Development of PainFace software to simplify, standardize, and scale up mouse grimace analyses.

ABSTRACT: Facial grimacing is used to quantify spontaneous pain in mice and other mammals, but scoring relies on humans with different levels of proficiency. Here, we developed a cloud-based software platform called PainFace (http://painface.net) that uses machine learning to detect 4 facial action units of the mouse grimace scale (orbitals, nose, ears, whiskers) and score facial grimaces of black-coated C57BL/6 male and female mice on a 0 to 8 scale. Platform accuracy was validated in 2 different laboratories, with 3 conditions that evoke grimacing-laparotomy surgery, bilateral hindpaw injection of carrageenan, and intraplantar injection of formalin. PainFace can generate up to 1 grimace score per second from a standard 30 frames/s video, making it possible to quantify facial grimacing over time, and operates at a speed that scales with computing power. By analyzing the frequency distribution of grimace scores, we found that mice spent 7x more time in a "high grimace" state following laparotomy surgery relative to sham surgery controls. Our study shows that PainFace reproducibly quantifies facial grimaces indicative of nonevoked spontaneous pain and enables laboratories to standardize and scale-up facial grimace analyses.

Acute inflammatory response via neutrophil activation protects against the development of chronic pain.

The transition from acute to chronic pain is critically important but not well understood. Here, we investigated the pathophysiological mechanisms underlying the transition from acute to chronic low back pain (LBP) and performed transcriptome-wide analysis in peripheral immune cells of 98 participants with acute LBP, followed for 3 months. Transcriptomic changes were compared between patients whose LBP was resolved at 3 months with those whose LBP persisted. We found thousands of dynamic transcriptional changes over 3 months in LBP participants with resolved pain but none in those with persistent pain. Transient neutrophil-driven up-regulation of inflammatory responses was protective against the transition to chronic pain. In mouse pain assays, early treatment with a steroid or nonsteroidal anti-inflammatory drug (NSAID) also led to prolonged pain despite being analgesic in the short term; such a prolongation was not observed with other analgesics. Depletion of neutrophils delayed resolution of pain in mice, whereas peripheral injection of neutrophils themselves, or S100A8/A9 proteins normally released by neutrophils, prevented the development of long-lasting pain induced by an anti-inflammatory drug. Analysis of pain trajectories of human subjects reporting acute back pain in the UK Biobank identified elevated risk of pain persistence for subjects taking NSAIDs. Thus, despite analgesic efficacy at early time points, the management of acute inflammation may be counterproductive for long-term outcomes of LBP sufferers.

Olfactory exposure to late-pregnant and lactating mice causes stress-induced analgesia in male mice.

In an attempt to improve reproducibility, more attention is being paid to potential sources of stress in the laboratory environment. Here, we report that the mere proximity of pregnant or lactating female mice causes olfactory-mediated stress-induced analgesia, to a variety of noxious stimuli, in gonadally intact male mice. We show that exposure to volatile compounds released in the urine of pregnant and lactating female mice can themselves produce stress and associated pain inhibition. This phenomenon, a novel form of female-to-male chemosignaling, is mediated by female scent marking of urinary volatiles, such as n-pentyl-acetate, and likely signals potential maternal aggression aimed at defending against infanticide by stranger males.

Long-term male-specific chronic pain via telomere- and p53­mediated spinal cord cellular senescence.

Mice with experimental nerve damage can display long­lasting neuropathic pain behavior. We show here that 4 months and later after nerve injury, male but not female mice displayed telomere length (TL) reduction and p53­mediated cellular senescence in the spinal cord, resulting in maintenance of pain and associated with decreased lifespan. Nerve injury increased the number of p53­positive spinal cord neurons, astrocytes, and microglia, but only in microglia was the increase male­specific, matching a robust sex specificity of TL reduction in this cell type, which has been previously implicated in male­specific pain processing. Pain hypersensitivity was reversed by repeated intrathecal administration of a p53­specific senolytic peptide, only in male mice and only many months after injury. Analysis of UK Biobank data revealed sex-specific relevance of this pathway in humans, featuring male­specific genetic association of the human p53 locus (TP53) with chronic pain and a male-specific effect of chronic pain on mortality. Our findings demonstrate the existence of a biological mechanism maintaining pain behavior, at least in males, occurring much later than the time span of virtually all extant preclinical studies.

Immediate effects of transcutaneous electrical nerve stimulation (TENS) administered during resistance exercise on pain intensity and physical performance of healthy subjects: a randomized clinical trial.

PURPOSE: Exercise-induced muscle pain is a self-limiting condition which impacts physical activity habits. Transcutaneous electrical nerve stimulation (TENS) promotes pain reduction and functional improvement in different pain conditions. We propose that applying TENS during exercise might reduce pain and improve physical performance. Thus, we aimed to investigate immediate effects of TENS applied during resistance exercise. METHODS: Healthy subjects of both sexes, irregularly active or sedentary were assigned into two groups: active (n = 24) or placebo (n = 22) TENS. The study was conducted over five moments: on day 0, subjects were recruited, on day 1 subjects performed the one-repetition maximum test (1RM); 72 h later, on day 2, 1RM was retested; 48 h later, on day 3, TENS was applied during a functional-resisted exercise protocol for upper limbs (bench press and rowing), with an intensity of 80% of 1RM; and 24 h after, on day 4, subjects were reevaluated. Assessment included pain intensity at rest and with movement, pressure pain thresholds, and muscle fatigue. RESULTS: TENS did not reduce pain intensity when compared to placebo (p > 0.05). TENS reduce PPT in the latissmus dorsi: p = 0.02 and anterior tibialis: p = 0.04 in immediate reassessment. Immediate effects of TENS were significant for fatigue perception at rest (p = 0.01) and number of maximum repetitions during exercise sets, starting from the 5th set of rowing exercise (p = 0.002). CONCLUSION: Our results show that TENS did not reduce pain perception in healthy individuals, but its use induced increased muscle action, contributing to a greater fatigue perception.

The hearing of rural workers exposed to noise and pesticides.

n work environments, different physical and chemical agents that may pose a risk to workers' hearing health coexist. In this context, occupational hearing loss stands out. It has mostly been attributed to only noise exposure, although there are other agents, that is, pesticides that might contribute to occupational hearing loss. In this report, two cases will be presented that consider rural workers exposed to pesticides and intense noise generated by an adapted rudimentary vehicle. The noise measured in this vehicle was 88.3 dBA up to 93.4 dBA. Pure-tone audiometry, distortion product otoacoustic emissions, and high-frequency audiometry tests were performed. This report is unusual because of the short time of exposure to noise and pesticides and the hearing loss found, indicating a synergy between those agents.

Contribution to FE modeling for intraoperative pedicle screw strength prediction.

Although the use of pedicle screws is considered safe, mechanical issues still often occur. Commonly reported issues are screw loosening, screw bending and screw fracture. The aim of this study was to develop a Finite Element (FE) model for the study of pedicle screw biomechanics and for the prediction of the intraoperative pullout strength. The model includes both a parameterized screw model and a patient-specific vertebra model. Pullout experiments were performed on 30 human cadaveric vertebrae from ten donors. The experimental force-displacement data served to evaluate the FE model performance. µCT images were taken before and after screw insertion, allowing the creation of an accurate 3D-model and a precise representation of the mechanical properties of the bone. The experimental results revealed a significant positive correlation between bone mineral density (BMD) and pullout strength (Spearman ρ = 0.59, p < 0.001) as well as between BMD and pullout stiffness (Spearman ρ = 0.59, p < 0.001). A high positive correlation was also found between the pullout strength and stiffness (Spearman ρ = 0.84, p < 0.0001). The FE model was able to reproduce the linear part of the experimental force-displacement curve. Moreover, a high positive correlation was found between numerical and experimental pullout stiffness (Pearson ρ = 0.96, p < 0.005) and strength (Pearson ρ = 0.90, p < 0.05). Once fully validated, this model opens the way for a detailed study of pedicle screw biomechanics and for future adjustments of the screw design.

Short-duration physical activity prevents the development of activity-induced hyperalgesia through opioid and serotoninergic mechanisms.

Regular physical activity prevents the development of chronic muscle pain through the modulation of central mechanisms that involve rostral ventromedial medulla (RVM). We tested if pharmacological blockade or genetic deletion of mu-opioid receptors in physically active mice modulates excitatory and inhibitory systems in the RVM in an activity-induced hyperalgesia model. We examined response frequency to mechanical stimulation of the paw, muscle withdrawal thresholds, and expression of phosphorylation of the NR1 subunit of the N-methyl-D-aspartate receptor (p-NR1) and serotonin transporter (SERT) in the RVM. Mice that had performed 5 days of voluntary wheel running prior to the induction of the model were compared with sedentary mice. Sedentary mice showed significant increases in mechanical paw withdrawal frequency and a reduction in muscle withdrawal threshold; wheel running prevented the increase in paw withdrawal frequency. Naloxone-treated and MOR mice had increases in withdrawal frequency that were significantly greater than that in physically active control mice and similar to sedentary mice. Immunohistochemistry in the RVM showed increases in p-NR1 and SERT expression in sedentary mice 24 hours after the induction of the model. Wheel running prevented the increase in SERT, but not p-NR1. Physically active, naloxone-treated, and MOR mice showed significant increases in SERT immunoreactivity when compared with wild-type physically active control mice. Blockade of SERT in the RVM in sedentary mice reversed the activity-induced hyperalgesia of the paw and muscle. These results suggest that analgesia induced by 5 days of wheel running is mediated by mu-opioid receptors through the modulation of SERT, but not p-NR1, in RVM.

Does exercise increase or decrease pain? Central mechanisms underlying these two phenomena.

Exercise is an integral part of the rehabilitation of patients suffering a variety of chronic musculoskeletal conditions, such as fibromyalgia, chronic low back pain and myofascial pain. Regular physical activity is recommended for treatment of chronic pain and its effectiveness has been established in clinical trials for people with a variety of pain conditions. However, exercise can also increase pain making participation in rehabilitation challenging for the person with pain. Animal models of exercise-induced pain have been developed and point to central mechanisms underlying this phenomena, such as increased activation of NMDA receptors in pain-modulating areas. Meanwhile, a variety of basic science studies testing different exercise protocols, show exercise-induced analgesia involves activation of central inhibitory pathways. Opioid, serotonin and NMDA mechanisms acting in rostral ventromedial medulla promote analgesia associated with exercise. This review explores and discusses current evidence on central mechanisms underlying exercised-induced pain and analgesia.

Influence of Therapeutic Approach in the TENS-induced Hypoalgesia.

INTRODUCTION: The present study aimed to determine how the therapist's approach about intervention may influence transcutaneous electrical nerve stimulation (TENS)-induced hypoalgesia. METHODS: One hundred and sixty-one pain-free individuals agreed to participate in this study and had their demographics, perceived pain intensity, pressure pain threshold, anxiety level, and the state of anxiety inventory score measured. Subsequently, participants were randomly assigned into 6 study groups, 3 active and 3 placebo TENS associated with positive, negative, or neutral approaches about electrical stimulation, as given by the investigator. After the treatment, all parameters were reassessed. RESULTS: Active TENS-treated participants receiving either positive or neutral expectations about intervention showed a significant increase in pressure pain threshold (P<0.02) compared with pretreatment; however, this was not observed in the active TENS group when associated with negative expectations. The intensity of perceived pain was significantly reduced (P<0.02) only in the active TENS groups in association with either positive or neutral expectations. There was no significant difference in any of the variables assessed in the groups receiving placebo TENS intervention. DISCUSSION: The negative expectations induced prior to the proposed intervention promoted unfavorable outcomes with respect to the analgesic properties of TENS, suggesting that the approach taken by the physical therapist should be used to convey positive expectations and avoid those negatives, to promote more efficacious treatment.