Role of ERK in gender difference of fibromyalgia pain.

This study investigated the ERK pathway of the peripheral nervous system and discovered a gender-specific pattern of ERK activation in the dorsal root ganglion of an acid-induced chronic widespread muscular pain model. We employed a twice acid-induced chronic musculoskeletal pain model in rats to evaluate mechanical pain behavior in both male and female groups. We further conducted protein analysis of dissected dorsal root ganglions from both genders. Both male and female rats exhibited a similar pain behavior trend, with females demonstrating a lower pain threshold. Protein analysis of the dorsal root ganglion (DRG) showed a significant increase in phosphorylated ERK after the second acid injection in all groups. However, phosphorylation of ERK was observed in the dorsal root ganglion, with higher levels in the male ipsilateral group compared to the female group. Moreover, there was a no difference between the left and right sides in males, whereas the significant difference was observed in females. In conclusions, the administration of acid injections induced painful behavior in rats, and concurrent with this, a significant upregulation of pERK was observed in the dorsal root ganglia, with a greater magnitude of increase in males than females, and in the contralateral side compared to the ipsilateral side. Our findings shed light on the peripheral mechanisms underlying chronic pain disorders and offer potential avenues for therapeutic intervention.

Novel Pulsed Ultrahigh-frequency Spinal Cord Stimulation Inhibits Mechanical Hypersensitivity and Brain Neuronal Activity in Rats after Nerve Injury.

BACKGROUND: Spinal cord stimulation (SCS) is an important pain treatment modality. This study hypothesized that a novel pulsed ultrahigh-frequency spinal cord stimulation (pUHF-SCS) could safely and effectively inhibit spared nerve injury-induced neuropathic pain in rats. METHODS: Epidural pUHF-SCS (± 3V, 2-Hz pulses comprising 500-kHz biphasic sinewaves) was implanted at the thoracic vertebrae (T9 to T11). Local field brain potentials after hind paw stimulation were recorded. Analgesia was evaluated by von Frey-evoked allodynia and acetone-induced cold allodynia. RESULTS: The mechanical withdrawal threshold of the injured paw was 0.91 ± 0.28 g lower than that of the sham surgery (24.9 ± 1.2 g). Applying 5-, 10-, or 20-min pUHF-SCS five times every 2 days significantly increased the paw withdrawal threshold to 13.3 ± 6.5, 18.5 ± 3.6, and 21.0 ± 2.8 g at 5 h post-SCS, respectively (P = 0.0002, < 0.0001, and < 0.0001; n = 6 per group) and to 6.1 ± 2.5, 8.2 ± 2.7, and 14.3 ± 5.9 g on the second day, respectively (P = 0.123, 0.013, and < 0.0001). Acetone-induced paw response numbers decreased from pre-SCS (41 ± 12) to 24 ± 12 and 28 ± 10 (P = 0.006 and 0.027; n = 9) at 1 and 5 h after three rounds of 20-min pUHF-SCS, respectively. The areas under the curve from the C component of the evoked potentials at the left primary somatosensory and anterior cingulate cortices were significantly decreased from pre-SCS (101.3 ± 58.3 and 86.9 ± 25.5, respectively) to 39.7 ± 40.3 and 36.3 ± 20.7 (P = 0.021, and 0.003; n = 5) at 60 min post-SCS, respectively. The intensity thresholds for pUHF-SCS to induce brain and sciatic nerve activations were much higher than the therapeutic intensities and thresholds of conventional low-frequency SCS. CONCLUSIONS: Pulsed ultrahigh-frequency spinal cord stimulation inhibited neuropathic pain-related behavior and paw stimulation evoked brain activation through mechanisms distinct from low-frequency SCS.

Efficacy and safety of cervicothoracic epidural blood patch for patients with spontaneous intracranial hypotension.

BACKGROUND: Epidural blood patch (EBP) is a generally effective treatment for spontaneous intracranial hypotension (SIH) caused by cerebrospinal fluid (CSF) leakage through the spinal dura mater. It is still unclear; however, whether application near the leakage site (targeted EBP) is more effective than distal application (untargeted EBP). Further, EBP targeted to high thoracic or cervical spine levels is infrequent due to greater technical requirements and potential complications. Here, we examined the safety and efficacy of EBP applied to high thoracic or cervical spine levels. METHODS: We retrospectively reviewed the clinical and outcome data of 13 patients receiving cervical or high thoracic EBP for SIH. All patients were referred by neurologists following poor response to conservative treatment and presented with persistent headache aggravated by orthostatic changes. RESULTS: Neuroimaging confirmed CSF leakage and targeted EBP resulted in immediate pain improvement. Repeated injections provided additional improvement for patients with recurrent headache. No serious adverse events were documented during follow-up. CONCLUSION: Based on recent studies and our clinical experience, we conclude that EBP targeted to the high thoracic and cervical spine is safe and effective for early-stage SIH.

Behavioral Survey of Effects of Pulsed Radiofrequency on Neuropathic and Nociceptive Pain in Rats: Treatment Profile and Device Implantation.

OBJECTIVES: Pulsed radiofrequency (PRF) stimulation is widely used for intractable pain; however, there is no consensus on treatment protocols and appropriate types of pain. We compared effectiveness of bipolar and unipolar PRF on neuropathic or inflammatory pains, and of targets at the dorsal root ganglion (DRG) and sciatic nerve (SN). We also examined efficacy of repetitive PRF stimulations. This preclinical study could serve as an extensive survey before human trials. MATERIALS: Spare nerve injury (SNI)-induced neuropathic pain and complete Freund's adjuvant (CFA) injection-induced inflammatory pain were used. Behavioral responses were measured using von Frey test, acetone test, and Hargreave's test at preinjury and postinjury time points. In both models, we evaluated results of DRG stimulation with unipolar PRF (45 V) versus bipolar PRF (5 V), stimulation at DRG vs. SN, and repetitive stimulations. RESULTS: Both unipolar and bipolar PRFs reduced SNI- or CFA-induced pain for a similar duration. In the SNI model, PRF-DRG had a stronger effect on tactile pain than PRF-SN but lower effect on cold allodynia, whereas in the CFA model PRF-DRG and PRF-SN showed similar effects. Repetitive PRF stimulation, by open technique or implantation method, produced analogous effect by each stimulus, and no evident analgesic tolerance or neurological deficit was shown. CONCLUSIONS: PRF temporarily attenuates neuropathic and inflammatory pain. Bipolar PRF generates significant analgesia with a much lower electrical power than unipolar PRF. Meanwhile, the minor variant effects between PRF-DRG and PRF-SN may indicate distinct mechanisms. The sustained-analgesia by repetitive treatments suggests implantation technique could be a promising choice.

miR-200a-3p modulates gene expression in comorbid pain and depression: Molecular implication for central sensitization.

Chronic pain and depression are often comorbid exhibiting common clinical presentations and biological connections related to central nervous system sensitization. Epigenetic regulation of gene expression in the brain plays a crucial role in response to long-lasting stress and chronic pain, and microRNA imbalance in the prefrontal cortex (PFC) might be involved in central sensitization. Male Sprague Dawley rats were subjected to unpredictable chronic mild stress (UCMS) and spared nerve injury (SNI) to initiate depressive-like behavior and chronic pain behavior, respectively. The next-generation sequencing technique was employed to analyze PFC microRNAs in both the UCMS and SNI models. Rats exposed to either UCMS or SNI exhibited both depressive-like and chronic pain behaviors. Five specific microRNAs (miR-10a-5p, miR-182, miR-200a-3p, miR-200b-3p, and miR-429) were simultaneously down-regulated in the depressive-like and chronic pain models after 4 weeks of short-term stress. Gene ontology revealed that the 4-week period of stress enhanced neurogenesis. Only the miR-200a-3p level was continuously elevated under prolonged stress, suggesting roles of reduced neurogenesis, inflammatory activation, disturbed circadian rhythm, lipid metabolism, and insulin secretion in the co-existence of pain and depression. Thus we conclude that miR-200a-3p might be a specific biomarker of central sensitization in chronic pain and depression.

Laser acupuncture-induced analgesic effect and molecular alterations in an incision pain model: a comparison with electroacupuncture-induced effects.

Low-level laser acupuncture (LLLA) produces photobiomodulation through acupuncture point and is an alternative to low-level laser therapy. Although the analgesic effect of LLLA on chronic pain has been proven, its effect on acute postincisional pain has yet to be investigated. A plantar incision (PI) model was used to mimic human postsurgical pain. Male adult rats received GaAlAs laser irradiation at the right ST36 acupoint immediately after operation and on the following 4 days. Three laser treatment groups (two red laser groups with a 30- or 15-min treatment duration and one 30-min near-infrared laser group) were compared with sham LLLA and naive groups and an electroacupuncture (EA) group (separate study). Behavioral withdrawal thresholds of both hind paws were measured before and after incision. Expression of mitogen-activated protein kinases (p-ERK and p-p38), inducible nitric oxide synthase (iNOS), and tumor necrosis factor (TNF) in the spinal cord was analyzed. All three LLLA treatments attenuated post-PI tactile allodynia in the ipsilateral paw, but only the 30-min red laser treatment affected the contralateral paw and had similar efficacy to that of EA. All laser treatments barely reduced heat hyperalgesia in both hind paws. At 3 days after PI, the 30-min red laser group showed reversed increases of PI-induced p-ERK, p-p38, and iNOS but not TNF expression in the spinal cord. Repetitive LLLA treatments ameliorated PI-induced mechanical pain. The inhibition of multiple sensitization signals highlights the unique clinical role of LLLA. Thus, LLLA is an alternative to EA as an adjuvant for postoperative pain control.

Risk of Acute Myocardial Infarction in Pneumoconiosis: Results from a Retrospective Cohort Study.

BACKGROUND: Pneumoconiosis (PCN) has several comorbidities, most notably pulmonary and cardiovascular diseases. However, much is still unknown about the relationship between PCN and acute myocardial infarction (AMI). The present study aimed to clarify the association between PCN and subsequent AMI risk using a retrospective cohort study design. METHODS: This was a population-based, retrospective cohort study that used data from Taiwan's National Health Insurance Database. A total of 7556 newly diagnosed patients with PCN and 7556 individuals without PCN were included in the PCN and comparison cohort (PC and CC), respectively, between 2008 and 2018, with propensity score matching for age, gender, comorbidity, medication, and date of PCN diagnosis. The occurrence of AMI was monitored until the end of 2019, and AMI risk was assessed using Cox proportional hazard regression models. RESULTS: The overall incidence of AMI was 1.34-fold higher in the PC than in the CC (4.33 vs. 3.23 per 1000 person-years, respectively, p < 0.05), with an adjusted hazard ratio (aHR) of 1.36 (95% confidence interval (CI): 1.08-1.72) after controlling for age, gender, comorbidity, and medication. Further analyses showed a higher risk of AMI with increased annual number of emergency department visits among patients with PCN (aHR: 1.30, 95% CI: 1.01-1.66 (<1) and aHR: 1.68, 95% CI: 1.13-2.50 (≥1)). CONCLUSION: Patients with PCN had a significantly higher risk of developing AMI than those without PCN. Clinicians should pay more attention to prevent AMI episodes in patients with PCN.

Combination of nerve blockade and intravenous alfentanil is better than single treatment in relieving postoperative pain.

BACKGROUND/PURPOSE: Multimodal analgesia can improve perioperative analgesia but knowledge of combination protocols is still incomplete. This study was designed to evaluate whether the combination of sciatic nerve blockade (SNB) and intravenous alfentanil (IVA) is more effective than either single treatment in relieving postoperative pain in rats. METHODS: In a plantar incision model, withdrawal thresholds were evaluated by von Frey test before incision as baselines and for 7 days after incision. The animals were randomly allocated into various groups to receive SNB with 1% or 2% lidocaine, IVA of 50 or 150 µg/kg, or combined treatments (SNB 1% + 50 µg/kg IVA or SNB 2% + 150 µg/kg IVA) before incision. The results were compared with those of sham procedures--i.e., injections of peri-sciatic or intravenous saline, or a combination of both. RESULTS: Plantar incision caused postoperative allodynia for 3 days. SNB with 2% lidocaine reduced allodynia at 1 hour, 3 hours, day 1, and day 2, but not at postoperative 5 hours or days 3-7, whereas 150 µg/kg IVA produced short analgesia for only 3 hours after surgery. Neither low-dose SNB nor low-dose IVA had a significant effect. When high-dose SNB and high-dose IVA were combined, a strong antiallodynic effect was shown in an additive manner. No synergism was evidently displayed by the combination. CONCLUSION: Our results indicated that in an incisional pain model, multimodal analgesia is superior to single or no pretreatment; however, the combination of multimodal analgesic treatments should be individually discerned depending on nociceptive types and analgesic mechanisms.

Prescription Opioid Use among Patients with Chronic Noncancer Pain before and after the COVID-19 Outbreak in Taiwan: A Multicenter Prospective Observational Study.

BACKGROUND: The COVID-19 outbreak disrupted medical access for patients receiving chronic opioid therapy. This study investigated their prescription opioid dosages before and after the 2020 outbreak in Taiwan. METHODS: A prospective questionnaire survey was conducted among registered outpatients receiving long-term opioids before July 2019 in Taiwan. The questionnaire included items from the Taiwanese Brief Pain Inventory and quality of life assessment. Follow-up surveys in outpatient departments through October 2020 were conducted to collect opioid prescription data. RESULTS: After a mean of 531 days, the questionnaire responses of 103 of the initial 117 respondents were reviewed. Daily opioid doses decreased for 31 respondents (30.1%), remained roughly equivalent (defined as ±2.5%) for 27 (26.2%), and increased for 45 (43.7%) after the first wave of the pandemic. The use of strong opioids and nonopioid medications did not significantly differ among the three groups, but less fentanyl patch use was noted in the decreased-dose group after the outbreak. More than 70% of the patients received daily high-dose opioids (≥90 morphine milligram equivalents); moreover, 60% reported constipation. No deaths due to opioid overdose occurred during the study period. CONCLUSIONS: The COVID-19 outbreak in 2020 did not interrupt access to long-term opioid prescriptions for most registered patients with chronic pain in Taiwan. Less fentanyl patch use was observed in participants whose opioid dose was tapering.

Microglia: a promising target for treating neuropathic and postoperative pain, and morphine tolerance.

Management of chronic pain, such as nerve-injury-induced neuropathic pain associated with diabetic neuropathy, viral infection, and cancer, is a real clinical challenge. Major surgeries, such as breast and thoracic surgery, leg amputation, and coronary artery bypass surgery, also lead to chronic pain in 10-50% of individuals after acute postoperative pain, partly due to surgery-induced nerve injury. Current treatments mainly focus on blocking neurotransmission in the pain pathway and have only resulted in limited success. Ironically, chronic opioid exposure might lead to paradoxical pain. Development of effective therapeutic strategies requires a better understanding of cellular mechanisms underlying the pathogenesis of neuropathic pain. Progress in pain research points to an important role of microglial cells in the development of chronic pain. Spinal cord microglia are strongly activated after nerve injury, surgical incision, and chronic opioid exposure. Increasing evidence suggests that, under all these conditions, the activated microglia not only exhibit increased expression of microglial markers CD 11 b and Iba 1, but also display elevated phosphorylation of p38 mitogen-activated protein kinase. Inhibition of spinal cord p38 has been shown to attenuate neuropathic and postoperative pain, as well as morphine-induced antinociceptive tolerance. Activation of p38 in spinal microglia results in increased synthesis and release of the neurotrophin brain-derived neurotrophic factor and the proinflammatory cytokines interleukin-1ß, interleukin-6, and tumor necrosis factor-α. These microglia-released mediators can powerfully modulate spinal cord synaptic transmission, leading to increased excitability of dorsal horn neurons, that is, central sensitization, partly via suppressing inhibitory synaptic transmission. Here, we review studies that support the pronociceptive role of microglia in conditions of neuropathic and postoperative pain and opioid tolerance. We conclude that targeting microglial signaling might lead to more effective treatments for devastating chronic pain after diabetic neuropathy, viral infection, cancer, and major surgeries, partly via improving the analgesic efficacy of opioids.

Gender Differences in Depression and Sex Hormones among Patients Receiving Long-Term Opioid Treatment for Chronic Noncancer Pain in Taiwan-A Multicenter Cross-Sectional Study.

BACKGROUND: Long-term use of opioids for chronic noncancer pain is associated with sex hormone disturbances. The interferences with sex hormones, sexual function, and depression were investigated in patients with chronic noncancer pain. METHODS: A cross-sectional multicenter survey was conducted on 170 officially registered outpatients receiving long-term opioid treatment in nine medical centers in Taiwan between October 2018 and July 2019. Serum sex hormone levels were examined after the collection of self-administered questionnaires containing the Taiwanese version of the Brief Pain Inventory, depressive status, and sexual function interference. RESULTS: Among 117 (68.8%) questionnaire responses from 170 enrolled outpatients, 38 women and 62 men completed the sex hormone tests, among whom only 23 (23%) had previously received blood hormone tests. Low serum total testosterone levels were detected in 34 (89.5%) women (<30 ng/dL) and 31 (50%) men (<300 ng/dL). Over 60% of women and men reported reduced sexual desire and function despite a nearly 50% reduction in pain intensity and daily function interference over the previous week after opioid treatment. Women generally had higher risks of a depression diagnosis (p = 0.034) and severe depressive symptoms (p = 0.003) and nonsignificantly lower opioid treatment duration (median 81 vs. 120 months) and morphine milligram equivalent (median 134 vs. 165 mg/day) compared with men. CONCLUSIONS: This survey demonstrated the high prevalence of depression diagnosis, low sex hormone levels, and reduced sexual function among Taiwanese patients with chronic noncancer pain receiving prolonged opioid therapy. Regular hypogonadal screenings are recommended for further management.

Increased spinal prodynorphin gene expression in reinflammation-associated hyperalgesia after neonatal inflammatory insult.

BACKGROUND: Neuroplasticity induced by neonatal inflammation is the consequence of a combination of activity-dependent changes in neurons. We investigated neuronal sensitivity to a noxious stimulus in a rat model of neonatal hind-paw peripheral inflammation and assessed changes in pain behaviour at the physiological and molecular levels after peripheral reinflammation in adulthood. RESULTS: A decrease in paw withdrawal latency (PWL) after a heat stimulus was documented in rats that received inflammatory injections in their left hind paws on postnatal day one (P1) and a reinflammation stimulus at postnatal 6-8 weeks of age, compared with normal rats. An increase in the expression of the prodynorphin (proDYN) gene was noted after reinflammation in the spinal cord ipsilateral to the afferents of the neonatally treated hind paw. The involvement of the activation of extracellular signal-regulated kinases (ERK) in peripheral inflammatory pain hypersensitivity was evidenced evident by the increase in phospho-ERK (pERK) activity after reinflammation. CONCLUSIONS: Our results indicate that peripheral inflammation in neonates can permanently alter the pain processing pathway during the subsequent sensory stimulation of the region. Elucidation of the mechanism underlying the developing pain circuitry will provide new insights into the understanding of the early pain behaviours and the subsequent adaptation to pain.

DNIC-mediated analgesia produced by a supramaximal electrical or a high-dose formalin conditioning stimulus: roles of opioid and alpha2-adrenergic receptors.

BACKGROUND: Diffuse noxious inhibitory controls (DNIC) can be produced by different types of conditioning stimuli, but the analgesic properties and underlying mechanisms remain unclear. The aim of this study was to differentiate the induction of DNIC analgesia between noxious electrical and inflammatory conditioning stimuli. METHODS: First, rats subjected to either a supramaximal electrical stimulation or an injection of high-dose formalin in the hind limb were identified to have pain responses with behavioral evidence and spinal Fos-immunoreactive profiles. Second, suppression of tail-flick latencies by the two noxious stimuli was assessed to confirm the presence of DNIC. Third, an opioid receptor antagonist (naloxone) and an alpha2-adrenoreceptor antagonist (yohimbine) were injected, intraperitoneally and intrathecally respectively, before conditioning noxious stimuli to test the involvement of descending inhibitory pathways in DNIC-mediated analgesia. RESULTS: An intramuscular injection of 100 microl of 5% formalin produced noxious behaviors with cumulative pain scores similar to those of 50 microl of 2% formalin in the paw. Both electrical and chemical stimulation significantly increased Fos expression in the superficial dorsal horns, but possessed characteristic distribution patterns individually. Both conditioning stimuli prolonged the tail-flick latencies indicating a DNIC response. However, the electrical stimulation-induced DNIC was reversed by yohimbine, but not by naloxone; whereas noxious formalin-induced analgesia was both naloxone- and yohimbine-reversible. CONCLUSIONS: It is demonstrated that DNIC produced by different types of conditioning stimuli can be mediated by different descending inhibitory controls, indicating the organization within the central nervous circuit is complex and possibly exhibits particular clinical manifestations.

Activation of p38 mitogen-activated protein kinase in spinal microglia contributes to incision-induced mechanical allodynia.

BACKGROUND: Recent studies have implicated the activation of stress-activated mitogen-activated protein kinase (MAPK) p38 in spinal microglial cells for development of neuropathic and inflammatory pain. The aim of the present study was to investigate whether phosphorylation of p38 (p-p38) also mediates mechanical allodynia and thermal hyperalgesia induced by plantar incision. METHODS: After rats received a plantar incision surgery, mechanical allodynia and thermal hyperalgesia were determined by von Frey filaments and radiant heat, respectively, and the number of p-p38 immunoreactive cells in the dorsal horn was quantified to determine p38 activation at different time points after incision. The p38 inhibitor FR167653 was administered intrathecally 30 min before hind paw plantar incision to determine the role of p38 in postoperative pain. RESULTS: A significant increase in number of p-p38 immunoreactive cells was observed in the ipsilateral L4-5 spinal dorsal horn from 1 h to 3 days after the incision. p-p38 was found predominantly in microglia. However, microglial activation (assessed by OX-42 upregulation) was not evident until 3 days after plantar incision. Intrathecal pretreatment of FR167653 attenuated incision-induced mechanical allodynia from 1 h to day 2 and significantly reduced activation of p38 in the dorsal horn 1 day after plantar incision. However, FR167653 only inhibited heat hyperalgesia at an early time point. CONCLUSIONS: Plantar incision-induced mechanical allodynia can be prevented by the p38 inhibitor. Our results suggest that p38 activation in spinal microglia play a role in incision-induced mechanical allodynia in rats. Therefore, p38 inhibition may be useful in treating postsurgical pain.

Ovarian Hormone-dependent and Spinal ERK Activation-regulated Nociceptive Hypersensitivity in Female Rats with Acid Injection-induced Chronic Widespread Muscle Pain.

Symptoms of chronic widespread muscle pain (CWP) meet most of the diagnostic criteria for fibromyalgia syndrome, which is prevalent in females. We used an acid injection-induced muscle pain (AIMP) model to mimic CWP. After female rats received an ovariectomy (OVX), acid saline solution was injected into the left gastrocnemius muscle. Time courses of changes in pain behaviours and p-ERK in the spinal cord were compared between groups. Intrathecal injections of oestradiol (E2) to the OVX group before two acid injections and E2 or progesterone (P4) injections in male rats were compared to evaluate hormone effects. We found that repeated acid injections produced mechanical hypersensitivity and enhanced p-ERK expression in the spinal dorsal horn. OVX rats exhibited significantly less tactile allodynia than did the rats in the other groups. The ERK inhibitor U0126 alleviated mechanical allodynia with lower p-ERK expression in the sham females but did not affect the OVX rats. Intrathecal E2 reversed the attenuated mechanical hypersensitivity in the OVX group, and E2 or P4 induced transient hyperalgesia in male rats. Accordingly, our results suggested that ovarian hormones contribute to AIMP through a spinal p-ERK-mediated pathway. These findings may partially explain the higher prevalence of fibromyalgia in females than males.

A peptide c-Jun N-terminal kinase (JNK) inhibitor blocks mechanical allodynia after spinal nerve ligation: respective roles of JNK activation in primary sensory neurons and spinal astrocytes for neuropathic pain development and maintenance.

Optimal management of neuropathic pain is a major clinical challenge. We investigated the involvement of c-Jun N-terminal kinase (JNK) in neuropathic pain produced by spinal nerve ligation (SNL) (L5). SNL induced a slow (>3 d) and persistent (>21 d) activation of JNK, in particular JNK1, in GFAP-expressing astrocytes in the spinal cord. In contrast, p38 mitogen-activated protein kinase activation was found in spinal microglia after SNL, which had fallen to near basal level by 21 d. Intrathecal infusion of a JNK peptide inhibitor, D-JNKI-1, did not affect normal pain responses but potently prevented and reversed SNL-induced mechanical allodynia, a major symptom of neuropathic pain. Intrathecal D-JNKI-1 also suppressed SNL-induced phosphorylation of the JNK substrate, c-Jun, in spinal astrocytes. However, SNL-induced upregulation of GFAP was not attenuated by spinal D-JNKI-1 infusion. Furthermore, SNL induced a rapid (<12 h) but transient activation of JNK in the L5 (injured) but not L4 (intact) DRG. JNK activation in the DRG was mainly found in small-sized C-fiber neurons. Infusion of D-JNKI-1 into the L5 DRG prevented but did not reverse SNL-induced mechanical allodynia. Finally, intrathecal administration of an astroglial toxin, l-alpha-aminoadipate, reversed mechanical allodynia. Our data suggest that JNK activation in the DRG and spinal cord play distinct roles in regulating the development and maintenance of neuropathic pain, respectively, and that spinal astrocytes contribute importantly to the persistence of mechanical allodynia. Targeting the JNK pathway in spinal astroglia may present a new and efficient way to treat neuropathic pain symptoms.

A minimal stress model for the assessment of electroacupuncture analgesia in rats under halothane.

The use of anesthetics in acupuncture analgesia is controversial. We evaluate a steady-state light anesthesia model to test whether minimal stress manipulation and reliable measurement of analgesia could be simultaneously achieved during electroacupuncture (EA) in animals. A series of experiments were performed. Firstly, EA compliance and tail-flick latencies (TFL) were compared in rats under 0.1%, 0.3%, 0.5%, 0.7%, or 1.1% halothane for 120min. Under 0.5% halothane, TFL were then measured in groups receiving EA at intensity of 3, 10 or 20 volt (V), 1 or 2mg/kg morphine, 20V EA plus naloxone, or control. Subsequently, the effect of EA on formalin-induced hyperalgesia was tested and c-fos expression in the spinal dorsal horn was analyzed. Rats exhibited profound irritable behaviors and highly variable TFL under 0.1% or 0.3% halothane, as well as a time-dependent increase of TFL under 0.7% or 1.1% halothane. TFL remained constant at 0.5% halothane, and needle insertion and electrical stimulation were well tolerated. Under 0.5% halothane, EA increased TFL and suppressed formalin-induced hyperalgesia in an intensity-dependent and naloxone-reversible manner. EA of 20V prolonged TFL by 74%, suppressed formalin-induced hyperalgesia by 32.6% and decreased c-fos expression by 29.7% at the superficial and deep dorsal horn with statistically significant difference. In conclusion, 0.5% halothane provides a steady-state anesthetic level which enables the humane application of EA stimulus with the least interference on analgesic assessment. This condition serves as a minimal stress EA model in animals devoid of stress-induced analgesia while maintaining physiological and biochemical response in the experiment.

A novel fuzzy pain demand index derived from patient-controlled analgesia for postoperative pain.

A multilayer hierarchical structure for an intelligent analysis system is described in this paper. Four levels (patients', measurement, Web-based, and interpreting) are used to collect massive amounts from clinical information and analyze it with both traditional and artificial intelligent methods. To support this, a novel fuzzy pain demand (FPD) index derived from the interval of each bolus of patient-controlled analgesia (PCA) is designed and documented in a large-scale clinical survey. The FPD index is modeled according to a fuzzy modeling algorithm to interpret the self-titration of the drug delivery. A total of 255 patients receiving intravenous PCA using morphine (1 mg/ml) tested this index by offline analysis from this system. We found the FPD index modeled from a fuzzy modeling algorithm to interpret the self-titration of the drug delivery can show the patients' dynamic demand and past efforts to overcome the postoperative pain. Moreover, it could become an online system to monitor patients' demand or intent to treat their pain so these factors could be entered into a patient's chart along with temperature, blood pressure, pulse, and respiration rates when medical practitioners check the patients.

Rapid and Delayed Effects of Pulsed Radiofrequency on Neuropathic Pain: Electrophysiological, Molecular, and Behavioral Evidence Supporting Long-Term Depression.

BACKGROUND: Pulsed radiofrequency (PRF) has been widely employed for ameliorating clinical neuropathic pain. How PRF alters electrophysiological transmission and modulates biomolecular functions in neural tissues has yet to be clarified. We previously demonstrated that an early application of low-voltage bipolar PRF adjacent to the dorsal root ganglion (DRG) reduced acute neuropathic pain in animals. By contrast, the present study investigated how PRF alters postsynaptic sensitization to produce early and delayed effects on neuropathic pain. OBJECTIVES: Our objective was to test the hypothesis that a 5-minute session of PRF could rapidly produce selective long-term depression (LTD) on C-fiber-mediated spinal sensitization and sustain the effect through the long-lasting inhibition of injury-induced ERK-MAPK activation. This may explain the prolonged analgesic effect of PRF on chronic neuropathic pain. STUDY DESIGN: Experiments were conducted on both normal rats and neuropathic pain rats that received spinal nerve ligation (SNL) 8 days prior. SETTING: An animal laboratory in a medical center of a university in Taiwan. METHODS: We first compared changes in field potentials in the L5 superficial spinal dorsal horn (SDH) that were evoked by conditioning electrical stimuli in the sciatic nerve in male adult rats before (as the baseline) and after PRF stimulation for at least 2 hours. Bipolar PRF was applied adjacent to the L5 DRG at an intensity of 5 V for 5 minutes, whereas the control rats were treated with sham applications. The electrophysiological findings were tested for any correlation with induction of spinal phospho-ERK (p-ERK) in normal and neuropathic pain rats. We then investigated the delayed effect of PRF on SNL-maintained pain behaviors for 2 weeks as well as p-ERK in SDH among the control, SNL, and PRF groups. Finally, potential injury in the DRGs after PRF stimulation was evaluated through behavioral observations and ATF-3, a neuronal stress marker. RESULTS: In the evoked field-potential study, the recordings mediated through A- and C-afferent fibers were identified as A-component and C-component, respectively. PRF significantly reduced the C-components over 2 hours in both the normal and SNL rats, but it did not affect the A-components. In the SNL rats, the C-component was significantly depressed in the PRF group compared with the sham group. PRF also inhibited acute p-ERK induced by mechanical nociception in both the control and SNL rats. For a longer period, PRF ameliorated SNL-maintained mechanical allodynia for 10 days and thermal analgesia for 14 days, and it significantly reduced late ERK activation within spinal neurons and astrocytes 14 days afterward. Moreover, PRF in the normal rats did not alter basal withdrawal thresholds or increase the expression and distribution of ATF-3 in the DRGs. LIMITATIONS: Several issues should be considered before translating the animal results to clinical applications. CONCLUSIONS: Low-voltage bipolar PRF produces LTD through selective suppression on the C-component, but not on the A-component. It also inhibits ERK activation within neurons and astrocytes in SDHs. The findings suggest that PRF alleviates long-lasting neuropathic pain by selectively and persistently modulating C-fiber-mediated spinal nociceptive hypersensitivity.Key words: Pulsed radiofrequency (PRF), dorsal root ganglion (DRG), neuropathic pain, ERK activation, evoked field potential, ATF-3, long-term depression (LTD), spinal nerve ligation (SNL).

Spinal p38 activity and analgesic effect after low- and high-intensity electroacupuncture stimulation in a plantar incision rat model.

AIMS: Postoperative pain is a major problem. Electroacupuncture (EA) has been accepted as a useful and low-risk complementary therapy for post-operative pain. Animal studies indicate that surgical incision activates p38 MAPK in the spinal microglia, which critically contributes to post-incisional nociceptive development. How EA affects incision-induced p38 activation is important but yet to be fully elucidated. METHODS: Male adult rats received plantar incision (PI) at the right hind paw followed by 30-min EA of 4-Hz, one of two intensities (3 and 10mA), and at right ST36 (Zusanli) acupoint immediately after PI and for 3 successive days. EA analgesia was evaluated by von Frey fibers and Hargreaves' tests. Spinal p38 activation was examined by immunostaining. In separate groups, SB203580, a p38 inhibitor, was intrathecally injected alone or with EA to test the combining effect on nociception and spinal phospho-p38. KEY FINDINGS: EA of 10-mA significantly ameliorated mechanical allodynia, but 3-mA did not. None of them altered thermal hyperalgesia. Repeated EA could not inhibit phospho-p38 in the PI rats, contrarily, EA per se significantly induced phospho-p38 in the normal rats. Intrathecal SB203580 injection dose-dependently prevented PI-induced allodynia. Combination of low-dose SB203580 and 3-mA EA, which were ineffective individually, profoundly reduce post-PI allodynia. SIGNIFICANCE: We demonstrated that 10-mA EA exerts a significant inhibition against post-PI mechanical hypersensitivity via a p38-independent pathway. Importantly, co-treatment with low-dose p38 inhibitor and 3-mA EA can counteract spinal phospho-p38 to exert strong analgesic effect. Our finding suggests a novel strategy to improve EA analgesic quality.