Emotion dysregulation and depressive symptoms mediate the association between inhibitory control difficulties and aggressive behaviour in children with ADHD.

Background/objectives: Impulsive aggressive behaviour, although not a core symptom, is often part of the clinical presentation of attention-deficit/hyperactivity disorder (ADHD). Recently, impulsive aggression has been attributed to emotion dysregulation, which is currently conceptualised as a transdiagnostic factor and seems to contribute to the co-occurrence of other problems in ADHD. Thus, this study investigated the presence of impulsive aggressive behaviour and explored whether emotion dysregulation mediates the relationship between inhibitory control difficulties and aggressive behaviour in children with ADHD. Because ADHD may act as a risk factor for the development of other conditions, such as internalising problems, we aimed to understand whether depressive symptoms contribute to this relationship. Methods: Seventy-two children were recruited from a hospital and the community, 38 of whom had ADHD and 34 were typically developing (TD). Parents completed the Child Behaviour Checklist, the Behaviour Rating Inventory of Executive Function, and the Emotion Regulation Checklist. Simple mediation and serial mediation models were performed to test our hypotheses. Results: Aggressive behaviour was significantly higher in ADHD children compared to TD children. Emotion dysregulation fully mediated the relationship between inhibitory control difficulties and aggressive behaviour in ADHD children. Adding depressive symptoms to the model increased the explained variance in aggressive behaviour. Conclusion: The main result of our study supports the role of emotion dysregulation and depressive symptoms in mediating the relationship between inhibitory control difficulties and impulsive aggressive behaviour in children with ADHD. This highlights that aggressive behaviour is, in part, a result of the inability of the child to appropriately regulate their emotions. Future interventions may be tailored to improve emotion regulation skills to address aggressive behaviour.

Comprehensive quantitative sensory testing shows altered sensory function in women with chronic pelvic pain: results from the Translational Research in Pelvic Pain (TRiPP) Study.

ABSTRACT: Chronic pelvic pain (CPP), despite its high prevalence, is still relatively poorly understood mechanistically. This study, as part of the Translational Research in Pelvic Pain (TRiPP) project, has used a full quantitative sensory testing (QST) paradigm to profile n = 85 women with and without CPP (endometriosis or bladder pain specifically). We used the foot as a control site and abdomen as the test site. Across 5 diagnostically determined subgroups, we found features which are common across different aetiologies, eg, gain of function in pressure pain threshold (PPT) when assessing responses from the lower abdomen or pelvis (referred pain site). However, disease-specific phenotypes were also identified, eg, greater mechanical allodynia in endometriosis, despite there being large heterogeneities within diagnostic groups. The most common QST sensory phenotype was mechanical hyperalgesia (>50% across all the groups). A "healthy' sensory phenotype was seen in <7% of CPP participants. Specific QST measures correlated with sensory symptoms assessed by the painDETECT questionnaire (pressure-evoked pain [painDETECT] and PPT [QST] [ r = 0.47, P < 0.001]; mechanical hyperalgesia (painDETECT) and mechanical pain sensitivity [MPS from QST] [ r = 0.38, P = 0.009]). The data suggest that participants with CPP are sensitive to both deep tissue and cutaneous inputs, suggesting that central mechanisms may be important in this cohort. We also see phenotypes such as thermal hyperalgesia, which may be the result of peripheral mechanisms, such as irritable nociceptors. This highlights the importance of stratifying patients into clinically meaningful phenotypes, which may have implications for the development of better therapeutic strategies for CPP.

Eating Patterns and Dietary Interventions in ADHD: A Narrative Review.

Attention Deficit Hyperactivity Disorder (ADHD) is one of the most common neurodevelopmental disorders in childhood, affecting ~7% of children and adolescents. Given its adverse health outcomes and high healthcare and societal costs, other treatment options beyond pharmacotherapy have been explored. Case-control studies have shown that dietary patterns may influence the risk of ADHD, and specific dietary interventions have been proposed as coadjuvant treatments in this disorder. These include nutritional supplements, gut microbiome-targeted interventions with biotics, and elimination diets. The purpose of this review is to examine which dietary patterns are most associated with ADHD and to summarize the existing evidence for the clinical use of dietary interventions. The literature showed that non-healthy dietary patterns were positively associated with ADHD, whereas healthy patterns were negatively associated. As for nutritional supplements, only vitamin D and vitamin D + magnesium appeared to improve ADHD symptoms when baseline levels of vitamin D were insufficient/deficient. Regarding biotics, evidence was only found for Lactobacillus rhamnosus GG and for multi-species probiotic supplementation. Elimination diets have scarce evidence and lead to nutritional deficiencies, so caution is advised. Overall, more robust scientific evidence is required for these dietary interventions to be implemented as part of ADHD therapy.

Gut Microbiome and Organ Fibrosis.

Fibrosis is a pathological process associated with most chronic inflammatory diseases. It is defined by an excessive deposition of extracellular matrix proteins and can affect nearly every tissue and organ system in the body. Fibroproliferative diseases, such as intestinal fibrosis, liver cirrhosis, progressive kidney disease and cardiovascular disease, often lead to severe organ damage and are a leading cause of morbidity and mortality worldwide, for which there are currently no effective therapies available. In the past decade, a growing body of evidence has highlighted the gut microbiome as a major player in the regulation of the innate and adaptive immune system, with severe implications in the pathogenesis of multiple immune-mediated disorders. Gut microbiota dysbiosis has been associated with the development and progression of fibrotic processes in various organs and is predicted to be a potential therapeutic target for fibrosis management. In this review we summarize the state of the art concerning the crosstalk between intestinal microbiota and organ fibrosis, address the relevance of diet in different fibrotic diseases and discuss gut microbiome-targeted therapeutic approaches that are current being explored.

TLR4 Antagonism Reduces Movement-Induced Nociception and ATF-3 Expression in Experimental Osteoarthritis.

INTRODUCTION: Toll-like receptor 4 (TLR4) is a pattern recognition receptor involved in the detection of pathogen-associated molecular patterns (PAMPs), but also a "danger-sensing" receptor that recognizes host-derived endogenous molecules called damage-associated molecular patterns (DAMPs). The involvement of TLR4 in rheumatic diseases is becoming evident, as well as its potential role as a target for therapeutic intervention. Moreover, increasing evidence also suggests that TLR4 is implicated in chronic pain states. Thus, in this study, we evaluated whether a systemic administration of a synthetic antagonist of TLR4 (TLR4-A1) could decrease nociception and cartilage degradation in experimental osteoarthritis (OA). Furthermore, as the activation transcription factor (ATF)-3 serves as a negative regulator for TLR4-stimulated inflammatory response, we also evaluated the effect of TLR4 inhibition on ATF-3 expression in primary afferent neurons at the dorsal root ganglia (DRG). METHODS: OA was induced in adult male Wistar rats through an intra-articular injection of 2 mg of sodium mono-iodoacetate (MIA) into the left knee. From days 14 to 28 after OA induction, animals received an intraperitoneal injection of either TLR4-A1 (10 mg/kg) or vehicle. Movement- and loading-induced nociception was evaluated in all animals, by the Knee-Bend and CatWalk tests, before and at several time-points after TLR4-A1/vehicle administration. Immunofluorescence for TLR4 and ATF-3 was performed in L3-L5 DRG. Knee joints were processed for histopathological evaluation. RESULTS: Administration of TLR4-A1 markedly reduced movement-induced nociception in OA animals, particularly in the Knee-Bend test. Moreover, the increase of ATF-3 expression observed in DRG of OA animals was significantly reduced by TLR4-A1. However, no effect was observed in cartilage loss nor in the neuronal cytoplasmic expression of TLR4 upon antagonist administration. CONCLUSION: The TLR4 antagonist administration possibly interrupts the TLR4 signalling cascade, thus decreasing the neurotoxic environment at the joint, which leads to a reduction in ATF-3 expression and in nociception associated with experimental OA.

Glial activation in the collagenase model of nociception associated with osteoarthritis.

Background Experimental osteoarthritis entails neuropathic-like changes in dorsal root ganglia (DRG) neurons. Since glial activation has emerged as a key player in nociception, being reported in numerous models of neuropathic pain, we aimed at evaluating if glial cell activation may also occur in the DRG and spinal cord of rats with osteoarthritis induced by intra-articular injection of collagenase. Methods Osteoarthritis was induced by two injections, separated by three days, of 500 U of type II collagenase into the knee joint of rats. Movement-induced nociception was evaluated by the Knee-Bend and CatWalk tests during the following six weeks. Glial fibrillary acidic protein (GFAP) expression in satellite glial cells of the DRG was assessed by immunofluorescence and Western Blot analysis; the pattern of GFAP and activating transcription factor-3 (ATF-3) expression was also compared through double immunofluorescence analysis. GFAP expression in astrocytes and IBA-1 expression in microglia of the L3-L5 spinal cord segments was assessed by immunohistochemistry and Western Blot analysis. The effect of the intrathecal administration of fluorocitrate, an inhibitor of glial activation, on movement-induced nociception was evaluated six weeks after the first collagenase injection. Results GFAP expression in satellite glial cells of collagenase-injected animals was significantly increased six weeks after osteoarthritis induction. Double immunofluorescence showed GFAP upregulation in satellite glial cells surrounding ATF-3-positive neurons. In the spinal cord of collagenase-injected animals, an ipsilateral upregulation of GFAP and IBA-1 was also observed. The inhibition of glial activation with fluorocitrate decreased movement- and loading-induced nociception. Conclusion Collagenase-induced knee osteoarthritis leads to the development of nociception associated with movement of the affected joint and to the activation of glial cells in both the DRG and the spinal cord. Inhibition of glial cell activation by fluorocitrate decreases these osteoarthritis-associated nociceptive behaviours. These results suggest that glial cell activation may play a role in the development of chronic pain in this experimental model of osteoarthritis.

Intra-articular injection of collagenase in the knee of rats as an alternative model to study nociception associated with osteoarthritis.

INTRODUCTION: Animal models currently used in osteoarthritis-associated pain research inadequately reproduce the initiating events and structural pathology of human osteoarthritis. Conversely, intra-articular injection of collagenase is a structurally relevant model, as it induces articular degeneration both by digesting collagen from cartilage and by causing articular instability, thereby reproducing some of the main events associated with osteoarthritis onset and development. Here, we evaluated if the intra-articular injection of collagenase can be an alternative model to study nociception associated with osteoarthritis. METHODS: Osteoarthritis was induced by two intra-articular injections of either 250 U or 500 U of collagenase into the left knee joint of adult male Wistar rats. A six weeks time-course assessment of movement- and loading-induced nociception was performed by the Knee-Bend and CatWalk tests. The effect of morphine, lidocaine and diclofenac on nociceptive behaviour was evaluated in animals injected with 500 U of collagenase. Joint histopathology was scored for both doses throughout time. The expression of transient receptor potential vanilloid 1 (TRPV1) in ipsilateral dorsal root ganglia (DRG) was evaluated. RESULTS: An increase in nociceptive behaviour associated with movement and loading of affected joints was observed after intra-articular collagenase injection. With the 500 U dose of collagenase, there was a significant correlation between the behavioural and the histopathological osteoarthritis-like structural changes developed after six weeks. One week after injection of 500 U collagenase, swelling of the injected knee and inflammation of the synovial membrane were also observed, indicating the occurrence of an early inflammatory reaction. Behavioural changes induced by the 500 U dose of collagenase were overall effectively reversed by morphine and lidocaine. Diclofenac was effective one week after injection. TRPV1 expression increased six weeks after 500 U collagenase injection. CONCLUSION: We conclude that the intra-articular injection of 500 U collagenase in the knee of rats can be an alternative model for the study of nociception associated with osteoarthritis, since it induces significant nociceptive alterations associated with relevant osteoarthritis-like joint structural changes.

Dose-dependent expression of neuronal injury markers during experimental osteoarthritis induced by monoiodoacetate in the rat.

BACKGROUND: It was recently reported that the mono-iodoacetate (MIA) experimental model of osteoarthritis (OA) courses with changes of neurons innervating the affected joints that are commonly interpreted as a neuronal response to axonal injury. To better characterize these changes, we evaluated the expression of two markers of neuronal damage, ATF-3 and NPY, and the growth associated protein GAP-43, in primary afferent neurons of OA animals injected with three different doses of MIA (0.3, 1 or 2 mg). Measurements were performed at days 3, 7, 14, 21 and 31 post-MIA injection. RESULTS: OA animals showed the characteristic histopathological changes of the joints and the accompanying nociceptive behaviour, evaluated by the Knee-Bed and CatWalk tests. An increase of ATF-3 expression was detected in the DRG of OA animals as early as 3 days after the injection of 1 or 2 mg of MIA and 7 days after the injection of 0.3 mg. NPY expression was increased in animals injected with 1 or 2 mg of MIA, at day 3 or in all time-points, respectively. From day 7 onwards there was a massive increase of GAP-43 expression in ATF-3 cells. CONCLUSIONS: The expression of the neuronal injury markers ATF-3 and NPY as well as an up-regulation of GAP-43 expression, indicative of peripheral fibre regeneration, suggests that axonal injury and a regeneration response may be happening in this model of OA. This opens new perspectives in the unravelling of the physiopathology of the human disease.

Analgesic effects of lidocaine, morphine and diclofenac on movement-induced nociception, as assessed by the Knee-Bend and CatWalk tests in a rat model of osteoarthritis.

Pain is the major symptom of osteoarthritis (OA) and the main reason for patients seeking medical care, but its treatment is not optimal. Animal studies are necessary to elucidate mechanisms underlying OA-induced pain and assess analgesics' efficacy. Previously, we showed that the Knee-Bend test and dynamic weight bearing by the CatWalk test are clinically relevant methods for assessing movement-induced nociception in the mono-iodoacetate (MIA) OA model. Using the same tests, in the present study we investigate the effects of lidocaine (5 mg, 10% solution, intra-articular), morphine (6 mg/kg, subcutaneous) and diclofenac (30 mg/kg per os) on nociceptive behavior in OA animals, on days 3 and 20 of OA evolution. Morphine reduced nociceptive behavior in both tests at both time-points. Lidocaine also decreased nociceptive behavior in both tests on day 3, but on day 20 only reduced the Knee-Bend score. Diclofenac was highly effective in both tests on day 3, while on day 20 it induced a less pronounced decrease in the Knee-Bend score and was ineffective in the CatWalk test. The results showed that the Knee-Bend and CatWalk tests are reliable alternative methods for evaluating movement-induced nociception in OA animals, and measure nociception in a clinically relevant way, since an analgesic profile similar to the one described in humans was observed. Therefore, these tests might be important as good predictors of drug efficacy.

Phenotypic alterations of neurons that innervate osteoarthritic joints in rats.

OBJECTIVE: Pain is a prominent feature of osteoarthritis (OA). To further understand the primary mechanisms of nociception in OA, we studied the expression of the phenotype markers calcitonin gene-related peptide (CGRP), isolectin B4 (IB4), and neurofilament 200 (NF200) in sensory neurons innervating the OA knee joint in rats. METHODS: OA was induced in rats by intraarticular injection of 2 mg of mono-iodoacetate (MIA) into the knee. Neurons innervating the joint were identified by retrograde labeling with fluorogold in dorsal root ganglia (DRG) and colocalized with neurochemical markers by immunofluorescence. The total number of DRG cells was determined by stereologic methods in Nissl-stained sections. RESULTS: A 37% decrease in the number of fluorogold-backlabeled cells was observed in rats with OA when compared with control rats, even though no decrease in the total number of cells was observed. However, an increase in the number of medium/large cell bodies and a decrease in the number of the smallest cells were observed, suggesting the occurrence of perikarya hypertrophy. The percentage of CGRP-positive cells increased significantly, predominantly in medium/large cells, suggesting the occurrence of a phenotypic switch. Colocalization of CGRP and NF200 revealed no significant changes in the percentage of double-labeled cells, but an increase in the number of medium/large double-labeled cells was observed. No differences in the expression of either IB4 or NF200 were observed in fluorogold-backlabeled cells. CONCLUSION: These results indicate that MIA-induced OA causes an up-regulation of CGRP in different subpopulations of primary afferent neurons in DRG due to a phenotypic switch and/or cell hypertrophy which may be functionally relevant in terms of the onset of pain in this pathologic condition.

Assessment of movement-evoked pain in osteoarthritis by the knee-bend and CatWalk tests: a clinically relevant study.

UNLABELLED: Although there are several reports on pain behavioral tests in rat models of knee osteoarthritis (OA), most of them focus on the paw. The aim of this study was to investigate pain-related behaviors on the affected knee joint, the primary source of nociception, in animals with mono-iodoacetate-induced OA, using the knee-bend (which provides information on movement pain) and pin-prick tests, and to evaluate nociception elicited by walking using the CatWalk test. The von Frey and Randall-Selitto tests applied to the paw allowed us to compare our study results with previous studies. A further aim was to compare the behavioral nociceptive responses of the most used doses of mono-iodoacetate, 2 and 3 mg. Knee-bend score of OA animals was higher than those of control animals throughout the study (P < .05). At every time point, the ipsilateral hind-paw load of OA rats, as measured by the CatWalk test, was lower than that of control rats (P < .05), and paw withdraw threshold to von Frey filaments was also decreased (P < .01). No changes were observed in pin-prick and Randall-Selitto tests. Results obtained with the 2 doses of mono-iodoacetate were similar. The knee-bend and CatWalk tests are effective for evaluating movement-related nociception, a hallmark of clinical OA, which was present throughout the experimental period. PERSPECTIVE: Behavioral characterization of models of OA pain is important and useful for use in future studies to test pharmacological treatments. Furthermore, it is important to find methods that correlate better with the human symptoms of OA.

Delta opioid receptor mRNA expression is changed in the thalamus and brainstem of monoarthritic rats.

Changes in the mRNA expression of neurotransmitters receptors under chronic pain conditions have been described in various areas of the central nervous system (CNS). Delta opioid receptors (DORs) have been implicated in pain mechanisms but, although its mRNA expression has been studied in the rat CNS, there are no reports describing its distribution in specific thalamic and brainstem nuclei during chronic inflammatory pain. Here, in situ hybridization for DOR mRNA was performed in brain sections from control and monoarthritic (MA) rats with 2, 4, 7 and 14 days of inflammation. Grain densities were determined bilaterally in the ventrobasal complex (VB), posterior (Po), centromedial/centrolateral (CM/CL) and reticular (Rt) nuclei of the thalamus, and in the dorsal reticular (DRt), lateral reticular (LRt) and parvocellular reticular (PCRt) nuclei of the brainstem. Control animals exhibited weak mRNA expression in the VB, Po and CM/CL, as well as in PCRt, while moderate grain densities were observed in the Rt, DRt and LRt. During MA, DOR mRNA expression was significantly decreased (22%) in the Rt contralateral to the affected joint at both 7 and 14 days of inflammation, as compared to controls. A bilateral reduction (35%) was also observed in the DRt at 14 days of MA, while a contralateral increase was found in the PCRt at 7 days (+39%). No significant changes were observed in the other regions analyzed. Thus, data show changes in the DOR mRNA expression during the development of chronic inflammatory pain, in thalamic and brainstem nuclei implicated in pain processing mechanisms.

GABA(B2) receptor subunit mRNA decreases in the thalamus of monoarthritic animals.

Many studies have implicated GABA(B) receptors in pain transmission mechanisms, especially in the spinal cord. In the thalamus, mRNA expression of the GABA(B(1b)) isoform was shown to be regulated in relay nuclei in response to chronic noxious input arising from experimental monoarthritis. GABA(B(1a)) and GABA(B2) mRNA expression was here determined by in situ hybridisation in the brain of control, 2, 4, 7 and 14 days monoarthritic rats, to evaluate whether this expression was regulated by chronic noxious input in thalamic nuclei. mRNA labelling was analysed quantitatively in the ventrobasal complex, posterior, central medial/central lateral and reticular thalamic nuclei; the thalamic visual relay and dentate gyrus were examined for control. No mRNA expression was detected for GABA(B(1a)) in control and monoarthritic animals. Similarly, GABA(B2) mRNA was not found in the reticular nucleus. However, GABA(B2) mRNA expression was observed in the ventrobasal complex, posterior and central medial/central lateral nuclei of control animals. A significant decrease of 42% at 2 days and 27% at 4 days of monoarthritis was observed in the ventrobasal complex contralaterally, when compared with controls, returning to basal levels at 7 days of monoarthritis. In the ipsilateral posterior nucleus, there was a significant decrease of 38% at 2 days of monoarthritis. No significant changes were observed in central medial/central lateral nuclei. The data suggest that GABA(B2) mRNA expression in the ventrobasal complex and posterior nucleus is regulated by noxious input and that GABA(B) receptors might play a role in the plasticity of these relay nuclei during chronic inflammatory pain.

Differential expression of GABA(B(1b)) receptor mRNA in the thalamus of normal and monoarthritic animals.

GABA(B) receptors have been implicated in the plastic changes occurring in the spinal cord during the development of chronic inflammatory pain. In this study, we evaluated whether the expression of GABA(B(1b)) receptor mRNA is regulated supraspinally, namely in the thalamus, as part of the response to chronically enhanced noxious input arising from experimental monoarthritis (MA). In situ hybridization with [(35)S]-labelled oligonucleotide probes was performed in sections of control, 2, 4, 7 and 14 days MA rats' brains (n = 6/group). The distribution of GABA(B(1b)) mRNA was determined bilaterally in the ventrobasal complex (VB), posterior (Po), centromedial/centrolateral (CM/CL) and reticular (Rt) thalamic nuclei. The amount of GABA(B(1b)) mRNA was expressed as times fold of background values. In normal animals, values of mRNA expression were very similar in VB, Po and CM/CL, ranging from 2.2 +/- 0.2 to 2.7 +/- 0.4 (mean +/- S.E.M.) times higher than background levels. No expression of GABA(B(1b)) mRNA was found in the Rt of control or MA animals. A significant decrease of 26% at 4 days, and 37% at 7 days of MA, was observed in the VB contralateral to the affected joint. On the contrary, in the Po there was a significant bilateral increase at 2 days (38% contralaterally, 25% ipsilaterally), returning to basal levels at 4 days MA. No significant changes were observed in CM/CL. These results suggest that the expression of GABA(B(1b)) in the VB and Po is regulated by noxious input, and might contribute to the functional changes that occur in the thalamus during chronic inflammatory pain.