Give me a pain that I am used to: distinct habituation patterns to painful and non-painful stimulation

Pain habituation is associated with a decrease of activation in brain areas related to pain perception. However, little is known about the specificity of these decreases to pain, as habituation has also been described for other responses like spinal reflexes and other sensory responses. Thus, it might be hypothesized that previously reported reductions in activation are not specifically related to pain habituation. For this reason, we performed a 3 T fMRI study using either painful or non-painful electrical stimulation via an electrode attached to the back of the left hand. Contrasting painful vs. non-painful stimulation revealed significant activation clusters in regions well-known to be related to pain processing, such as bilateral anterior and posterior insula, primary/secondary sensory cortices (S1/S2) and anterior midcingulate cortex (aMCC). Importantly, our results show distinct habituation patterns for painful (in aMCC) and non-painful (contralateral claustrum) stimulation, while similar habituation for both types of stimulation was identified in bilateral inferior frontal gyrus (IFG) and contralateral S2. Our findings thus distinguish a general habituation in somatosensory processing (S2) and reduced attention (IFG) from specific pain and non-pain related habituation effects where pain-specific habituation effects within the aMCC highlight a change in affective pain perception.

Pharmacological Blockade of PPAR Isoforms Increases Conditioned Fear Responding in the Presence of Nociceptive Tone

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors with three isoforms (PPARα, PPARβ/δ, PPARγ) and can regulate pain, anxiety, and cognition. However, their role in conditioned fear and pain-fear interactions has not yet been investigated. Here, we investigated the effects of systemically administered PPAR antagonists on formalin-evoked nociceptive behaviour, fear-conditioned analgesia (FCA), and conditioned fear in the presence of nociceptive tone in rats. Twenty-three and a half hours following fear conditioning to context, male Sprague-Dawley rats received an intraplantar injection of formalin and intraperitoneal administration of vehicle, PPARα (GW6471), PPARβ/δ (GSK0660) or PPARγ (GW9662) antagonists, and 30 min later were re-exposed to the conditioning arena for 15 min. The PPAR antagonists did not alter nociceptive behaviour or fear-conditioned analgesia. The PPARα and PPARβ/δ antagonists prolonged context-induced freezing in the presence of nociceptive tone without affecting its initial expression. The PPARγ antagonist potentiated freezing over the entire trial. In conclusion, pharmacological blockade of PPARα and PPARβ/δ in the presence of formalin-evoked nociceptive tone, impaired short-term, within-trial fear-extinction in rats without affecting pain response, while blockade of PPARγ potentiated conditioned fear responding. These results suggest that endogenous signalling through these three PPAR isoforms may reduce the expression of conditioned fear in the presence of nociceptive tone.

Pain in tones - Is it possible to hear the pain quality? A pilot trial

OBJECTIVE

The adequate treatment of chronic pain also calls for measuring its quality not only its intensity. For this reason, this pilot study investigated the non-verbal description of pain quality based on tones, distinguishing between nociceptive and neuropathic pain.

METHODS

A nociceptive and a neuropathic pain stimulus were applied to 80 chronic pain patients and 80 healthy subjects. Using a tone generator, all participants matched both pain stimuli to an appropriate tone (in Hz). The stimulus intensity was measured using the NRS-scale, and the PainDETECT questionnaire was completed.

RESULTS

Both groups matched a significantly higher tone to the neuropathic than to the nociceptive pain stimulus. Compared to healthy participants, chronic pain patients allocated higher tones to both pain stimuli. Higher values were also shown for the neuropathic pain stimulus, and chronic pain patients indicated an overall higher intensity of pain as healthy participants.

CONCLUSIONS

It is possible to differentiate pain stimuli non-verbally through tones, however, whether quality or intensity, was the key factor remains unknown. Future studies could investigate the influence of additional factors.

PRACTICAL IMPLICATIONS

A practical tool using tones should be developed to detect pain quality in patients - without verbal descriptions - quickly and more precisely.

Lipopolysaccharide from Rhodobacter sphaeroides (TLR4 antagonist) attenuates hypersensitivity and modulates nociceptive factors

CONTEXT

Accumulating evidence has demonstrated that Toll-like receptors (TLRs), especially TLR4 localized on microglia/macrophages, may play a significant role in nociception.

OBJECTIVE

We examine the role of TLR4 in a neuropathic pain model. Using behavioural/biochemical methods, we examined the influence of TLR4 antagonist on levels of hypersensitivity and nociceptive factors whose contribution to neuropathy development has been confirmed.

MATERIALS AND METHODS

Behavioural (von Frey's/cold plate) tests were performed with Wistar male rats after intrathecal administration of a TLR4 antagonist (LPS-RS ULTRAPURE (LPS-RSU), 20 μG: lipopolysaccharide from Rhodobacter sphaeroides, InvivoGen, San Diego, CA) 16 H and 1 h before chronic constriction injury (cci) to the sciatic nerve and then daily for 7 d. three groups were used: an intact group and two cci-exposed groups that received vehicle or LPS-RSU. tissue [spinal cord/dorsal root ganglia (DRG)] for western blot analysis was collected on day 7.

RESULTS

The pharmacological blockade of TLR4 diminished mechanical (from ca. 40% to 16% that in the INTACT group) and thermal (from ca. 51% to 32% that in the INTACT group) hypersensitivity despite the enhanced activation of IBA-1-positive cells in DRG. Moreover, LPS-RSU changed the ratio between IL-18/IL-18BP and MMP-9/TIMP-1 in favour of the increase of antinociceptive factors IL-18BP (25%-spinal; 96%-DRG) and TIMP-1 (15%-spinal; 50%-DRG) and additionally led to an increased IL-6 (40%-spinal; 161%-DRG), which is known to have analgesic properties in neuropathy.

CONCLUSIONS

Our results provide evidence that LPS-RSU influences pain through the expression of TLR4. TLR4 blockade has analgesic properties and restores the balance between nociceptive factors, which indicates its engagement in neuropathy development.

Anti-nociceptive effect of methanol extract of leaves of Senna singueana in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Senna singueana (Del.) Lock (Fabaceae) is a shrub or tree found in Ethiopia and other African countries. It has been traditionally used for different conditions including treatment of pain conditions in humans and animals. Although various reports are available in the literature claiming different activities of the plant, scientific studies supporting analgesic potential of S. singueana are lacking and the present study aimed to investigate the antinociceptive effect of methanol extract of leaves of S. singueana in mice.

MATERIALS AND METHODS

Anti-nociceptive activity of S. singueana (200 mg/kg and 400 mg/kg, p.o) was investigated using acetic acid-induced writhing, formalin-induced paw licking, and hot plate tests. Acute oral toxicity was determined using a slightly modified guideline (423) of the Organization for Economic Cooperation and Development.

RESULTS

S. singueana extract increased the percentage of inhibition of writhing response and licking response (neurogenic and inflammatory phase) in acetic acid-induced writhing and formalin-induced paw licking tests, respectively. It also significantly (p ≤ 0.05) increased the percentage of mean maximal effect (%MPE) compared to control group in the hot-plate test. In all models, the combination of S. singueana with either diclofenac or morphine produced statistically significant increase (p ≤ 0.05) in the percentage of inhibition of writhing, paw licking, and %MPE compared to single treatment groups. It was also found that the 400 mg/kg extract produced higher antinociceptive effects (p ≤ 0.05) compared to the 200 mg/kg.

CONCLUSION

S. singueana leaves may have analgesic effect that is mediated through both peripheral and central mechanisms and could be used as adjuvant treatment to the modern analgesics.

Comparison of pain burden and psychological factors in Brazilian women living with HIV and chronic neuropathic or nociceptive pain: An exploratory study

Psychological factors including pain catastrophizing and resilience associate with adjustment and quality of life in people living with chronic pain. Nevertheless, their presentation among females living with HIV and chronic pain has been poorly studied. Given that chronic pain in those living with HIV might occur due to different mechanisms (nociceptive or neuropathic), we hypothesize that the associated psychological states could also differ between these groups. We aimed to compare pain frequency and interference, psychological factors and sleep quality between females living with chronic nociceptive or neuropathic pain. Also, we explored correlations between psychological factors, pain severity and interference in females living with HIV and chronic pain. We performed a cross sectional study assessing females living with HIV and chronic pain, and compared it with a female HIV-positive, pain-free control sample in Brazil. To discriminate the most likely underlying mechanism for the chronic pain, we applied the Leeds Assessment for Neuropathic Signs and Symptoms (LANSS). Forty-nine females living with HIV and chronic pain were assessed, and divided in control (n = 12), nociceptive (n = 10) and neuropathic pain (n = 27) groups. Using validated scales, their pain catastrophizing, resilience, depression, anxiety and sleep disorders were assessed between May 2014 and August 2015. Compared to controls, females living with HIV and neuropathic chronic pain had higher pain frequency (p<0.001), interference on activities (p = 0.002), interference with emotions (p<0.001), catastrophizing (p<0.001), depression (p = 0.015), and lower resilience (p = 0.011). Catastrophizing was also significantly correlated to the burden of chronic pain. The type of chronic pain in females living with HIV should raise concerns regarding significant burden in psychological states in this population (particularly neuropathic pain). Using scales such as the LANSS to identify the type of choric pain, could be of use to address relevant issues for the patients, and to propose tailored therapies.

Pregabalin versus placebo in targeting pro-nociceptive mechanisms to prevent chronic pain after whiplash injury in at-risk individuals - a feasibility study for a randomised controlled trial

BACKGROUND

Whiplash-associated disorders (WAD) are an enormous and costly burden to Australian society. Up to 50% of people who experience a whiplash injury will never fully recover. Whiplash is resistant to treatment and no early management approach has yet been shown to prevent chronic pain. The early presence of central sensitization is associated with poor recovery. Pregabalin's effects on central sensitization indicate the potential to prevent or modulate these processes after whiplash injury and to improve health outcomes, but this has not been investigated. This paper describes the protocol for a feasibility study for a randomised controlled trial of pregabalin plus evidence-based advice compared to placebo plus evidence-based advice for individuals with acute whiplash injury who are at risk of poor recovery.

METHODS

This double blind, placebo-controlled randomised feasibility study will examine the feasibility and potential effectiveness of pregabalin and evidence-based advice (intervention) compared to placebo and evidence-based advice (control) for individuals with acute whiplash injury at risk of poor recovery. Thirty participants (15 per group) aged 18-65 years with Grade II WAD, within 48 hours of injury and currently experiencing at least moderate pain (NRS: ≥ 5/10) will be recruited from Emergency Departments of public hospitals in Queensland, Australia. Pregabalin will be commenced at 75 mg bd and titrated up to 300 mg bd as tolerated for 4 weeks followed by 1 week of weaning.

RESULTS

The feasibility of trial procedures will be tested, as well as the potential effect of the intervention on the outcomes. The primary outcome of neck pain intensity at 3 months from randomisation will be compared between the treatment groups using standard analysis of variance techniques.

DISCUSSION

Feasibility and potential effectiveness data will inform an appropriately powered full trial, which if successful, will provide an effective and cost-effective intervention for a costly and treatment resistant condition. It will also have implications for the early management of other traumatic conditions beyond whiplash.

TRIAL REGISTRATION

Clinical Trials Primary Registry: Australian and New Zealand Clinical Trials Registry.

CLINICAL TRIAL REGISTRATION NUMBER

ACTRN12617000059369 . Date of Registration: 11/01/2017. Primary Trial Sponsor: The University of Queensland, Brisbane QLD 4072 Australia.

Chronic Monosodium Glutamate Administration Induced Hyperalgesia in Mice

Monosodium glutamate (MSG) is a widely used food additive. Although it is generally considered safe, some questions regarding the impact of its use on general health have arisen. Several reports correlate MSG consumption with a series of unwanted reactions, including headaches and mechanical sensitivity in pericranial muscles. Endogenous glutamate plays a significant role in nociceptive processing, this neurotransmitter being associated with hyperalgesia and central sensitization. One of the mechanisms underlying these phenomena is the stimulation of Ca2+/calmodulin sensitive nitric oxide synthase, and a subsequent increase in nitric oxide production. This molecule is a key player in nociceptive processing, with implications in acute and chronic pain states. Our purpose was to investigate the effect of this food additive on the nociceptive threshold when given orally to mice. Hot-plate and formalin tests were used to assess nociceptive behaviour. We also tried to determine if a correlation between chronic administration of MSG and variations in central nitric oxide (NO) concentration could be established. We found that a dose of 300 mg/kg MSG given for 21 days reduces the pain threshold and is associated with a significant increase in brain NO level. The implications of these findings on food additive-drug interaction, and on pain perception in healthy humans, as well as in those suffering from affections involving chronic pain, are still to be investigated.

Antinociceptive and anticonvulsant effects of the monoterpene linalool oxide

CONTEXT

Linalool oxide (OXL) (a monoterpene) is found in the essential oils of certain aromatic plants, or it is derived from linalool. The motivation for this work is the lack of psychopharmacological studies on this substance.

OBJECTIVE

To evaluate OXL's acute toxicity, along with its anticonvulsant and antinociceptive activities in male Swiss mice.

MATERIAL AND METHODS

OXL (50, 100 and 150 mg/kg, i.p.) was investigated for acute toxicity and in the Rota-rod test. Antinociceptive activity was evaluated by the acetic acid-induced writhing test, and by formalin testing. Anticonvulsant effects were demonstrated by testing for pentylenetetrazol (PTZ)-induced seizures and by Maximum Electroshock headset (MES) test. OXL was administered to the animals intraperitoneally 30 min before for pharmacological tests.

RESULTS

OXL showed an LD₅₀ of ∼721 (681-765) mg/kg. In the Rota-rod test, it was observed that OXL caused no damage to the animal's motor coordination. OXL significantly reduced (p < .001) the number of writhings. OXL also significantly decreased (p < .05, p < .01 or p < .001) paw-licking time in the two phases of the formalin test. OXL significantly reduced (p < .01 or p < .001) the duration of tonic seizures in the MES test, and at the dose 150 mg/kg, significantly increased (p < .01) the latency to first seizure in the PTZ test.

CONCLUSION

The tested doses of OXL were safe, with no motor impairment, and show clear antinociceptive and anticonvulsant potential. Future investigations with this monoterpene may lead to the development of a new molecule with even higher potency and selectivity.

Corneal antinociceptive effect of (-)-α-bisabolol

CONTEXT

(-)-α-Bisabolol (BISA) is a sesquiterpene alcohol widely used as scent in cosmetic preparations, perfumes, shampoos, toilet soaps and other toiletries with potential for use in the pharmaceutical area.

OBJECTIVE

To evaluate the corneal antinociceptive efficacy of BISA and to analyze the best solubilizing agent.

MATERIALS AND METHODS

Acute corneal nociception was induced by the local application of hypertonic saline (5 M NaCl; 20 μL) to the corneal surface of Swiss mice (n = 8/group) 60 min after topical treatment with solutions or ointment containing BISA (50-200 mg/mL). The number of eye wipes performed with the ipsilateral forepaw was counted for a period of 30 s. Control groups (vehicles) were included.

RESULTS

BISA (50, 100 or 200 mg/mL) solubilized with Tween 80 did not reduce the number of eye wipes. Animals treated with the ointment (BISA 50, 100 or 200 mg/mL; p < 0.001), as well the solution containing propylene glycol (BISA 100 mg/mL; p < 0.05), showed significant reduction in the number of nociceptive behaviours. Solutions containing propylene glycol and isopropyl myristate had no effects.

DISCUSSION AND CONCLUSION

BISA possess corneal antinociceptive activity. Although the ointment presented antinociceptive effect, it is concluded that BISA when associated with propylene glycol has better potential for corneal nociceptive pain since it is more comfortable to use, leading to greater acceptance by patients.

Visual reminders of death enhance nociceptive-related cortical responses and event-related alpha desynchronisation

Previous research suggests that prompting individuals to think on their own mortality affects their perception of painful somatic stimuli and related brain activity. Grounded on the assumption that reminders of mortality may recruit threat-defence mechanisms similar to the ones activated by painful nociceptive stimuli, we hypothesize that the effects exerted by linguistic reminders of death on pain perception and brain activity would be elicited by passive observation of death-related pictures vs. more generic threat-related pictures. Results showed an increase of the laser evoked P2 amplitude and oscillatory theta activity when participants observed death-related images. However, no change in pain ratings was found. Moreover, observation of death-related content was linked to increased oscillatory alpha desynchronisation but not to variations of visual evoked potentials amplitude. Our findings indicate that pairing potentially noxious stimuli with death-related images exerts a preferential modulation of nociceptive and visual cortical representations.

Synthesis, antinociceptive activity and structure activity relationship of flavone derivatives

Flavonoids are phenolic compounds that have always attracted pharmaceutical researchers and food manufacturers. Nature has indirectly provided us flavones in our daily diet i.e. tea, fruits, juices and vegetables. Flavones have got special position in research field of natural and synthetic organic chemistry due to their biological capabilities. Flavone derivative has been synthesized in good yield from ketone and corresponding aldehydes. The structures have been established by different spectroscopic techniques like ¹H NMR, ¹³C NMR, IR and elemental analysis. The compounds were then screened for its acute toxicity and antinociceptive response in mice models with writhings induced by acetic acid, tail immersion and formalin-induced nociception assay procedures and structure activity relationship was established. The compounds were safe up to a maximum dose of 1200 mg/kg body weight in mice. The effects following pretreatment with naloxone were also studied to reveal the involvement of opioid receptors in the antinociceptive action. The flavone derivatives showed significant reduction in number of abdominal constrictions, increase in paw licking response time in both phases and a significant raise in latency time in nociception models. Moreover, the antinociceptive response was significantly attenuated by pretreatment with naloxone suggesting the involvement of opioid system in the antinociceptive action. The promising effects were shown by halogenated flavone. The flavone derivatives showed analgesic response in all models of nociception suggesting the involvement of opioid system in the antinociceptive action.

Evidence of anti-inflammatory and antinociceptive activities of Plinia edulis leaf infusion

ETHNOPHARMACOLOGICAL RELEVANCE

Plinia edulis (Vell.) Sobral (Myrtaceae) is native and endemic to the Brazilian Atlantic Rainforest. Popularly known as "cambucá", it has been used in folk medicine for the treatment of stomach disorders, diabetes, bronchitis, inflammation and as tonic. Although there are numerous records concerning its popular use as analgesic and anti-inflammatory, scientific information regarding these pharmacological activities is limited. Therefore, the aim of this study was to characterize the anti-inflammatory and antinociceptive activity of P. edulis leaf infusion (AEPe) in mice.

MATERIALS AND METHODS

The acetic acid-induced writhing response and mechanical nociceptive paw tests were used to evaluate the antinociceptive activity. Carrageenan-induced paw edema and lipopolysaccharide-induced peritonitis were used to investigate the anti-inflammatory activity. The substances in AEPe were identified by HPLC-MS analysis.

RESULTS

At the test doses 30-300mg/kg p.o., AEPe has clearly exhibited anti-inflammatory effects, reducing carrageenan-induced paw edema and inhibiting leukocyte recruitment into the peritoneal cavity. The infusion has shown significant antinociceptive activity in both models of nociception. Gallic acid, myricitrin, guaijaverin, quercitrin, quercetin, corosolic acid, maslinic acid, oleanolic acid and ursolic acid were identified in AEPe.

CONCLUSION

P. edulis infusion presented antinociceptive and anti-inflammatory activities in all experiments realized in this study, which could be related to the presence of triterpenoids and flavonoids. These results provide scientific support for the traditional use of this species in the management of pain and inflammation.

Tabernaemontana catharinensis ethyl acetate fraction presents antinociceptive activity without causing toxicological effects in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Tabernaemontana catharinensis (Apocynaceae) is a medicinal plant used for the treatment of painful and inflammatory disorders. Here, we investigated the antinociceptive potential of the ethyl acetate fraction (Eta) from T. catharinensis leaves and assessed its toxic effects in mice to validate its popular use.

MATERIALS AND METHODS

Adult male Swiss mice (30-35g) were used. The Eta antinociceptive effect (200-800mg/kg, oral route (p.o.)) was evaluated in the acetic acid, formalin, capsaicin and tail-immersion tests. Adverse effects were analyzed using rotarod and open-field tests, body temperature, biochemical analysis and gastric lesions assessment. To evaluate the acute (OECD 423) or sub-acute (OECD 407) toxicity of the Eta, it was administered orally at a single (2000mg/kg) or repeated doses (100-400mg/kg/day for 28 days), respectively. Mortality, behavioral changes, biochemical and hematological parameters were evaluated. The Eta effect on cellular viability also was evaluated.

RESULTS

Eta (200-800mg/kg) inhibited the nociception caused by acetic acid (93.9±1.5%), formalin (86.2±10.8%) or capsaicin (75.4±3.3%) without inducing gastric lesions. Moreover, Eta neither altered the body temperature, biochemical parameters, nor forced or spontaneous locomotor activity of mice. The acute administration of the Eta (2000mg/kg) promoted a decrease in blood glucose levels and alanine aminotransferase activity. In the sub-acute toxicity study, Eta increased the aspartate aminotransferase activity (400mg/kg) and platelet distribution width (200mg/kg). Furthermore, Eta did not alter the cellular viability in cortical slices.

CONCLUSIONS

Eta presents antinociceptive effects and mild toxicity in mice. These results support its traditional use as a potential analgesic.

MRI scanner environment increases pain perception in a standardized nociceptive paradigm

Functional magnetic resonance imaging (MRI) has been widely used in neuroscientific studies to investigate neural correlates of perception and higher cognitive functions. Early on, the MR-scanning procedure itself has been identified to create discomfort and anxiety in some individuals, which may influence task performance and perception. The present study analyzed behavioral differences in pain intensity ratings obtained in two distinct situations: MR environment and laboratory setting. Within our longitudinal study design twenty healthy volunteers were exposed daily to an identical paradigm consisting of 60 repeated noxious heat stimuli (46 °C) on 21 consecutive days. After each block of ten stimuli, participants were prompted to rate pain intensity on a visual analog scale (VAS). On days 1, 8, 14, and 21 ratings scores were obtained during a functional imaging scan, whereas on the remaining days the sessions were conducted in a laboratory. It has come to our attention that pain intensity ratings acquired in MR environment were significantly higher than behavioral data collected in the lab setting. Given that the stimuli were standardized and no task or distraction confounded the ratings, it is likely that the attentional focus on noxious stimulation was identical in both conditions. It seems that the highly artificial scanner environment as such is sufficient to increase awareness/alertness. Given that salience rather than pure nociceptive input has been suggested to explain functional imaging results in painful conditions, these findings highlight concerns regarding the comparability of behavioral data assembled across inconsistent settings.

Evaluation of antinociceptive and antidiarrhoeal properties of Manilkara zapota leaves in Swiss albino mice

Context Manilkara zapota (L.). P. Royen. (Sapotaceae) has been used in folk medicine to treat pain, diarrhoea, inflammation, arthralgia, and other disorders. Objective Screening of Manilkara zapota leaves ethanol extract and its different solvent soluble fractions for possible antinociceptive and antidiarrhoeal activities in Swiss albino mice. Materials and methods The extract and various fractions (200 and 400 mg/kg body weight; p.o.) were tested for peripheral and central antinociceptive activity by acetic acid-induced writhing and radiant heat tail-flick method, respectively; castor oil-induced diarrhoeal model was used to evaluate antidiarrhoeal activity at both doses. All the samples were administered once in a day and the duration of study was approximately 5 h. Results Ethanol extract (400 mg/kg), petroleum ether fraction (400 mg/kg), and ethyl acetate fraction (400 mg/kg) showed significant peripheral antinociceptive activity having 59.89, 58.24, and 46.7% (p < 0.001) of writhing inhibition, respectively, which is comparable with that of standard diclofenac (59.34% inhibition). The ethanol extract (400 mg/kg) and petroleum ether fraction (400 mg/kg) also showed promising central analgesic activity having 74.15 and 82.15% (p < 0.001) elongation of reaction time, respectively, at 90 min after administration of sample which is also similar to that obtained by morphine (85.84% elongation). In antidiarrhoeal activity screening, ethanol extract (200 and 400 mg/kg) showed significant inhibition of defecation by 53.57 and 60.71%, respectively (p < 0.001) compared with that of loperamide (71.42%). Discussion and conclusion The findings of the studies demonstrated antinociceptive and antidiarrhoeal activities of M. zapota leaves which could be the therapeutic option against pain and diarrhoeal disease.

Assessment of anti-inflammatory, antinociceptive, immunomodulatory, and antioxidant activities of Cajanus cajan L. seeds cultivated in Egypt and its phytochemical composition

CONTEXT

Cajanus cajan L. (Fabaceae), a food crop, is widely used in traditional medicine.

OBJECTIVES

The phytochemical composition of C. cajan seeds and evaluation of the anti-inflammatory, immunomodulatory, antinociceptive, and antioxidant activities were studied.

MATERIALS AND METHODS

Unsaponifiable matter and fatty acids were analyzed by GC and GC/MS. The n-butanol fraction was chromatographed on polyamide column. The anti-inflammatory activity of hexane extract (200 and 400 mg/kg, p.o.) was evaluated using the carrageenan-induced rat paw edema at 1, 2, and 3 h. The serum tumor necrosis factor-α, interleukin-6, and immunoglobulin G levels were detected by ELISA. The hexane extract antinociceptive activity was determined by adopting the writhing test in mice. DPPH radical scavenging, total reduction capability, and inhibition of lipid peroxidation of butanol fraction were evaluated.

RESULTS AND CONCLUSION

Twenty-one unsaponifiable compounds (mainly phytol, 2,6-di-(t-butyl)-4-hydroxy-4-methyl-2,5-cyclohexadiene-1-one, β-sitosterol, stigmasterol, and campesterol), as well as 12 fatty acids (primarily 9,12-octadecadienoic and palmitic acids) were identified in hexane extract of C. cajan seeds. n-BuOH fraction contains quercetin-3-O-β-d-glucopyranoside, orientin, vitexin, quercetin, luteolin, apigenin, and isorhamnetin. For the first time, quercetin-3-O-β-d-glucopyranoside is isolated from C. cajan plant. The hexane extract (200 and 400 mg/kg) inhibited carrageenan-induced inflammation by 85 and 95%, respectively, 3 h post-carrageenan challenge. This was accompanied by an 11 and 20%, 8 and 13%, respectively, decrease of TNF-α and IL-6, as well as significant decrease in IgG serum levels. Moreover, hexane extract (200 and 400 mg/kg) decreased the number of writhings by 61 and 83%, respectively. The butanol fraction showed DPPH radical scavenging (inhibitory concentration (IC50) value: 9.07 μg/ml).

Mechanical Conflict System: A Novel Operant Method for the Assessment of Nociceptive Behavior

A new operant test for preclinical pain research, termed the Mechanical Conflict System (MCS), is presented. Rats were given a choice either to remain in a brightly lit compartment or to escape to a dark compartment by crossing an array of height-adjustable nociceptive probes. Latency to escape the light compartment was evaluated with varying probe heights (0, .5, 1, 2, 3, and 4 mm above compartment floor) in rats with neuropathic pain induced by constriction nerve injury (CCI) and in naive control rats. Escape responses in CCI rats were assessed following intraperitoneal administration of pregabalin (10 and 30 mg/kg), morphine (2.5 and 5 mg/kg), and the tachykinin NK1 receptor antagonist, RP 67580 (1 and 10 mg/kg). Results indicate that escape latency increased as a function of probe height in both naive and CCI rats. Pregabalin (10 and 30 mg/kg) and morphine (5 mg/kg), but not RP 67580, decreased latency to escape in CCI rats suggesting an antinociceptive effect. In contrast, morphine (10 mg/kg) but not pregabalin (30 mg/kg) increased escape latency in naive rats suggesting a possible anxiolytic action of morphine in response to light-induced fear. No order effects following multiple test sessions were observed. We conclude that the MCS is a valid method to assess behavioral signs of affective pain in rodents.

Antinociceptive properties of selective MT(2) melatonin receptor partial agonists

Melatonin is a neurohormone involved in the regulation of both acute and chronic pain whose mechanism is still not completely understood. We have recently demonstrated that selective MT2 melatonin receptor partial agonists have antiallodynic properties in animal models of chronic neuropathic pain by modulating ON/OFF cells of the descending antinociceptive system. Here, we examined the antinociceptive properties of the selective MT2 melatonin receptor partial agonists N-{2-[(3-methoxyphenyl)phenylamino]ethyl}acetamide (UCM765) and N-{2-[(3-bromophenyl)-(4-fluorophenyl)amino]ethyl}acetamide (UCM924) in two animal models of acute and inflammatory pain: the hot-plate and formalin tests. UCM765 and UCM924 (5-40 mg/kg, s.c.) dose-dependently increased the temperature of the first hind paw lick in the hot-plate test, and decreased the total time spent licking the injected hind paw in the formalin test. Antinociceptive effects of UCM765 and UCM924 were maximal at the dose of 20mg/kg. At this dose, the effects of UCM765 and UCM924 were similar to those produced by 200 mg/kg acetaminophen in the hot-plate test, and by 3 mg/kg ketorolac or 150 mg/kg MLT in the formalin test. Notably, antinociceptive effects of the two MT2 partial agonists were blocked by the pre-treatment with the MT2 antagonist 4-phenyl-2-propionamidotetralin (4P-PDOT, 10 mg/kg) in both paradigms. These results demonstrate the antinociceptive properties of UCM765 and UCM924 in acute and inflammatory pain models and corroborate the concept that MT2 melatonin receptor may be a novel target for analgesic drug development.

Oxytocin - a multifunctional analgesic for chronic deep tissue pain

The treatment of chronic pain arising from deep tissues is currently inadequate and there is need for new pharmacological agents to provide analgesia. The endogenous paracrine hormone/neurotransmitter oxytocin is intimately involved in the modulation of multiple physiological and psychological functions. Recent experiments have given clear evidence for a role of oxytocin in the modulation of nociception. The present article reviews the existent human and basic science data related to the direct and indirect effects of oxytocin on pain. Due to its analgesic, anxiolytic, antidepressant and other central nervous system effects, there is strong evidence that oxytocin and other drugs acting through the oxytocin receptor could act as multifunctional analgesics with unique therapeutic value.

Non-pharmacological interventions for chronic pain in people with spinal cord injury

BACKGROUND

Chronic pain is frequent in persons living with spinal cord injury (SCI). Conventionally, the pain is treated pharmacologically, yet long-term pain medication is often refractory and associated with side effects. Non-pharmacological interventions are frequently advocated, although the benefit and harm profiles of these treatments are not well established, in part because of methodological weaknesses of available studies.

OBJECTIVES

To critically appraise and synthesise available research evidence on the effects of non-pharmacological interventions for the treatment of chronic neuropathic and nociceptive pain in people living with SCI.

SEARCH METHODS

The search was run on the 1st March 2011. We searched the Cochrane Injuries Group's Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (OvidSP), Embase (OvidSP), PsycINFO (OvidSP), four other databases and clinical trials registers. In addition, we manually searched the proceedings of three major scientific conferences on SCI. We updated this search in November 2014 but these results have not yet been incorporated.

SELECTION CRITERIA

Randomised controlled trials of any intervention not involving intake of medication or other active substances to treat chronic pain in people with SCI.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed risk of bias in the included studies. The primary outcome was any measure of pain intensity or pain relief. Secondary outcomes included adverse events, anxiety, depression and quality of life. When possible, meta-analyses were performed to calculate standardised mean differences for each type of intervention.

MAIN RESULTS

We identified 16 trials involving a total of 616 participants. Eight different types of interventions were studied. Eight trials investigated the effects of electrical brain stimulation (transcranial direct current stimulation (tDCS) and cranial electrotherapy stimulation (CES); five trials) or repetitive transcranial magnetic stimulation (rTMS; three trials). Interventions in the remaining studies included exercise programmes (three trials); acupuncture (two trials); self-hypnosis (one trial); transcutaneous electrical nerve stimulation (TENS) (one trial); and a cognitive behavioural programme (one trial). None of the included trials were considered to have low overall risk of bias. Twelve studies had high overall risk of bias, and in four studies risk of bias was unclear. The overall quality of the included studies was weak. Their validity was impaired by methodological weaknesses such as inappropriate choice of control groups. An additional search in November 2014 identified more recent studies that will be included in an update of this review.For tDCS the pooled mean difference between intervention and control groups in pain scores on an 11-point visual analogue scale (VAS) (0-10) was a reduction of -1.90 units (95% confidence interval (CI) -3.48 to -0.33; P value 0.02) in the short term and of -1.87 (95% CI -3.30 to -0.45; P value 0.01) in the mid term. Exercise programmes led to mean reductions in chronic shoulder pain of -1.9 score points for the Short Form (SF)-36 item for pain experience (95% CI -3.4 to -0.4; P value 0.01) and -2.8 pain VAS units (95% CI -3.77 to -1.83; P value < 0.00001); this represented the largest observed treatment effects in the included studies. Trials using rTMS, CES, acupuncture, self-hypnosis, TENS or a cognitive behavioural programme provided no evidence that these interventions reduce chronic pain. Ten trials examined study endpoints other than pain, including anxiety, depression and quality of life, but available data were too scarce for firm conclusions to be drawn. In four trials no side effects were reported with study interventions. Five trials reported transient mild side effects. Overall, a paucity of evidence was found on any serious or long-lasting side effects of the interventions.

AUTHORS' CONCLUSIONS

Evidence is insufficient to suggest that non-pharmacological treatments are effective in reducing chronic pain in people living with SCI. The benefits and harms of commonly used non-pharmacological pain treatments should be investigated in randomised controlled trials with adequate sample size and study methodology.

Evaluation of outcome of surgical excision of the nidus of osteoid osteoma of long bone

Osteoid osteoma is a benign bone tumour usually found in the lower extremities of children and young adults. This tiny bone tumour causes pain out of all proportion to its size and hinders the daily activities. This Quasi-experimental study conducted in the department of Orthopaedic surgery of BSMMU from January 2008 to December 2009. Twenty one patients were included in the study where purposive sampling technique was used on the basis of inclusion and exclusion criteria and all the ethical conditions were fulfilled. Diagnosis was almost obtained by taking history, clinical examination, and relevant investigations. Clinical variables were age, sex, site, pain, swelling, deformity and outcome variables were painless active life, removal of swelling, prevention of deformity, rate of recurrence. After localization of the tumour with the help of C arm, the nidus was excised in a small block of bone. The outcome is categorized by consensus, as clinically successful, only if the patient was free of pain and was taking no medication. The treatment was considered to have failed if a subsequent procedure had been performed to remove tumour. Among 21 cases, 14(66.7%) were male and 7(33.7%) were female. Maximum number of patients 15(71.4%) was between 10 years to 20 years. Most of the patients (76.2%) affected by osteoid osteoma were young students and most of the patients (95.2%) experienced moderate aching pain, usually aggravating at night which was typically relieved by aspirin or other NSAIDs (71.4%). Lower limbs (76.2%) particularly femur and tibia were commonly affected. Out of 21 patients, 19(90.5%) patients have got immediate pain relief or required no medication. In only 2 patients (9.5%), subsequent procedure has been performed to relief pain. So, successful outcome (in 19 out of 21) was significantly (p<0.001) higher in comparison to failed. Surgical excision of the nidus is a simple and easy procedure and does not require extensive resection of bone. If localization is done properly success rate is high and patients can return to normal daily activities.

Strategies to reduce or eliminate wound pain

Wound pain is often underestimated and poorly managed. This article explains the different types of pain and how to assess wound pain, and gives practical advice on how to manage or minimise the pain experienced by patients with wounds.

Synergistic analgesia of duloxetine and celecoxib in the mouse formalin test: a combination analysis

Duloxetine, a serotonin and noradrenaline reuptake inhibitor, and celecoxib, a non-steroidal anti-inflammatory drug, are commonly used analgesics for persistent pain, however with moderate gastrointestinal side effects or analgesia tolerance. One promising analgesic strategy is to give a combined prescription, allowing the maximal or equal efficacy with fewer side effects. In the current study, the efficacy and side effects of combined administration of duloxetine and celecoxib were tested in the mouse formalin pain model. The subcutaneous (s.c.) injection of formalin into the left hindpaw induced significant somatic and emotional pain evaluated by the biphasic spontaneous flinching of the injected hindpaw and interphase ultrasonic vocalizations (USVs) during the 1 h after formalin injection, respectively. Pretreatment with intraperitoneal (i.p.) injection of duloxetine or celecoxib at 1 h before formalin injection induced the dose-dependent inhibition on the second but not first phase pain responses. Combined administration of duloxetine and celecoxib showed significant analgesia for the second phase pain responses. Combination analgesia on the first phase was observed only with higher dose combination. A statistical difference between the theoretical and experimental ED₅₀ for the second phase pain responses was observed, which indicated synergistic interaction of the two drugs. Concerning the emotional pain responses revealed with USVs, we assumed that the antinociceptive effects were almost completely derived from duloxetine, since celecoxib was ineffective when administered alone or reduced the dosage of duloxetine when given in combination. Based on the above findings, acute concomitant administration of duloxetine and celecoxib showed synergism on the somatic pain behavior but not emotional pain behaviors.

Maternal deprivation is associated with sex-dependent alterations in nociceptive behavior and neuroinflammatory mediators in the rat following peripheral nerve injury

Early-life stress is associated with an increased risk of developing affective disorders and chronic pain conditions. This study examined the effect of maternal deprivation (MD) on nociceptive responding prior to and following peripheral nerve injury (L5-L6 spinal nerve ligation [SNL]). Because neuroimmune signaling plays an important role in pain and affective disorders, associated alterations in glial and cytokine expression were assessed in key brain regions associated with emotional and nociceptive responding, the hippocampus and prefrontal cortex. MD female, but not male, rats exhibited thermal hypoalgesia and mechanical allodynia compared with control (non-MD) counterparts. SNL resulted in mechanical and cold allodynia in MD and control rats of both sexes. However, MD females exhibited enhanced SNL-induced allodynic responding compared with non-MD counterparts. Interleukin 6 (IL-6) expression was reduced in the prefrontal cortex of MD-SNL males when compared with non-SNL counterparts. Glial fibrillary acidic protein and IL-1β expression in the hippocampus of MD-SNL males was increased compared with non-MD controls. MD-SNL females exhibited reduced tumor necrosis factor alpha in the prefrontal cortex with a concomitant increase in IL-6 and tumor necrosis factor alpha expression in the hippocampus, compared with either MD or SNL alone. In conclusion, MD female, but not male, rats exhibit enhanced nociceptive responding following peripheral nerve injury, effects that may relate to the distinct neuroinflammatory profile observed in female versus male rats.

PERSPECTIVE

This study demonstrates that females rats exposed to early-life stress exhibit enhanced neuropathic pain responding, effects that are associated with alterations in neuroinflammatory mediators. Increased understanding of the interactions among early-life stress, gender, and pain may lead to the identification of novel therapeutic targets for the treatment of chronic pain disorders.

Pharmacological characteristics of endokinin C/D-derived peptides in nociceptive and inflammatory processing in rats

Endokinins designated from the human TAC4 gene consist of endokinin A, endokinin B, endokinin C (EKC) and endokinin D (EKD). EKC/D is a peptide using the common carboxyl-terminal in EKC and EKD and consists of 12 amino acids, and exerts antagonistic effects on the induction of scratching behavior by substance P (SP). Some of SP-preferring receptor antagonists have several d-tryptophan (d-Trp); however, the pharmacological effect of EKC/D-derived peptides with d-Trp remains to be solved. Therefore, to clarify the pharmacological characteristics of EKC/D-derived peptides, effects of pretreatment with these peptides on SP-induced scratching and thermal hyperalgesia, formalin-induced flinching and carrageenan-induced inflammation were evaluated. Intrathecal administration of [d-Trp(8)]-EKC/D and [d-Trp(10)]-EKC/D showed a markedly long inhibitory effect, at least 14 h, whereas the antagonistic effects of [d-Trp(8,10)]-EKC/D and EKC/D without d-Trp disappeared after 1h. Furthermore, the inhibitory effect of [d-Trp(10)]-EKC/D-derived peptides was dependent on the number of amino acids from the amino-terminus, and the more numerous the amino acids, the more marked the antagonistic effect. Thus, these results indicate that the effective duration of EKC/D-derived peptides is dependent on the number of d-Trp in the carboxyl-terminal region and the amino-terminal region regulates the antagonistic effect of EKC/D.

Psychological factors contributing to perceptions pain intensity after acute orthopaedic injury

Psychological factors are capable of influencing an individual's perception of pain and may mediate the evolution from acute to chronic pain. Personality characteristics, such as alexithymia and anxiety sensitivity, can also influence perception of pain by somatising psychological distress associated with acute pain. The aim of this study was to understand if alexithymia and anxiety sensitivity interact with psychological distress at an early stage of recovery from orthopaedic injury, to accentuate perception of pain intensity and potentially mediate the development of chronic pain disorder. 62 patients who had recently suffered orthopaedic injury completed the British Pain Society Pain Rating Scale plus the Hospital Anxiety and Depression Scale, as well as measures of alexithymia and anxiety sensitivity. Pain intensity correlated with each of the psychological measures but a regression analysis found that only depression, in combination with anxiety sensitivity, contributed to a significant amount of the variance in pain scores. The authors suggest that early screening after orthopaedic injury could identify those vulnerable to developing persisting pain disorders. This could lead to effective early intervention using psychological methods of pain management to reduce the risk of acute pain evolving into a chronic pain disorder.

The impact of tramadol and dihydrocodeine treatment on quality of life of patients with cancer pain

BACKGROUND

Tramadol and dihydrocodeine (DHC) are analgesics of step 2 WHO analgesic ladder (opioids for mild to moderate pain, weak opioids) frequently used in the treatment of cancer pain of moderate intensity. The aim of the study was to assess the impact of tramadol and DHC treatment on quality of life (QL) and performance status (PS) of patients with cancer pain.

PATIENTS AND METHODS

Randomised, cross-over, clinical study of 40 opioid-naive patients with nociceptive cancer pain who received tramadol or DHC controlled release tablets for 7 days, and then drugs were switched and administered for another 7 days. Pain was assessed by visual analogue scale (VAS), QL by EORTC QLQ C 30, and PS by Eastern Cooperative Oncology Group (ECOG) and Karnofsky.

RESULTS

From 40 patients recruited, 30 completed the study. DHC treatment provided better analgesia (VAS). In QL functional scales, better emotional functioning in tramadol group and better global QL and cognitive functioning in DHC group were observed. In symptom scales, less fatigue, pain and sleep disturbances, less nausea and vomiting and better appetite in DHC group were noted. In tramadol group, less constipation and less financial problems were observed. No differences in dyspnoea and diarrhoea were noted. ECOG and Karnofsky PS were low and did not differ between tramadol and DHC groups.

CONCLUSIONS

Dihydrocodeine treatment was associated with better global QL, cognitive functioning, analgesia and appetite, less fatigue, sleep disturbances, nausea and vomiting. Tramadol therapy was connected with better emotional functioning, less constipation and financial problems. PS deteriorated in both tramadol and DHC groups.