BackgroundMicroRNAs (miRNAs) are short non-coding RNAs that inhibit translation of target genes by binding to their mRNAs. The expression of numerous brain-specific miRNAs with a high degree of temporal and spatial specificity suggests that miRNAs play an important role in gene regulation in health and disease. Here we investigate the time course gene expression profile of miR-1, -16, and -206 in mouse dorsal root ganglion (DRG), and spinal cord dorsal horn under inflammatory and neuropathic pain conditions as well as following acute noxious stimulation.ResultsQuantitative real-time polymerase chain reaction analyses showed that the mature form of miR-1, -16 and -206, is expressed in DRG and the dorsal horn of the spinal cord. Moreover, CFA-induced inflammation significantly reduced miRs-1 and -16 expression in DRG whereas miR-206 was downregulated in a time dependent manner. Conversely, in the spinal dorsal horn all three miRNAs monitored were upregulated. After sciatic nerve partial ligation, miR-1 and -206 were downregulated in DRG with no change in the spinal dorsal horn. On the other hand, axotomy increases the relative expression of miR-1, -16, and 206 in a time-dependent fashion while in the dorsal horn there was a significant downregulation of miR-1. Acute noxious stimulation with capsaicin also increased the expression of miR-1 and -16 in DRG cells but, on the other hand, in the spinal dorsal horn only a high dose of capsaicin was able to downregulate miR-206 expression.ConclusionsOur results indicate that miRNAs may participate in the regulatory mechanisms of genes associated with the pathophysiology of chronic pain as well as the nociceptive processing following acute noxious stimulation. We found substantial evidence that miRNAs are differentially regulated in DRG and the dorsal horn of the spinal cord under different pain states. Therefore, miRNA expression in the nociceptive system shows not only temporal and spatial specificity but is also stimulus-dependent.

Treatment of neuropathic pain is a clinical challenge likely because of the time-dependent changes in many neurotransmitter systems, growth factors, ionic channels, membrane receptors, transcription factors, and recruitment of different cell types. Conversely, an increasing number of reports have shown the ability of extended and regular physical exercise in alleviating neuropathic pain throughout a wide range of mechanisms. In this study, we investigate the effect of swim exercise on molecules associated with initiation and maintenance of nerve injury-induced neuropathic pain. BALB/c mice were submitted to partial ligation of the sciatic nerve followed by a 5-week aerobic exercise program. Physical training reversed mechanical hypersensitivity, which lasted for an additional 4 weeks after exercise interruption. Swim exercise normalized nerve injury-induced nerve growth factor, and brain-derived neurotrophic factor (BDNF) enhanced expression in the dorsal root ganglion, but had no effect on the glial-derived neurotrophic factor. However, only BDNF remained at low levels after exercise interruption. In addition, exercise training significantly reduced the phosphorylation status of PLCγ-1, but not CREB, in the spinal cord dorsal horn in response to nerve injury. Finally, prolonged swim exercise reversed astrocyte and microglia hyperactivity in the dorsal horn after nerve lesion, which remained normalized after training cessation. Together, these results demonstrate that exercise therapy induces long-lasting analgesia through various mechanisms associated with the onset and advanced stages of neuropathy. Moreover, the data support further studies to clarify whether appropriate exercise intensity, volume, and duration can also cause long-lasting pain relief in patients with neuropathic pain.

Objective: We investigated the time course of thermoregulation, nitric oxide (NO) formation and hydroelectrolytic alterations, as well as mean arterial pressure and arginine vasopressin (AVP) secretion, in experimental sepsis induced by cecal ligation and puncture (CLP). Methods: Male Wistar rats submitted to CLP or a sham operation were divided into 4 groups, as follows: group 1, for survival rate evaluation for 24 h; group 2, for body temperature (Tb) analysis; group 3, for mean arterial pressure registration, and group 4, for blood collection and processing of the neurohypophysis and hypothalamic nuclei 0, 2, 4, 6 and 24 h after surgery. AVP levels and content were measured in plasma, neurohypophysis and the hypothalamic paraventricular and supraoptic nuclei. Results: Animals which underwent CLP showed high mortality, a progressive decrease in mean arterial pressure and an increase in plasma NO. Tb dropped during the first 4 h and showed a progressive increase 6 h after surgery. Plasma AVP levels increased immediately after CLP surgery and again at 6 h, before returning to basal levels at 24 h. This was followed by a depletion of neurohypophyseal AVP content at 4 h that continued until 24 h. AVP content in the supraoptic nucleus was elevated 24 h after CLP surgery, while in the paraventricular nucleus, an increase was observed at 6 h and 24 h. Conclusions: In the present study, laparotomy and hypotension may have been responsible for the increase in plasma AVP in the initial phase of polymicrobial sepsis, and this may have contributed to the observed hypothermia. Moreover, an apparently impaired replenishment of AVP content in the neurohypophysis, possibly due to increased NO formation, may explain the impaired AVP secretion in the late phase of severe sepsis.

Our data indicate that HPA axis activation in acute and chronic pain models is time dependent and may be dissociated from evoked hyperalgesia. Therefore, HPA-axis activation represents an important variable to be considered when designing experimental assays of persistent pain as well as for interpretation of data.

Aerobic exercise training can improve insulin sensitivity in many tissues; however, the relationship among exercise, insulin, and cancer cell growth is unclear. We tested the hypothesis that aerobic exercise training begun during adolescence can attenuate Walker 256 tumor growth in adult rats and alter insulin secretion. Thirty-day-old male Wistar rats engaged in treadmill running for 8 weeks, 3 days/week, 44 min/day, at 55–65% VO2max until they were 90 days old (TC, Trained Control). An equivalently aged group was kept inactive during the same period (SC, Sedentary Control). Then, half the animals of the SC and TC groups were reserved as the control condition and the other half were inoculated with Walker 256 cancer cells, yielding two additional groups (Sedentary Walker and Trained Walker). Zero mortalities were observed in tumor-bearing rats. Body weight (BW), food intake, plasma glucose, insulin levels, and peripheral insulin sensitivity were analyzed before and after tumor cell inoculation. We also evaluated tumor growth, metastasis and cachexia. Isolated pancreatic islets secretory activity was analyzed. In addition, we evaluated mechanic sensibility. Our results showed improved physical performance according to the final workload and VO2max and reduced BW in trained rats at the end of the running protocol. Chronic adaptation to the aerobic exercise training decreased tumor weight, cachexia and metastasis and were associated with low glucose and insulin levels and high insulin sensitivity before and after tumor cell inoculation. Aerobic exercise started at young age also reduced pancreatic islet insulin content and insulin secretion in response to a glucose stimulus, without impairing islet morphology in trained rats. Walker 256 tumor-bearing sedentary rats also presented reduced pancreatic islet insulin content, without changing insulin secretion through isolated pancreatic islets. The mechanical sensitivity test indicated that aerobic exercise training did not cause injury or trigger inflammatory processes prior to tumor cell inoculation. Taken together, the current study suggests that aerobic exercise training applied during adolescence may mitigate tumor growth and related disorders in Walker 256 tumor-bearing adult rats. Improved insulin sensibility, lower glucose and insulin levels and/or reduced insulin secretion stimulated by glucose may be implicated in this tumor attenuation.