Animal Studies

Neuropathic pain is an unfavorable pathological pain, often persistent over time, thus leading to significant impairment of quality of life and public health burden. Notably, microRNAs (miRNAs) have been implicated in the pathophysiological process of neuropathic pain. The potential mechanism by which miR-34c-5p functions in neuropathic pain remains unclear. This study aimed to test the hypothesis that miR-34c-5p can modulate neuropathic pain in rat models with chronic constriction injury (CCI) of sciatic nerve, via interaction with the SIRT1/STAT3 signaling pathway Firstly, SIRT1 was validated as a target gene of miR-34c-5p and could be negatively regulated by miR-34c-5p. We induced miR-34c-5p overexpression/inhibition, SIRT1 knockdown, and STAT3 knockdown in the model rats to assess pain behavior patterns. Meanwhile, dorsal root ganglion (DRG) was transduced with overexpression or knockdown of miR-34c-5p or lipopolysaccharide to induce the production of inflammatory factors. It was observed that miR-34c-5p was up-regulated, and SIRT1 was under-expressed in the DRG neurons of dorsal spinal cords of the CCI rats. Furthermore, the ectopic expression of miR-34c-5p and knockdown of SIRT1 in CCI rats resulted in increased hyperalgesia and inflammation, corresponding to reduced paw withdrawal threshold and paw withdrawal latency, and elevated levels of IL-6, IL-1β and TNF-α. More importantly, miR-34c-5p inhibition reduced the hyperalgesia and inflammation by blocking the STAT3 signaling pathway through up-regulation of SIRT1. Conjointly, our results indicated that the down-regulation of miR-34c-5p could potentially provide sustained relief in neuropathic pain by promoting SIRT1 expression through STAT3 signaling pathway inactivation.

Myeloid zinc finger 1 (MZF1) belongs to the Kruppel family of zinc-finger transcription factors. Recent studies have demonstrated that in dorsal root ganglion (DRG) neurons, MZF1 is involved in the development and maintenance of neuropathic pain. However, the role of MZF1 in inflammatory pain still remains unknown. In the present study, the mechanism of MZF1 in chronic inflammatory pain was investigated in rats received an intraplantar injection of complete Freund's adjuvant (CFA). Subsequently, a series of assays including Western blotting, qRT-PCR, immunohistochemistry, and chromatin immunoprecipitation (ChIP) were performed. We found that CFA led to MZF1 upregulation in ipsilateral L4/5 DRGs. Pre- and post-microinjection of MZF1 siRNA into the ipsi-L5 DRG blocked the development of CFA-induced chronic inflammatory pain and alleviated the mechanical allodynia and thermal hyperalgesia in the maintenance phase. CFA also increased MMP-2/9 and Nav1.8 expression but reduced Kv1.2 and Cav1.2 expression in L4/L5 DRGs. Microinjection of MZF1 siRNA into DRG diminished the CFA-induced changes in MMP-2/9 and Kv1.2 expression. However, the expressions of Nav1.8 and Cav1.2 were not changed by the treatment. Double immunofluorescence staining showed that MMP-2/9 and Kv1.2 were co-localized with MZF1 in DRGs. The ChIP-PCR results revealed that MZF1 binds directly to the promoter region of MMP-2/9 gene. Together, the above results imply that upregulation of MZF1 in DRGs might contribute to the development and maintenance of CFA-induced chronic inflammatory pain by regulating MMP-2/9 and Kv1.2 expression. Targeting DRG-localized MZF1 might be a promising therapeutic strategy for the treatment of chronic inflammatory pain in the clinic.

To assess the supraspinal working mechanisms of the Burst spinal cord stimulation (SCS)-mode we used functional magnetic resonance imaging (fMRI) in chronic neuropathic rats. We hypothesized that active recharge Burst SCS would induce a more profound BOLD signal increase in areas associated with cognitive-emotional aspects of pain, as compared to Tonic SCS.

Pulmonary tuberculosis, a disease caused by Mycobacterium tuberculosis (Mtb), manifests with a persistent cough as both a primary symptom and mechanism of transmission. The cough reflex can be triggered by nociceptive neurons innervating the lungs, and some bacteria produce neuron-targeting molecules. However, how pulmonary Mtb infection causes cough remains undefined, and whether Mtb produces a neuron-activating, cough-inducing molecule is unknown. Here, we show that an Mtb organic extract activates nociceptive neurons in vitro and identify the Mtb glycolipid sulfolipid-1 (SL-1) as the nociceptive molecule. Mtb organic extracts from mutants lacking SL-1 synthesis cannot activate neurons in vitro or induce cough in a guinea pig model. Finally, Mtb-infected guinea pigs cough in a manner dependent on SL-1 synthesis. Thus, we demonstrate a heretofore unknown molecular mechanism for cough induction by a virulent human pathogen via its production of a complex lipid.

Functional-anatomical changes in reward related brain circuits are described in chronic pain patients who report anhedonia or depressed mood. In pre-clinical rodent models of neuropathic pain there are varying reports of the effects of nerve injury on the motivation to consume sucrose, although hedonic responses to sucrose appear unchanged. These observations are derived from brief periods of exposure to sucrose. When sucrose is available ad libitum over a period of 21 days, there are marked individual differences in consumption. The motivation for, and hedonic experience of, drinking sucrose is mediated in part by dopamine-D2 and µ-opioid receptors in the nucleus accumbens (NAc). This study investigated the effects of chronic constriction injury (CCI) on ad libitum sucrose consumption in male Sprague Dawley rats and the expression of accumbal dopamine D2 and µ-opioid receptors. Nerve injury reduced sucrose drinking predominantly in rats with the highest pre-injury consumption levels. Despite these reductions in consumption, sucrose preferences were stable. In the NAc of rats whose sucrose consumption was affected by CCI, immunohistochemical analyses revealed bilateral reductions of dopamine D2-receptor expression in the core and shell; and a lateralised reduction of µ-opioid receptor expression in the core and dorsomedial shell of the right NAc. These alterations in receptor expression are located in regions which have been identified as hedonic hot and coldspots along an affective-motivational keyboard which directs behaviours either towards, or away from salient stimuli. These changes likely underlie the reduction in sucrose consumption observed in a subgroup of rats following nerve injury.