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Chronic pain is a substantial health burden and options for treating chronic pain remain minimally effective. Ketogenic diets are emerging as well-tolerated, effective therapeutic strategies in preclinical models of chronic pain, especially diabetic neuropathy. We tested whether a ketogenic diet is antinociceptive through ketone oxidation and related activation of ATP-gated potassium (KATP) channels in mice. We demonstrate that consumption of a ketogenic diet for one week reduced evoked nocifensive behaviors (licking, biting, lifting) following intraplantar injection of different noxious stimuli (methylglyoxal, cinnamaldehyde, capsaicin, or Yoda1) in mice. A ketogenic diet also decreased the expression of p-ERK, an indicator of neuronal activation in the spinal cord, following peripheral administration of these stimuli. Using a genetic mouse model with deficient ketone oxidation in peripheral sensory neurons, we demonstrate that protection against methylglyoxal-induced nociception by a ketogenic diet partially depends on ketone oxidation by peripheral neurons. Injection of tolbutamide, a KATP channel antagonist, prevented ketogenic diet-mediated antinociception following intraplantar capsaicin injection. Tolbutamide also restored the expression of spinal activation markers in ketogenic diet-fed, capsaicin-injected mice. Moreover, activation of KATP channels with the KATP channel agonist diazoxide reduced pain-like behaviors in capsaicin-injected, chow-fed mice, similar to the effects observed with a ketogenic diet. Diazoxide also reduced the number of p-ERK+ cells in capsaicin-injected mice. These data support a mechanism that includes neuronal ketone oxidation and activation of KATP channels to provide ketogenic diet-related analgesia. This study also identifies KATP channels as a new target to mimic the antinociceptive effects of a ketogenic diet.
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Chronic pain is a substantial health burden and options for treating chronic pain remain minimally effective. Ketogenic diets are emerging as well-tolerated, effective therapeutic strategies in preclinical models of chronic pain, especially diabetic neuropathy. We tested whether a ketogenic diet is antinociceptive through ketone oxidation and related activation of ATP-gated potassium (KATP) channels in mice. We demonstrate that consumption of a ketogenic diet for one week reduced evoked nocifensive behaviors (licking, biting, lifting) following intraplantar injection of different noxious stimuli (methylglyoxal, cinnamaldehyde, capsaicin, or Yoda1) in mice. A ketogenic diet also decreased the expression of p-ERK, an indicator of neuronal activation in the spinal cord, following peripheral administration of these stimuli. Using a genetic mouse model with deficient ketone oxidation in peripheral sensory neurons, we demonstrate that protection against methylglyoxal-induced nociception by a ketogenic diet partially depends on ketone oxidation by peripheral neurons. Injection of tolbutamide, a KATP channel antagonist, prevented ketogenic diet-mediated antinociception following intraplantar capsaicin injection. Tolbutamide also restored the expression of spinal activation markers in ketogenic diet-fed, capsaicin-injected mice. Moreover, activation of KATP channels with the KATP channel agonist diazoxide reduced pain-like behaviors in capsaicin-injected, chow-fed mice, similar to the effects observed with a ketogenic diet. Diazoxide also reduced the number of p-ERK+ cells in capsaicin-injected mice. These data support a mechanism that includes neuronal ketone oxidation and activation of KATP channels to provide ketogenic diet-related analgesia. This study also identifies KATP channels as a new target to mimic the antinociceptive effects of a ketogenic diet.
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Ketogenic diets are emerging as protective interventions in preclinical and clinical models of somatosensory nervous system disorders. Additionally, dysregulation of succinyl-CoA 3-oxoacid CoA-transferase 1 (SCOT, encoded by Oxct1), the fate-committing enzyme in mitochondrial ketolysis, has recently been described in Friedreich's ataxia and amyotrophic lateral sclerosis. However, the contribution of ketone metabolism in the normal development and function of the somatosensory nervous system remains poorly characterized. We generated sensory neuron-specific, Advillin-Cre knockout of SCOT (Adv-KO-SCOT) mice and characterized the structure and function of their somatosensory system. We used histological techniques to assess sensory neuronal populations, myelination, and skin and spinal dorsal horn innervation. We also examined cutaneous and proprioceptive sensory behaviors with the von Frey test, radiant heat assay, rotarod, and grid-walk tests. Adv-KO-SCOT mice exhibited myelination deficits, altered morphology of putative Aδ soma from the dorsal root ganglion, reduced cutaneous innervation, and abnormal innervation of the spinal dorsal horn compared to wildtype mice. Synapsin 1-Cre-driven knockout of Oxct1 confirmed deficits in epidermal innervation following a loss of ketone oxidation. Loss of peripheral axonal ketolysis was further associated with proprioceptive deficits, yet Adv-KO-SCOT mice did not exhibit drastically altered cutaneous mechanical and thermal thresholds. Knockout of Oxct1 in peripheral sensory neurons resulted in histological abnormalities and severe proprioceptive deficits in mice. We conclude that ketone metabolism is essential for the development of the somatosensory nervous system. These findings also suggest that decreased ketone oxidation in the somatosensory nervous system may explain the neurological symptoms of Friedreich's ataxia.
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Ataxia de Friedreich , Animales , Ratones , Ataxia de Friedreich/patología , Ratones Noqueados , Cetonas , Oxidación-Reducción , Células Receptoras Sensoriales/patologíaRESUMEN
Ketogenic diets are emerging as protective interventions in preclinical and clinical models of somatosensory nervous system disorders. Additionally, dysregulation of succinyl-CoA 3-oxoacid CoA-transferase 1 (SCOT, encoded by Oxct1 ), the fate-committing enzyme in mitochondrial ketolysis, has recently been described in Friedreich's ataxia and amyotrophic lateral sclerosis. However, the contribution of ketone metabolism in the normal development and function of the somatosensory nervous system remains poorly characterized. We generated sensory neuron-specific, Advillin-Cre knockout of SCOT (Adv-KO-SCOT) mice and characterized the structure and function of their somatosensory system. We used histological techniques to assess sensory neuronal populations, myelination, and skin and spinal dorsal horn innervation. We also examined cutaneous and proprioceptive sensory behaviors with the von Frey test, radiant heat assay, rotarod, and grid-walk tests. Adv-KO-SCOT mice exhibited myelination deficits, altered morphology of putative Aδ soma from the dorsal root ganglion, reduced cutaneous innervation, and abnormal innervation of the spinal dorsal horn compared to wildtype mice. Synapsin 1-Cre-driven knockout of Oxct1 confirmed deficits in epidermal innervation following a loss of ketone oxidation. Loss of peripheral axonal ketolysis was further associated with proprioceptive deficits, yet Adv-KO-SCOT mice did not exhibit drastically altered cutaneous mechanical and thermal thresholds. Knockout of Oxct1 in peripheral sensory neurons resulted in histological abnormalities and severe proprioceptive deficits in mice. We conclude that ketone metabolism is essential for the development of the somatosensory nervous system. These findings also suggest that decreased ketone oxidation in the somatosensory nervous system may explain the neurological symptoms of Friedreich's ataxia.
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ABSTRACT: Methylglyoxal (MGO) is a reactive dicarbonyl byproduct of glycolysis implicated in a growing number of neuropathic pain conditions, including chemotherapy-induced peripheral neuropathy, diabetic peripheral neuropathy, and radiculopathy with lumbar disk herniation. Recent studies show success in preclinical models treating these disorders with an interventional ketogenic diet. Here, we tested the hypothesis that a ketogenic diet modifies pathological MGO signaling as a mechanism underlying neuropathy improvement. We found that mice injected with MGO displayed nocifensive behaviors, whereas mice prefed a ketogenic diet were resistant to mechanical allodynia elicited by MGO. In addition, levels of circulating MGO were reduced in ketogenic diet-fed mice and negatively correlated with levels of the ketone body ß-hydroxybutyrate (ß-HB). Methylglyoxal is normally scavenged by the glyoxalase system, and ketogenic diet-fed mice displayed increased glyoxalase 1 activity compared with chow-fed control mice. Recent studies also suggest that ketone bodies contribute to MGO detoxification, consistent with a negative correlation between ß-HB and MGO. To assess whether ketone bodies modified MGO-evoked nociception through direct MGO detoxification, we coincubated either acetoacetate or ß-HB with MGO before injection. Mice receiving intraplantar MGO injection exhibit increased nociceptive behavior (lifting, licking, biting, and scratching), which was significantly reduced by coincubation with either acetoacetate or ß-HB. Methylglyoxal increased phospho-extracellular signal-regulated kinase-positive cells in the spinal dorsal horn, and this evoked spinal activation was ameliorated by preincubation with acetoacetate or ß-HB. These results suggest that a ketogenic diet and ketone bodies ameliorate MGO-evoked nociception, partially through detoxification of MGO, and provide rationale for therapeutic intervention with a ketogenic diet in MGO-driven pathologies.
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Dieta Cetogénica , Piruvaldehído , Ratones , Animales , Piruvaldehído/toxicidad , Acetoacetatos , Nocicepción , Óxido de Magnesio , Cuerpos Cetónicos , Ácido 3-HidroxibutíricoRESUMEN
ABSTRACT: Dietary interventions are promising approaches to treat pain associated with metabolic changes because they impact both metabolic and neural components contributing to painful neuropathy. Here, we tested whether consumption of a ketogenic diet could affect sensation, pain, and epidermal innervation loss in type 1 diabetic mice. C57Bl/6 mice were rendered diabetic using streptozotocin and administered a ketogenic diet at either 3 weeks (prevention) or 9 weeks (reversal) of uncontrolled diabetes. We quantified changes in metabolic biomarkers, sensory thresholds, and epidermal innervation to assess impact on neuropathy parameters. Diabetic mice consuming a ketogenic diet had normalized weight gain, reduced blood glucose, elevated blood ketones, and reduced hemoglobin-A1C levels. These metabolic biomarkers were also improved after 9 weeks of diabetes followed by 4 weeks of a ketogenic diet. Diabetic mice fed a control chow diet developed rapid mechanical allodynia of the hind paw that was reversed within a week of consumption of a ketogenic diet in both prevention and reversal studies. Loss of thermal sensation was also improved by consumption of a ketogenic diet through normalized thermal thresholds. Finally, diabetic mice consuming a ketogenic diet had normalized epidermal innervation, including after 9 weeks of uncontrolled diabetes and 4 weeks of consumption of the ketogenic diet. These results suggest that, in mice, a ketogenic diet can prevent and reverse changes in key metabolic biomarkers, altered sensation, pain, and axon innervation of the skin. These results identify a ketogenic diet as a potential therapeutic intervention for patients with painful diabetic neuropathy and/or epidermal axon loss.
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Diabetes Mellitus Experimental , Neuropatías Diabéticas , Dieta Cetogénica , Animales , Biomarcadores , Neuropatías Diabéticas/tratamiento farmacológico , Humanos , Hiperalgesia/etiología , Ratones , Ratones Endogámicos C57BL , DolorRESUMEN
Acute pain is prevalent following burn injury and can often transition to chronic pain. Prolonged acute pain is an important risk factor for chronic pain and there is little preclinical research to address this problem. Using a mouse model of second-degree burn, we investigated whether pre-existing stress influences pain(sensitivity) after a burn injury. We introduced a contribution of stress in two different ways: (1) the use of foot-shock as a pre-injury stressor or (2) the use of A/J mice to represent higher pre-existing stress compared to C57Bl/6 mice. C57Bl/6 and A/J mice were exposed to repeated mild foot shock to induce stress for 10 continuous days and mice underwent either burn injury or sham burn injury of the plantar surface of the right hind paw. Assessments of mechanical and thermal sensitivities of the injured and uninjured paw were conducted during the shock protocol and at intervals up to 82-day post-burn injury. In both strains of mice that underwent burn injury, thermal hypersensitivity and mechanical allodynia appeared rapidly in the ipsilateral paw. Mice that were stressed took much longer to recover their hind paw mechanical thresholds to baseline compared to non-stressed mice in both burn and non-burn groups. Analysis of the two mouse strains revealed that the recovery of mechanical thresholds in A/J mice which display higher levels of baseline anxiety was shorter than C57Bl/6 mice. No differences were observed regarding thermal sensitivities between strains. Our results support the view that stress exposure prior to burn injury affects mechanical and thermal thresholds and may be relevant to as a risk factor for the transition from acute to chronic pain. Finally, genetic differences may play a key role in modality-specific recovery following burn injury.
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Quemaduras , Animales , Quemaduras/complicaciones , Modelos Animales de Enfermedad , Hiperalgesia/genética , Ratones , Ratones Endogámicos C57BL , Dolor/etiologíaRESUMEN
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 8â¯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.
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Dieta Cetogénica , Hiperalgesia/dietoterapia , Hiperalgesia/etiología , Síndrome Metabólico/complicaciones , Síndrome Metabólico/dietoterapia , Nervios Periféricos/crecimiento & desarrollo , Adiposidad , Animales , Axones/patología , Glucemia/metabolismo , Dieta Alta en Grasa , Insulina/sangre , Masculino , Síndrome Metabólico/patología , Ratones , Ratones Endogámicos C57BL , Neuritas , Nervios Periféricos/patología , Condicionamiento Físico Animal , Pérdida de PesoRESUMEN
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.
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Dieta Alta en Grasa/efectos adversos , Hiperalgesia/genética , Síndrome Metabólico/complicaciones , Síndrome Metabólico/etiología , Animales , Modelos Animales de Enfermedad , Genotipo , Hiperalgesia/etiología , Ratones , Ratones Endogámicos C57BL , Umbral del Dolor/fisiologíaRESUMEN
Insulin is known to have neurotrophic properties and loss of insulin support to sensory neurons may contribute to peripheral diabetic neuropathy (PDN). Here, genetically-modified mice were generated in which peripheral sensory neurons lacked the insulin receptor (SNIRKO mice) to determine whether disrupted sensory neuron insulin signaling plays a crucial role in the development of PDN and whether SNIRKO mice develop symptoms of PDN due to reduced insulin neurotrophic support. Our results revealed that SNIRKO mice were euglycemic and never displayed significant changes in a wide range of sensorimotor behaviors, nerve conduction velocity or intraepidermal nerve fiber density. However, SNIRKO mice displayed elevated serum insulin levels, glucose intolerance, and increased insulin content in the islets of Langerhans of the pancreas. These results contribute to the growing idea that sensory innervation of pancreatic islets is key to regulating islet function and that a negative feedback loop of sensory neuron insulin signaling keeps this regulation in balance. Our results suggest that a loss of insulin receptors in sensory neurons does not lead to peripheral nerve dysfunction. The SNIRKO mice will be a powerful tool to investigate sensory neuron insulin signaling and may give a unique insight into the role that sensory neurons play in modifying islet physiology.
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Eliminación de Gen , Insulina/metabolismo , Páncreas/metabolismo , Receptor de Insulina/deficiencia , Células Receptoras Sensoriales/metabolismo , Animales , Glucemia/metabolismo , Femenino , Masculino , Ratones , Ratones Noqueados , Ratones Transgénicos , Proteínas de Microfilamentos/biosíntesis , Proteínas de Microfilamentos/genética , Páncreas/citología , Receptor de Insulina/genéticaRESUMEN
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.
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Conducción Nerviosa/fisiología , Dolor , Enfermedades del Sistema Nervioso Periférico , Resistencia Física/fisiología , Animales , Femenino , Metabolismo , Dolor/etiología , Dolor/metabolismo , Dolor/fisiopatología , Enfermedades del Sistema Nervioso Periférico/complicaciones , Enfermedades del Sistema Nervioso Periférico/metabolismo , Enfermedades del Sistema Nervioso Periférico/fisiopatología , Condicionamiento Físico Animal , Ratas , Carrera/fisiologíaRESUMEN
OBJECTIVES: To compare the frequency of abnormalities in epidermal nerve fiber density (ENFD) and quantitative sudomotor axon reflex (QSART) in patients with diabetic distal symmetric polyneuropathy (DSPN). METHODS: Nerve conduction studies, ENFD, and QSART data were obtained pre- and postexercise, in patients enrolled in a prospective diabetic neuropathy study. McNemar's test was applied to compare the yield of ENFD and QSART. RESULTS: Eighteen patients (58 ± 4 years) were enrolled, with 36 data collection points. In diabetic DSPN and diabetic large fiber DSPN (DSPN-L), abnormal ENFD (77% and 100% respectively) is more frequent than abnormal QSART (39% and 35%, respectively) (P value = 0.001 in diabetic DSPN and P value = 0.0002 in diabetic DSPN-L), whereas in diabetic small fiber DSPN (DSPN-S), both tests have similar yields (47%). CONCLUSIONS: ENFD has a high diagnostic yield in diabetic DSPN and DSPN-L. Including QSART data adds little to the sensitivity of EFND in DSPN-S.
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Axones/fisiología , Neuropatías Diabéticas/patología , Neuropatías Diabéticas/fisiopatología , Reflejo/fisiología , Piel/patología , Biopsia , Femenino , Hemoglobina Glucada/metabolismo , Humanos , Masculino , Persona de Mediana Edad , Fibras Nerviosas/fisiología , Conducción Nerviosa/fisiología , Índice de Severidad de la Enfermedad , Piel/inervación , Ubiquitina Tiolesterasa/metabolismoRESUMEN
FNDC5/irisin, has recently been identified as a novel protein that stimulates the "browning" of white adipose by inducing thermogenesis via increased uncoupling protein 1 (UCP1). We tested the hypothesis that high fat diet-induced prediabetic mice would exhibit increased FNDC5 and this effect would be attenuated by chronic exercise. C57BL/6 mice were randomized into three groups for the 4 week intervention: Standard diet (Std, n = 12), High fat diet (HF, n = 14), or High fat diet and free access to a running wheel (HFEX, n = 14). Body weight, glucose, insulin, and the homeostatic model assessment of insulin resistance (HOMA-IR) were greater in HF compared to Std and HFEX after the 4 week intervention. In support of our hypothesis, FNDC5 was higher in HF in both skeletal muscle and adipose compared to Std and was lower in adipose only in HFEX compared to HF mice. Following the same pattern, PGC-1α was significantly higher in HF compared to Std in skeletal muscle and significantly lower in HFEX compared to HF in adipose. UCP1 was significantly lower in HFEX versus Std (in skeletal muscle) and versus HF (in adipose). HOMA-IR was significantly correlated with FNDC5 protein levels in adipose. Increased FNDC5 in adipose and skeletal muscle may be a compensatory mechanism to offset high fat diet-induced weight gain and insulin resistance by increasing energy expenditure.
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Dieta Alta en Grasa/efectos adversos , Fibronectinas/metabolismo , Resistencia a la Insulina , Condicionamiento Físico Animal , Tejido Adiposo/metabolismo , Animales , Glucemia/metabolismo , Peso Corporal , Fibronectinas/genética , Insulina/sangre , Masculino , Ratones , Ratones Endogámicos C57BL , Músculo Esquelético/metabolismo , Coactivador 1-alfa del Receptor Activado por Proliferadores de Peroxisomas gamma/genética , Coactivador 1-alfa del Receptor Activado por Proliferadores de Peroxisomas gamma/metabolismo , Proteína Desacopladora 1/genética , Proteína Desacopladora 1/metabolismoRESUMEN
Dietary-associated diseases have increased tremendously in our current population, yet key molecular changes associated with high-fat diets that cause clinical pre-diabetes, obesity, hyperglycemia, and peripheral neuropathy remain unclear. This study examines molecular and metabolic aspects altered by voluntary exercise and a high-fat diet in the mouse dorsal root ganglion. Mice were examined for changes in mRNA and proteins encoding anti-inflammatory mediators, metabolic-associated molecules, and pain-associated ion channels. Proteins involved in the synaptosomal complex and pain-associated TRP ion channels decrease in the dorsal root ganglion of high-fat exercise animals relative to their sedentary controls. Exercise reversed high-fat diet induced mechanical allodynia without affecting weight gain, elevated blood glucose, and utilization of fat as a fuel source. Independent of weight or fat mass changes, high-fat exercised mice display reduced inflammation-associated mRNAs. The benefits of exercise on abnormal peripheral nerve function appear to occur independent of systemic metabolic changes, suggesting that the utilization of fats and inflammation in the peripheral nervous system may be key for diet-induced peripheral nerve dysfunction and the response to exercise.
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Citocinas/metabolismo , Dieta Alta en Grasa/efectos adversos , Metabolismo Energético/fisiología , Regulación de la Expresión Génica/fisiología , Hiperalgesia/etiología , Inflamación/metabolismo , Animales , Glucemia , Composición Corporal/efectos de los fármacos , Peso Corporal/fisiología , Citocinas/genética , Ganglios Espinales/metabolismo , Proteínas HSP70 de Choque Térmico/genética , Proteínas HSP70 de Choque Térmico/metabolismo , Hiperalgesia/diagnóstico por imagen , Hiperalgesia/patología , Hiperalgesia/rehabilitación , Inflamación/etiología , Cetonas/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , PPAR alfa/genética , PPAR alfa/metabolismo , Condicionamiento Físico Animal/métodos , Frecuencia Respiratoria/fisiología , Canales Catiónicos TRPV/genética , Canales Catiónicos TRPV/metabolismoRESUMEN
Early adverse events have been shown to increase the incidence of interstitial cystitis/painful bladder syndrome in adulthood. Despite high clinical relevance and reports of stress-related symptom exacerbation, animal models investigating the contribution of early life stress to female urological pain are lacking. We examined the impact of neonatal maternal separation (NMS) on bladder sensitivity and visceral neuroimmune status both prior-to, and following, water avoidance stress (WAS) in adult female mice. The visceromotor response to urinary bladder distension was increased at baseline and 8d post-WAS in NMS mice, while colorectal sensitivity was transiently increased 1d post-WAS only in naïve mice. Bladder micturition rate and output, but not fecal output, were also significantly increased following WAS in NMS mice. Changes in gene expression involved in regulating the stress response system were observed at baseline and following WAS in NMS mice, and WAS reduced serum corticosterone levels. Cytokine and growth factor mRNA levels in the bladder, and to a lesser extent in the colon, were significantly impacted by NMS and WAS. Peripheral mRNA levels of stress-responsive receptors were differentially influenced by early life and adult stress in bladder, but not colon, of naïve and NMS mice. Histological evidence of mast cell degranulation was increased in NMS bladder, while protein levels of protease activated receptor 2 (PAR2) and transient receptor potential ankyrin 1 (TRPA1) were increased by WAS. Together, this study provides new insight into mechanisms contributing to stress associated symptom onset or exacerbation in patients exposed to early life stress.
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Estrés Psicológico/complicaciones , Estrés Psicológico/fisiopatología , Enfermedades de la Vejiga Urinaria/etiología , Enfermedades de la Vejiga Urinaria/fisiopatología , Vejiga Urinaria/fisiopatología , Animales , Animales Recién Nacidos , Colon/fisiopatología , Corticosterona/sangre , Citocinas/metabolismo , Modelos Animales de Enfermedad , Femenino , Hipocampo/metabolismo , Hipocampo/patología , Péptidos y Proteínas de Señalización Intercelular/metabolismo , Mastocitos/metabolismo , Mastocitos/patología , Privación Materna , Ratones Endogámicos C57BL , ARN Mensajero/metabolismo , Receptor PAR-2/metabolismo , Recto/fisiopatología , Estrés Psicológico/patología , Canal Catiónico TRPA1 , Canales de Potencial de Receptor Transitorio/metabolismo , Enfermedades de la Vejiga Urinaria/patologíaRESUMEN
Experiencing early life stress or injury increases a woman's likelihood of developing vulvodynia and concomitant dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. To investigate the outcome of neonatal vaginal irritation (NVI), female mouse pups were administered intravaginal zymosan on postnatal days 8 and 10 and were assessed as adults for vaginal hypersensitivity by measuring the visceromotor response to vaginal balloon distension (VBD). Western blotting and calcium imaging were performed to measure transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1) in the vagina and innervating primary sensory neurons. Serum corticosterone (CORT), mast cell degranulation, and corticotropin-releasing factor receptor 1 (CRF1) expression were measured as indicators of peripheral HPA axis activation. Colorectal and hind paw sensitivity were measured to determine cross-sensitization resulting from NVI. Adult NVI mice had significantly larger visceromotor response during VBD than naive mice. TRPA1 protein expression was significantly elevated in the vagina, and calcium transients evoked by mustard oil (TRPA1 ligand) or capsaicin (TRPV1 ligand) were significantly decreased in dorsal root ganglion from NVI mice, despite displaying increased depolarization-evoked calcium transients. Serum CORT, vaginal mast cell degranulation, and CRF1 protein expression were all significantly increased in NVI mice, as were colorectal and hind paw mechanical and thermal sensitivity. Neonatal treatment with a CRF1 antagonist, NBI 35965, immediately before zymosan administration largely attenuated many of the effects of NVI. These results suggest that NVI produces chronic hypersensitivity of the vagina, as well as of adjacent visceral and distant somatic structures, driven in part by increased HPA axis activation.
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Colon/inervación , Hipersensibilidad/fisiopatología , Sistema Hipotálamo-Hipofisario/fisiología , Sistema Hipófiso-Suprarrenal/fisiología , Vagina/inervación , Acenaftenos/farmacología , Animales , Animales Recién Nacidos , Células Cultivadas , Toxina del Cólera/metabolismo , Corticosterona/sangre , Hormona Liberadora de Corticotropina/antagonistas & inhibidores , Hormona Liberadora de Corticotropina/metabolismo , Femenino , Ganglios Espinales/citología , Estudios Longitudinales , Ratones , Ratones Endogámicos C57BL , Planta de la Mostaza/toxicidad , Neuronas/metabolismo , Neuronas Aferentes/fisiología , Estimulación Física/efectos adversos , Aceites de Plantas/toxicidad , Potasio/farmacologíaRESUMEN
BACKGROUND: A reduction in peripheral nervous system (PNS) insulin signaling is a proposed mechanism that may contribute to sensory neuron dysfunction and diabetic neuropathy. Neuronal insulin resistance is associated with several neurological disorders and recent evidence has indicated that dorsal root ganglion (DRG) neurons in primary culture display altered insulin signaling, yet in vivo results are lacking. Here, experiments were performed to test the hypothesis that the PNS of insulin-resistant mice displays altered insulin signal transduction in vivo. For these studies, nondiabetic control and type 2 diabetic ob/ob mice were challenged with an intrathecal injection of insulin or insulin-like growth factor 1 (IGF-1) and downstream signaling was evaluated in the DRG and sciatic nerve using Western blot analysis. RESULTS: The results indicate that insulin signaling abnormalities documented in other "insulin sensitive" tissues (i.e. muscle, fat, liver) of ob/ob mice are also present in the PNS. A robust increase in Akt activation was observed with insulin and IGF-1 stimulation in nondiabetic mice in both the sciatic nerve and DRG; however this response was blunted in both tissues from ob/ob mice. The results also suggest that upregulated JNK activation and reduced insulin receptor expression could be contributory mechanisms of PNS insulin resistance within sensory neurons. CONCLUSIONS: These findings contribute to the growing body of evidence that alterations in insulin signaling occur in the PNS and may be a key factor in the pathogenesis of diabetic neuropathy.
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Ganglios Espinales/fisiopatología , Resistencia a la Insulina/fisiología , Nervio Ciático/fisiopatología , Animales , Glucemia/fisiología , Western Blotting , Diabetes Mellitus Experimental/fisiopatología , Neuropatías Diabéticas/fisiopatología , Hiperalgesia/fisiopatología , Insulina/metabolismo , Factor I del Crecimiento Similar a la Insulina/metabolismo , Proteínas Quinasas JNK Activadas por Mitógenos/metabolismo , Masculino , Ratones Transgénicos , Proteína Oncogénica v-akt/metabolismo , Umbral del Dolor , TactoRESUMEN
Alterations in peripheral nervous system (PNS) insulin support may contribute to diabetic neuropathy (DN); yet, PNS insulin signaling is not fully defined. Here, we investigated in vivo insulin signaling in the PNS and compared the insulin responsiveness to that of muscle, liver, and adipose. Non-diabetic mice were administered increasing doses of insulin to define a dose-response relationship between insulin and Akt activation in the dorsal root ganglion (DRG) and sciatic nerve. Resulting EC50 doses were used to characterize the PNS insulin signaling time course and make comparisons between insulin signaling in the PNS and other peripheral tissues (i.e., muscle, liver, and adipose). The results demonstrate that the PNS is responsive to insulin and that differences in insulin signaling pathway activation exist between PNS compartments. At a therapeutically relevant dose, Akt was activated in the muscle, liver, and adipose at 30 min, correlating with the changes in blood glucose levels. Interestingly, the sciatic nerve showed a similar signaling profile as insulin-sensitive tissues; however, there was not a comparable activation in the DRG or spinal cord. These results present new evidence regarding PNS insulin signaling pathways in vivo and provide a baseline for studies investigating the contribution of disrupted PNS insulin signaling to DN pathogenesis.
Asunto(s)
Hipoglucemiantes/farmacología , Insulina/farmacología , Nervio Ciático/efectos de los fármacos , Transducción de Señal/efectos de los fármacos , Análisis de Varianza , Animales , Relación Dosis-Respuesta a Droga , Inhibidores Enzimáticos/farmacología , Ganglios Espinales/efectos de los fármacos , Masculino , Ratones , Ratones Endogámicos C57BL , Fosforilación/efectos de los fármacos , Proteínas Proto-Oncogénicas c-akt/metabolismo , Serina/metabolismo , Treonina/metabolismo , Factores de TiempoRESUMEN
Recent research suggests that exercise can be effective in reducing pain in animals and humans with neuropathic pain. To investigate mechanisms in which exercise may improve hyperalgesia associated with prediabetes, C57Bl/6 mice were fed either standard chow or a high-fat diet for 12 weeks and were provided access to running wheels (exercised) or without access (sedentary). The high-fat diet induced a number of prediabetic symptoms, including increased weight, blood glucose, and insulin levels. Exercise reduced but did not restore these metabolic abnormalities to normal levels. In addition, mice fed a high-fat diet developed significant cutaneous and visceral hyperalgesia, similar to mice that develop neuropathy associated with diabetes. Finally, a high-fat diet significantly modulated neurotrophin protein expression in peripheral tissues and altered the composition of epidermal innervation. Over time, mice that exercised normalized with regards to their behavioral hypersensitivity, neurotrophin levels, and epidermal innervation. These results confirm that elevated hypersensitivity and associated neuropathic changes can be induced by a high-fat diet and exercise may alleviate these neuropathic symptoms. These findings suggest that exercise intervention could significantly improve aspects of neuropathy and pain associated with obesity and diabetes. Additionally, this work could potentially help clinicians determine those patients who will develop painful versus insensate neuropathy using intraepidermal nerve fiber quantification.
Asunto(s)
Dieta Alta en Grasa/efectos adversos , Dimensión del Dolor/métodos , Enfermedades del Sistema Nervioso Periférico/terapia , Condicionamiento Físico Animal/fisiología , Estado Prediabético/terapia , Animales , Neuropatías Diabéticas/fisiopatología , Neuropatías Diabéticas/terapia , Masculino , Ratones , Ratones Endogámicos C57BL , Dolor/fisiopatología , Enfermedades del Sistema Nervioso Periférico/fisiopatología , Condicionamiento Físico Animal/métodos , Estado Prediabético/fisiopatologíaRESUMEN
BACKGROUND: Present literature and clinical practice provide strong support for the use of aerobic exercise in reducing pain and improving function for individuals with chronic musculoskeletal pain syndromes. However, the molecular basis for the positive actions of exercise remains poorly understood. Recent studies suggest that neurotrophin-3 (NT-3) may act in an analgesic fashion in various pain states. OBJECTIVE: The purpose of the present study was to examine the effects of moderate-intensity aerobic exercise on pain-like behavior and NT-3 in an animal model of widespread pain. DESIGN: This was a repeated-measures, observational cross-sectional study. METHODS: Forty female mice were injected with either normal (pH 7.2; n=20) or acidic (pH 4.0; n=20) saline in the gastrocnemius muscle to induce widespread hyperalgesia and exercised for 3 weeks. Cutaneous (von Frey monofilament) and muscular (forceps compression) mechanical sensitivity were assessed. Neurotrophin-3 was quantified in 2 hind-limb skeletal muscles for both messenger RNA (mRNA) and protein levels after exercise training. Data were analyzed with 2-factor analysis of variance for repeated measures (group x time). RESULTS: Moderate-intensity aerobic exercise reduced cutaneous and deep tissue hyperalgesia induced by acidic saline and stimulated NT-3 synthesis in skeletal muscle. The increase in NT-3 was more pronounced at the protein level compared with mRNA expression. In addition, the increase in NT-3 protein was significant in the gastrocnemius muscle but not in the soleus muscle, suggesting that exercise can preferentially target NT-3 synthesis in specific muscle types. LIMITATIONS: Results are limited to animal models and cannot be generalized to chronic pain syndromes in humans. CONCLUSIONS: This is the first study demonstrating the effect of exercise on deep tissue mechanical hyperalgesia in a rodent model of pain and providing a possible molecular basis for exercise training in reducing muscular pain.