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Functional abdominal pain disorders (FAPD) are common among young individuals. To date, relatively little is known regarding the function of the endogenous analgesic mechanisms in this vulnerable group. Therefore, this case-control study aimed to compare conditioned pain modulation (CPM), pressure algometry and psychosocial variables in 39 young children (aged 6-12 years) with FAPD and 36 age-and sex-matched pain-free controls. Pressure algometry was used to assess pressure pain thresholds at both symptomatic (umbilicus) as remote (trapezius and tibia) test sites. CPM was recorded as an increase in the pressure pain threshold at the trapezius test site in response to experimental conditioning pain imposed by the cold pressure task (12°C ± 1°C). The assessors were blinded to the diagnoses. Parent-proxy and/or self-reported questionnaires were used to assess child's pain intensity, functional disability, pain-related fear and parental pain catastrophizing. Compared with pain-free controls, young children with FAPD showed lower pressure pain thresholds at all test sites (P<0.05), a lower CPM response (P=0.02), more functional disability (P<0.001) and pain-related fear (P<0.001). Parents of children with FAPD catastrophized more about their child's pain than parents of healthy children (P<0.001). No sex differences were found for the experimental pain measurements (P>0.05), nor was there a significant correlation between the child-and parent questionnaires and the CPM-effect (P>0.05). In summary, young children with FAPD demonstrated secondary hyperalgesia and decreased functioning of endogenous analgesia.
Learn More >Although chronic postsurgical pain (CPSP) is a major health care problem, pain-related functional interference has rarely been investigated. Using the PAIN OUT registry we evaluated patients' pain-related outcomes on the first postoperative day, and their pain-related interference with daily living (Brief Pain Inventory) and neuropathic symptoms (DN4: douleur neuropathique en 4 questions) at six months after surgery. Endpoints were pain interference total scores (PITS) and their association with pain and DN4 scores. Furthermore, possible risk factors associated with impaired function at M6 were analyzed by ordinal regression analysis with PITS groups (no to mild, moderate and severe interference) as a dependent three-stage factor. Odds ratios (OR) with 95% confidence intervals (CI) were calculated. Of 2,322 patients, 15.3% reported CPSP with an average pain score ≥3 (NRS 0-10). Risk for a higher PITS group increased by 190% (OR (95%-CI): 2.9 (2.7-3.2); p<0.001) in patients with, compared to without CPSP. A positive DN4 independently increased risk by 29% (1.3 (1.12-1.45), p<0.001). Pre-existing chronic pain (3.6 (2.6-5.1); p<0.001), time spent in severe acute pain (2.9 (1.3-6.4); p=0.008), neurosurgical back surgery in males (3.6 (1.7-7.6); p<0.001) and orthopedic surgery in females (1.7 (1.0-3.0); p=0.036) were the variables with strongest association with PITS. PITS might provide more precise information about patients' outcomes than pain scores only. As neuropathic symptoms increase PITS, a suitable instrument for their routine assessment should be defined.
Learn More >The role of sex hormones on postsurgical pain perception is basically unclear. Here we studied the role of endogenous gonadal hormones for pain and hyperalgesia in human volunteers after experimental incision.A 4-mm incision was made in the volar forearm of 15 female volunteers both in the follicular and the luteal phase (random block design). Somatosensory profiles were assessed at baseline and 1-72 h after incision by quantitative sensory testing (QST), compared between both cycle phases and related to individual plasma levels of gonadal hormones.Sensory testing at baseline revealed significantly lower pain thresholds (25 vs. 46 mN, p<0.005) and increased pain ratings to pinprick (0.96 vs. 0.47, p<0.0001) in the luteal phase; similar, one hour after incision, pain intensity to incision (38 vs. 21/100, p<0.005), pinprick hyperalgesia by rating (p<0.05) and area of secondary hyperalgesia (p<0.001) were enhanced in the luteal phase. Multiple regression analysis revealed that pinprick pain sensitivity at baseline was significantly predicted by progesterone (partial r= 0.67, p<0.001), FSH (partial r=0.61, p<0.005) and negatively by testosterone (partial r=-0.44, p<0.05). Likewise, incision-induced pain and pinprick hyperalgesia (rating and area) were significantly predicted by progesterone (partial r=0.70, r=0.46 and r=0.47, respectively; p<0.05-0.0001) and in part by FSH; the contribution of estrogen, however, was fully occluded by progesterone for all measures.In conclusion, pinprick pain as well as incision-induced pain and mechanical hyperalgesia were greater in the luteal phase and predicted by progesterone suggesting a major role for progesterone. Other hormones involved are testosterone (protective) and in part FSH.
Learn More >Pain is the leading cause of disability in the developed world but remains a poorly treated condition. Specifically, post-surgical pain continues to be a frequent and undermanaged condition. Here, we investigate the analgesic potential of pharmacological NaV1.7 inhibition in a mouse model of acute post-surgical pain, based on incision of the plantar skin and underlying muscle of the hind paw. We demonstrate that local and systemic treatment with the selective NaV1.7 inhibitor μ-theraphotoxin-Pn3a is effectively anti-allodynic in this model and completely reverses mechanical hypersensitivity in the absence of motor adverse effects. In addition, the selective NaV1.7 inhibitors ProTx-II and PF-04856264 as well as the clinical candidate CNV1014802 also reduced mechanical allodynia. Interestingly, co-administration of the opioid receptor antagonist naloxone completely reversed analgesic effects of Pn3a, indicating an involvement of endogenous opioids in the analgesic activity of Pn3a. Additionally, we found super-additive antinociceptive effects of sub-therapeutic Pn3a doses not only with the opioid oxycodone but also with the GABAB receptor agonist baclofen. Transcriptomic analysis of gene expression changes in dorsal root ganglia of mice post-surgery did not reveal any changes in mRNA expression of endogenous opioids or opioid receptors, however several genes involved in pain, including Runx1 (Runt related transcription factor 1), Cacna1a (CaV2.1) and Cacna1b (CaV2.2) were downregulated. In summary, these findings suggest that pain after surgery can be successfully treated with NaV1.7 inhibitors alone or in combination with baclofen or opioids, which may present a novel and safe treatment strategy for this frequent and poorly managed condition.
Learn More >This review describes the pharmacology of each antidepressant class as it applies to migraine prevention, summarizes the evidence base for each medication, and describes relevant side effects and clinical considerations. Use of antidepressants for migraine prevention in clinical practice is also discussed.
Learn More >Gap junctions (GJs) are novel molecular targets for pain therapeutics due to their pain-promoting function. INI-0602, a new GJ inhibitor, exerts a neuroprotective role, while its role in neuropathic pain is unclear. The objective was to investigate the analgesic role and mechanisms of INI-0602 in neuropathic pain induced by spared nerve injury (SNI), and whether INI-0602 attenuated pain-induced depression-like behaviors. Rats were randomly assigned to saline treatment groups (sham+NS and SNI+NS) or INI-0602 treatment groups (sham+INI-0602 and SNI+INI-0602). The von Frey test was used to assess pain behavior, and the sucrose preference test, the forced swimming test, and the tail suspension test were used to assess depression-like behaviors. Gap junction intercellular communication (GJIC) was measured by parachute assay. Western blots were used to determine the protein expression. In vitro, INI-0602 significantly suppressed GJIC by decreasing connexin43 and connexin32 expression. In vivo, INI-0602 significantly suppressed mechanical allodynia during initiation (7 days after SNI) and the maintenance phase (21 days after SNI) and simultaneously attenuated accompanying depression-like behaviors. Furthermore, INI-0602 markedly suppressed the activation of astrocytes and microglia on days 7 and 21 by reducing GJIC. Finally, INI-0602 reversed the changes in the brain-derived neurotrophic factor and Nr2b subunits of the N-methyl-D-aspartate receptor in SNI rats, suggesting that these effects of INI-0602 were related to its analgesic effect. Our findings demonstrated that blocking GJs with INI-0602 attenuated mechanical pain hypersensitivity and related depression-like behaviors in SNI rats by reducing glial activation.
Learn More >Low-voltage activated T-type calcium channels mediate essential functions in the nervous system, and alteration of channel activity is causally linked to a number of neurological conditions. Therefore, T-type channels hold great promise as pharmacological targets for new medicines. In this Viewpoint, we discuss the potential of T-type channels as druggable targets and reevaluate the strategies available for developing therapeutically efficient and specific modulators of this channel.
Learn More >Sleep loss increases the experience of pain. However, the brain mechanisms underlying altered pain processing following sleep deprivation are unknown. Moreover, it remains unclear whether ecologically modest night-to-night changes in sleep, within an individual, confer consequential day-to-day changes in experienced pain. Here, we demonstrate that acute sleep-deprivation amplifies pain reactivity within human (male and female) primary somatosensory cortex yet blunts pain-reactivity in higher-order valuation and decision-making regions of the striatum and insula cortex. Consistent with this altered neural signature, we further show that sleep deprivation expands the temperature range for classifying a stimulus as painful, specifically through a lowering of pain thresholds. Moreover, the degree of amplified reactivity within somatosensory cortex following sleep deprivation significantly predicts this expansion of experienced pain across individuals. Finally, outside of the laboratory setting, we similarly show that even modest nightly changes in sleep quality (increases and decreases) an individual determine consequential day-to-day changes in experienced pain (decreases and increases, respectively). Together, these data provide a central brain framework underlying the impact of sleep loss on pain, and furthermore, establish that the association between sleep and pain is expressed in a night-to-day, bidirectional relationship within a sample of the general population. More broadly, our findings highlight sleep as a novel therapeutic target for pain management within and outside the clinic, including circumstances where sleep is frequently short yet pain is abundant (e.g. the hospital setting).Are you experiencing pain? Did you have a bad night of sleep? This study provides underlying brain and behavioral mechanisms explaining this common co-occurrence. We show that sleep deprivation enhances pain responsivity within the primary sensing regions of the brain's cortex yet blunts activity in other regions that modulate pain processing-the striatum and insula. We further establish that even subtle night-to-night changes in sleep in a sample of the general population predict consequential day-to-day changes in pain (bidirectionally). Considering the societal rise in chronic pain conditions in lock-step with the decline in sleep time through the industrial world, our data support the hypothesis that these two trends may not simply be co-occurring but are significantly inter-related.
Learn More >Gastrin-releasing peptide (GRP) is a spinal itch transmitter expressed by a small population of dorsal horn interneurons (GRP neurons). The contribution of these neurons to spinal itch relay is still only incompletely understood and their potential contribution to pain-related behaviors remains controversial. Here, we have addressed this question in a series of experiments performed in GRP::cre and GRP::eGFP transgenic male mice. We combined behavioral tests with neuronal circuit tracing, morphology, chemogenetics, optogenetics, and electrophysiology to obtain a more comprehensive picture. We found that GRP neurons form a rather homogenous population of central cell-like excitatory neurons located in lamina II of the superficial dorsal horn. Multicolor high-resolution confocal microscopy and optogenetic experiments demonstrated that GRP neurons receive direct input from MrgprA3-positive pruritoceptors. Anterograde herpes simplex virus-based neuronal tracing initiated from GRP neurons revealed ascending polysynaptic projections to distinct areas and nuclei in the brainstem, midbrain, thalamus, and the somatosensory cortex. Spinally restricted ablation of GRP neurons reduced itch-related behaviors to different pruritogens while their chemogenetic excitation elicited itch-like behaviors and facilitated responses to several pruritogens. By contrast, responses to painful stimuli remained unaltered. These data confirm a critical role of dorsal horn GRP neurons in spinal itch transmission, but do not support a role in pain. Dorsal horn GRP neurons serve a well-established function in the spinal transmission of pruritic (itch) signals. A potential role in the transmission of nociceptive (pain) signals has remained controversial. Our results provide further support for a critical role of dorsal horn GRP neurons in itch circuits, but we failed to find evidence supporting a role in pain.
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