The contribution of pain to disability in experimentally induced arthritis

Effects of long term polyarthritis and subsequent NSAID treatment on activity with disassociation of tactile allodynia in the mouse

Chronic pain has profound effects on activity. Previous reports indicate chronic inflammatory conditions result in reduced activity which normalizes upon pain treatment. However, there is little systematic investigation of this process. Rheumatoid arthritis is an autoimmune disorder that causes significant joint pain. The K/BxN serum transfer mouse has been characterized as a model for rheumatoid arthritis and chronic pain. We investigated the activity of mice following K/BxN serum transfer vs. control serum and observed the activity changes following delivery of an NSAID, ketorolac. Previous studies have used running wheels and laser beams to monitor activity; we chose to validate a model using cost-effective infrared sensors on individual cages. Each mouse had its baseline activity obtained, which showed significant variation between individual C57Bl/6 mice. Arthritic mice had significantly decreased activity for only the first 11 nights. Conversely, previous work has shown that these animals display tactile allodynia that persists for at least 45 days. Mice were treated with ketorolac in their drinking water (10mg/kg, 15mg/kg, or 20mg/kg) for nights 6-8. The two highest doses showed significant normalization of activity levels. Four nights after ketorolac was stopped, treated animals were still significantly more active than control. The reversal of the reduced activity provides support that the depression relates to the arthritic pain state of the animal. These results indicate the efficacy of activity monitoring to better investigate behavior in persistent pain states. However, insofar as depressed activity reflects pain and disability, the present work raises questions as to the relevance of the tactile thresholds in defining behaviorally relevant pain states.

Evaluation of long-term antinociceptive properties of stabilized hyaluronic acid preparation (NASHA) in an animal model of repetitive joint pain

Introduction

Clinical trials provided controversial results on whether the injection of hyaluronan preparations into osteoarthritic joints reduces pain. Problems of clinical studies may be the substantial placebo effects of intra-articular injections, different severity and rate of progression of the disease and others. We hypothesize that the use of preclinical pain models may help to clarify whether a certain hyaluronan exerts antinociceptive effects upon intra-articular injection. In the present study we tested in the bradykinin/prostaglandin E₂ (PGE₂) model primarily the putative antinociceptive effect of stabilized hyaluronic acid from a non animal source (NASHA), a stabilized hyaluronic acid based gel for intra-articular treatment of OA. We established a dose-response relationship for NASHA and we compared NASHA to other hyaluronans with different formulations that are in clinical use.

Methods

To induce transient joint pain episodes bradykinin and PGE₂ were repetitively administered intra-articularly and unilaterally into rat knee joints during short anaesthesia. After establishment of the predrug nociceptive responses, a single intra-articular injection of saline or NASHA at different concentrations was administered and pain responses to further bradykinin/PGE₂ injections were monitored up to 56 days after NASHA. Furthermore, the obtained effective dose was compared to clinically defined concentrations of Hylan GF20 and sodium hyaluronate. The primary outcome measures were primary mechanical hyperalgesia at the knee joint and pain-induced weight bearing.

Results

On day 1 after injection, all tested hyaluronan preparations showed an antinociceptive effect >50% compared to saline. Single injections of higher doses of NASHA (50, 75 and 100 μl) were antinociceptive up to 56 days. When injection volumes in rat knee joints were adapted to clinical injection volumes in humans, the antinociceptive effects of the cross-linked NASHA and Hylan GF20 had a longer duration than that of the non cross-linked sodium hyaluronate (with a slightly better effect of NASHA than Hylan GF20).

Conclusions

In the bradykinin/PGE₂ model of joint pain a single injection of all hyaluronan preparations provided significant antinociceptive effects compared to saline. It appeared that the duration of the antinociceptive effect of the cross-linked hyaluronan preparations NASHA and Hylan GF20 was more prolonged. In addition, the gel beads structure allowing only a slow release of hyaluronic acid (NASHA) may even enhance this prolonged antinociceptive effect.

Enhancement of the anti-inflammatory and anti-arthritic effects of theophylline by a low dose of a nitric oxide donor or non-specific nitric oxide synthase inhibitor

BACKGROUND AND PURPOSE

Although there are many new specific phosphodiesterase inhibitors with anti-inflammatory activity, none have yet reached the market because of their low therapeutic efficacy. Our study was aimed to evaluate the anti-inflammatory and anti-arthritic effect of an established phosphodiesterase inhibitor, theophylline, and to investigate the effect of the nitric oxide (NO) donor, sodium nitroprusside (SNP) or NO synthase inhibitor, L-N(G)-monomethyl arginine (L-NMMA) on its actions.

EXPERIMENTAL APPROACH

The effects of theophylline alone and combined with SNP or L-NMMA on the pathogenesis of adjuvant-induced arthritis in rats were evaluated.

KEY RESULTS

Prophylactic or therapeutic doses of theophylline significantly ameliorated the pathogenesis of adjuvant arthritis in rats as evidenced by a significant decrease in the arthritis index, hind paws volume, ankle joint diameter, fever, body weight loss and hyperalgesia in a dose-dependent manner. Inflammatory cellular infiltrate in synovium of ankle joint and pannus formation were also markedly inhibited. Interleukin-10 (IL-10) levels were significantly increased in arthritic rats given theophylline alone or in combination with either SNP or L-NMMA. Co-administration of a low dose of SNP or L-NMMA enhanced significantly the anti-inflammatory and anti-arthritic effect of theophylline. In contrast, a high dose of SNP counteracted the anti-inflammatory and anti-arthritic effects of theophylline.

CONCLUSIONS AND IMPLICATION

These findings confirm the anti-inflammatory and anti-arthritic activities of theophylline and suggest a new approach to enhance the anti-inflammatory and anti-arthritic effects of theophylline would be to administer it in combination with a low dose of a NO donor or a non-specific NO synthase inhibitor.

Neurogenic inflammation and arthritis

Inflammation and inflammatory diseases are sexually dimorphic, but the underlying causes for this observed sexual dimorphism are poorly understood. We discuss neural-immune mechanisms that underlie sexual dimorphism in three critical aspects of the inflammatory process-plasma extravasation, neutrophil function, and inflammatory hyperalgesia. Plasma extravasation and accumulation/activation of leukocytes into tissues are critical components in inflammation and are required for several other aspects of the inflammatory response. Pain (hyperalgesia) also markedly influences the magnitude of other components of the inflammatory response and induces a feedback control of plasma extravasation and neutrophil function. More important, this feedback control itself is powerfully modulated by vagal afferent activity and both the function of the primary afferent nociceptor and the modulation of inflammatory hyperalgesia by vagal afferent activity are highly sexually dimorphic.

Pathogenesis of sciatic pain: a study of spontaneous behavior in rats exposed to experimental disc herniation

STUDY DESIGN

A new way to study pain in experimental animals without handling of the animals and based on registration of spontaneous behavior using video recordings.

OBJECTIVES

To evaluate if experimental disc herniation in the rat may induce changes in spontaneous behavior.

SUMMARY OF BACKGROUND DATA

The knowledge regarding the basic pathophysiologic mechanisms of sciatica has increased dramatically during the last decade. However, studies have mainly assessed nerve dysfunction rather than pain. Existing methods to study pain generally comprise a certain amount of handling and registration of changes in sensory thresholds. In the present study we introduce a new way to assess pain that focuses on changes in behavior rather than on changes in thresholds.

METHODS

Forty rats were divided equally into four experimental series: sham exposure of the left L4 dorsal root ganglion, exposure of the left L4 dorsal root ganglion and incision of the L4-L5 disc, exposure and slight displacement of the left L4 dorsal root ganglion, and combination of disc incision and displacement. The rats were videotaped the day before surgery and on day 1, 3, 7, 14, and 21 after surgery. Spontaneous behavior was categorized into 10 behaviors and recorded during 20 minutes of observation.

RESULTS

Disc incision and displacement per se did not induce any behaviors different from that observed in the sham-operated group. In the series with the combination of disc incision and displacement there was increased focal pain, seen as increased lifting of the hind paw on the operated side and increased rotation of the head toward the operated side. This pain pattern was most pronounced the day after surgery. Fourteen days after surgery there were no detectable differences in behavior between this group and the sham group. At day 21 after surgery, however, another picture of increased immobility and decreased locomotion was seen in this group, possibly indicating more generalized pain.

CONCLUSIONS

The study demonstrates that it is possible to detect changes in spontaneous behavior after experimental disc herniation. However, such changes may only be seen if disc incision and slight mechanical deformation are combined. This is in agreement with previous clinical and experimental observations. The present model allows for convenient assessment of pain in a way that focuses on spontaneous behavior rather than changes in pain thresholds and that reduces the interference of the researcher and environment on the outcome of the assessment.

Acute non-traumatic pain increases the hepatic amino- to urea-N conversion in normal man

BACKGROUND/AIM

Severe stress results in a catabolic state with nitrogen (N) loss via hepatic urea synthesis, and in most situations a sensation of pain. Our purpose was to establish whether pain per se upregulates liver function as to urea synthesis.

METHODS

Ten healthy male volunteers were investigated on 3 occasions in a crossover design. Self-controlled electrical pain was applied to the abdominal skin for 30 min to an intensity of 8 on a visual analogue scale from 0 to 10. Next, the electric profile was reproduced during local analgesia (mepivacaine 2.5 mg/kg bw), and the pain was scored to only 0.5. Finally, there was a control experiment with no intervention. Alanine infusion (1 mmol/kg/h) was started 2 h before intervention and continued throughout the investigation. Urea-N synthesis rate (UNSR) was estimated hourly as urinary excretion corrected for accumulation in body water and gut hydrolysis.

RESULTS

Pain increased the Functional Hepatic Nitrogen Clearance (FHNC) assessed by the ratio UNSR/AAN (in the 3 h following pain) by 20% (22.7+/-1.2 vs 19.0+/-0.7 l/h (control), p<0.05). FHNC during local analgesia was in between (21.1+/-1.1 l/h) but not significantly different from either of the two other experiments. Mean blood amino-N concentration (AAN) and mean UNSR were comparable in the three situations. There was no difference in serum glucagon among experiments, but pain increased serum cortisol (452+/-15 vs 233+/-20 nmol/l (control), p<0.001) and plasma adrenaline (104+/-16 vs 58+/-9 pg/ml (control), p<0.05).

CONCLUSION

Acute, severe atraumatic pain induces an increase in the ability of the liver to convert amino- to urea-N, and thus acts as a catabolic stimulus via regulation of liver function. The measurements of known endocrine regulators of urea synthesis do not explain the phenomenon. The present data, however, suggest the hypothesis that the effects of pain were attenuated by local analgesia. If this is confirmed by further experiments, it would indicate a signal transmission to the liver which has not been previously described.

Pain-related disability and effects of chronic morphine in the adjuvant-induced arthritis model of chronic pain

Functional disability has been identified as one of the most important aspects of chronic pain, yet modeling pain-related disability has received little attention. Adjuvant-induced arthritis was induced, and one group of arthritic rats was implanted with SC 75-mg morphine pellets 1 week postadjuvant, and reimplanted every 2 weeks thereafter. The results confirm that the rodent adjuvant-induced arthritis model of severe chronic pain can be used to model pain-related disability: spontaneous activity levels and ambulatory function were reduced in arthritic rats and they exhibited substantial weight loss. The results of the present study suggest that the operant delayed nonmatching-to-position task can be used as a measure of pain-related disability, which may be especially relevant to the effects of chronic pain on performance in a work setting. The delayed nonmatching-to-position operant bar-pressing task is an "apical" test that is sensitive to deficits across a wide range of behavioral functions: motor ability, attention, motivation, learning, and memory, and arthritic rats were severely impaired in this task. In addition, analgesic treatments that impair functional abilities in normal healthy rats may actually improve the performance of rats exhibiting pain-related disability. Previous work demonstrated that acute morphine injections of only 4 mg/kg impaired performance in the delayed matching-to-position task. The results of the present study demonstrate that chronic morphine attenuates the degree of pain-related disability exhibited by arthritic rats in the test of ambulatory function and the delayed nonmatching-to-position bar-pressing test. These results demonstrate that novel analgesic treatments can be screened preclinically, both with respect to their direct analgesic effects, and with respect to their ability to reduce pain-related disability.

Localization of bradykinin-like immunoreactivity in the rat spinal cord: effects of capsaicin, melittin, dorsal rhizotomy and peripheral axotomy

A putative role for bradykinin has been proposed in the processing of sensory information at the level of the spinal cord. Autoradiographic studies have demonstrated the presence of B2 kinin receptor binding sites in superficial laminae of the dorsal horn and a down-regulation of those receptors in rat models of pain injury. In this study, classical immunocytochemistry and confocal microscopy immunofluorescence were used first to localize bradykinin-like immunoreactivity in all major spinal cord segments of naive rats; second, to assess bradykinin-like immunoreactivity changes that occur in animals subjected to various chemical treatments and surgical lesions. High densities of bradykinin-like immunoreactivity were observed in motoneuron of the ventral horn, deeper laminae and nucleus dorsalis of the dorsal horn. Higher magnification of ventral horn showed strong immunostaining of motoneuron perikaryas and their proximal processes. Two types of bradykinin-like immunoreactivity immunostained cellular bodies were observed in deeper laminae of the dorsal horn. These interneurons, morphologically corresponding to islets and antenna-type cells project dendrites to adjacent laminae. Furthermore, numerous strongly marked dendrites, transversally cut, suggest the presence of projection neurons to higher cervical centres. Following unilateral lumbar dorsal rhizotomy (L1-L6) or peripheral lesion of the sciatic nerve, important increases of bradykinin-like immunoreactivity were found in laminae III and IV of the ipsilateral dorsal horn. In contrast, significant decreases of immunodeposits were observed in both cell bodies and numerous dendrites of motoneuron surrounding neuropil. Specific destructions of sensory afferent fibres with capsaicin or selective activation of kallikreins with melittin caused increases of bradykinin-like immunoreactivity in both the dorsal and ventral horns of the spinal cord. These results which demonstrate the cellular localization of bradykinin-like immunoreactivity in both dorsal and ventral horns of the rat spinal cord, further reveal the plasticity of this non-sensory peptidergic system following various chemical and surgical treatments. Hence, these anatomical findings along with earlier functional and receptor autoradiographic studies reinforce the putative role of bradykinin in sensory function.

Attenuation of pain-related hyperventilation in adjuvant arthritic rats with adrenal medullary transplants in the spinal subarachnoid space

The adjuvant arthritic rat model has been utilized for the study of chronic pain, as polyarthritic rats present a variety of symptoms similar to those seen in human chronic pain conditions. In particular, hyperventilatory responses are notable in both and may more accurately reflect basal ongoing pain than do evoked noxious stimuli. To assess whether adrenal medullary transplants in the spinal subarachnoid space can alleviate basal arthritic pain, respiratory parameters were determined using whole body plesthmography in polyarthritic rats. Arthritis was induced by inoculation with an intradermal injection of complete Freund's adjuvant. Steady-state ventilation was monitored at weekly intervals in arthritic animals with adrenal medullary or control striated muscle transplants. Results revealed that adjuvant arthritis produced significant hyperventilation in animals with control transplants, as indicated by increased tidal volumes and minute ventilation, which paralleled the progression of the inflammatory process. In contrast, this hyperventilation was eliminated by adrenal medullary transplants. A role for catecholamines and opioid peptides released from the transplants was suggested by the reversal of these effects with phentolamine and naloxone. In addition, the retardation in weight gain normally observed in polyarthritic animals was markedly attenuated by adrenal medullary, but not control transplants. These findings indicate that adrenal medullary transplants in the spinal subarachnoid space can alleviate basal chronic pain as assessed in adjuvant arthritis.

Update on cellular transplantation into the CNS as a novel therapy for chronic pain

The transplantation of cells that secrete neuroactive substances with analgesic properties into the CNS is a novel method that challenges current approaches in treating chronic pain. This review covers pre-clinical and clinical studies from both allogeneic and xenogeneic sources. One cell source that has been utilized successfully is the adrenal chromaffin cell, since such cells constitutively release catecholamines, opioid peptides, and neurotrophic factors; release can be augmented with nicotine. Other graft sources include AtT-20 and B-16 cell lines which release enkephalins and catecholamines, respectively. For grafting in rodents, adrenal medullary tissue pieces are transplanted to the subarachnoid space. Chromaffin cell transplants can decrease pain sensitivity in normal rats using standard acute pain tests (paw-pinch, hot-plate, and tail-flick). In addition, transplants can restore normal pain thresholds in rodent models of chronic pain (formalin, adjuvant-induced arthritis, and sciatic-nerve tie) which closely similate the pathologies of human chronic pain conditions. Xenografts have been studied due to concerns that future application for human pain may be limited by donor availability. Despite immune privileges of the CNS, xenografts require at least short-term immunosuppression to obtain a viable graft. Cell encapsulation is one method of sustaining a xenograft (in rat and human hosts) while circumventing the need for immunosuppression. Clinical studies have been initiated for terminal cancer patients with promising results as assessed by markedly reduced narcotic intake, visual analog scale ratings, and increased CSF levels of catecholamines and met-enkephalin.

Adrenal medullary grafts suppress c-fos induction in spinal neurons of arthritic rats

Expression of immediate-early genes such as c-fos is thought to reflect patterns of neuronal activity in the central nervous system. Prolonged increases in Fos-protein-like-immunoreactivity (FOS-LI) are seen in the dorsal horn of adjuvant arthritic rats, and parallel increased pain behavior. Grafts of adrenal medullary, but not control tissue, into the spinal subarachnoid space reduce pain behavior and suppress the induction of spinal Fos-LI in arthritic rats. This reduction is particularly marked in superficial laminae (I-II), but is also significant in deeper laminae (III-IV and V-VI). The results of this study suggest that adrenal medullary transplants reduce spinal cord hyperactivation consequent to painful peripheral inflammation.

Effects of the molecular weight of hyaluronic acid and its action mechanisms on experimental joint pain in rats

OBJECTIVES

It has been shown previously that hyaluronic acid (HA) has an analgesic action on bradykinin induced pain in the knee joints of rats. This study further clarifies the effects of the molecular weight of HA and its mechanism of action in the same model using HA of molecular weight 800 to 2.3 x 10(6) daltons and a bradykinin antagonist.

METHODS

Bradykinin and the test HA preparations were given to rats by intra-articular injection, and the severity of pain was evaluated by a change in the walking behaviour.

RESULTS

HA with a molecular weight greater than 40 kilodaltons produces analgesic effects with a simultaneous or earlier injection. The ID50 values of HA with molecular weight 40, 310, 860, and 2300 kilodaltons were greater than 2.5, 0.6, 0.07, and 0.06 mg/joint respectively. The duration of the analgesic effect of 860 and 2300 kilodalton HA was 72 hours at 10 mg/ml, whereas that of 310 kilodalton HA was short, being undetectable after 24 hours. The analgesic action of HA of 860 kilodaltons was not changed by pretreatment with four saccharide HA and inhibited by pretreatment with HA larger than six to eight saccharides, capable of binding to HA receptors. Further, HA did not interfere with the analgesic action of the bradykinin antagonist, indicating that HA does not directly bind with bradykinin receptors.

CONCLUSIONS

HA with a molecular weight of greater than 40 kilodaltons produced an analgesic effect, and HA of 860 and 2300 kilodaltons produced high and long-lasting analgesia. These effects of HA appear to be caused by the interaction between HA and HA receptors.

The pharmacologic evaluation of locomotor activity versus inflammatory parameters in rat adjuvant arthritis

Adjuvant-induced arthritis (AA) is an experimental model of inflammatory joint disease in the rat which mimics rheumatoid arthritis. Although paw inflammation (e.g., swelling) is commonly used to monitor the efficacy of antiarthritic drugs, a reduction in locomotor function may provide a more sensitive evaluation of "functional disability" in AA rats. The purpose of the present study was to investigate the effect of dietary therapy with prednisolone or ibuprofen on locomotor activity as well as arthritic symptoms in established AA (days 20-42). AA rats demonstrated an increase in arthritis scores, spleen weights, fibrinogen, and WBC along with a reduction in locomotor function. Prednisolone (2 mg/kg/day) exhibited a positive therapeutic effect on all these parameters. Ibuprofen (50 mg/kg/day) consistently lowered arthritis scores and fibrinogen; however, locomotor function only improved on day 35. In conclusion, the measurement of locomotor activity in concert with other experimental parameters may provide a more meaningful evaluation of disease severity or improvement in AA.

Anatomy of the rat knee joint and fibre composition of a major articular nerve

Several recent reports discuss the role of joint nerves in arthritis. Many of these are based on studies in the rat. The aim of this study is to examine the anatomy of the rat knee joint, in search for a primary articular nerve, and to analyze the fibre composition of that nerve. The results show that the structure of the joint differs in some respects from the human knee. At the upper end of the bony patella a cartilaginous patella extends proximally, forming the anterior wall of the suprapatellar bursa. Distinct collateral ligaments are integrated in the joint capsule. The extensor digitorum longus muscle bridges the knee joint, originating from the lateral femoral epicondyle. The well-developed menisci contain pyramid-shaped ossicles. The cruciate ligaments are arranged like in the human knee. A large posterior (PAN) and a small medial (MAN) articular nerve can be identified. The PAN is composed of some 400 axons, about 80% of which are unmyelinated. All myelinated fibres are sensory. They present a unimodal size spectrum with a size range of 1-8 microns, and a predominance of small fibres. Specific denervations indicate that about 1/3 of the unmyelinated axons represent afferents, and some 2/3 are sympathetic efferents. Interestingly, neonatal capsaicin treatment did not influence the number of unmyelinated PAN axons. The functional significance of the numerous unmyelinated sympathetic and sensory PAN axons in the normal knee joint remains to be elucidated.

Increased calcitonin gene-related peptide (CGRP), substance P, and enkephalin immunoreactivities in dorsal spinal cord and loss of CGRP-immunoreactive motoneurons in arthritic rats depend on intact peripheral nerve supply

The distribution of peptides thought to be involved in pain modulation--substance P, calcitonin gene-related peptide (CGRP), and enkephalin--were studied in the spinal cord and dorsal root ganglia of polyarthritic rats and in rats with one sciatic nerve sectioned prior to induction of arthritis. In arthritic rats there was a bilateral increase of CGRP- and substance P-immunoreactive fibers and appearance of enkephalin-immunoreactive cell bodies in the dorsal horn of the lumbar (L4) spinal cord when compared to controls. In the corresponding dorsal root ganglia there were significant increases of CGRP- (P less than 0.02) and substance P- (P less than 0.001) immunoreactive cell bodies compared to controls. In the ventral horn of the control rats CGRP-immunoreactive motoneurons were abundant but were significantly (P less than 0.001) reduced in the arthritic spinal cord. Less pronounced changes were seen in the contralateral L4 spinal cord of arthritic rats with unilateral sciatic nerve section. In the ipsilateral dorsal horn, however, CGRP- and substance P-immunoreactive fibers were markedly depleted, and no enkephalin cell bodies were present. Furthermore, a number of CGRP-immunoreactive motoneurons were observed. In the ipsilateral L4 ganglia CGRP- (P less than 0.02) and substance P- (P less than 0.02) immunoreactive cells were significantly decreased compared to the contralateral side. The data suggest that pain perception is linked to complex interactions between CGRP, substance P, and enkephalin in sensory pathways and an intact peripheral input. The loss of CGRP-immunoreactive motoneurons may reflect muscular dysfunction associated with the arthritic condition.

Opioid systems in the response to inflammatory pain: sustained blockade suggests role of kappa- but not mu-opioid receptors in the modulation of nociception, behaviour and pathology

One day after intraplantar inoculation of Mycobacterium butyricum into the right hind-paw, unilaterally inflamed and control rats were implanted subcutaneously with osmotic mini-pumps delivering naloxone at 0.16 or 3.0 mg/kg/h or vehicle. As determined three days after implantation, 0.16 mg/kg/h of naloxone completely antagonized the antinociceptive action of the mu-agonist, morphine, but did not affect antinociception evoked by the kappa-agonist, U69,593. In contrast, at 3.0 mg/kg/h, naloxone blocked both morphine- and U69,593-induced antinociception. Thus, 0.16 mg/kg ("low dose") and 3.0 mg/kg ("high dose") of naloxone block mu, or mu- plus kappa-opioid receptors, respectively. Pumps were removed one week following their implantation. Inoculation was associated with a sustained hyperalgesia of the inflamed paw to noxious pressure, and elevation in resting core temperature, a loss of body weight, hypophagia, hypodipsia and a reduction in mobility. These parameters were differentially modified by the high as compared to the low dose of naloxone. Two days following implantation of pumps delivering the high dose of naloxone, the hyperalgesia of the inflamed paw was potentiated: by six days, this effect was lost. Further, one day after removal of pumps yielding the high dose, the inflamed paw showed a normalization of thresholds, that is a "rebound antinociception". One day later, this effect had subsided. In distinction, at no time did the low dose of naloxone modify nociceptive thresholds. The high dose of naloxone enhanced the reduction in body weight and food intake shown by unilaterally inflamed rats whereas the low dose was ineffective. Neither dose affected the reduction in water intake or hypothermia of unilaterally inflamed animals. The high dose of naloxone reduced the mobility of unilaterally inflamed rats whereas the low dose was ineffective. Finally, by 10 days following pump removal, pathology had transferred to the contralateral paw. In rats which had received the high but not the low dose, this transfer was blocked. It is concluded that blockade of kappa-opioid receptors with a high dose of naloxone experts pronounced functional effects in unilaterally inflamed rats. In distinction, selective blockade of mu-receptors with a low dose is ineffective. The changes seen include not only an enhancement of the hyperalgesia of the inflamed tissue, but also an exacerbation of variables (body weight, food intake and motility) which reflect pain states.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatostatin is increased in the dorsal root ganglia of adjuvant-inflamed rat

To determine whether biosynthesis of somatostatin is enhanced in the primary sensory neurons by inflammatory pain, we examined the effects of adjuvant inoculation on the content of immunoreactive somatostatin, mainly composed of somatostatin-14 and somatostatin-28, in the dorsal root ganglia and the spinal cord of the rat. The adjuvant inoculation, which produced long-lasting inflammation and hyperalgesia, increased the content of immunoreactive somatostatin, especially somatostatin-14, in the dorsal root ganglia at L4-L6 levels with no change in the dorsal and ventral horns of lumbar enlargement. Such an increase was enhanced by an intrathecal injection of colchicine (0.2 mg) that inhibits axonal flow of somatostatin. Chronic administration of the anti-inflammatory analgesic, sodium diclofenac (3 mg.kg-1.d-1), abolished an adjuvant-induced increase in the content of immunoreactive somatostatin in the dorsal root ganglia. These results suggest that the turnover (biosynthesis and axonal flow) of somatostatin in the primary sensory neurons is enhanced in the presence of persisting inflammatory pain, and support the idea that somatostatin-containing primary afferents are involved in the transmission of pain in the spinal dorsal horn.

Adrenal medullary implants in the rat spinal cord reduce nociception in a chronic pain model

Previous work in this laboratory has indicated that the transplantation of adrenal medullary tissue into the subarachnoid space of the rat spinal cord can reduce pain sensitivity to acute noxious stimuli, particularly following stimulation by nicotine. This most likely results from the stimulated release of opioid peptides and catecholamines from the transplanted chromaffin cells. However, chronic pain models may more closely resemble human clinical pain, and the arthritic rat model has been used for screening potential therapeutic strategies. The purpose of the present study was to assess the potential for adrenal medullary tissue implanted into the spinal subarachnoid space to alleviate chronic pain. Adrenal medullary tissue was implanted into adjuvant-induced arthritic rats, and changes in body weight and vocalization responses were monitored over the 10 week course of the disease. Results indicate that the severe weight reduction normally associated with this inflammatory arthritis was attenuated by adrenal medullary, but not control, implants. In addition, vocalizations were reduced in animals implanted with adrenal medullary, but not control tissue following nicotine stimulation. This reduction was blocked by the opiate antagonist, naloxone, and partially attenuated by the alpha-adrenergic antagonist, phentolamine. Together, these results suggest that the transplantation of adrenal medullary tissue into the subarachnoid space of the spinal cord may provide a local source of opioid peptides and catecholamines for the reduction of chronic pain.

Coping with arthritis pain. A review of the literature

Pain associated with arthritis is the primary reason patients with arthritis seek medical attention. The complex and multidimensional nature of pain among arthritis patients is examined. Self-reports of pain, the impact of pain, cognitive factors associated with pain, and the treatment of arthritis pain are reviewed. Psychosocial pain management programs emphasizing improved coping appear to be important as an adjunct to medical treatment. Implications for future research are discussed.

Neuromodulation of synovitis: capsaicin effect on severity of experimental arthritis

This study addresses the effect of capsaicin on the severity of inflammation in experimental arthritis in the cat. Animals were sensitized with methylated bovine serum albumin (mBSA) and sequential serum antibody levels measured by enzyme-linked immunosorbent assay (ELISA). Synovitis was induced by intra-articular injection of mBSA. Histopathology revealed marked inflammatory cell infiltration and synovial cell hypercellularity, in comparison with the saline-injected control joint which showed no synovitis. In animals given intra-articular capsaicin concurrently with mBSA, there was consistently a diminution in the severity of inflammation compared with contralateral joints receiving mBSA alone. In this experimental system capsaicin appears to moderate the severity of inflammation in feline antigen-induced arthritis.

Differential effects of acetylsalicylic acid and acetaminophen on sleep abnormalities in a rat chronic pain model

We studied the effects of two non-steroidal anti-inflammatory analgesics (NSAIAs), acetylsalicylic acid (ASA) and acetaminophen, on sleep patterns in rats with adjuvant-induced arthritis. We found that in the normal rat both NSAIAs reduced non-rapid eye movement (NREM) sleep. In arthritic rats ASA and acetaminophen had opposite effects on sleep. ASA increased wakefulness and decreased all sleep stages and acetaminophen decreased wakefulness and increased NREM sleep and paradoxical sleep during the light hours (the hours of maximal sleep in the normal rat). When the effects of severity of arthritis were factored out, both drugs still had large and significant effects on sleep and wakefulness. Thus, two prostaglandin synthetase inhibitors showed differential effects on sleep and wakefulness in the normal rat and in rats experiencing chronic pain. Although ASA is important in the treatment of pain in rheumatic diseases, it may contribute to abnormal sleep patterns.

Calcitonin gene-related peptide increases in the dorsal root ganglia of adjuvant arthritic rat

We examined the effect of adjuvant arthritis on the content of immunoreactive calcitonin gene-related peptide (iCGRP) in the dorsal root ganglia at L4-L6 levels and the spinal cord at a lumbar level in rats. Arthritis was induced by inoculating adjuvant into both hind-paws twice at a 10 day interval. In the arthritic rats 15 days after the first inoculation (day 15), the content of iCGRP was significantly increased in the dorsal root ganglia, with no change in the dorsal and ventral horns. The content in the dorsal root ganglia was still high on day 26 and had decreased by day 40. An intrathecal injection of colchicine (0.2 mg, 18 hr before killing) enhanced the increase of iCGRP in the dorsal root ganglia and decreased it in the dorsal horn of arthritic rats, although in noninoculated rats such treatment produced no significant changes in the content of iCGRP in both regions. The arthritis-induced increase in the content of iCGRP in the dorsal root ganglia was significantly reduced after treatment with the antiinflammatory analgesic, diclofenac sodium, in a dose of 3 mg/kg/day, PO for 10 days. Swelling and hyperalgesia in the hind-paw were depressed after such treatment. These results suggest that adjuvant arthritis with long-lasting inflammation with pain facilitates the turnover, especially biosynthesis, of CGRP in primary afferent neurons.

Sleep fragmentation in the arthritic rat

We examined the diurnal sleep-wake patterns in the adjuvant arthritic rat. In contrast to control rats, arthritic rats lacked a normal diurnal variation in sleep and wakefulness. Thus, arthritic rats exhibited no differences in the mean number or duration of bouts of sleep and episodes of wakefulness between light and dark hours. Arthritic rats also had a marked increase in the fragmentation of their sleep manifested by an increased number of sleep bouts and episodes of wakefulness and a decrease in the duration of episodes of deep sleep recorded both during the time of maximal sleep (08.00-11.00 h) and of maximal wakefulness (20.00-23.00 h). The possibility that the experience of chronic pain causes these marked changes in sleep patterns in the arthritic rat is discussed.

Team versus non-team outpatient care in rheumatoid arthritis. A comprehensive outcome evaluation including an overall health measure

In a rheumatology department, 2 randomized groups of female outpatients with rheumatoid arthritis were studied prospectively for 1 year. The outcome of multidisciplinary team care (T group, 31 patients) was compared with that of regular outpatient clinic care (NT group, 28 patients). Pharmacologic treatment and orthopedic specialist consultations were similar in both groups, but use of paramedical care was higher in the T group. Outcome measures of disease activity, specific joint function, and self-rated physical discomfort disclosed no significant differences between the 2 groups. Mental well-being increased in the T group. Overall health, measured by the Sickness Impact Profile, improved significantly only in the T group. This improvement was also significant compared with the NT group.