therapy. Different regional analgesic techniques and continuous infusions of local analgesics are described. The synergistic action of low dosages of local anaesthetics (bupivacaine 0.006%) with low dosages of fentanyl 0.0001-0.0002% are of interest for the treatment of obstetric pain and for pain in opioid-tolerant patients. Investigations performed by the author of this review have shown that epidural infusion of highly diluted mixtures of bupivacaine/fentanyl is highly effective in the analgesic treatment of patients undergoing prostatectomy, providing excellent physical mobilization. The potential dangers of drug combinations and contraindications are also discussed. The concept of using balanced analgesia to induce additive or synergistic effects following the administration of analgesic drugs requires further clinical studies.

Management of postoperative pain: influence of anesthetic and analgesic choice

Improved control of postoperative pain is being increasingly scrutinized yet concomitantly demanded by patients, physicians, and even the federal government. Our ever-increasing subspecialization in medicine has compartmentalized much of perioperative care and has created substantial difficulty for physicians in understanding the overall influence of other physicians' perioperative decisions, including control of pain. Clearly, intraoperative anesthetic management can affect patients' pain and perioperative course remote from the surgical procedure through modulation of analgesic and perioperative stress responses. Additionally, outcome studies show that provision of improved analgesia and minimization of the perioperative stress response enhance clinical outcome in both low- and high-risk patients. This article highlights new information on how anesthetic and analgesic management influences perioperative pain and decreases the incidence of complications in surgical patients.