Intracerebroventricular injection of interleukin-1 beta induces hyperalgesia in rats

The exploration of active components of 701 Dieda Zhentong patch and analgesic properties on chronic constriction injury rats

An increasing number of traditional Chinese medicine(TCM) have been confirmed to possess analgesic bioactivity. 701 Dieda Zhentong patch(701-DZP) which includes 14 kinds of TCMs exhibited excellent efficacy in alleviating back or leg pain after a soft-tissue injury. In this study, UPLC/MS was used to construct the fingerprint of 701-DZP and excavate the potential bioactive ingredients of it. 21 compounds were detected and identified in the fingerprint including 12 compounds that pass through the skin and 6 compounds observed in the plasma. Then, the role of 701-DZP in neuropathic pain(NPP) was assessed by network pharmacology and CCI rats. 701-DZP inhibited pain sensitization(MWT and TWL) and the release of inflammation mediators(IL-1β and IL-6) in CCI rats which were in keeping with the core targets of the PPI network. The results of IHC and Western blot showed that the expression of the P2X3 receptor in the DRG and SC of CCI rats was significantly reduced after the treatment with 701-DZP. Moreover, the 701-DZP down-regulated the level of phosphorylation of ERK1/2 MAPK instead of P38 MAPK in the DRG of CCI rats. In conclusion, this study has clarified 6 potential analgesic active compounds of 701-DZP and explored the analgesic properties, which may inhibit the expression of the P2X3 receptor to reduce the release of inflammatory mediators based on the ERK1/2 MAPK pathway to alleviate the NPP.

Imbalance of Th1 and Th2 Cytokines and Stem Cell Therapy in Pathological Pain

The pathophysiological importance of T helper 1 (Th1) and Th2 cell cytokines in pathological pain has been highly debated in recent decades. However, the analgesic strategy targeting individual cytokines still has a long way to go for clinical application. In this review, we focus on the contributions of Th1 cytokines (TNF-α, IFN-γ, and IL-2) and Th2 cytokines (IL-4, IL-5, IL-10, and IL-13) in rodent pain models and human pain-related diseases. A large number of studies have shown that Th1 and Th2 cytokines have opposing effects on pain modulation. The imbalance of Th1 and Th2 cytokines might determine the final effect of pain generation or inhibition. However, increasing evidence indicates that targeting the individual cytokine is not sufficient for the treatment of pathological pain. It is practical to suggest a promising therapeutic strategy against the combined effects of Th1 and Th2 cytokines. We summarize the current advances in stem cell therapy for pain-related diseases. Preclinical and clinical studies show that stem cells inhibit proinflammatory cytokines and release enormous Th2 cytokines that exhibit a strong analgesic effect. Therefore, a shift of the imbalance of Th1 and Th2 cytokines induced by stem cells will provide a novel therapeutic strategy against intractable pain. It is extremely important to reveal the cellular and molecular mechanisms of stem cell-mediated analgesia. The efficiency and safety of stem cell therapy should be carefully evaluated in animal models and patients with pathological pain.

Morphine and Fentanyl Repeated Administration Induces Different Levels of NLRP3-Dependent Pyroptosis in the Dorsal Raphe Nucleus of Male Rats via Cell-Specific Activation of TLR4 and Opioid Receptors

Morphine promotes neuroinflammation after NOD-like receptor protein 3 (NLRP3) oligomerization in glial cells, but the capacity of other opioids to induce neuroinflammation and its relationship to the development of analgesic tolerance is unknown. We studied the effects of morphine and fentanyl on NLRP3 inflammasome activation in glial and neuronal cells in the dorsal raphe nucleus (DRN), a region involved in pain regulation. Male Wistar rats received i.p. injections of morphine (10 mg/kg) or fentanyl (0.1 mg/kg) 3 × daily for 7 days and were tested for nociception. Two hours after the last (19th) administration, we analyzed NLRP3 oligomerization, caspase-1 activation and gasdermin D-N (GSDMD-N) expression in microglia (CD11b positive cells), astrocytes (GFAP-positive cells) and neurons (NeuN-positive cells). Tolerance developed to both opioids, but only fentanyl produced hyperalgesia. Morphine and fentanyl activated NLRP3 inflammasome in astrocytes and serotonergic (TPH-2-positive) neurons, but fentanyl effects were more pronounced. Both opioids increased GFAP and CD11b immunoreactivity, caspase-1 and GSDMD activation, indicating pyroptotic cell death. The opioid receptor antagonist (-)-naloxone, but not the TLR4 receptor antagonist (+)-naloxone, prevented microglia activation and NLRP3 oligomerization. Only (+)-naloxone prevented astrocytes' activation. The anti-inflammatory agent minocycline and the NLRP3 inhibitor MCC950 delayed tolerance to morphine and fentanyl antinociception and prevented fentanyl-induced hyperalgesia. MCC950 also prevented opioid-induced NLRP3 oligomerization. In conclusion, morphine and fentanyl differentially induce cell-specific activation of NLRP3 inflammasome and pyroptosis in the DRN through TLR4 receptors in astrocytes and through opioid receptors in neurons, indicating that neuroinflammation is involved in opioid-induced analgesia and fentanyl-induced hyperalgesia after repeated administrations.

Effect of ethanolic extract of Solanum virginianum Linn. on neuropathic pain using chronic constriction injury rat model and molecular docking studies

The present research work was designed to examine the neuroprotective effect of ethanolic extract of Solanum virginianum Linn. (SV) in chronic construction injury (CCI) of sciatic nerve-induced neuropathic pain in rats. The extract was initially standardized by high-performance thin-layer chromatography using solasodine as a biomarker and was then subjected to assess the degree of mechanical allodynia, thermal allodynia, mechanical hyperalgesia, thermal hyperalgesia and biochemical evaluations. Administration of SV (100 and 200 mg/kg; p.o.) and pregabalin (10 mg/kg; p.o.) as a reference standard significantly debilitated hyperalgesia and allodynia and notably restored the altered antioxidant level and pro-inflammatory cytokine (IL-1β and TNF-α) expression in a dose-dependent manner. Further, to appraise the mechanistic approach of solasodine, docking simulation studies were done on the 3D structure of the voltage-gated N-type calcium channel (Cav 2.2), R-type calcium channel (Cav 2.3) and sodium channel (Nav 1.7), and the results revealed that solasodine properly positioned into Phe 19, Leu 32, Met 51 and Met 71 (FLMM pocket) of Cav 2.2 and Cav 2.3 and being a competitor of Ca²⁺/N-lobe it may inactivate these calcium channels but did not bind into the desired binding pocket of Nav 1.7. Thus, the study confirmed the role of solasodine as a major biomarker for the observed neuroprotective nature of Solanum virginianum.

The longitudinal effects of seated isometric yoga on blood biomarkers, autonomic functions, and psychological parameters of patients with chronic fatigue syndrome: a pilot study

BACKGROUND

In a previous randomized controlled trial, we found that practicing seated isometric yoga regularly for 2 months improved the fatigue of patients with chronic fatigue syndrome (CFS) who are resistant to conventional therapy. The aim of this pilot study was to investigate the possible mechanisms behind this finding by comparing blood biomarkers, autonomic nervous function, and psychological indices before versus after an intervention period of seated isometric yoga practice.

METHODS

Fifteen patients with CFS who did not show satisfactory improvements after at least 6 months of conventional therapy practiced seated isometric yoga (biweekly 20-min sessions with a yoga instructor and daily practice at home) for 2 months. The longitudinal effects of seated isometric yoga on fatigue, blood biomarkers, autonomic function, and psychological state were investigated by comparing the following parameters before and after the intervention period: Fatigue severity was assessed by the Chalder fatigue scale (FS) score. Levels of the blood biomarkers cortisol, DHEA-S, TNF-α, IL-6, prolactin, carnitine, TGF-β1, BDNF, MHPG, HVA, and α-MSH were measured. The autonomic nervous functions assessed were heart rate (HR) and HR variability. Psychological indices included the 20-item Toronto Alexithymia Scale (TAS-20) and the Hospital Anxiety and Depression Scale (HADS).

RESULTS

Practicing seated isometric yoga for 2 months resulted in significant reductions in the Chalder FS (P = 0.002) and HADS-depression (P = 0.02) scores. No significant changes were observed in any other parameter evaluated. The change in Chalder FS score was not correlated with the change in HADS-depression score. However, this change was positively correlated with changes in the serum TNF-α levels (P = 0.048), the high frequency component of HR variability (P = 0.042), and TAS-20 scores (P = 0.001).

CONCLUSIONS

Regular practice of seated isometric yoga for 2 months reduced the fatigue and depressive symptom scores of patients with CFS without affecting any other parameters we investigated. This study failed to identify the markers responsible for the longitudinal fatigue-relieving effect of seated isometric yoga. However, considering that the reduced fatigue was associated with decreased serum TNF-α level and TAS-20 scores, fatigue improvement might be related to reduced inflammation and improved alexithymia in these patients.

TRIAL REGISTRATION

University Hospital Medical Information Network (UMIN CTR) UMIN000009646. Registered Dec 27, 2012.

Red nucleus interleukin-1β evokes tactile allodynia through activation of JAK/STAT3 and JNK signaling pathways

We previously reported that interleukin-1β (IL-1β) in the red nucleus (RN) is involved in pain modulation and exerts a facilitatory effect in the development of neuropathic pain. Here, we explored the actions of signaling pathways, including the Janus kinase/signal transducer and activator of transcription 3 (JAK/STAT3), c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor-κB (NF-κB) pathways, on RN IL-1β-mediated pain modulation. After a single dose of recombinant rat IL-1β (rrIL-1β, 10 ng) injected into the RN in normal rats, a tactile allodynia was evoked in the contralateral but not ipsilateral hindpaw, commencing 75 min and peaking 120 min postinjection. Up-regulated protein levels of phospho-STAT3 (p-STAT3) and p-JNK were observed in the RN 120 min after rrIL-1β injection, the increases of p-STAT3 and p-JNK were blocked by anti-IL-1β antibody. However, the expression levels of p-ERK, p-p38 MAPK, and NF-κB in the RN were not affected by rrIL-1β injection. RN neurons and astrocytes contributed to IL-1β-evoked up-regulation of p-STAT3 and p-JNK. Further studies demonstrated that injection of the JAK2 antagonist AG490 or JNK antagonist SP600125 into the RN 30 min prior to the administration of rrIL-1β could completely prevent IL-1β-evoked tactile allodynia, while injection of the ERK antagonist PD98059, p38 MAPK antagonist SB203580, or NF-κB antagonist PDTC did not affect IL-1β-evoked tactile allodynia. In conclusion, our data provide additional evidence that RN IL-1β is involved in pain modulation, and that it exerts a facilitatory effect by activating the JAK/STAT3 and JNK signaling pathways.

Stress-induced hyperthermia and hypothermia

Stress affects core body temperature (T_c). Many kinds of stress induce transient, monophasic hyperthermia, which diminishes gradually if the stressor is terminated. Stronger stressors produce a longer-lasting effect. Repeated/chronic stress induces anticipatory hyperthermia, reduces diurnal changes in T_c, or slightly increases T_c throughout the day. Animals that are exposed to chronic stress or a cold environment exhibit an enhanced hyperthermic response to a novel stress. These changes persist for several days after cessation of stress exposure. In contrast, long-lasting inescapable stress sometimes induces hypothermia. In healthy humans, psychologic stress induces slight increases in T_c, which are within the normal range of T_c or just above it. Some individuals, however, develop extremely high T_c (up to 41°C) when they are exposed to emotional events or show persistent low-grade high T_c (37-38°C) during or after chronic stress situations. In addition to the nature of the stressor itself, such stress-induced thermal responses are modulated by sex, age, ambient temperature, cage mates, past stressful experiences and cold exposure, and coping. Stress-induced hyperthermia is driven by mechanisms distinct from infectious fever, which requires inflammatory mediators. However, both stress and infection activate the dorsomedial hypothalamus-rostral medullary raphe region-sympathetic nerve axis to increase T_c.

Lifetime Modulation of the Pain System via Neuroimmune and Neuroendocrine Interactions

Chronic pain is a debilitating condition that still is challenging both clinicians and researchers. Despite intense research, it is still not clear why some individuals develop chronic pain while others do not or how to heal this disease. In this review, we argue for a multisystem approach to understand chronic pain. Pain is not only to be viewed simply as a result of aberrant neuronal activity but also as a result of adverse early-life experiences that impact an individual's endocrine, immune, and nervous systems and changes which in turn program the pain system. First, we give an overview of the ontogeny of the central nervous system, endocrine, and immune systems and their windows of vulnerability. Thereafter, we summarize human and animal findings from our laboratories and others that point to an important role of the endocrine and immune systems in modulating pain sensitivity. Taking "early-life history" into account, together with the past and current immunological and endocrine status of chronic pain patients, is a necessary step to understand chronic pain pathophysiology and assist clinicians in tailoring the best therapeutic approach.

Early life programming of pain: focus on neuroimmune to endocrine communication

Chronic pain constitutes a challenge for the scientific community and a significant economic and social cost for modern societies. Given the failure of current drugs to effectively treat chronic pain, which are based on suppressing aberrant neuronal excitability, we propose in this review an integrated approach that views pain not solely originating from neuronal activation but also the result of a complex interaction between the nervous, immune, and endocrine systems. Pain assessment must also extend beyond measures of behavioural responses to noxious stimuli to a more developmentally informed assessment given the significant plasticity of the nociceptive system during the neonatal period. Finally integrating the concept of perinatal programming into the pain management field is a necessary step to develop and target interventions to reduce the suffering associated with chronic pain. We present clinical and animal findings from our laboratory (and others) demonstrating the importance of the microbial and relational environment in programming pain responsiveness later in life via action on hypothalamo-pituitary adrenal (HPA) axis activity, peripheral and central immune system, spinal and supraspinal mechanisms, and the autonomic nervous system.

Microglial interleukin-1β in the ipsilateral dorsal horn inhibits the development of mirror-image contralateral mechanical allodynia through astrocyte activation in a rat model of inflammatory pain

Damage on one side of the body can also result in pain on the contralateral unaffected side, called mirror-image pain (MIP). Currently, the mechanisms responsible for the development of MIP are unknown. In this study, we investigated the involvement of spinal microglia and interleukin-1β (IL-1β) in the development of MIP using a peripheral inflammatory pain model. After unilateral carrageenan injection, mechanical allodynia (MA) in both hind paws and the expression levels of spinal Iba-1, IL-1β, and GFAP were evaluated. Ipsilateral MA was induced beginning at 3 hours after carrageenan injection, whereas contralateral MA showed a delayed onset occurring 5 days after injection. A single intrathecal (i.t.) injection of minocycline, a tetracycline derivative that displays selective inhibition of microglial activation, or an interleukin-1 receptor antagonist (IL-1ra) on the day of carrageenan injection caused an early temporary induction of contralateral MA, whereas repeated i.t. treatment with these drugs from days 0 to 3 resulted in a long-lasting contralateral MA, which was evident in its advanced development. We further showed that IL-1β was localized to microglia and that minocycline inhibited the carrageenan-induced increases in spinal Iba-1 and IL-1β expression. Conversely, minocycline or IL-1ra pretreatment increased GFAP expression as compared with that of control rats. However, i.t. pretreatment with fluorocitrate, an astrocyte inhibitor, restored minocycline- or IL-1ra-induced contralateral MA. These results suggest that spinal IL-1β derived from activated microglia temporarily suppresses astrocyte activation, which can ultimately prevent the development of contralateral MA under inflammatory conditions. These findings imply that microglial IL-1β plays an important role in regulating the induction of inflammatory MIP.

Neuropathic Pain Phenotype Does Not Involve the NLRP3 Inflammasome and Its End Product Interleukin-1β in the Mice Spared Nerve Injury Model

The NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome is one of the main sources of interleukin-1β (IL-1β) and is involved in several inflammatory-related pathologies. To date, its relationship with pain has not been studied in depth. The aim of our study was to elucidate the role of NLRP3 inflammasome and IL-1β production on neuropathic pain. Results showed that basal pain sensitivity is unaltered in NLRP3^-/- mice as well as responses to formalin test. Spared nerve injury (SNI) surgery induced the development of mechanical allodynia and thermal hyperalgesia in a similar way in both genotypes and did not modify mRNA levels of the NLRP3 inflammasome components in the spinal cord. Intrathecal lipopolysaccharide (LPS) injection increases apoptosis-associated speck like protein (ASC), caspase-1 and IL-1β expression in both wildtype and NLRP3^-/- mice. Those data suggest that NLRP3 is not involved in neuropathic pain and also that other sources of IL-1β are implicated in neuroinflammatory responses induced by LPS.

Psychogenic fever: how psychological stress affects body temperature in the clinical population

Psychogenic fever is a stress-related, psychosomatic disease especially seen in young women. Some patients develop extremely high core body temperature (Tc) (up to 41°C) when they are exposed to emotional events, whereas others show persistent low-grade high Tc (37-38°C) during situations of chronic stress. The mechanism for psychogenic fever is not yet fully understood. However, clinical case reports demonstrate that psychogenic fever is not attenuated by antipyretic drugs, but by psychotropic drugs that display anxiolytic and sedative properties, or by resolving patients' difficulties via natural means or psychotherapy. Animal studies have demonstrated that psychological stress increases Tc via mechanisms distinct from infectious fever (which requires proinflammatory mediators) and that the sympathetic nervous system, particularly β3-adrenoceptor-mediated non-shivering thermogenesis in brown adipose tissue, plays an important role in the development of psychological stress-induced hyperthermia. Acute psychological stress induces a transient, monophasic increase in Tc. In contrast, repeated stress induces anticipatory hyperthermia, reduces diurnal changes in Tc, or slightly increases Tc throughout the day. Chronically stressed animals also display an enhanced hyperthermic response to a novel stress, while past fearful experiences induce conditioned hyperthermia to the fear context. The high Tc that psychogenic fever patients develop may be a complex of these diverse kinds of hyperthermic responses.

Prior chronic stress induces persistent polyI:C-induced allodynia and depressive-like behavior in rats: Possible involvement of glucocorticoids and microglia

When animals suffer from viral infections, they develop a set of symptoms known as the "sickness response." Recent studies suggest that psychological stress can modulate the sickness response. However, it remains uncertain whether acute and chronic psychosocial stresses have the same effect on viral infection-induced sickness responses. To address this question, we compared changes in polyI:C-induced sickness responses, such as fever, change of body weight and food intake, mechanical allodynia, and depressive-like behavior, in rats that had been pre-exposed to single and repeated social defeat stresses. Intraperitoneal injection of polyI:C induced a maximal fever of 38.0°C 3h after injection. Rats exposed to prior social defeat stress exhibited blunted febrile responses, which were more pronounced in the repeated stress group. Furthermore, only the repeated stress group showed late-onset and prolonged mechanical allodynia lasting until 8days after injection in the von Frey test and prolonged immobility time in the forced swim test 9days post-injection. To assess the role of glucocorticoids and microglia in the delayed and persistent development of these sickness responses in rats exposed to repeated stress, we investigated the effect of pretreatment with RU486, a glucocorticoid receptor antagonist, and minocycline, an inhibitor of microglial activation, on polyI:C-induced allodynia and depressive-like behavior. Pretreatment with either drug inhibited both the delayed allodynia and depressive-like behavior. The present study demonstrates that repeated, but not single, social defeat stress followed by systemic polyI:C administration induced prolonged allodynia and depressive-like behavior in rats. Our results show that even though a single-event psychosocial stress does not have any effect by itself, animals may develop persistent allodynia and depressive-like behavior when they suffer from an infectious disease if they are pre-exposed to repeated or chronic psychosocial stress. Furthermore, this study suggests that stress-induced corticosterone and microglial activation play a pivotal role in this phenomenon.

Programming of formalin-induced nociception by neonatal LPS exposure: Maintenance by peripheral and central neuroimmune activity

The immune and nociceptive systems are shaped during the neonatal period where they undergo fine-tuning and maturation. Painful experiences during this sensitive period of development are known to produce long-lasting effects on the immune and nociceptive responses. It is less clear, however, whether inflammatory pain responses are primed by neonatal exposure to mild immunological stimuli, such as with lipopolysaccharide (LPS). Here, we examine the impact of neonatal LPS exposure on inflammatory pain responses, peripheral and hippocampal interleukin-1β (IL-1β), as well as mast cell number and degranulation in preadolescent and adult rats. Wistar rats were injected with LPS (0.05mg/kg IP, Salmonella enteritidis) or saline on postnatal days (PNDs) 3 and 5 and later subjected to the formalin test at PNDs 22 and 80-97. At both time-points, and one-hour after formalin injection, blood and hippocampus were collected for measuring circulating and central IL-1β levels using ELISA and Western blot, respectively. Paw tissue was also isolated to assess mast cell number and degree of degranulation using Toluidine Blue staining. Behavioural analyses indicate that at PND 22, LPS-challenged rats displayed enhanced flinching (p<.01) and licking (p<.01) in response to formalin injection. At PNDs 80-97, LPS-challenged rats exhibited increased flinching (p<.05), an effect observed in males only. Furthermore, neonatal LPS exposure enhanced circulating IL-1β and mast cell degranulation in preadolescent but not adult rats following formalin injection. Hippocampal IL-1β levels were increased in LPS-treated adult but not preadolescent rats in response to formalin injection. These data suggest neonatal LPS exposure produces developmentally regulated changes in formalin-induced behavioural responses, peripheral and central IL-1β levels, as well as mast cell degranulation following noxious stimulation later in life. These findings highlight the importance of immune activation during the neonatal period in shaping immune response and pain sensitivity later in life. This is of clinical relevance given the high prevalence of bacterial infection during the neonatal period, particularly in the vulnerable population of preterm infants admitted to neonatal intensive care units.

Involvement of pro- and antinociceptive factors in minocycline analgesia in rat neuropathic pain model

In neuropathic pain the repeated minocycline treatment inhibited the mRNA and protein expression of the microglial markers and metalloproteinase-9 (MMP-9). The minocycline diminished the pronociceptive (IL-6, IL-18), but not antinociceptive (IL-1alpha, IL-4, IL-10) cytokines at the spinal cord level. In vitro primary cell culture studies have shown that MMP-9, TIMP-1, IL-1beta, IL-1alpha, IL-6, IL-10, and IL-18 are of microglial origin. Minocycline reduces the production of pronociceptive factors, resulting in a more potent antinociceptive effect. This change in the ratio between pro- and antinociceptive factors, in favour of the latter may be the mechanism of minocycline analgesia in neuropathy.

Pioglitazone prevents morphine antinociceptive tolerance via ameliorating neuroinflammation in rat cerebral cortex

BACKGROUND

Opioid induced neuroinflammation is shown to be implicated in opioid analgesic tolerance development. In the present study the effect of pioglitazone on morphine-induced tolerance and neuroinflammation in the cerebral cortex of the rat was investigated.

MATERIALS AND METHODS

Various groups of rats received morphine (10mg/kg; ip) and vehicle (po), or morphine (10mg/kg) and pioglitazone (20 or 40 mg/kg; po) once a day for 17 days. In order to determine the possible involvement of PPAR-γ in the pioglitazone effect, one group of rats received PPAR-γ antagonist, GW-9662 (2mg/kg; sc), and pioglitazone (40 mg/kg) and morphine once daily for 17 days. Nociception was assessed using a tail flick apparatus and the percentage of the maximal possible effect was calculated as well. On 18th day, 2h after the last morphine injection, the cerebral cortex of the animals were harvested and the tissue levels of tumour necrosis factor alpha, interleukin-1beta, interleukin-6, interleukin-10 and nuclear factor-kappa B activity were determined.

RESULTS

Co-administration of pioglitazone (40 mg/kg) with morphine not only attenuated morphine-induced tolerance, but also prevented the up-regulation of pro-inflammatory cytokines (tumour necrosis factor alpha, interleukin-1beta, interleukin-6) and nuclear factor-kappa B activity in the rat cerebral cortex. Moreover, GW-9662 (2mg/kg) administration 30 min before pioglitazone, antagonized the above mentioned pioglitazone-induced effects.

CONCLUSION

It is concluded that oral administration of pioglitazone attenuates morphine-induced tolerance. This effect of pioglitazone may be, at least in part, due to its anti-inflammatory property which suppressed the cortical pro-inflammatory cytokine and inhibited of nuclear factor-kappa B activity.

Targeting interleukin-1β reduces intense acute swimming-induced muscle mechanical hyperalgesia in mice

Objectives

The role of interleukin (IL)-1β in intense acute swimming-induced muscle mechanical hyperalgesia was investigated in mice.

Methods

Untrained mice were submitted to one session of intense acute swimming for 120 min or were submitted to sham conditions (30 s exposure to water), and muscle mechanical hyperalgesia (before and 6–48 h after swimming session), IL-1β production (skeletal muscle and spinal cord), myeloperoxidase activity, reduced glutathione (GSH) levels (skeletal muscle and spinal cord), and cortisol, glucose, lactate and creatine kinase (CK) levels (plasma) were analysed.

Key findings

Intense acute swimming-induced muscle mechanical hyperalgesia was dose-dependently inhibited by IL-1ra treatment. IL-1β levels were increased in soleus, but not gastrocnemius muscle and spinal cord 2 and 4 h after the session, respectively. Intense acute swimming-induced increase of myeloperoxidase activity and reduced GSH levels in soleus muscle were reversed by IL-1ra treatment. In the spinal cord, exercise induced an increase of GSH levels, which was reduced by IL-1ra. Finally, IL-1ra treatment reduced plasma levels of CK, an indicator of myocyte damage.

Conclusions

IL-1β mediates intense acute swimming-induced muscle mechanical hyperalgesia by peripheral (soleus muscle) and spinal cord integrative mechanisms and could be considered a potential target to treat exercise-induced muscle pain.

Altered neuropathic pain behaviour in a rat model of depression is associated with changes in inflammatory gene expression in the amygdala

The association between chronic pain and depression is widely recognized, the comorbidity of which leads to a heavier disease burden, increased disability and poor treatment response. This study examined nociceptive responding to mechanical and thermal stimuli prior to and following L5-L6 spinal nerve ligation (SNL), a model of neuropathic pain, in the olfactory bulbectomized (OB) rat model of depression. Associated changes in the expression of genes encoding for markers of glial activation and cytokines were subsequently examined in the amygdala, a key brain region for the modulation of emotion and pain. The OB rats exhibited mechanical and cold allodynia, but not heat hyperalgesia, when compared with sham-operated counterparts. Spinal nerve ligation induced characteristic mechanical and cold allodynia in the ipsilateral hindpaw of both sham and OB rats. The OB rats exhibited a reduced latency and number of responses to an innocuous cold stimulus following SNL, an effect positively correlated with interleukin (IL)-6 and IL-10 mRNA expression in the amygdala, respectively. Spinal nerve ligation reduced IL-6 and increased IL-10 expression in the amygdala of sham rats. The expression of CD11b (cluster of differentiation molecule 11b) and GFAP (glial fibrillary acidic protein), indicative of microglial and astrocyte activation, and IL-1β in the amygdala was enhanced in OB animals when compared with sham counterparts, an effect not observed following SNL. This study shows that neuropathic pain-related responding to an innocuous cold stimulus is altered in an animal model of depression, effects accompanied by changes in the expression of neuroinflammatory genes in the amygdala.

Enhancement by interleukin-1β of AMPA and NMDA receptor-mediated currents in adult rat spinal superficial dorsal horn neurons

Background

Proinflammatory cytokine interleukin-1β (IL-1β) released from spinal microglia plays an important role in the maintenance of acute and chronic pain states. However, the cellular basis of this action remains poorly understood. Using whole-cell patch-clamp recordings, we examined the action of IL-1β on AMPA- and NMDA-receptor-mediated currents recorded from substantia gelatinosa (SG) neurons of adult rat spinal cord slices which are key sites for regulating nociceptive transmission from the periphery.

Results

AMPA- and NMDA-induced currents were increased in peak amplitude by IL-1β in a manner different from each other in SG neurons. These facilitatory actions of IL-1β were abolished by IL-1 receptor (IL-1R) antagonist (IL-1ra), which by itself had no detectable effects on AMPA- and NMDA-induced currents. The AMPA- but not NMDA-induced current facilitated by IL-1β was recovered to control level 30 min after IL-1β washout and largely depressed in Na⁺-channel blocker tetrodotoxin-containing or nominally Ca²⁺-free Krebs solution. Minocycline, a microglia inhibitor, blocked the facilitatory effect of IL-1β on AMPA- but not NMDA-induced currents, where minocycline itself depressed NMDA- but had not any effects on AMPA-induced currents.

Conclusions

IL-1β enhances AMPA and NMDA responses in SG neurons through IL-1R activation; the former but not latter action is reversible and due to an increase in neuronal activity in a manner dependent on extracellular Ca²⁺ and minocycline. It is suggested that AMPA and NMDA receptors are positively modulated by IL-1β in a manner different from each other; the former but not latter is mediated by a neurotransmitter released as a result of an increase in neuronal activity. Since IL-1β contributes to nociceptive behavior induced by peripheral nerve or tissue injury, the present findings also reveal an important cellular link between neuronal and glial cells in the spinal dorsal horn.

Importance of glial activation in neuropathic pain

Glia plays a crucial role in the maintenance of neuronal homeostasis in the central nervous system. The microglial production of immune factors is believed to play an important role in nociceptive transmission. Pain may now be considered a neuro-immune disorder, since it is known that the activation of immune and immune-like glial cells in the dorsal root ganglia and spinal cord results in the release of both pro- and anti-inflammatory cytokines, as well as algesic and analgesic mediators. In this review we presented an important role of cytokines (IL-1alfa, IL-1beta, IL-2, IL-4, IL-6, IL-10, IL-15, IL-18, TNFalpha, IFNgamma, TGF-beta 1, fractalkine and CCL2); complement components (C1q, C3, C5); metaloproteinases (MMP-2,-9) and many other factors, which become activated on spinal cord and DRG level under neuropathic pain. We discussed the role of the immune system in modulating chronic pain. At present, unsatisfactory treatment of neuropathic pain will seek alternative targets for new drugs and it is possible that anti-inflammatory factors like IL-10, IL-4, IL-1alpha, TGF-beta 1 would fulfill this role. Another novel approach for controlling neuropathic pain can be pharmacological attenuation of glial and immune cell activation. It has been found that propentofylline, pentoxifylline, minocycline and fluorocitrate suppress the development of neuropathic pain. The other way of pain control can be the decrease of pro-nociceptive agents like transcription factor synthesis (NF-kappaB, AP-1); kinase synthesis (MEK, p38MAPK, JNK) and protease activation (cathepsin S, MMP9, MMP2). Additionally, since it is known that the opioid-induced glial activation opposes opioid analgesia, some glial inhibitors, which are safe and clinically well tolerated, are proposed as potential useful ko-analgesic agents for opioid treatment of neuropathic pain. This review pointed to some important mechanisms underlying the development of neuropathic pain, which led to identify some possible new approaches to the treatment of neuropathic pain, based on the more comprehensive knowledge of the interaction between the nervous system and glial and immune cells.

A functional relationship between trigeminal astroglial activation and NR1 expression in a rat model of temporomandibular joint inflammation

OBJECTIVE

To examine the hypothesis that glial activation would regulate the expression of the N-methyl-D-aspartate receptor subunit 1 (NR1) in the trigeminal subnucleus caudalis (Sp5C) after temporomandibular joint (TMJ) inflammation.

METHODS

Inflammation of TMJ was produced in rats by injecting 50 μL complete Freund's adjuvant (CFA) into unilateral TMJ space. Sham control rats received incomplete Freund's adjuvant injection. Mechanical nociception in the affected and non-affected TMJ site was tested by using a digital algometer. Fractalkine, fluorocitrate, and/or MK801 were intracisternally administrated to examine the relationship between astroglial activation and NR1 upregulation.

RESULTS

CFA TMJ injection resulted in persistent ipsilateral mechanical hyperalgesia 1, 3, and 5 days after CFA injection. The inflammation also induced significant upregulation of CX3C chemokine receptor 1 and glial fibrillary acidic protein (GFAP) beginning on day 1 and of NR1 beginning on day 3 within the ipsilateral Sp5C. Intracisternal administration of fluorocitrate for 5 days blocked the development of mechanical hyperalgesia as well as the upregulation of GFAP and NR1 in the Sp5C. Conversely, intracisternal injection of fractalkine for 5 days exacerbated the expression of NR1 in Sp5C and mechanical hyperalgesia induced by TMJ inflammation. Moreover, once daily intracisternal fractalkine administration for 5 days in naïve rats induced the upregulation of NR1 and mechanical hyperalgesia.

CONCLUSIONS

These results suggest that astroglial activation contributes to the mechanism of TMJ pain through the regulation of NR1 expression in Sp5C.

Minocycline and fluorocitrate suppress spinal nociceptive signaling in intrathecal IL-1β-induced thermal hyperalgesic rats

We previously demonstrated that intrathecal IL-1β caused thermal hyperalgesia in rats. This study was conducted to examine the effects and cellular mechanisms of glial inhibitors on IL-1β-induced nociception in rats. The effects of minocycline (20 μg), fluorocitrate (1 nmol), and SB203580 (5 μg) on IL-1β (100 ng) treatment in rats were measured by nociceptive behaviors, western blotting of p38 mitogen-activated protein kinase (MAPK) and inducible nitric oxide synthase (iNOS) expression, cerebrospinal fluid nitric oxide (NO) levels, and immunohistochemical analyses. The results demonstrated that intrathecal IL-1β activated microglia and astrocytes, but not neurons, in the dorsal horn of the lumbar spinal cord, as evidenced by morphological changes and increased immunoreactivity, phosphorylated p38 (P-p38) MAPK, and iNOS expression; the activation of microglia and astrocytes peaked at 30 min and lasted for 6 h. The immunoreactivities of microglia and astrocytes were significantly increased at 30 min (6.6- and 2.7-fold, respectively) and 6 h (3.3- and 4.0-fold, respectively) following IL-1β injection, as compared with saline controls at 30 min (all P < 0.01). IL-1β induced P-p38 MAPK and iNOS expression predominantly in microglia and less in astrocytes. Minocycline, fluorocitrate, or SB203580 pretreatment suppressed this IL-1β-upregulated P-p38 MAPK mainly in microglia and iNOS mainly in astrocytes; minocycline exhibited the most potent effect. Minocycline and fluorocitrate pretreatment abrogated IL-1β-induced NO release and thermal hyperalgesia in rats. In conclusion, minocycline, fluorocitrate, and SB203580 effectively suppressed the IL-1β-induced central sensitization and hyperalgesia in rats.

Interleukin-13 reduces hyperalgesia and the level of interleukin-1β in BALB/c mice infected with Leishmania major with an up-regulation of interleukin-6

The anti-inflammatory cytokines interleukin-10 (IL-10) and interleukin-13 (IL-13) were shown to reduce hyperalgesia in some models such as rats exposed to UV rays. In addition, IL-10 was also shown to reduce hyperalgesia in high dose of Leishmania major-induced inflammation in BALB/c mice accompanied by a significant decrease in the levels of interleukin-1β (IL-1β) in the paws of infected mice, while no effect on the levels of IL-6 was observed. In this study, we injected BALB/c mice with a high dose of L. major and treated them with IL-13 (15 ng/animal) for twelve days (excluding the weekends) and hyperalgesia was assessed using thermal pain tests. Furthermore, the levels of IL-1β and IL-6 were also assessed at different post-infection days. Our results show that IL-6 and more importantly IL-1β don't play a direct role in the L. major-induced hyperalgesia and that IL-13 induces this hyperalgesia through the down-regulation of IL-1β and another proinflammatory cytokine (most probably TNF-α). Furthermore, our data show that IL-13 leads to the upregulation of the level IL-6 which initially seems to have no direct role in the induced hyperalgesia. Therefore, we suggest that the L. major-induced hyperalgesia is mainly mediated by the cytokine cascade leading to the production of sympathetic amines.

Cancer pain and its relationship to systemic inflammation: an exploratory study

Pain is the commonest symptom in cancer patients, whereas inflammation is implicated in cancer development and progression. The relationship between pain and inflammation in cancer is therefore of interest; however, it is challenging to examine because multiple factors may affect these variables. This study assessed the relationship between cancer pain and systemic inflammation using a retrospective analysis of 2 clinical trial datasets of patients with cancer cachexia. Included patients had gastrointestinal, lung, or pancreatic cancer. Pain was assessed using the pain subscale of the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire C-30. Inflammation was assessed using C-reactive protein (CRP). A regression analysis between pain and logarithmically transformed CRP was run, and Pearson correlation coefficients were calculated. A total of 718 patients entered the trials, of whom 449 had CRP measured. Both trial populations were well matched. Pain positively correlated with CRP. The Pearson correlation coefficients were 0.126 and 0.163 for trials 1 and 2, respectively. This correlation was statistically significant at the P<.05 level. These findings support that pain is related to systemic inflammation in a cohort of cancer patients. Many factors can affect pain and inflammation in cancer, demonstrating that any relationship that exists between pain and inflammation is of interest. This is in keeping with work showing this relationship in nonmalignant pain. Studies targeting inflammation and assessing its effect on pain in cancer would be an important step in the research agenda.

Stress and IL-1beta contribute to the development of depressive-like behavior following peripheral nerve injury

The physiological link between neuropathic pain and depression remains unknown despite a high comorbidity between these two disorders. A mouse model of spared nerve injury (SNI) was used to test the hypothesis that nerve injury precipitates depression through the induction of inflammation in the brain, and that prior exposure to stress exacerbates the behavioral and neuroinflammatory consequences of nerve injury. As compared with sham surgery, SNI induced mechanical allodynia, and significantly increased depressive-like behavior. Moreover, SNI animals displayed increased interleukin-1beta (IL-1beta) gene expression within the frontal cortex and concurrent increases in the expression of glial fibrillary acidic protein (GFAP) within the periaqueductal grey (PAG). Additionally, exposure to chronic restraint stress for 2 weeks before SNI exacerbated mechanical allodynia and depressive-like behavior, and resulted in an increase in IL-1beta gene expression in the frontal cortex and brain-derived neurotrophic factor (BDNF) gene expression in PAG. Treatment with metyrapone (MET), a corticosteroid synthesis inhibitor, before stress eliminated deleterious effects of chronic stress on SNI. Finally, this study showed that interference with IL-1beta signaling, through administration of IL-1 receptor antagonist (IL-1ra), ameliorated the effects of neuropathic pain on depressive-like behavior. Taken together, these data suggest that peripheral nerve injury leads to increased cytokine expression in the brain, which in turn, contributes to the development of depressive-like behavior. Furthermore, stress can facilitate the development of depressive-like behavior after nerve injury by promoting IL-1beta expression.

Pyrogenic cytokines did not mediate a stress interview-induced hyperthermic response in a patient with psychogenic fever: a case report

OBJECTIVE

To investigate if pyrogenic cytokines mediated psychological stress-induced hyperthermic response in a patient with psychogenic fever. Despite many case reports on psychogenic fever, the mechanism responsible for how psychological stress increases core body temperature (Tc) in humans is not yet known.

CASE PRESENTATION

A 13-year-old girl with fever (>38 degrees C) of unknown causes was referred to our department because psychogenic fever was suspected. To determine if the fever was actually induced by psychological stress, we conducted a 60-minute stress interview. Her baseline oral temperature was 36.60 degrees C and it began to increase immediately after commencement of the interview, reaching a maximum of 37.42 degrees C 20 minutes after the end of the interview. The plasma level of prostaglandin E(2) and the serum interleukin-6 level were increased 90 minutes after the interview. Serum levels of interleukin-1alpha, interleukin-1beta, and macrophage inflammatory protein-1alpha were all less than their minimum detectable level throughout the observation period. We also measured the patient's thermal preference by immersing her hands in warm (40 degrees C) and cold (20 degrees C) water. Her preference changed from cold to warm only during the increasing phase of oral temperature.

CONCLUSIONS

This case report shows that a stress interview actually increased Tc in a patient with psychogenic fever. This study suggests that, although pyrogenic cytokines are not involved, the stress interview-induced increase in Tc was an active hyperthermia under the control of the brain, as is infection-induced fever.

[Cytokine regulation and pain. Results of experimental and clinical research]

Cytokines are soluble peptides and proteins that are predominantly produced and secreted by immune cells. In numerous animal experiments the endogenous increase or application of exogenous pro-inflammatory cytokines is associated with pain behavior. In turn, cytokine inhibitors reduce such pain behavior in inflammatory and neuropathic pain models. Several clinical studies point out that cytokines are also important in different human pain states. Several chronic pain syndromes are associated with systemic pro-inflammatory cytokine profiles. In some pain syndromes these pro-inflammatory profiles are accompanied by a lack of analgesic anti-inflammatory cytokines. Numerous case reports and open clinical studies, but also some controlled trials show successful analgesic treatment using cytokine inhibitors. The following review article summarizes the main data of animal experiments and clinical trials concerning the role of cytokines in pain and the potential importance of cytokine modulation in pain treatment.

Microinjection of IL-1β into the trigeminal transition zone produces bilateral NMDA receptor-dependent orofacial hyperalgesia involving descending circuitry

Our recent studies indicate that the prototypic proinflammatory cytokine IL-1β is upregulated in astroglial cells in the trigeminal interplolaris/caudalis (Vi/Vc) transition zone, a region of the spinal trigeminal complex involved in trigeminal pain processing, after masseter muscle inflammation. Here we investigated the effect of microinjection of IL-1β into the Vi/Vc transition zone on orofacial nociception. The mechanical sensitivity of the orofacial site was assessed with von Frey microfilaments. The EF(50) values, defined as the von Frey filament force (g) that produces a 50% response frequency, were derived and used as a measure of mechanical sensitivity. A significant reduction in EF(50) indicates the occurrence of mechanical hyperalgesia/allodynia. Unilateral intra-Vi/Vc IL-1β (0.016-160 fmol) produced hyperalgesia/allodynia dose-dependently, which appeared at bilateral facial sites. The hyperalgesia was detectable as early as 30 min and lasted for 2-6 h (n=6, p<0.01). Intra-Vi/Vc pretreatment with an IL-1receptor antagonist (1 nmol) attenuated the IL-1β-induced hyperalgesia (p<0.01). Pre-injection of AP-5 (10 pmol) and MK-801 (20 pmol), two NMDA receptor antagonists, significantly attenuated IL-1β-induced hyperalgesia (p<0.05). Pretreatment with glial inhibitors fluorocitrate (120 pmol), minocycline (200 pmol) and propentofylline (10 pmol) did not attenuate IL-1β-induced hyperalgesia. Excitotoxic lesions of the rostral ventromedial medulla with ibotenic acid (2 μg) abolished IL-1β-induced contralateral hyperalgesia, suggesting a contribution of descending facilitatory drive. These results suggest that the IL-1β-produced effect on nociception was downstream to glial activation and involves interaction with NMDA receptors.

Interleukin-1 (IL-1): a central regulator of stress responses

Ample evidence demonstrates that the pro-inflammatory cytokine interleukin-1 (IL-1), produced following exposure to immunological and psychological challenges, plays an important role in the neuroendocrine and behavioral stress responses. Specifically, production of brain IL-1 is an important link in stress-induced activation of the hypothalamus-pituitary-adrenal axis and secretion of glucocorticoids, which mediate the effects of stress on memory functioning and neural plasticity, exerting beneficial effects at low levels and detrimental effects at high levels. Furthermore, IL-1 signaling and the resultant glucocorticoid secretion mediate the development of depressive symptoms associated with exposure to acute and chronic stressors, at least partly via suppression of hippocampal neurogenesis. These findings indicate that whereas under some physiological conditions low levels of IL-1 promote the adaptive stress responses necessary for efficient coping, under severe and chronic stress conditions blockade of IL-1 signaling can be used as a preventive and therapeutic procedure for alleviating stress-associated neuropathology and psychopathology.

Regulation of the trigeminal NR1 subunit expression induced by inflammation of the temporomandibular joint region in rats

Expression of the N-methyl-d-aspartate (NMDA) receptor in trigeminal nuclei has been shown to play a role in the mechanisms of trigeminal pain. Here, we examined the hypothesis that the upregulation of the NR1 subunit of the NMDA receptor (NR1) in the trigeminal subnucleus caudalis (Sp5c) following inflammation of the temporomandibular joint (TMJ) region would be regulated by interleukin-6 (IL-6) and the nuclear factor-kappa B (NF-kappaB). Inflammation of a unilateral TMJ region was produced in rats by injecting 50mul of complete Freund's adjuvant (CFA) into a TMJ and adjacent tissues, which resulted in persistent pain behavior as assessed using algometer before (baseline) and on days 1, 3, and 7 after the CFA injection. The CFA injection also induced a significant upregulation of NR1 and NF-kappaB on days 3 and 7, and of IL-6 on days 1, 3, and 7, within the ipsilateral Sp5c, as compared with the sham TMJ injection group. Once daily intracisternal injection of an IL-6 antiserum or NF-kappaB inhibitor (PDTC) for 6 days, beginning on day 1 immediately after the CFA injection, prevented both the upregulation of NR1 in the ipsilateral Sp5C and pain behavior. Moreover, once daily intracisternal IL-6 administration for 6 days in naïve rats induced the NR1 upregulation and pain behavior similar to that after TMJ inflammation. These results indicate that the upregulation of IL-6 and NF-kappaB after inflammation of the unilateral TMJ region is a critical regulatory mechanism for the expression of NR1 in the ipsilateral Sp5c, which contributed to the development of TMJ pain behavior in rats.

Role of interleukin-1beta during pain and inflammation

The cytokine cascade in pain and inflammatory processes is a tremendously complex system, involving glial, immune, and neuronal cell interactions. IL-1beta is a pro-inflammatory cytokine that has been implicated in pain, inflammation and autoimmune conditions. This review will focus on studies that shed light on the critical role of IL-1beta in various pain states, including the role of the intracellular complex, the inflammasome, which regulates IL-1beta production. Evidence will be presented demonstrating the importance of IL-1beta in both the induction of pain and in the maintenance of pain in chronic states, such as after nerve injury. Additionally, the involvement of IL-1beta as a key mediator in the interaction between glia and neurons in pain states will be discussed. Taken together, the evidence presented in the current review showing the importance of IL-1beta in animal and human pain states, suggests that blockade of IL-1beta be considered as a therapeutic opportunity.

The IKK-NF-kappaB pathway: a source for novel molecular drug targets in pain therapy?

Several studies indicate that the nuclear factor-kappa B (NF-kappaB) -activation cascade plays a crucial role not only in immune responses, inflammation, and apoptosis but also in the development and processing of pathological pain. Accordingly, a pharmacological intervention into this pathway may have antinociceptive effects and could provide novel treatment strategies for pain and inflammation. In this review we summarize the role of NF-kappaB in the nervous system, its impact on nociception, and several approaches that investigated the effects of various modulators of the classical I-kappaB-kinase-NF-kappaB signal transduction pathway in inflammatory nociception and neuropathic pain. The results indicate that NF-kappaB has an impact on nociceptive transmission and processing and that a number of substances that inhibit the NF-kappaB-activating cascade are capable of reducing the nociceptive response in different animal models. Therefore, a modulation of specific participants in the NF-kappaB signal transduction might exert a useful approach for the development of new painkillers.

Interleukin-1 alpha has antiallodynic and antihyperalgesic activities in a rat neuropathic pain model

Nerve injury and the consequent release of interleukins (ILs) are processes implicated in pain transmission. To study the potential role of IL-1 in the pathogenesis of allodynia and hyperalgesia, IL-1alpha and comparative IL-1beta, IL-6, and IL-10 mRNA levels were quantified using competitive RT-PCR of the lumbar spinal cord and dorsal root ganglia (DRG; L5-L6) three and seven days after chronic constriction injury (CCI) in rats. Microglial and astroglial activation in the ipsilateral spinal cord and DRG were observed after injury. In naive and CCI-exposed rats, IL-1alpha mRNA and protein were not detected in the spinal cord. IL-1beta and IL-6 mRNAs were strongly ipsilaterally elevated on day seven after CCI. In the ipsilateral DRG, IL-1alpha, IL-6, and IL-10 mRNA levels were increased on days three and seven; IL-1beta was elevated only on day seven. Western blot analysis revealed both the presence of IL-1alpha proteins (45 and 31 kDa) in the DRG and the down-regulation of these proteins after CCI. Intrathecal administration of IL-1alpha (50-500 ng) in naive rats did not influence nociceptive transmission, but IL-1beta (50-500 ng) induced hyperalgesia. In rats exposed to CCI, an IL-1alpha or IL-1 receptor antagonist dose-dependently attenuated symptoms of neuropathic pain; however, no effect of IL-1beta was observed. In sum, the first days after CCI showed a high abundance of IL-1alpha in the DRG. Together with the antiallodynic and antihyperalgesic effects observed after IL-1alpha administration, this finding indicates an important role for IL-1alpha in the development of neuropathic pain symptoms.

Interleukin-1 signaling modulates stress-induced analgesia

Exposure to stressful stimuli is often accompanied by reduced pain sensitivity, termed "stress-induced analgesia" (SIA). In the present study, the hypothesis that interleukin-1 (IL-1) may play a modulatory role in SIA was examined. Two genetic mouse models impaired in IL-1-signaling and their wild-type (WT) controls were employed. Another group of C57 mice was acutely administered with IL-1 receptor antagonist (IL-1ra). Mice were exposed to 2min swim stress at one of three water temperatures: 32 degrees C (mild stress), 20-23 degrees C (moderate stress), or 15 degrees C (severe stress); and then tested for pain sensitivity using the hot-plate test. Corticosterone levels were assessed in separate groups of WT and mutant mice following exposure to the three types of stress. Mild stress induced significant analgesia in the two WT strains and saline-treated mice, but not in the mutant strains or the IL-1ra-treated mice. Similarly, mild stress induced significantly elevated corticosterone levels in WT mice, and blunted corticosterone response in mutant mice. In contrast, both WT and mutant strains, as well as IL-1ra-treated mice, displayed analgesic and corticosterone responses following moderate and severe stress. Interestingly, the analgesic response to moderate stress was markedly potentiated in the mutant strains, as compared with their WT controls. The present results support our previous findings that in the absence of IL-1, stress response to mild stress is noticeably diminished. However, the analgesic response to moderate stress is markedly potentiated in mice with impaired IL-1 signaling, corroborating the anti-analgesic role of IL-1 in several pain modulatory conditions, including SIA.

Expression of IL-1beta in supraspinal brain regions in rats with neuropathic pain

We examined mRNA expression of the pro-inflammatory cytokine IL-1beta in the brainstem, thalamus, and prefrontal cortex in two rat models of neuropathic pain. Rats received a neuropathic injury: spared nerve injury (SNI) or chronic constriction injury (CCI), sham injury, or were minimally handled (control). Neuropathic pain-like behavior was monitored by tracking tactile thresholds. SNI-injured animals showed a robust decrease in tactile thresholds of the injured foot, while CCI-injured animals did not show tactile threshold changes. Ten or 24 days after nerve injury, IL-1beta gene expression in the brain was determined by RT-PCR. IL-1beta expression changes were observed mainly at 10 days after injury in the SNI animals, contralateral to the injury side, with increased expression in the brainstem and prefrontal cortex. The results indicate that neuro-immune activation in neuropathic pain conditions includes supraspinal brain regions, suggesting cytokine modulation of supraspinal circuitry of pain in neuropathic conditions.

Interleukin-1β and Serotonin Transporter Gene Polymorphisms in Burning Mouth Syndrome Patients

Burning mouth syndrome (BMS) is a chronic pain syndrome that encompasses all forms of burning sensations in the oral cavity when the oral mucosa is clinically normal. Neural, psychologic, and cytokine factors may be implicated in the pathogenesis of BMS. There are no studies of genetic factors associated with psychologic behavior and cytokine pain sensitivity in BMS patients. The purpose of the present study was to investigate a possible association between functional genetic polymorphisms, +3,954 (C/T) interleukin-1beta, and the polymorphic site on promoter region of the serotonin transporter gene (5-HTTLPR) in a sample of Brazilian patients. Thirty patients affected by BMS and 31 healthy volunteers were genotyped for 5-HTTLPR and IL-1beta gene. The chi-squared test was used for statistical analysis. There was no statistical difference in 5-HTTLPR genotypes between the case and control groups (P = .60), however a significant increase was observed in the IL-1beta high production genotype CT in BMS subjects (P = .005). In conclusion, the present study shows association between BMS and IL-1beta high producer genotype.

PERSPECTIVE

This article shows evidence that genetic polymorphisms associated with IL-1beta high production genotype are implicated on the pathogenesis of BMS. The modulation of IL1beta production may be an interesting tool in BMS management.

Hypernociceptive role of cytokines and chemokines: targets for analgesic drug development?

Pain is one of the classical signs of the inflammatory process in which sensitization of the nociceptors is the common denominator. This sensitization causes hyperalgesia or allodynia in humans, phenomena that involve pain perception (emotional component+nociceptive sensation). As this review focuses mainly on animal models, which don't allow discrimination of the emotional component, the terms nociception and hypernociception are used to describe overt behavior induced by mechanical stimulation and increase of nociceptor sensitivity, respectively. Pro- and anti-inflammatory cytokines and chemokines are endogenous small protein mediators released by local or migrating cells whose balance modulates the intensity of inflammatory response. The inflammatory stimuli or tissue injuries stimulate the release of characteristic cytokine cascades, which ultimately trigger the release of final mediators responsible for inflammatory pain. These final mediators, such as prostanoids or sympathetic amines, act directly on the nociceptors to cause hypernociception, which results from the lowering of threshold due to modulation of specific voltage-dependent sodium channels. Furthermore, a direct effect of cytokines on nociceptors is also described. On the other hand, there are also anti-inflammatory cytokines, such as interleukin (IL)-10, IL-4 and IL-13, and IL-1 receptor antagonists (IL-1ra), which inhibit the production of hypernociceptive cytokines and/or the final hypernociceptive mediators, preventing the installation of or the increase in the hypernociception. This review highlights the importance of the direct and indirect actions of cytokines and chemokines in inflammatory and neuropathic hypernociception, emphasizing the evidence suggesting these molecules are potential targets to develop novel drugs and therapies for the treatment of pain.

Effect of betamethasone on neuropathic pain and cerebral expression of NF-kappaB and cytokines

Glucocorticoids have been used to treat neuropathic pain for many years, but the underlying mechanisms are still unknown. Recent studies indicate that pathological pain states may be mediated by cytokines. We, therefore, examined the effect of betamethasone on neuropathic pain and the relationship between pain behavior and the expression of cytokines in the brain. Rats were given epidural injections of betamethasone (Diprospan) after L5 spinal nerve transection. Mechanical allodynia and thermal hyperalgesia were evaluated on post-operative days 1, 3, 7, 14 and 21 with von Frey and Hargreaves tests. Cerebral expression of NF-kappaB, TNFalpha, IL-1beta and IL-10 was quantified using electrophoretic mobility shift assay (EMSA) or enzyme-linked immunosorbent assay (ELISA). We found that spinal nerve injury caused long-lasting mechanical and thermal hyperalgesia in the hind paw and stimulated the expression of NF-kappaB, TNFalpha, IL-1beta and IL-10 in the brain. A single epidural injection of betamethasone at the time of nerve injury partially inhibited the development of neuropathic hyperalgesia and reduced the subsequent elevated levels of pro-inflammatory cytokines in the brain, while stimulating the expression of the anti-inflammatory cytokine IL-10. These data support our hypothesis that pro-inflammatory cytokines in the brain may mediate the hyperalgesic effects of spinal nerve injury and that the long-acting anti-hyperalgesic effects of epidural glucocorticoid treatment are due to an inhibitory effect on pro-inflammatory cytokine levels and a stimulatory effect on anti-inflammatory cytokine levels in the brain.

Intraneural injection of interleukin-1beta and tumor necrosis factor-alpha into rat sciatic nerve at physiological doses induces signs of neuropathic pain

Proinflammatory cytokines are mediators of inflammatory and neuropathic pain. Here, we investigated pain-related behavior in rats after intraneural injection of different doses of rat recombinant interleukin-1beta (rrIL-1beta) and tumor necrosis factor-alpha (rrTNF) into the sciatic nerve. Doses ranged between 0.25 and 2500pg/ml for rrIL-1beta and 0.25-250pg/ml for rrTNF. Thermal hyperalgesia as measured according to the Hargreaves method was most prominent with 2.5pg/ml of rrIL-1beta or rrTNF. Mechanical allodynia as assessed using von Frey hairs was seen consistently with 2.5pg/ml of rrIL-1beta and 0.25-2.5pg/ml of rrTNF. Higher and lower doses had no significant effect on pain-related behavior. Morphometric analysis of semithin sections of the sciatic nerve 10 days after the injections revealed no significant fiber loss. The fiber size distribution was not significantly altered by any of the treatments. Particularly with injections of rrIL-1beta, an increase of epineurial macrophages was observed at all doses. The immunohistochemical expression of cellular markers of neuronal damage (activating transcription factor 3) or activation (phosphorylated p38 mitogen-activated kinase, NF-kappa B p65) in dorsal root ganglia (DRG) tended to increase with both cytokine injections. However, this did not reflect the extent of behavioral changes. In summary, we found a bell-shaped dose-response curve for the algesic effects of rrIL-1beta and rrTNF, peaking at doses equivalent to those of endogenous cytokines released locally after nerve injury. The absence of corresponding morphological changes in nerves supports the concept of a functional effect of the cytokines at these doses.

Effect of mechanical compression on the lumbar nerve root: localization and changes of intraradicular inflammatory cytokines, nitric oxide, and cyclooxygenase

STUDY DESIGN

Investigation of intraradicular inflammation induced by mechanical compression.

OBJECTIVE

To investigate the mechanism of nerve root pain, this study used a lumbar nerve root compression model.

SUMMARY OF BACKGROUND DATA

The manifestation of pain at sites of inflammation has a close relationship with the release of mediators from macrophages. However, the mediators involved in inflammation of nerve roots as a result of mechanical compression remain almost unknown.

METHODS

In this study, the seventh lumbar nerve root of dogs was compressed with a clip for 3 weeks to observe the changes caused by compression. Immunohistochemistry was performed using the avidin-biotin-peroxidase complex method to observe the changes of T cells (CD45) and macrophages (Mac-1) after compression. Antibodies against as interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), inducible nitric oxide synthase (i-NOS), and cyclooxygenase (COX)-1 and 2 were used to examine the localization and changes of these mediators caused by nerve root compression.

RESULTS

In control animals, resident T cells were detected, but there were no macrophages. IL-1beta and COX-2 were positive in the Schwann cells and vascular endothelial cells, while COX-1 was detected in the vascular endothelial cells. However, no cells showed TNF-alpha or i-NOS positively. After nerve root compression, numerous T cells and macrophages appeared among the demyelinized nerve fibers. The macrophages were positive for IL-1beta, TNF-alpha, i-NOS, and COX-2.

CONCLUSION

Inflammatory cytokines, NO, and COX-2 may be deeply involved in radiculitis caused by mechanical compression, and these mediators seem to be important in the manifestation of root pain.