BackgroundNeuropeptide Y (NPY) Y2 receptor (Y2) antagonist BIIE0246 can both inhibit and facilitate nociception. The authors hypothesized that Y2 function depends on inflammation or nerve injury status. MethodsThe authors implemented a battery of behavioral tests in mice of both sexes that received (1) no injury; (2) an incision model of postoperative pain; (3) a spared nerve injury model of neuropathic pain; and (4) a latent sensitization model of chronic postsurgical pain. In addition to Y2 gene expression assays, spinal Y2 G-protein coupling was studied with guanosine-5 '-O-(3-[35S]thio)triphosphate ([35S]GTP gamma S) binding assays. ResultsThe authors report that intrathecal BIIE0246 increased mechanical and cold hypersensitivity, produced behavioral signs of spontaneous nociception and itch, and produced conditioned place aversion and preference in normal, uninjured mice. BIIE0246 did not change heat hypersensitivity or motor coordination. Conditional (sensory neuron-specific) Y2 deletion prevented BIIE0246-induced mechanical and cold hypersensitivity, nocifensive behaviors, and aversion. Both conditional deletion and pharmacologic blockade of Y2 reduced mechanical and thermal hypersensitivity after incision or nerve injury. SNI did not change the sensitivity of Y2 G-protein coupling with the Y2 agonist peptide YY (3-36) (PYY3-36), but increased the population of Y2 that effectively coupled G-proteins. Intrathecal PYY3-36 failed to reduce spared nerve injury- or incision-induced hypersensitivity in C57BL/6N mice. Incision did not change Npy2r gene expression in dorsal root ganglion. ConclusionsThe authors conclude that Y2 at central terminals of primary afferent neurons provides tonic inhibition of mechanical and cold nociception and itch. This switches to the promotion of mechanical and thermal hyperalgesia in models of acute and chronic postsurgical and neuropathic pain, perhaps due to an increase in the population of Y2 that effectively couples to G-proteins. These results support the development of Y2 antagonists for the treatment of chronic postsurgical and neuropathic pain.

BACKGROUND:There is evidence that aerobic exercise is beneficial for brain health, but these effects are variable between individuals and the underlying mechanisms that modulate these benefits remain unclear. OBJECTIVE:We sought to characterize the acute physiological response of bioenergetic and neurotrophic blood biomarkers to exercise in cognitively healthy older adults, as well as relationships with brain blood flow. METHODS:We measured exercise-induced changes in lactate, which has been linked to brain blood flow, as well brain-derived neurotrophic factor (BDNF), a neurotrophin related to brain health. We further quantified changes in brain blood flow using arterial spin labeling. RESULTS:As expected, lactate and BDNF both changed with time post exercise. Intriguingly, there was a negative relationship between lactate response (area under the curve) and brain blood flow measured acutely following exercise. Finally, the BDNF response tracked strongly with change in platelet activation, providing evidence that platelet activation is an important mechanism for trophic-related exercise responses. CONCLUSIONS:Lactate and BDNF respond acutely to exercise, and the lactate response tracks with changes in brain blood flow. Further investigation into how these factors relate to brain health-related outcomes in exercise trials is warranted.

Exposure to stress early in life has been associated with adult-onset comorbidities such as chronic pain, metabolic dysregulation, obesity, and inactivity. We have established an early-life stress model using neonatal maternal separation (NMS) in mice, which displays evidence of increased body weight and adiposity, widespread mechanical allodynia, and hypothalamic-pituitary-adrenal axis dysregulation in male mice. Early-life stress and consumption of a Western-style diet contribute to the development of obesity; however, relatively few preclinical studies have been performed in female rodents, which are known to be protected against diet-induced obesity and metabolic dysfunction. In this study, we gave naïve and NMS female mice access to a high-fat/high-sucrose (HFS) diet beginning at 4 wk of age. Robust increases in body weight and fat were observed in HFS-fed NMS mice during the first 10 wk on the diet, driven partly by increased food intake. Female NMS mice on an HFS diet showed widespread mechanical hypersensitivity compared with either naïve mice on an HFS diet or NMS mice on a control diet. HFS diet-fed NMS mice also had impaired glucose tolerance and fasting hyperinsulinemia. Strikingly, female NMS mice on an HFS diet showed evidence of hepatic steatosis with increased triglyceride levels and altered glucocorticoid receptor levels and phosphorylation state. They also exhibited increased energy expenditure as observed via indirect calorimetry and expression of proinflammatory markers in perigonadal adipose. Altogether, our data suggest that early-life stress exposure increased the susceptibility of female mice to develop diet-induced metabolic dysfunction and pain-like behaviors.

Exposure to stress early in life has been associated with adult-onset co-morbidities such as chronic pain, metabolic dysregulation, obesity, and inactivity. We have established an early life stress model using neonatal maternal separation (NMS) in mice, which displays evidence of increased body weight and adiposity, widespread mechanical allodynia, and hypothalamic-pituitary-adrenal axis dysregulation in male mice. Early life stress and consumption of a western style diet contribute to the development of obesity, however, relatively few pre-clinical studies have been performed in female rodents, which are known to be protected against diet induced obesity and metabolic dysfunction. In this study we gave naïve and NMS female mice access to a high-fat/high-sucrose (HFS) diet beginning at 4 weeks of age. Robust increases in body weight and fat were observed in HFS-fed NMS mice during the first 10 weeks on the diet, driven partly by increased food intake. Female NMS mice on a HFS diet showed widespread mechanical hypersensitivity compared to either naïve mice on a HFS diet or NMS mice on a control diet. HFS diet-fed NMS mice also had impaired glucose tolerance and fasting hyperinsulinemia. Strikingly, female NMS mice on a HFS diet showed evidence of hepatic steatosis with increased triglyceride levels and altered glucocorticoid receptor levels and phosphorylation state. They also exhibited increased energy expenditure as observed via indirect calorimetry and expression of pro-inflammatory markers in perigonadal adipose. Altogether, our data suggest that early life stress exposure increased the susceptibility of female mice to develop diet-induced metabolic dysfunction and pain-like behaviors.

Exposure to stress early in life has been associated with adult-onset co-morbidities such as chronic pain, obesity, and metabolic disorders. We have established a mouse model of early life stress using neonatal maternal separation (NMS) that results in urogenital hypersensitivity and increased body weight and adiposity compared to naive (non-separated) mice. In this study we tested the hypothesis that consumption of a high fat/high sucrose (HFS) diet will worsen NMS-related outcomes. Male and female naive and NMS mice were pair-housed with a sex matched littermate. At 4-weeks of age mice were assigned to either control diet or HFS diet and weight gain and food intake were measured weekly. Mechanical sensitivity and body composition were measured at 22-weeks of age. At 25-29 weeks of age mice were subject to a glucose tolerance test. Mice were then sacrificed, and tissues were fixed and frozen. Adipose tissue was analyzed via RT-PCR and fixed liver tissue was stained and analyzed for steatosis. NMS mice on a HFS diet were found to have increased body weight and percent body fat compared to naive mice on a HFS diet and to NMS mice on a control diet. Additionally, both NMS and the HFS diet resulted in significantly lower hind paw mechanical withdrawal thresholds indicative of hypersensitivity. Both NMS and HFS diet consumption were found to result in impaired glucose homeostasis. Upon histological examination of the liver, HFS diet fed NMS mice were observed to have increased steatosis and hepatocyte ballooning. Our results suggest that HFS diet exacerbates the outcomes of NMS in both males and females, resulting in widespread hypersensitivity, weight gain, glucose intolerance, and steatosis. Future work will explore possible underlying mechanisms for the increased weight gain and sensitivity associated with stress and diet. Grant support from RO1DK099611 (JAC), RO1DK103872 (JAC), T32HD057850 (OCE), COBRE grant P20GM104936, IDeA grant P20GM103418, core support from IDDRC grant P30HD002528. Exposure to stress early in life has been associated with adult-onset co-morbidities such as chronic pain, obesity, and metabolic disorders. We have established a mouse model of early life stress using neonatal maternal separation (NMS) that results in urogenital hypersensitivity and increased body weight and adiposity compared to naive (non-separated) mice. In this study we tested the hypothesis that consumption of a high fat/high sucrose (HFS) diet will worsen NMS-related outcomes. Male and female naive and NMS mice were pair-housed with a sex matched littermate. At 4-weeks of age mice were assigned to either control diet or HFS diet and weight gain and food intake were measured weekly. Mechanical sensitivity and body composition were measured at 22-weeks of age. At 25-29 weeks of age mice were subject to a glucose tolerance test. Mice were then sacrificed, and tissues were fixed and frozen. Adipose tissue was analyzed via RT-PCR and fixed liver tissue was stained and analyzed for steatosis. NMS mice on a HFS diet were found to have increased body weight and percent body fat compared to naive mice on a HFS diet and to NMS mice on a control diet. Additionally, both NMS and the HFS diet resulted in significantly lower hind paw mechanical withdrawal thresholds indicative of hypersensitivity. Both NMS and HFS diet consumption were found to result in impaired glucose homeostasis. Upon histological examination of the liver, HFS diet fed NMS mice were observed to have increased steatosis and hepatocyte ballooning. Our results suggest that HFS diet exacerbates the outcomes of NMS in both males and females, resulting in widespread hypersensitivity, weight gain, glucose intolerance, and steatosis. Future work will explore possible underlying mechanisms for the increased weight gain and sensitivity associated with stress and diet. Grant support from RO1DK099611 (JAC), RO1DK103872 (JAC), T32HD057850 (OCE), COBRE grant P20GM104936, IDeA grant P20GM103418, core support from IDDRC grant P30HD002528.

Peripheral nerve injury sensitizes a complex network of spinal cord dorsal horn (DH) neurons to produce allodynia and neuropathic pain. The identification of a druggable target within this network has remained elusive, but a promising candidate is the neuropeptide Y (NPY) Y1 receptor-expressing interneuron (Y1-IN) population. We report that spared nerve injury (SNI) enhanced the excitability of Y1-INs and elicited allodynia (mechanical and cold hypersensitivity) and affective pain. Similarly, chemogenetic or optogenetic activation of Y1-INs in uninjured mice elicited behavioral signs of spontaneous, allodynic, and affective pain. SNI-induced allodynia was reduced by chemogenetic inhibition of Y1-INs, or intrathecal administration of a Y1-selective agonist. Conditional deletion of Npy1r in DH neurons, but not peripheral afferent neurons prevented the anti-hyperalgesic effects of the intrathecal Y1 agonist. We conclude that spinal Y1-INs are necessary and sufficient for the behavioral symptoms of neuropathic pain and represent a promising target for future pharmacotherapeutic development of Y1 agonists.

Inflammation plays a key role in the progression and maintenance of chronic pain, which impacts the lives of millions of Americans. Despite growing evidence that chronic pain can be improved by treating underlying inflammation, successful treatments are lacking and pharmaceutical interventions are limited due to drug side effects. Here we are testing whether a 'healthy human' diet (HHD), with or without anti-inflammatory components (HHAID), improves pain-like behaviors in a preclinical model of chronic widespread hypersensitivity induced by neonatal maternal separation (NMS). The HHD and HHAID are isocaloric and macronutrient-matched, have a low glycemic index, and fat content (35 kcal%) that is high in omega-3 fatty acids, while only the HHAID includes a combination of key anti-inflammatory compounds, at clinically relevant doses. Mice on these diets were compared to mice on a control diet with a macronutrient composition commonly used in rodents (20% protein, 70% carbohydrate, 10% fat). Our results demonstrate a benefit of the HHAID on pain-like behaviors in both male and female mice, despite increased caloric intake, adiposity, and weight gain. In female mice, HHAID specifically increased measures of metabolic syndrome and inflammation compared to the HHD and control diet groups. Male mice were susceptible to worsening metabolic measures on both the HHAID and HHD. This work highlights important sexual dimorphic outcomes related to early life stress exposure and dietary interventions, as well as a potential disconnect between improvements in pain-like behaviors and metabolic measures.

AbstractInflammation plays a key role in the progression and maintenance of chronic pain, which impacts the lives of millions of Americans. Despite growing evidence that chronic pain can be improved by treating underlying inflammation, successful treatments are lacking and pharmaceutical interventions are limited due to drug side effects. Here we are testing whether an anti-inflammatory diet (AID) containing a combination of key anti-inflammatory compounds, at clinically relevant doses, improves pain-like behaviors in a preclinical model of chronic widespread hypersensitivity induced by neonatal maternal separation (NMS). Our results demonstrate a benefit of the AID on pain-like behaviors, despite the diet being high in fat, which led to increased caloric intake, adiposity, and weight gain. The AID specifically increased measures of metabolic syndrome and inflammation in female mice, compared to an isocaloric, macronutrient-matched diet lacking the anti-inflammatory compounds. Male mice, especially those exposed to NMS, were equally susceptible to both diets worsening metabolic measures. This work highlights important sexual dimorphic outcomes related to early life stress exposure and dietary interventions, as well as a potential disconnect between improvements in pain-like behaviors and metabolic measures.

Acute pain is a prevalent and debilitating complication following burn injury and has the potential in certain individuals to become chronic pain. There is a paucity of preclinical and clinical research that has addressed this large clinical problem. Our recent work has been focused on developing a burn injury model that will allow for mechanistic investigations for acute and chronic burn injury pain. Our group has previously reported that mice given a high fat/rich carbohydrate diet (54% kcal from fat, 25% kcal from carbohydrate (CHO))develop mechanical allodynia. The present work sought to examine whether this high fat, high CHO diet may affect pain behaviors related to acute burn injury and whether it would lead to prolonged pain behaviors consistent with chronic burn pain. Mice were given either a normal chow or a high fat/high CHO diet and then either were given burn or sham injury on the right hind paw. Pain behaviors were observed over a 28 day period after the burn injury and included mechanical and thermal assessments. Results indicate that both normal chow and high fat diet burn injured mice exhibited significantly reduced mechanical pain thresholds for two weeks after burn injury. After 14 days, both burn injury groups displayed increased mechanical pain thresholds that by 28 days, were surprisingly higher than baseline. Overall, the high fat diet burn group was not found to display greater levels of allodynia compared to the normal chow burn group and there was no evidence that the current model or the high fat diet led to pain behaviors consistent with chronic pain. Preliminary investigations into proportions of mast cell degranulation show that burn injury led to a higher percentage of degranulated mast cells compared to sham injury and that dietary influence may also have a small impact.

Pain is significantly impacted by the increasing epidemic of obesity and the metabolic syndrome. Our understanding of how these features impact pain is only beginning to be developed. Herein, we have investigated how small genetic differences among C57BL/6 mice from 2 different commercial vendors lead to important differences in the development of high-fat diet-induced mechanical sensitivity. Two substrains of C57BL/6 mice from Jackson Laboratories (Bar Harbor, ME; C57BL/6J and C57BL/6NIH), as well as C57BL/6 from Charles Rivers Laboratories (Wilmington, MA; C57BL/6CR) were placed on high-fat diets and analyzed for changes in metabolic features influenced by high-fat diet and obesity, as well as measures of pain-related behaviors. All 3 substrains responded to the high-fat diet; however, C57BL/6CR mice had the highest weights, fat mass, and impaired glucose tolerance of the 3 substrains. In addition, the C57BL/6CR mice were the only strain to develop significant mechanical sensitivity over the course of 8 weeks. Importantly, the C57BL/6J mice were protected from mechanical sensitivity, which may be based on increased physical activity compared with the other 2 substrains. These findings suggest that activity may play a powerful role in protecting metabolic changes associated with a high-fat diet and that these may also be protective in pain-associated changes as a result of a high-fat diet. These findings also emphasize the importance of selection and transparency in choosing C57BL/6 substrains in pain-related research. PERSPECTIVE: Obesity and the metabolic syndrome play an important role in pain. This study identifies key differences in the response to a high-fat diet among substrains of C57BL/6 mice and differences in intrinsic physical activity that may influence pain sensitivity. The results emphasize physical activity as a powerful modulator of obesity-related pain sensitivity.

Current experiments investigated whether a ketogenic diet impacts neuropathy associated with obesity and prediabetes. Mice challenged with a ketogenic diet were compared to mice fed a high-fat diet or a high-fat diet plus exercise. Additionally, an intervention switching to a ketogenic diet following 8 weeks of high-fat diet was performed to compare how a control diet, exercise, or a ketogenic diet affects metabolic syndrome-induced neural complications. When challenged with a ketogenic diet, mice had reduced bodyweight and fat mass compared to high-fat-fed mice, and were similar to exercised, high-fat-fed mice. High-fat-fed, exercised and ketogenic-fed mice had mildly elevated blood glucose; conversely, ketogenic diet-fed mice were unique in having reduced serum insulin levels. Ketogenic diet-fed mice never developed mechanical allodynia contrary to mice fed a high-fat diet. Ketogenic diet fed mice also had increased epidermal axon density compared all other groups. When a ketogenic diet was used as an intervention, a ketogenic diet was unable to reverse high-fat fed induced metabolic changes but was able to significantly reverse a high-fat diet-induced mechanical allodynia. As an intervention, a ketogenic diet also increased epidermal axon density. In vitro studies revealed increased neurite outgrowth in sensory neurons from mice fed a ketogenic diet and in neurons from normal diet-fed mice given ketone bodies in the culture medium. These results suggest a ketogenic diet can prevent certain complications of prediabetes and provides significant benefits to peripheral axons and sensory dysfunction.

Cytosolic NADH­cytochrome­b5­oxidoreductase (NCB5OR) is ubiquitously expressed in animal tissues. We have previously reported that global ablation of NCB5OR in mice results in early-onset lean diabetes with decreased serum leptin levels and increased metabolic and feeding activities. The conditional deletion of NCB5OR in the mouse cerebellum and midbrain (conditional knock out, CKO mice) results in local iron dyshomeostasis and altered locomotor activity. It has been established that lesion to or removal of the cerebellum leads to changes in nutrient organization, visceral response, feeding behavior, and body weight. This study assessed whether loss of NCB5OR in the cerebellum and midbrain altered feeding or metabolic activity and had an effect on serum T3, cortisol, prolactin, and leptin levels. Metabolic cage data revealed that 16 week old male CKO mice had elevated respiratory quotients and decreased respiratory water expulsion, decreased voluntary exercise, and altered feeding and drinking behavior compared to wild-type littermate controls. Most notably, male CKO mice displayed higher consumption of food during refeeding after a 48­h fast. Echo MRI revealed normal body composition but decreased total water content and hydration ratios in CKO mice. Increased serum osmolality measurements confirmed the dehydration status of male CKO mice. Serum leptin levels were significantly elevated in male CKO mice while prolactin, T3, and cortisol levels remain unchanged relative to wild-type controls, consistent with elevated transcript levels for leptin receptors (short form) in the male CKO mouse cerebellum. Taken together, these findings suggest altered feeding response post starvation as a result of NCB5OR deficiency in the cerebellum.

Behavioral phenotyping is a crucial step in validating animal models of human disease. Most traditional behavioral analyses rely on investigator observation of animal subjects, which can be confounded by inter-observer variability, scoring consistency, and the ability to observe extremely rapid, small, or repetitive movements. Force-Plate Actimeter (FPA)-based assessments can quantify locomotor activity and detailed motor activity with an incredibly rich data stream that can reveal details of movement unobservable by the naked eye. This report describes four specific examples of FPA analysis of behavior that have been useful in specific rat or mouse models of human neurological disease, which show how FPA analysis can be used to capture and quantify specific features of the complex behavioral phenotypes of these animal models. The first example quantifies nociceptive behavior of the rat following injection of formalin into the footpad as a common model of persistent inflammatory pain. The second uses actimetry to quantify intense, rapid circling behaviors in a transgenic mouse that overexpresses human laminin α5, a basement membrane protein. The third example assesses place preference behaviors in a rat model of migraine headache modeling phonophobia and photophobia. In the fourth example, FPA analysis revealed a unique movement signature emerged with age in a digenic mutant mouse model of Tourette Syndrome. Taken together, these approaches demonstrate the power and usefulness of the FPA in the examination and quantification of minute details of motor behaviors, greatly expanding the scope and detail of behavioral phenotyping of preclinical models of human disease.

High levels of bilirubin in infants can cause kernicterus, which includes basal ganglia damage and dystonia. Stem cell transplantation may be an effective treatment for this disease. In this study, we transplanted human neural progenitor cells differentiated toward propriospinal interneurons into the striatum of 20-day-old spontaneously jaundiced (jj) Gunn rats and nonjaundiced (Nj) littermates. Using immunohistochemical methods, we found that grafted cells survived and grew fibers in jj and Nj brains 3 weeks after transplantation. Grafted cells had a higher survival rate in jj than in Nj brains, suggesting that slightly elevated bilirubin may protect graft survival due to its antioxidative and immunosuppressive effects. Despite their survival, only a small portion of grafted neurons expressed GAD-6 or ChAT, which mark GABAergic and cholinergic neurons, respectively, and are the cells that we are attempting to replace in kernicterus. Thus, NPCs containing large populations of GABAergic and cholinergic neurons should be used for further study in this field.

Acute and chronic pain is a prevalent and debilitating complication following burn injury. However, burn injury pain remains largely an untreatable condition and current strategies only address ongoing pain control. Little research has addressed this large clinical problem, with only a few studies using an animal model to explore molecular and cellular mechanisms underlying this form of acute and chronic pain. This paucity of information has hampered clinicians in developing effective treatment strategies for patients that suffer burn-related pain. Currently, there are a number of proposed mechanisms that lead to acute and chronic pain in burn injuries. Alterations in inflammation or neurotrophic factor expression are thought to modulate both acute and chronic pain. Our studies have shown that exercise intervention can modify each of these factors and exercise can correct alterations in pro-nociceptive peripheral nervous system adaptations. Together, our multidisciplinary team has developed a murine model of burn injury that leads to robust pain behaviors and pathological changes consistent with acute and chronic burn injury neuropathic pain. Furthermore, our preliminary studies show that mice with burn-injured hind paws voluntarily exercise on running wheels. Future studies will identify mechanisms of how exercise can modulate these acute and chronic neuropathic pain associated with burn injury. Importantly, our approaches are readily translatable to human studies and may be applicable to other forms of chronic pain. These studies will also aid future experiments to investigate predictive features regarding diet, lifestyle, and activity that will be important in treating chronic pain associated with burn injury.

Diet, activity, and inflammation are increasingly recognized as important modulators of nervous system disease, including pain. Sex differences have also been well established in the development of chronic pain. Experimental studies of exercise consistently reveal a positive benefit of exercise on pain. Here, we have assessed a genetic rat model that has selected for traits that promote high exercise capacity or low exercise capacity. Low capacity runners (LCR) have diverged from high capacity runners (HCR) based on rats' inability to exercise, leading to many differences in their metabolic status. This study focused on female rats in order to understand differences related to metabolic status and peripheral nerve function in females. Our analysis of a number of parameters of peripheral nerve function relevant to pain and neuropathy have revealed select differences between LCR and HCR female rats. LCR rats have reduced mechanical sensitivity, higher intraepidermal nerve fiber density and TrkA-positive epidermal axons, increased numbers of Langerhans and mast cells in cutaneous tissues, and a higher fat content despite similar overall body weights between LCR and HCR rats. Other aspects, including sensory and motor nerve conduction velocity, thermal sensitivity, and mRNA expression of selected genes relevant to peripheral sensation were not different. Overall, these results suggest that the differences in metabolic state and inflammation can lead to important changes in sensitivity and peripheral tissues. These baseline differences of the LCR rat that could lead to poor responses to tissue damage and painful stimuli with alterations in diet or disease state. The LCR and HCR rats should prove useful in future studies to assess how the interaction of metabolic status and inflammation impacts pain.

INTRODUCTION:Diet and activity are recognized as modulators of nervous system disease, including pain. Studies of exercise consistently reveal a benefit on pain. This study focused on female rats to understand differences related to metabolic status and peripheral nerve function in females.METHODS:Here, we investigated parameters of peripheral nerve function relevant to pain in rats selectively bred for high (high-capacity runners; HCR) or low endurance exercise capacity (low-capacity runners; LCR) resulting in divergent intrinsic aerobic capacities and susceptibility for metabolic conditions.RESULTS:LCR female rats have reduced mechanical sensitivity, higher intraepidermal nerve fiber density and TrkA-positive epidermal axons, increased numbers of Langerhans and mast cells in cutaneous tissues, and a higher fat content despite similar overall body weights compared to female HCR rats. Sensory and motor nerve conduction velocities, thermal sensitivity, and mRNA expression of selected genes relevant to peripheral sensation were not different.CONCLUSIONS:These results suggest that aerobic capacity and metabolic status influence sensory sensitivity and aspects of inflammation in peripheral tissues that could lead to poor responses to tissue damage and painful stimuli. The LCR and HCR rats should prove useful as models to assess how the metabolic status impacts pain.

Children with Rett syndrome show abnormal cutaneous sensitivity. The precise nature of sensory abnormalities and underlying molecular mechanisms remain largely unknown. Rats with methyl-CpG binding protein 2 (MeCP2) mutation, characteristic of Rett syndrome, show hypersensitivity to pressure and cold, but hyposensitivity to heat. They also show cutaneous hyperinnervation by nonpeptidergic sensory axons, which include subpopulations encoding noxious mechanical and cold stimuli, whereas peptidergic thermosensory innervation is reduced. MeCP2 knockdown confined to dorsal root ganglion sensory neurons replicated this phenotype in vivo, and cultured MeCP2-deficient ganglion neurons showed augmented axonogenesis. Transcriptome analysis revealed dysregulation of genes associated with cytoskeletal dynamics, particularly those controlling actin polymerization and focal-adhesion formation necessary for axon growth and mechanosensory transduction. Down-regulation of these genes by topoisomerase inhibition prevented abnormal axon sprouting. We identified eight key affected genes controlling actin signaling and adhesion formation, including members of the Arhgap, Tiam, and cadherin families. Simultaneous virally mediated knockdown of these genes in Rett rats prevented sensory hyperinnervation and reversed mechanical hypersensitivity, indicating a causal role in abnormal outgrowth and sensitivity. Thus, MeCP2 regulates ganglion neuronal genes controlling cytoskeletal dynamics, which in turn determines axon outgrowth and mechanosensory function and may contribute to altered pain sensitivity in Rett syndrome.

Rett Syndrome (RTT), an autism-related disorder caused by mutation of the X-linked Methyl CpG-binding Protein 2 (MECP2) gene, is characterized by severe cognitive and intellectual deficits. While cognitive deficits are well-documented in humans and rodent models, impairments of sensory, motor and metabolic functions also occur but remain poorly understood. To better understand non-cognitive deficits in RTT, we studied female rats heterozygous for Mecp2 mutation (Mecp2−/x); unlike commonly used male Mecp2−/y rodent models, this more closely approximates human RTT where males rarely survive. Mecp2−/x rats showed rapid, progressive decline of motor coordination through six months of age as assessed by rotarod performance, accompanied by deficits in gait and posture. Mecp2−/x rats were hyper-responsive to noxious pressure and cold, but showed visceral hyposensitivity when tested by colorectal distension. Mecp2−/x rats ate less, drank more, and had more body fat resulting in increased weight gain. Our findings reveal an array of progressive non-cognitive deficits in this rat model that are likely to contribute to the compromised quality of life that characterizes RTT.