Signaling mechanisms in mirror image pain pathogenesis

Mirror-Image Pain Update: Complex Interactions Between Central and Peripheral Mechanisms

The appearance of contralateral effects after unilateral injury has been shown in various experimental pain models, as well as in clinics. They consist of a diversity of phenomena in contralateral peripheral nerves, sensory ganglia, or spinal cord: from structural changes and altered gene or protein expression to functional consequences such as the development of mirror-image pain (MP). Although MP is a well-documented phenomenon, the exact molecular mechanism underlying the induction and maintenance of mirror-like spread of pain is still an unresolved challenge. MP has generally been explained by central sensitization mechanisms leading to facilitation of pain impulse transfer through neural connections between the two sides of the central nervous system. On the contrary, the peripheral nervous system (PNS) was usually regarded unlikely to evoke such a symmetrical phenomenon. However, recent findings provided evidence that events in the PNS could play a significant role in MP induction. This manuscript provides an updated and comprehensive synthesis of the MP phenomenon and summarizes the available data on the mechanisms. A more detailed focus is placed on reported evidence for peripheral mechanisms behind the MP phenomenon, which were not reviewed up to now.

Anti-inflammatory and anti-nociceptive effects of Cinnamon and Clove essential oils nanogels: an in vivo study

BACKGROUND

Cinnamon (Cinnamomum zeylanicum) and Clove (Syzygium aromaticum) essential oils are two medicinally important plant-derived substances with a wide range of biological properties. Besides, nanoemulsion-based gels have been widely used to increase topical drug delivery and effectiveness.

METHODS

This study aimed to explore the anti-inflammatory effect (paw edema test) and the anti-nociceptive effect (hot plate and formalin test) of nanoemulsion-based gels containing the essential oils in the animal model. Cinnamon and Clove essential oils nanoemulsions with droplet sizes of 28 ± 6 nm and 12 ± 3 nm were first prepared. By adding carboxymethylcellulose (3.5% w/v), the nanoemulsions were then gelified. Finally, the nanogels were characterized by ATR-FTIR analysis and were used as topical pre-treatment before induction of inflammation or pain in acute and chronic analgesic experimental studies.

RESULTS

The paw edema and formalin findings showed that the nanogels formulations possess significant anti-nociceptive and anti-inflammatory effects.

CONCLUSION

The prepared nanogels could be considered as analgesic drugs for inhibiting the inflammation and pain of diseases.

Nrf2 Activation Mediates Antiallodynic Effect of Electroacupuncture on a Rat Model of Complex Regional Pain Syndrome Type-I through Reducing Local Oxidative Stress and Inflammation

Complex regional pain syndrome type-I (CRPS-I) represents a type of neurovascular condition featured by severe pain in affected extremities. Few treatments have proven effective for CRPS-I. Electroacupuncture (EA) is an effective therapy for pain relief. We explored the mechanism through which EA ameliorates pain in a rat CRPS-I model. The chronic postischemic pain (CPIP) model was established using Sprague-Dawley rats to mimic CRPS-I. We found that oxidative stress-related biological process was among the predominant biological processes in affected hindpaw of CPIP rats. Oxidative stress occurred primarily in local hindpaw but not in the spinal cord or serum of model rats. Antioxidant N-acetyl cysteine (NAC) attenuated mechanical allodynia and spinal glia overactivation in CPIP model rats, whereas locally increasing oxidative stress is sufficient to induce chronic pain and spinal glia overactivation in naive rats. EA exerted remarkable antiallodynia on CPIP rats by reducing local oxidative stress via enhancing nuclear factor erythroid 2-related factor 2 (Nrf2) expression. Pharmacological blocking Nrf2 abolished antioxidative and antiallodynic effects of EA. EA reduced spinal glia overactivation, attenuated the upregulation of inflammatory cytokines, reduced the enhanced TRPA1 channel activity in dorsal root ganglion neurons innervating the hindpaws, and improved blood flow dysfunction in hindpaws of CPIP rats, all of which were mimicked by NAC treatment. Thus, we identified local oxidative injury as an important contributor to pathogenesis of animal CRPS-I model. EA targets local oxidative injury by enhancing endogenous Nrf2-mediated antioxidative mechanism to relieve pain and inflammation. Our study indicates EA can be an alternative option for CRPS-I management.

Gene Expression Profiling of Contralateral Dorsal Root Ganglia Associated with Mirror-Image Pain in a Rat Model of Complex Regional Pain Syndrome Type-I

Background

Mirror-image pain (MIP), which develops from the healthy body region contralateral to the actual injured site, is a mysterious pain phenomenon accompanying many chronic pain conditions, such as complex regional pain syndrome (CRPS). However, the pathogenesis of MIP still remains largely unknown. The purpose of this study is to perform an expression profiling to identify genes related to MIP in an animal model of CRPS-I.

Methods

We established a rat chronic post-ischemic pain (CPIP) model to mimic human CRPS-I. RNA-sequencing (RNA-Seq), bioinformatics, qPCR, immunostaining, and animal behavioral assays were used to screen potential genes in the contralateral dorsal root ganglia (DRG) that may be involved in MIP.

Results

The CPIP model rats developed robust and persistent MIP in contralateral hind paws. Bilateral DRG neurons did not exhibit obvious neuronal damage. RNA-Seq of contralateral DRG from CPIP model rats identified a total 527 differentially expressed genes (DEGs) vs sham rats. The expression changes of several representative DEGs were further verified by qPCR. Bioinformatics analysis indicated that the immune system process, innate immune response, and cell adhesion were among the mostly enriched biological processes, which are important processes involved in pain sensitization, neuroinflammation, and chronic pain. We further identified DEGs potentially involved in pain mechanisms or enriched in small- to medium-sized sensory neurons or TRPV1-lineage nociceptors. By comparing with published datasets summarizing genes enriched in pain mechanisms, we sorted out a core set of genes which might contribute to nociception and the pain mechanism in MIP.

Conclusion

We provided by far the first study to profile gene expression changes and pathway analysis of contralateral DRG for the studying of MIP mechanisms. This work may provide novel insights into understanding the mysterious mechanisms underlying MIP.

Chronic Orofacial Pain: Models, Mechanisms, and Genetic and Related Environmental Influences

Chronic orofacial pain conditions can be particularly difficult to diagnose and treat because of their complexity and limited understanding of the mechanisms underlying their aetiology and pathogenesis. Furthermore, there is considerable variability between individuals in their susceptibility to risk factors predisposing them to the development and maintenance of chronic pain as well as in their expression of chronic pain features such as allodynia, hyperalgesia and extraterritorial sensory spread. The variability suggests that genetic as well as environmental factors may contribute to the development and maintenance of chronic orofacial pain. This article reviews these features of chronic orofacial pain, and outlines findings from studies in animal models of the behavioural characteristics and underlying mechanisms related to the development and maintenance of chronic orofacial pain and trigeminal neuropathic pain in particular. The review also considers the role of environmental and especially genetic factors in these models, focussing on findings of differences between animal strains in the features and underlying mechanisms of chronic pain. These findings are not only relevant to understanding underlying mechanisms and the variability between patients in the development, expression and maintenance of chronic orofacial pain, but also underscore the importance for considering the strain of the animal to model and explore chronic orofacial pain processes.

Review of Literatures: Physiology of Orofacial Pain in Dentistry

The objective of this review of the literature is to summarize the physiology of orofacial pain in dentistry, particularly physiology of the pain pathway and molecular mechanisms on pathophysiology of pain, on account of new insights into classification of orofacial pain related diseases. This article will also focus on possible mechanisms of neuropathic orofacial pain which is distinguished from other types of pain.

Can within-subject comparisons of thermal thresholds be used for diagnostic purposes?

OBJECTIVE

Quantitative thermal testing (QTT) is a psychophysical assessment method of small nerve fibers that relies on reference material to assess function. Normal limits for within-subject comparisons of thermal thresholds are scarce, and their association with age, height and sex is not fully elucidated. The aim of this study was to investigate the normal limits for distal-proximal- and contralateral homologous comparisons of thermal thresholds with QTT, and their association with age, sex or height.

METHODS

Fifty healthy volunteers ages 20-79 participated in the experiment. Cold detection thresholds (CDT), warm detection thresholds (WDT), heat pain thresholds (HPT), and cold pain thresholds (CPT) were measured bilaterally at the thenar eminence, anterior thigh, distal medial leg and foot dorsum. Sample normal limits were calculated as (mean) ± 2 SD.

RESULTS

Forty-eight subjects were included in the analysis. CPT was excluded from all analyses due to a large floor-effect. Sample normal limits for side-differences ranged from 1.8 to 7.2 °C for CDT, 2.4-6.8 °C for WDT and 3.2-4.0 °C for HPT, depending on anatomical site. For distal-proximal comparisons, sample normal limits ranged from 4.0 to 8.7 °C for CDT, 6.0-14.0 °C for WDT and 4.2-9.0 °C for HPT, depending on the pairs compared. Age was associated with side-differences for CDT in the thenar eminences (p < 0.001) and distal medial legs (p < 0.002), and with 11 of 18 distal-proximal comparisons (p < 0.01).

CONCLUSIONS

The normal limits for distal-proximal- and contralateral homologous thermal thresholds were wide, and thus of limited use in a clinical setting, although the reported values may be somewhat inflated by low sample-size and consequent age-pooling. Age, but not sex or height, was associated with contralateral differences in CDT in the thenar eminences and distal medial legs, and with most distal-proximal differences.

SIGNIFICANCE

Due to wide normal limits, we advise caution when utilizing relative comparisons of thermal thresholds for diagnostic purposes.

Our experience of reinnervation of sole in diabetic sensorimotor polyneuropathy: A chance to change the natural history of disease

Diabetic sensorimotor polyneuropathy (DSPN) is the commonest form of neuropathy which leads to insensate sole, diabetic foot ulcers (DFU) and its complications. We share our experience in recovery of sensation in the sole after prophylactic surgery such as nerve decompression (ND) or sensory neurotization by nerve transfer (NT) in patients having Diabetic sensorimotor polyneuropathy DSPN. 32 patients (46 feet) were selected for either nerve decompression or sensory neurotization depending upon presence or absence of Tinel's sign at tarsal tunnel. At 6 month post-operatively perception of touch and pain recovered in all feet; temperature and pressure perception recovered in ∼95% feet; average vibration perception threshold returned to normal range and 2-Point Discrimination came down significantly. There were no ulcers or amputation in operated limbs during follow up period of 6 months. Prophylactic surgery in the form of ND and NT can be offered with minimal complications which significantly improve sensations in the sole in selected cases of DSPN. These have the potential to improve the quality of life of patient and change the natural course of disease.

Evolution of mirror-image pain in temporomandibular joint osteoarthritis mouse model

OBJECTIVE

Mirror-image pain is a kind of pain that occurs on the contralateral side, but its pathogenesis remains unclear. To develop an osteoarthritis mouse model for investigating mirror-image pain through observing nocifensive behaviors, histological changes, and nociceptive activity at days 3, 7, 14, 21, and 28 after the chemical induction of unilateral temporomandibular joint (TMJ) osteoarthritis.

METHODOLOGY

We randomly divided 6-week-old mice into sham and complete Freund adjuvant groups. To induce nocifensive behaviors, we applied 0.04 g of von Frey filament, 10 psi of air puff, and cold acetone on both sides of whisker pads at different days. The histology of TMJ on both sides was observed by hematoxylin/eosin staining and microcomputed tomography scanning. Furthermore, the nociceptive activity was evaluated using the phosphorylated cyclic AMP response element binding protein (pCREB) and a microglia marker at different days in the trigeminal subnucleus caudalis.

RESULTS

Nocifensive behaviors against mechanical and temperature stimuli on the contralateral side became stronger than the baseline on day 28, in agreement with the elevation of the pCREB and the microglia marker in the trigeminal subnucleus caudalis. Thus, hypernociception on the contralateral side occurred at day 28.

CONCLUSIONS

Clearly, the TMJ model with unilateral osteoarthritis exhibited mirror-image pain. Therefore, this model is useful in investigating the pathogenesis of pain and in developing treatments.

Electroacupuncture Alleviates Mechanical Allodynia of a Rat Model of CRPS-I and Modulates Gene Expression Profiles in Dorsal Root Ganglia

Complex regional pain syndrome type-I (CRPS-I) is chronic neurological disorder accompanied with devastating pain. Most conventional medical treatments lack effectiveness, making CRPS-I a challenging clinical condition. Electroacupuncture (EA) showed effectiveness in alleviating the pain symptoms of CRPS-I patients. However, the molecular mechanisms underlying EA's therapeutic effect are still not well-understood. Here, we established the rat chronic post-ischemic pain (CPIP) model to mimic CRPS-I and performed repetitive EA on bilateral hind limbs of the CPIP model rats. We then performed RNA-sequencing (RNA-Seq) to study the differences in gene expression, gene networks, and molecular pathways in ipsilateral DRGs innervating the hind limb of the CPIP model rats with and without repetitive EA treatment. Our results found that repetitive EA treatment significantly alleviated mechanical allodynia in bilateral hind limbs of CPIP model rats. RNA-Seq analysis indicated that EA modulated the expression of multiple genes and gene networks in the DRGs of CPIP model rats. Further bioinformatics analysis identified the up-regulation of an array of genes involved in biological process such as neutrophil chemotaxis and immune response in the DRGs of CPIP model rats after EA treatment. Thus, these results suggest that EA may alleviate pain response in CPIP model rats via regulating multiple genes. Our work may help to further advance the understandings of the molecular mechanisms underlying EA's therapeutic effects on CRPS-I and help to identify novel targets for CRPS-I treatment.

Tarsal tunnel release restores sensations in sole for diabetic sensorimotor polyneuropathy

BACKGROUND

Diabetic sensorimotor polyneuropathy (DSPN) is the commonest form of neuropathy. Loss of sensations in sole leads to diabetic foot ulcers (DFU) and its complications. Surgical decompression has been used in the treatment of diabetic peripheral neuropathy, however; its effectiveness has been questioned.Purpose of this study was to evaluate the sensory recovery in sole after tarsal tunnel decompression (TTD) in patients having DSPN.

METHODS

Thirteen patients (Age28-70 years, average 35.57 years; 7 Males, 6 Females; 20 feet) with DSPN and positive Tinel's sign over the tarsal tunnel were included in the study. Pre and post-operative sensory tests performed on the sole included tests for touch, pain, temperature, pressure, vibration perception threshold (VPT) and two-point discrimination (2-PD). Results were classified as per British Medical Research Council (MRC) scoring system.

RESULTS

-Sixteen feet were followed-up for 6 months. In all feet perception of touch, pain and pressure recovered. Temperature perception recovered in 75% feet. VPT came to normal range (16.81V) from 40.37 V and 2-PD came down to average of 6.0 mm from preoperative average of11.2 mm.MRC scale improved from S0 in 5 feet and S2 in 15 feet to S₃₊ in all 16 feet.There were no ulcers or amputation in operated limbs during follow up period of 6 months.

CONCLUSIONS

TTD improves plantar sensations in diabetic neuropathy and prevents ulcers and its related complications.

Evans Blue Reduces Neuropathic Pain Behavior by Inhibiting Spinal ATP Release

Upon peripheral nerve injury, vesicular ATP is released from damaged primary afferent neurons. This extracellular ATP subsequently activates purinergic receptors of the spinal cord, which play a critical role in neuropathic pain. As an inhibitor of the vesicular nucleotide transporter (VNUT), Evans blue (EB) inhibits the vesicular storage and release of ATP in neurons. Thus, we tested whether EB could attenuate neuropathic pain behavior induced by spinal nerve ligation (SNL) in rats by targeting VNUT. An intrathecal injection of EB efficiently attenuated mechanical allodynia for five days in a dose-dependent manner and enhanced locomotive activity in an SNL rat model. Immunohistochemical analysis showed that EB was found in VNUT immunoreactivity on neurons in the dorsal root ganglion and the spinal dorsal horn. The level of ATP in cerebrospinal fluid in rats with SNL-induced neuropathic pain decreased upon administration of EB. Interestingly, EB blocked ATP release from neurons, but not glial cells in vitro. Eventually, the loss of ATP decreased microglial activity in the ipsilateral dorsal horn of the spinal cord, followed by a reduction in reactive oxygen species and proinflammatory mediators, such as interleukin (IL)-1β and IL-6. Finally, a similar analgesic effect of EB was demonstrated in rats with monoiodoacetate-induced osteoarthritis (OA) pain. Taken together, these data demonstrate that EB prevents ATP release in the spinal dorsal horn and reduces the ATP/purinergic receptor-induced activation of spinal microglia followed by a decline in algogenic substances, thereby relieving neuropathic pain in rats with SNL.

LFA-1 antagonist (BIRT377) similarly reverses peripheral neuropathic pain in male and female mice with underlying sex divergent peripheral immune proinflammatory phenotypes

Aim:

The majority of preclinical studies investigating aberrant glial-neuroimmune actions underlying neuropathic pain have focused on male rodent models. Recently, studies have shown peripheral immune cells play a more prominent role than glial cells in mediating pathological pain in females. Here, we compared the onset and duration of allodynia in males and females, and the anti-allodynic action of a potentially novel therapeutic drug (BIRT377) that not only antagonizes the action of lymphocyte function-associated antigen-1 (LFA-1) to reduce cell migration in the periphery, but may also directly alter the cellular inflammatory bias.

Methods:

Male and female mice were subjected to peripheral nerve injury chronic constriction injury (CCI) applying two methods, using either 4–0 or 5–0 chromic gut suture material, to examine potential sex differences in the onset, magnitude and duration of allodynia. Hindpaw sensitivity before and after CCI and application of intravenous BIRT377 was assessed. Peripheral and spinal tissues were analyzed for protein (multiplex electrochemiluminescence technology) and mRNA expression (quantitative real-time PCR). The phenotype of peripheral T cells was determined using flow cytometry.

Results:

Sex differences in proinflammatory CCL2 and IL-1β and the anti-inflammatory IL-10 were observed from a set of cytokines analyzed. A profound proinflammatory T cell (Th17) response in the periphery and spinal cord was also observed in neuropathic females. BIRT377 reversed pain, reduced IL-1β and TNF, and increased IL-10 and transforming growth factor (TGF)-β1, also an anti-inflammatory cytokine, in both sexes. However, female-derived T cell cytokines are transcriptionally regulated by BIRT377, as demonstrated by reducing proinflammatory IL-17A production with concurrent increases in IL-10, TGF-β1 and the anti-inflammatory regulatory T cell-related factor, FOXP3.

Conclusion:

This study supports that divergent peripheral immune and neuroimmune responses during neuropathy exists between males and females. Moreover, the modulatory actions of BIRT377 on T cells during neuropathy are predominantly specific to females. These data highlight the necessity of including both sexes for studying drug efficacy and mechanisms of action in preclinical studies and clinical trials.

Antagonism of Transient Receptor Potential Ankyrin Type-1 Channels as a Potential Target for the Treatment of Trigeminal Neuropathic Pain: Study in an Animal Model

Transient receptor potential ankyrin type-1 (TRPA1) channels are known to actively participate in different pain conditions, including trigeminal neuropathic pain, whose clinical treatment is still unsatisfactory. The aim of this study was to evaluate the involvement of TRPA1 channels by means of the antagonist ADM_12 in trigeminal neuropathic pain, in order to identify possible therapeutic targets. A single treatment of ADM_12 in rats 4 weeks after the chronic constriction injury of the infraorbital nerve (IoN-CCI) significantly reduced the mechanical allodynia induced in the IoN-CCI rats. Additionally, ADM_12 was able to abolish the increased levels of TRPA1, calcitonin gene-related peptide (CGRP), substance P (SP), and cytokines gene expression in trigeminal ganglia, cervical spinal cord, and medulla induced in the IoN-CCI rats. By contrast, no significant differences between groups were seen as regards CGRP and SP protein expression in the pars caudalis of the spinal nucleus of the trigeminal nerve. ADM_12 also reduced TRP vanilloid type-1 (TRPV1) gene expression in the same areas after IoN-CCI. Our findings show the involvement of both TRPA1 and TRPV1 channels in trigeminal neuropathic pain, and in particular, in trigeminal mechanical allodynia. Furthermore, they provide grounds for the use of ADM_12 in the treatment of trigeminal neuropathic pain.

Involvement of leptin signaling in the development of cannabinoid CB2 receptor-dependent mirror image pain

Neuropathic pain typically appears in a region innervated by an injured or diseased nerve and, in some instances, also on the contralateral side. This so-called mirror image pain is often observed in mice lacking CB2 receptors after sciatic nerve injury, but the underlying mechanisms for this phenotype largely remain unclear. Here we focused on peripheral leptin signaling, which modulates neuropathic pain development and interacts with the endocannabinoid system. Leptin production is induced at the site of nerve injury in CB2-deficient mice (CB2-KO) mice and wild type controls (WT). However, induction of leptin receptor expression was only observed in the injured nerve of CB2-KO mice. This was paralleled by a stimulation of the leptin receptor-downstream STAT3 signaling and an infiltration of F4/80-positive macrophages. Interestingly, an upregulation of leptin receptor expression STAT3 activity and macrophage infiltration was also observed on the non-injured nerve of CB2-KO mice thus reflecting the mirror image pain in CB2-KO animals. Importantly, perineurally-administered leptin-neutralizing antibodies reduced mechanical hyperalgesia, blocked mirror image pain and inhibited the recruitment of F4/80-positive macrophages. These results identify peripheral leptin signaling as an important modulator of CB2 signaling in neuropathic pain.

Prenatal alcohol exposure potentiates chronic neuropathic pain, spinal glial and immune cell activation and alters sciatic nerve and DRG cytokine levels

A growing body of evidence indicates that prenatal alcohol exposure (PAE) may predispose individuals to secondary medical disabilities later in life. Animal models of PAE reveal neuroimmune sequelae such as elevated brain astrocyte and microglial activation with corresponding region-specific changes in immune signaling molecules such as cytokines and chemokines. The aim of this study was to evaluate the effects of moderate PAE on the development and maintenance of allodynia induced by chronic constriction injury (CCI) of the sciatic nerve in adult male rat offspring. Because CCI allodynia requires the actions of glial cytokines, we analyzed lumbar spinal cord glial and immune cell surface markers indicative of their activation levels, as well as sciatic nerve and dorsal root ganglia (DRG) cytokines in PAE offspring in adulthood. While PAE did not alter basal sensory thresholds before or after sham manipulations, PAE significantly potentiated adult onset and maintenance of allodynia. Microscopic analysis revealed exaggerated astrocyte and microglial activation, while flow cytometry data demonstrated increased proportions of immune cells with cell surface major histocompatibility complex II (MHCII) and β-integrin adhesion molecules, which are indicative of PAE-induced immune cell activation. Sciatic nerves from CCI rats revealed that PAE potentiated the proinflammatory cytokines interleukin (IL)-1β, IL-6 and tumor necrosis factor-alpha (TNFα) protein levels with a simultaneous robust suppression of the anti-inflammatory cytokine, IL-10. A profound reduction in IL-10 expression in the DRG of PAE neuropathic rats was also observed. Taken together, our results provide novel insights into the vulnerability that PAE produces for adult-onset central nervous system (CNS) pathological conditions from peripheral nerve injury.

Coupled cell networks are target cells of inflammation, which can spread between different body organs and develop into systemic chronic inflammation

Several organs in the body comprise cells coupled into networks. These cells have in common that they are excitable but do not express action potentials. Furthermore, they are equipped with Ca²⁺ signaling systems, which can be intercellular and/or extracellular. The transport of small molecules between the cells occurs through gap junctions comprising connexin 43. Examples of cells coupled into networks include astrocytes, keratinocytes, chondrocytes, synovial fibroblasts, osteoblasts, connective tissue cells, cardiac and corneal fibroblasts, myofibroblasts, hepatocytes, and different types of glandular cells. These cells are targets for inflammation, which can be initiated after injury or in disease. If the inflammation reaches the CNS, it develops into neuroinflammation and can be of importance in the development of systemic chronic inflammation, which can manifest as pain and result in changes in the expression and structure of cellular components. Biochemical parameters of importance for cellular functions are described in this review.

Injury-Dependent and Disability-Specific Lumbar Spinal Gene Regulation following Sciatic Nerve Injury in the Rat

Allodynia, hyperalgesia and spontaneous pain are cardinal sensory signs of neuropathic pain. Clinically, many neuropathic pain patients experience affective-motivational state changes, including reduced familial and social interactions, decreased motivation, anhedonia and depression which are severely debilitating. In earlier studies we have shown that sciatic nerve chronic constriction injury (CCI) disrupts social interactions, sleep-wake-cycle and endocrine function in one third of rats, a subgroup reliably identified six days after injury. CCI consistently produces allodynia and hyperalgesia, the intensity of which was unrelated either to the altered social interactions, sleep-wake-cycle or endocrine changes. This decoupling of the sensory consequences of nerve injury from the affective-motivational changes is reported in both animal experiments and human clinical data. The sensory changes triggered by CCI are mediated primarily by functional changes in the lumbar dorsal horn, however, whether lumbar spinal changes may drive different affective-motivational states has never been considered. In these studies, we used microarrays to identify the unique transcriptomes of rats with altered social behaviours following sciatic CCI to determine whether specific patterns of lumbar spinal adaptations characterised this subgroup. Rats underwent CCI and on the basis of reductions in dominance behaviour in resident-intruder social interactions were categorised as having Pain & Disability, Pain & Transient Disability or Pain alone. We examined the lumbar spinal transcriptomes two and six days after CCI. Fifty-four ‘disability-specific’ genes were identified. Sixty-five percent were unique to Pain & Disability rats, two-thirds of which were associated with neurotransmission, inflammation and/or cellular stress. In contrast, 40% of genes differentially regulated in rats without disabilities were involved with more general homeostatic processes (cellular structure, transcription or translation). We suggest that these patterns of gene expression lead to either the expression of disability, or to resilience and recovery, by modifying local spinal circuitry at the origin of ascending supraspinal pathways.