Neuropathic Pain Affects Quality of Life in Breast Cancer Survivors with Chemotherapy-Induced Peripheral Neuropathy.

BACKGROUND: Despite the significant impact of chemotherapy-induced peripheral neuropathy on the quality of life for breast cancer survivors, there is a notable lack of comprehensive research. Therefore, a crucial need exists for further systematic investigation and inquiry into this matter. AIMS: This study examined predictors of quality of life in breast cancer survivors with chemotherapy-induced peripheral neuropathy. DESIGN: A cross-sectional, correlational design. SETTINGS: This study was conducted at a medical center in northern Taiwan and a teaching hospital in northeastern Taiwan. PARTICIPANTS/SUBJECTS: One hundred and thirty adult women with breast cancer, who have undergone chemotherapy and obtained a Total Neuropathy Scale-Clinical Version score>0, were enrolled. METHODS: Neuropathic pain, sleep disturbances, depression, and quality of life were evaluated using multiple regression analysis to identify quality of life predictors. Clinical importance was established using the minimally important difference of Functional Assessment of Cancer Therapy-Breast. RESULTS: The study indicated that improving depression (B = -10.87, p < .001) and neuropathic pain (B = -8.33, p = .004) may enhance the quality of life of breast cancer survivors with chemotherapy-induced peripheral neuropathy. Moreover, the individual's marital status and family history of breast cancer were identified as predictive factors. CONCLUSIONS: This study illuminates quality of life determinants for breast cancer survivors with chemotherapy-induced peripheral neuropathy, advocating comprehensive care and addressing depression and neuropathic pain for better outcomes.

Classification of circadian pain rhythms and pain characteristics in chronic pain patients: An observational study.

ABSTRACT: This study aimed to perform cluster analysis in patients with chronic pain to extract groups with similar circadian rhythms and compare neuropathic pain and psychological factors among these groups to identify differences in pain-related outcomes. A total of 63 community-dwellers with pain lasting at least 3 months and Numerical Rating Scale scores of ≥2 were recruited from 3 medical institutions. Their pain circadian rhythms were evaluated over 7 days by measuring pain intensity at 6-time points per day using a 10-cm visual analog scale. Cluster analysis was performed using 6 variables with standardized visual analog scale values at 6-time points for individual participants to extract groups with similar pain circadian rhythms. The results of the Neuropathic Pain Symptom Inventory and psychological evaluations in each group were compared using the Kruskal-Wallis test. The results revealed 3 clusters with different circadian rhythms of pain. The total and evoked pain subscale Neuropathic Pain Symptom Inventory scores differed among the 3 clusters. The results suggest that a thorough understanding of circadian pain rhythms in chronic pain patients may facilitate the performance of activities of daily living and physical exercise from the perspective of pain management.

Analgesic effects of cuminic alcohol (4-isopropylbenzyl alcohol), a monocyclic terpenoid, in animal models of nociceptive and neuropathic pain: Role of opioid receptors, L-arginine/NO/cGMP pathway, and inflammatory cytokines.

Cuminic alcohol (4-isopropylbenzyl alcohol; 4-IPBA) is a monocyclic terpenoid found in the analgesic medicinal plants Cuminum cyminum and Bunium persicum. The current study assessed the analgesic effects of 4-IPBA in different animal models of pain. Hot plate, formalin, and acetic acid tests were used to evaluate nociceptive pain in mice. The involvement of opioid receptors and the L-arginine/NO/cGMP/K+ channel pathway in 4-IPBA effects were investigated. Allodynia and hyperalgesia were assessed following peripheral neuropathy induced by chronic constriction of the sciatic nerve in rats. The spinal levels of inflammatory cytokines were measured using the ELISA method. The drugs and compounds were administered intraperitoneally. The results showed that 4-IPBA (200 and 400 mg/kg) significantly prolonged the hot plate latency. This effect was antagonized by naloxone (2 mg/kg). 4-IPBA (25-100 mg/kg) also significantly attenuated formalin- and acetic acid-induced nociceptive pain. L-arginine (200 mg/kg), sodium nitroprusside (0.25 mg/kg), and sildenafil (0.5 mg/kg) reversed while L-NAME (30 mg/kg) and methylene blue (20 mg/kg) potentiated the antinociceptive effects of 4-IPBA in the writhing test. Glibenclamide (10 mg/kg) and tetraethylammonium chloride (4 mg/kg) did not have any influence on the 4-IPBA effect. Furthermore, 4-IPBA (6.25-25 mg/kg) significantly relieved mechanical allodynia, cold allodynia, and hyperalgesia in rats. The concentrations of TNF-α and IL-1ß in the spinal cord of rats were decreased by 4-IPBA. No evidence of 4-IPBA-induced toxicity was found in behavioral or histopathological examinations. These results demonstrate that 4-IPBA attenuates nociceptive and neuropathic pain through the involvement of opioid receptors, the L-arginine/NO/cGMP pathway, and anti-inflammatory functions.

Pain management in hidradenitis suppurativa and a proposed treatment algorithm.

Pain contributes substantially to reduced quality of life in individuals living with hidradenitis suppurativa (HS). Although improved understanding of HS pathogenesis and treatment has resulted in improved evidence-based HS management guidelines, comprehensive pain management guidelines have yet to be developed. Few HS-specific data exist to guide pharmacologic analgesia; however, recognizing HS pain as either acute or chronic and predominantly nociceptive (aching and gnawing pain due to tissue damage) versus neuropathic (burning-type pain due to somatosensory nervous system dysfunction) provides a conceptual framework for applying outside pain management practices to HS management. This article incorporates the best available evidence from the HS and pain literature to propose an HS pain algorithm that integrates psychological, pharmacologic, and complementary and alternative treatment modalities.

Peripheral neuropathic pain.

Neuropathic pain (NP) can have either central nervous system causes or ones from the peripheral nervous system. This article will focus on the epidemiology, classifications, pathology, non-invasive treatments and invasive treatments as a general review of NP involving the peripheral nervous system. NP has characteristic symptomatology such as burning and electrical sensations. It occurs in up to 10% of the general population. Its frequency can be attributed to its occurrence in neck and back pain, diabetes and patients receiving chemotherapy. There are a wide range of pharmacologic options to control this type of pain and when such measures fail, numerous interventional methods can be employed such as nerve blocks and implanted stimulators. NP has a cost to the patient and society in terms of emotional consequences, quality of life, lost wages and the cost of assistance from the medical system and thus deserves serious consideration for prevention, treatment and control.

Can insights from placebo and nocebo mechanisms studies improve the randomized controlled trial?

Background and aims The randomized controlled trial (RCT) is currently facing several challenges, one of these being that the placebo response appears to be increasing in RCTs, thereby making it difficult to demonstrate an effect of potentially new treatments over placebo. This problem has primarily been approached by predicting the magnitude of the placebo response via stable factors, such as demographic variables, and/or by developing complex designs aimed at reducing the placebo response in the hope that it will improve the test of the active treatment. Yet, the success of this approach has so far been limited. Methods A new approach toward improving the RCT is put forward based on placebo and nocebo mechanism studies, i.e. studies that investigate the mechanisms underlying placebo analgesia and nocebo hyperalgesia. In a series of meta-analyses the magnitude of placebo and nocebo effects were determined. Experimental studies across nociplastic and neuropathic pain conditions and across pharmacological and acupuncture treatments investigated psychological and neurobiological mechanisms underlying these effects. The obtained results were used to make approximations of expectations to see if that could predict the placebo response in RCTs and function as a new way of tapping into the placebo component of treatment effects. Results The magnitude of placebo and nocebo effects is large and highly variable. Placebo effects exist across chronic pain conditions with varying degrees of known etiology as well as across pharmacological and non-pharmacological treatments. Patients' perception of the treatment, the verbal suggestions given for pain relief, and the patients' expectations toward pain relief contribute to the magnitude of the placebo effect and to pain relief following placebo interventions. Also, unintentional unblinding and patients' perception of a treatment markedly influence the treatment outcome. By making approximations of expectations toward treatment effects it was possible to predict the magnitude of the placebo response in RCTs. Conclusions and implications The new approach of tapping into or directly asking patients about their perception and expectations toward a treatment, along with the account of the natural history of pain, has the potential to improve the information that can be obtained from RCTs. Thus, by interfacing insights from placebo and nocebo mechanism studies, it may be possible to enhance the information that can be obtained from RCTs and to account for a large part of the variability in the placebo component of the overall treatment effect. This approach has the potential to improve the scientific evaluation of treatments, as well as to illustrate how the effect of treatments can be optimized in clinical practice, which is the crux of evidence-based medicine.

Evidence for the Efficacy of Scrambler Therapy for Cancer Pain: A Systematic Review.

BACKGROUND: Certain types of cancer pain have remained hard to control even by highly skilled pain experts. Uncontrolled cancer pain can have severe effects on quality of life, physical functioning, and leads to psychological distress. From this perspective, nonpharmacologic modalities of treatment are important. Neuromodulatory techniques, such as transcutaneous electrical nerve stimulation and scrambler therapy (ST), have gained popularity in recent times. ST is a relatively new therapy that has been used for the management of cancer pain resistant to pharmacologic management. Several studies have shown that ST is an effective therapy for this type of pain. OBJECTIVES: The aim of this study was to detect possible gaps in the literature regarding the efficacy of ST for cancer pain and formulate recommendations for research through a systematic review of the literature. STUDY DESIGN: A systematic review of the literature was performed following the recommendations of the PRISMA Statement. METHODS: PubMed and EMBASE were searched for studies that met the inclusion criteria using a predetermined search strategy. Reference list of retrieved studies and Google Scholar were used to verify that no relevant studies had been omitted. Data were extracted from the studies with a data extraction sheet. A qualitative analyses of the extracted data was undertaken. RESULTS: Twenty-seven studies were retrieved. Ten were articles that were categorized as literature reviews, including 7 general literature reviews not following a specific review methodology, 1 editorial, and 2 systematic reviews. Seventeen were original studies, including 2 single-arm trials, 1 randomized controlled trial, 4 pilot trials, 4 case reports, 2 retrospective studies, and 4 prospective studies. By and large, the available literature supports the use of ST as an effective therapy for the management of refractory cancer pain. However, the level of evidence for its application to cancer pain is not particularly strong, and improvement in pain with ST may even be owing to a placebo effect. LIMITATIONS: This study was not a meta-review. Because of the limited number of clinical trials on ST in cancer pain, such a meta-review could not meaningfully be performed. CONCLUSIONS: Methodologically sound, large randomized control trials are needed in this area. However at this stage, ST may be considered a good option for cancer patients suffering from pain that does not respond to pharmacologic treatment. KEY WORDS: Scrambler therapy, cancer, cancer pain, neuropathic pain, Calmare therapy, evidence, noninvasive pain treatment, chronic pain.

Progressive Muscle Relaxation and Mindfulness Meditation on Neuropathic Pain, Fatigue, and Quality of Life in Patients With Type 2 Diabetes: A Randomized Clinical Trial.

PURPOSE: To examine the effects of progressive muscle relaxation and mindfulness meditation on the severity of diabetic peripheral neuropathic pain (DPNP), fatigue, and quality of life in patients with type 2 diabetes. DESIGN: An assessor-blinded prospective randomized controlled trial. METHODS: Participants were randomly assigned to the relaxation group (RG; n = 28), meditation group (MG; n = 25), or control group (CG; n = 24). The mean age of participants was 64.2 ± 8.1 years in the RG, 61.6 ± 8.0 years in the MG, and 64.1± 6.6 years in the CG. Patients in the intervention groups performed progressive muscle relaxation or mindfulness meditation at their home for 12 weeks, 20 min daily. The CG received only an attention-matched controlled education on pancreas anatomy and diabetes. Data collection was performed at baseline and at weeks 12 and 14 using the VAS, FACIT Fatigue Scale (FACIT-F), and Neuropathic Pain Impact on Quality of Life Questionnaire (NePIQoL). FINDINGS: VAS scores were significantly lower in the RG and MG at week 12 (p < .05) and were statistically significant in the RG at week 14. Additionally, fatigue severity decreased significantly in the RG at weeks 12 and 14, compared to that in the CG (p < .05). While no significant difference was found in the quality of life scores between the study groups at weeks 12 and 14 (p > .05), a significant improvement in quality of life scores in the RG were provided at week 12 compared to those at baseline and week 14 (p < .05). CONCLUSIONS: Both progressive muscle relaxation and mindfulness meditation had a positive impact on providing pain relief in patients with DPNP. Moreover, progressive muscle relaxation also appeared to have a beneficial effect on fatigue. CLINICAL RELEVANCE: Based on the results, progressive muscle relaxation and mindfulness meditation can be recommended as supportive therapies for the management of DPNP.

Preliminary Effectiveness of Auricular Point Acupressure on Chemotherapy-Induced Neuropathy: Part 2 Laboratory-Assessed and Objective Outcomes.

PURPOSE: To manage chemotherapy-induced neuropathy (CIN), this paper explores reliable and valid objectives measures to evaluate the treatment effects of auricular point acupressure (APA). DESIGN/METHOD: This study was a repeated-measures one-group design. Participants received four weeks of APA to manage their CIN. The laboratory-assessed and objective outcomes included quantitative sensory testing, grip and pinch strength, and inflammatory biomarkers. Wilcoxon matched pairs signed-rank tests were conducted to determine change scores of outcomes at pre- vs. post- and pre- vs. 1-month follow-up. Spearman's rho correlation coefficient was used to examine the linear association of score changes of all objective study outcomes. RESULTS: Comparing pre-and-post APA, (1) the mean score of the monofilament for all lower extremity sites tested decreased after APA, indicating sensory improvement; (2) the suprathreshold pinprick stimuli mean scores on the upper extremities increased, except the scores from the index finger and thumb; (3) the pain tolerance of thumb and trapezius areas increased; (4) decreasing IL1ß (p = .05), IFNγ (p = .02), IL-2 (p = .03), IL-6 (p = .05), IL-10 (p = .05), and IP10/CXCL10 (p = .04) were observed pre-post APA. Conditional pain modulation was significantly (p< .05) associated with pain intensity (r = 0.55), tingling (r = 0.59); and IL1ß concentration (r = 0.53) pre-post APA. The sustained effects of 4-week APA were observed at the 1-month follow-up. CONCLUSIONS: Our study findings demonstrated the promising effectiveness of APA in the management of CIN, and these treatment effects can be assessed using reliable and valid objective measures. CLINICAL IMPLICATIONS: If the efficacy of APA to manage CIN is confirmed in a larger sample, APA has the potential to be a scalable treatment for CIN because it is a reproducible, standardized, and easy-to-perform intervention.

Preliminary Effectiveness of Auricular Point Acupressure on Chemotherapy-Induced Neuropathy: Part 1 Self-Reported Outcomes.

PURPOSE: To reduce chemotherapy-induced neuropathy (CIN)-a significant challenge among cancer patients following chemotherapy-we explored the effects of auricular point acupressure (APA), which involves needleless, acupuncture-like stimulation on specific ear points. DESIGN/METHOD: This pilot study examined the effects of a 4-week APA intervention in the management of CIN. Descriptive analysis was used to examine the changes in study outcomes. RESULTS: Fifteen participants were enrolled. Two participants dropped out because they developed new medical conditions. Thirteen participants completed the study (87% retention rate). Study participants had more severe symptoms in their lower extremities (i.e., toes, feet, soles) than in their upper extremities (i.e., fingers, wrists, elbows). After the 4-week APA intervention, the mean percentage change scores ranged from 38% (tingling) to 49% (numbness); compared to pre-intervention, the therapeutic effects of APA were sustained at the 1-month follow-up. Function in both upper and lower extremities improved after the APA intervention (≥28%) and continued to improve at the 1-month follow-up (≥36%). CONCLUSIONS: Preliminary results from this small sample provide initial evidence of the effectiveness of APA on CIN. Future studies should confirm these results using a larger sample, a comparative sham control, and an examination of the underlying physiological mechanisms of the anti-CIN effects of APA. CLINICAL IMPLICATIONS: APA may provide an inexpensive and effective complementary approach for the self-management of CIN. Once the seeds have been taped to the patient's ear by the provider, patients are empowered to self-manage their CIN in their own environment.

ß-Caryophyllene, a Natural Sesquiterpene, Attenuates Neuropathic Pain and Depressive-Like Behavior in Experimental Diabetic Mice.

Neuropathic pain (NP) is associated with chronic hyperglycemia and emotional disorders such as depression in diabetic patients, complicating the course of treatment. Drugs currently used to treat NP have undesirable side effects, so research on other natural sources has been required. ß-caryophyllene (BCP), a natural sesquiterpene found in some food condiments and considered an agonist to cannabinoid receptor type 2, could have potential therapeutic effects to treat conditions such as NP and emotional disorders. For this reason, we assessed whether BCP modulates nociception, anxiety, and depressive-like behavior in streptozotocin (STZ)-induced experimental diabetic BALB/c female mice. BCP was orally chronic administrated (10 mg/kg/60 µL). Pain developed with STZ was evaluated with von Frey filament test, SMALGO®, and hot plate test. Anxiety and depression-like behavior were assessed by marbles test, forced swim test, and tail suspension test. BCP significantly reduced glycemia in experimental diabetic mice. The pain was also mitigated by BCP administration. Depression-like behavior assessed with tail suspension test was attenuated with orally chronic BCP administration. Substance P and cytokines such as interleukin-1ß (IL-1ß), tumor necrosis factor α (TNF-α), and interleukin-6 (IL-6) were also attenuated with BCP administration. NP was positively correlated with substance P and IL-6 and IL-1ß release. Our data using an orally chronic BCP administration in the STZ challenged mice to suggest that glycemia, diabetes-related NP, and depressive-like behavior could be prevented/reduced by dietary BCP.

Kappa opioid signaling in the right central amygdala causes hind paw specific loss of diffuse noxious inhibitory controls in experimental neuropathic pain.

Diffuse noxious inhibitory controls (DNICs) is a pain-inhibits-pain phenomenon demonstrated in humans and animals. Diffuse noxious inhibitory control is diminished in many chronic pain states, including neuropathic pain. The efficiency of DNIC has been suggested to prospectively predict both the likelihood of pain chronification and treatment response. Little is known as to why DNIC is dysfunctional in neuropathic pain. Here, we evaluated DNIC in the rat L5/L6 spinal nerve ligation (SNL) model of chronic pain using both behavioral and electrophysiological outcomes. For behavior, nociceptive thresholds were determined using response to noxious paw pressure on both hind paws as the test stimulus before, and after, injection of a conditioning stimulus of capsaicin into the left forepaw. Functionally, the spike firing of spinal wide-dynamic-range neuronal activity was evaluated before and during noxious ear pinch, while stimulating the ipsilateral paw with von Frey hairs of increased bending force. In both assays, the DNIC response was significantly diminished in the ipsilateral (ie, injured) paw of SNL animals. However, behavioral loss of DNIC was not observed on the contralateral (ie, uninjured) paw. Systemic application of nor-binaltorphimine, a kappa opioid antagonist, did not ameliorate SNL-induced hyperalgesia but reversed loss of the behavioral DNIC response. Microinjection of nor-binaltorphimine into the right central amygdala (RCeA) of SNL rats did not affect baseline thresholds but restored DNIC both behaviorally and electrophysiologically. Cumulatively, these data suggest that net enhanced descending facilitations may be mediated by kappa opioid receptor signaling from the right central amygdala to promote diminished DNIC after neuropathy.

Dissociable Contributions of Precuneus and Cerebellum to Subjective and Objective Neuropathy in HIV.

Neuropathy, typically diagnosed by the presence of either symptoms or signs of peripheral nerve dysfunction, remains a frequently reported complication in the antiretroviral (ART)-treated HIV population. This study was conducted in 109 healthy controls and 57 HIV-infected individuals to investigate CNS regions associated with neuropathy. An index of objective neuropathy was computed based on 4 measures: deep tendon ankle reflex, vibration sense (great toes), position sense (great toes), and 2-point discrimination (feet). Subjective neuropathy (self-report of pain, aching, or burning; pins and needles; or numbness in legs or feet) was also evaluated. Structural MRI data were available for 126/166 cases. The HIV relative to the healthy control group was impaired on all 4 signs of neuropathy. Within the HIV group, an objective neuropathy index of 1 (bilateral impairment on 1 measure) or 2 (bilateral impairment on at least 2/4 measures) was associated with older age and a smaller volume of the cerebellar vermis. Moderate to severe symptoms of neuropathy were associated with more depressive symptoms, reduced quality of life, and a smaller volume of the parietal precuneus. This study is consistent with the recent contention that ART-treated HIV-related neuropathy has a CNS component. Distinguishing subjective symptoms from objective signs of neuropathy allowed for a dissociation between the precuneus, a brain region involved in conscious information processing and the vermis, involved in fine tuning of limb movements. Graphical Abstract In HIV patients, objective signs of neuropathy correlated with smaller cerebellar vermis (red) volumes whereas subjective symptoms of neuropathy were associated with smaller precuneus (blue) volumes.

QAPSA: post-marketing surveillance of capsaicin 8% patch for long-term use in patients with peripheral neuropathic pain in France.

OBJECTIVE: To describe the characteristics of patients treated with the capsaicin 8% patch, prescribing conditions, long-term effects of repeat treatment on pain intensity and perception, quality of life, and impact on concomitant medication. METHODS: A national, longitudinal, prospective, non-interventional, post-marketing open study was conducted in 50 French pain centers. Adult volunteer non-diabetic patients with peripheral neuropathic pain receiving capsaicin 8% patch treatment were consecutively enrolled. Treatment could be repeated over a 12-month period, with 6 months' follow-up after last application. RESULTS: A total of 684 patients (age: 53.0 ± 14.9 years, mean ± standard deviation; post-traumatic/surgical peripheral neuropathic pain: 76.3%; pain intensity: 6.2 ± 1.7; pain duration: 3.0 years, median) were treated with 1 to 5 patches at 3/4 month intervals; 70.3% were naive to capsaicin 8% patch treatment at inclusion. Six months after last application, treatment was considered as successful for 21.8% (95% confidence interval: 17.5%-26.7%) of patients by a stringent criterion combining improvement according to the patient's global impression of change (PGIC) and at least 30% improvement on a numerical pain rating scale (NPRS). Clinically relevant improvement in health-related quality of life was observed at end-of-study. No unexpected safety concerns were observed with capsaicin 8% patch repeat treatment. CONCLUSIONS: The data of this post-marketing study meets the request by the French authorities for additional data on conditions of use in everyday practice. They confirmed the tolerance and long-term effect of capsaicin 8% patch in patients with peripheral neuropathic pain in real-world conditions.

Efficacy of Internet-Delivered Mindfulness for Improving Depression in Caregivers of People With Spinal Cord Injuries and Chronic Neuropathic Pain: A Randomized Controlled Feasibility Trial.

OBJECTIVES: To explore the feasibility and efficacy of web-based mindfulness training for carers of people with spinal cord injury (SCI). DESIGN: Randomized controlled feasibility study with 3-month follow-up. SETTING: Community setting. PARTICIPANTS: Spouses or family caregivers (N=55) of people with SCI and chronic neuropathic pain were recruited via the direct care team and advertisements. Participants were older than 18 years (no upper age limit), with Internet access for the duration of the study. Participants were randomly allocated to an 8-week online mindfulness training intervention (n=28), or to receive 8 weeks of psychoeducational materials on SCI and chronic pain (n=27). INTERVENTIONS: An established web-based, mindfulness training course was delivered over 8 weeks. Participants completed 10 minutes of mindfulness practices, twice per day, 6 days per week, totaling 960 minutes. The control group received a weekly e-mail with psychoeducational materials (based on the established elements) on SCI and pain for 8 weeks. MAIN OUTCOME MEASURE: Depression severity. RESULTS: Mindfulness reduced depression severity more than psychoeducation at T2 (mean difference= -.891; 95% confidence interval,-1.48 to -.30) and T3 (mean difference=-1.96; 95% confidence interval, -2.94 to -.97). Mindfulness training also reduced anxiety at T2 (mean difference=-.888; 95% confidence interval, -1.40 to -.38) and T3 (mean difference=-2.44; 95% confidence interval, -3.20 to -1.69). CONCLUSIONS: Results indicate that Internet-delivered mindfulness training offers unique benefits and is viable for caregivers of people with SCI and chronic neuropathic pain. Further work should explore the feasibility of combined education and mindfulness training incorporating both patient and caregiver, for optimum benefit.

Fear extinction learning ability predicts neuropathic pain behaviors and amygdala activity in male rats.

Background The amygdala plays a key role in fear learning and extinction and has emerged as an important node of emotional-affective aspects of pain and pain modulation. Impaired fear extinction learning, which involves prefrontal cortical control of amygdala processing, has been linked to neuropsychiatric disorders. Here, we tested the hypothesis that fear extinction learning ability can predict the magnitude of neuropathic pain. Results We correlated fear extinction learning in naive adult male rats with sensory and affective behavioral outcome measures (mechanical thresholds, vocalizations, and anxiety- and depression-like behaviors) before and after the induction of the spinal nerve ligation model of neuropathic pain compared to sham controls. Auditory fear conditioning, extinction learning, and extinction retention tests were conducted after baseline testing. All rats showed increased freezing responses after fear conditioning. During extinction training, the majority (75%) of rats showed a decline in freezing level to 50% in 5 min (fear extinction+), whereas 25% of the rats maintained a high freezing level (>50%, fear extinction-). Fear extinction- rats showed decreased open-arm preference in the elevated plus maze, reflecting anxiety-like behavior, but there were no significant differences in sensory thresholds, vocalizations, or depression-like behavior (forced swim test) between fear extinction+ and fear extinction- types. In the neuropathic pain model (four weeks after spinal nerve ligation), fear extinction- rats showed a greater increase in vocalizations and anxiety-like behavior than fear extinction+ rats. Fear extinction- rats, but not fear extinction+ rats, also developed depression-like behavior. Extracellular single unit recordings of amygdala (central nucleus) neurons in behaviorally tested rats (anesthetized with isoflurane) found greater increases in background activity, bursting, and evoked activity in fear extinction- rats than fear extinction+ rats in the spinal nerve ligation model compared to sham controls. Conclusion The data may suggest that fear extinction learning ability predicts the magnitude of neuropathic pain-related affective rather than sensory behaviors, which correlates with differences in amygdala activity changes.

Neuropathic Pain Creates an Enduring Prefrontal Cortex Dysfunction Corrected by the Type II Diabetic Drug Metformin But Not by Gabapentin.

Chronic pain patients suffer from pain-related cognitive deficits, even when taking commonly prescribed analgesics. These deficits are likely related to pain-related maladaptive plasticity in the frontal cortex. We sought to model cognitive deficits in mice with neuropathic pain to examine maladaptive morphological plasticity in the mPFC and to assess the effects of several therapeutics. We used an attentional set-shifting task in mice with spared nerve injury (SNI) who received either a single intrathecal injection of an analgesic dose of clonidine, 7 d of 100 mg/kg gabapentin, or 7 d of 200 mg/kg metformin. Male SNI mice were significantly more impaired in the set-shifting task than females. This deficit correlated with a loss of parvalbumin (PV) and reductions in axon initial segment (AIS) length in layers 5/6 of the infralimbic (IL) cortex. Acute pain relief with clonidine had no effect on set-shifting performance, whereas pain relief via 7 day treatment with gabapentin worsened the impairment in both SNI and sham mice. Gabapentin reversed the PV loss in the IL but had no effect on AIS length. Treatment with the AMPK-activator metformin completely reversed the pain-related cognitive impairment and restored AIS length in the IL but had little effect on PV expression. Our findings reveal that neuropathic pain-related cognitive impairments in male mice are correlated to bilateral morphological changes in PV interneurons and layer 5/6 IL pyramidal neuron AIS. Pain relief with metformin can reverse some of the functional and anatomical changes.SIGNIFICANCE STATEMENT Cognitive impairments are a comorbidity of neuropathic pain but are inadequately addressed by existing therapeutics. We used a neuropathic pain model in mice to demonstrate that male (but not female) mice show a robust pain-related deficit in attentional set-shifting, which is associated with structural plasticity in axon initial segments in the infralimbic cortex. These deficits were completely reversed by 7 day treatment with the antidiabetic drug metformin, suggesting that this drug can be repurposed for the treatment of neuropathic pain and its cognitive comorbidities. Our findings have implications for our understanding of how neuropathic pain causes structural plasticity in the brain, and they point to a marked sexual dimorphism in neuropathic pain mechanisms in mice.

Coping with Phantom Limb Pain.

Phantom limb pain is a chronic neuropathic pain that develops in 45-85% of patients who undergo major amputations of the upper and lower extremities and appears predominantly during two time frames following an amputation: the first month and later about 1 year. Although in most patients the frequency and intensity of pain diminish over time, severe pain persists in about 5-10%. It has been proposed that factors in both the peripheral and central nervous systems play major roles in triggering the development and maintenance of pain associated with extremity amputations. Chronic pain is physically and mentally debilitating, affecting an individual's capacity for self-care, but also diminishing an individual's daily capacity for personal and economic independence. In addition, the pain may lead to depression and feelings of hopelessness. A National Center for Biotechnology Information study found that in the USA alone, the annual cost of dealing with neuropathic pain is more than $600 billion, with an estimated 20 million people in the USA suffering from this condition. Although the pain can be reduced by antiepileptic drugs and analgesics, they are frequently ineffective or their side effects preclude their use. The optimal approach for eliminating neuropathic pain and improving individuals' quality of life is the development of novel techniques that permanently prevent the development and maintenance of neuropathic pain, or that eliminate the pain once it has developed. What is still required is understanding when and where an effective novel technique must be applied, such as onto the nerve stump of the transected peripheral axons, dorsal root ganglion neurons, spinal cord, or cortex to induce the desired influences. This review, the second of two in this journal volume, examines the techniques that may be capable of reducing or eliminating chronic neuropathic pain once it has developed. Such an understanding will improve amputees' quality of life by blocking the mechanisms that trigger and/or maintain PLP and chronic neuropathic pain.

Dopaminergic tone does not influence pain levels during placebo interventions in patients with chronic neuropathic pain.

Placebo effects have been reported in patients with chronic neuropathic pain. Expected pain levels and positive emotions are involved in the observed pain relief, but the underlying neurobiology is largely unknown. Patients with neuropathic pain are highly motivated for pain relief, and as motivational factors such as expectations of reward, as well as pain processing in itself, are related to the dopaminergic system, it can be speculated that dopamine release contributes to placebo effects in neuropathic pain. Nineteen patients with neuropathic pain after thoracic surgery were tested during a placebo intervention consisting of open and hidden applications of the pain-relieving agent lidocaine (2 mL) and no treatment. The dopamine antagonist haloperidol (2 mg) and the agonist levodopa/carbidopa (100/25 mg) were administered to test the involvement of dopamine. Expected pain levels, desire for pain relief, and ongoing and evoked pain were assessed on mechanical visual analog scales (0-10). Significant placebo effects on ongoing (P ≤ 0.003) and evoked (P ≤ 0.002) pain were observed. Expectancy and desire accounted for up to 41.2% and 71.5% of the variance in ongoing and evoked pain, respectively, after the open application of lidocaine. We found no evidence for an effect of haloperidol and levodopa/carbidopa on neuropathic pain levels (P = 0.071-0.963). Dopamine seemed to influence the levels of expectancy and desire, yet there was no evidence for indirect or interaction effects on the placebo effect. This is the first study to suggest that dopamine does not contribute to placebo effects in chronic neuropathic pain.

Loss of synaptic zinc transport in progranulin deficient mice may contribute to progranulin-associated psychopathology and chronic pain.

Affective and cognitive processing of nociception contributes to the development of chronic pain and vice versa, pain may precipitate psychopathologic symptoms. We hypothesized a higher risk for the latter with immanent neurologic diseases and studied this potential interrelationship in progranulin-deficient mice, which are a model for frontotemporal dementia, a disease dominated by behavioral abnormalities in humans. Young naïve progranulin deficient mice behaved normal in tests of short-term memory, anxiety, depression and nociception, but after peripheral nerve injury, they showed attention-deficit and depression-like behavior, over-activity, loss of shelter-seeking, reduced impulse control and compulsive feeding behavior, which did not occur in equally injured controls. Hence, only the interaction of 'pain x progranulin deficiency' resulted in the complex phenotype at young age, but neither pain nor progranulin deficiency alone. A deep proteome analysis of the prefrontal cortex and olfactory bulb revealed progranulin-dependent alterations of proteins involved in synaptic transport, including neurotransmitter transporters of the solute carrier superfamily. In particular, progranulin deficiency was associated with a deficiency of nuclear and synaptic zinc transporters (ZnT9/Slc30a9; ZnT3/Slc30a3) with low plasma zinc. Dietary zinc supplementation partly normalized the attention deficit of progranulin-deficient mice, which was in part reminiscent of autism-like and compulsive behavior of synaptic zinc transporter Znt3-knockout mice. Hence, the molecular studies point to defective zinc transport possibly contributing to progranulin-deficiency-associated psychopathology. Translated to humans, our data suggest that neuropathic pain may precipitate cognitive and psychopathological symptoms of an inherent, still silent neurodegenerative disease.