MicroRNA-96 is required to prevent allodynia by repressing voltage-gated sodium channels in spinal cord

Voltage-gated sodium channels (Na_vs) 1.7, 1.8, and 1.9 are predominately expressed in peripheral sensory neurons and are critical for action potential propagation in nociceptors. Unexpectedly, we found that expression of SCN9A, SCN10A, SCN11A, and SCN2A, the alpha subunit of Na_v1.7, Na_v1.8, Na_v1.9 and Na_v1.2, respectively, are up-regulated in spinal dorsal horn (SDH) neurons of miR-96 knockout mice. These mice also have de-repression of CACNA2D1/2 in DRG and display thermal and mechanical allodynia that could be attenuated by intrathecal or intraperitoneal injection of Na_v1.7 or Na_v1.8 blockers or Gabapentin. Moreover, Gad2::CreERT2 conditional miR-96 knockout mice phenocopied global knockout mice, implicating inhibitory neurons; nerve injury induced significant loss of miR-96 in SDH GABAergic and Glutamatergic neurons in mice which negatively correlated to up-regulation of Na_v1.7, Na_v1.8, Na_v1.9 and Scn2a, this dis-regulation of miR-96 and Na_vs in SDH neurons contributed to neuropathic pain which can be alleviated by intrathecal injection of Na_v1.7 or Na_v1.8 blockers. In conclusion, miR-96 is required to avoid allodynia through limiting the expression of VGCCs and Na_vs in DRG and Na_vs in SDH in naïve and nerve injury-induced neuropathic pain mice. Our findings suggest that central nervous system penetrating Na_v1.7 and Na_v1.8 blockers may be efficacious for pain relief.

Somatosensory Neurons Enter a State of Altered Excitability during Hibernation

Hibernation in mammals involves prolonged periods of inactivity, hypothermia, hypometabolism, and decreased somatosensation. Peripheral somatosensory neurons play an essential role in the detection and transmission of sensory information to CNS and in the generation of adaptive responses. During hibernation, when body temperature drops to as low as 2°C, animals dramatically reduce their sensitivity to physical cues [1, 2]. It is well established that, in non-hibernators, cold exposure suppresses energy production, leading to dissipation of the ionic and electrical gradients across the plasma membrane and, in the case of neurons, inhibiting the generation of action potentials [3]. Conceivably, such cold-induced elimination of electrogenesis could be part of a general mechanism that inhibits sensory abilities in hibernators. However, when hibernators become active, the bodily functions-including the ability to sense environmental cues-return to normal within hours, suggesting the existence of mechanisms supporting basal functionality of cells during torpor and rapid restoration of activity upon arousal. We tested this by comparing properties of somatosensory neurons from active and torpid thirteen-lined ground squirrels (Ictidomys tridecemlineatus). We found that torpid neurons can compensate for cold-induced functional deficits, resulting in unaltered resting potential, input resistance, and rheobase. Torpid neurons can generate action potentials but manifest markedly altered firing patterns, partially due to decreased activity of voltage-gated sodium channels. Our results provide insights into the mechanism that preserves somatosensory neurons in a semi-active state, enabling fast restoration of sensory function upon arousal. These findings contribute to the development of strategies enabling therapeutic hypothermia and hypometabolism.

Behavioral, cellular and molecular maladaptations covary with exposure to pyridostigmine bromide in a rat model of gulf war illness pain

Many veterans of Operation Desert Storm (ODS) struggle with the chronic pain of Gulf War Illness (GWI). Exposure to insecticides and pyridostigmine bromide (PB) have been implicated in the etiology of this multisymptom disease. We examined the influence of 3 (DEET (N,N-diethyl-meta-toluamide), permethrin, chlorpyrifos) or 4 GW agents (DEET, permethrin, chlorpyrifos, pyridostigmine bromide (PB)) on the post-exposure ambulatory and resting behaviors of rats. In three independent studies, rats that were exposed to all 4 agents consistently developed both immediate and delayed ambulatory deficits that persisted at least 16 weeks after exposures had ceased. Rats exposed to a 3 agent protocol (PB excluded) did not develop any ambulatory deficits. Cellular and molecular studies on nociceptors harvested from 16WP (weeks post-exposure) rats indicated that vascular nociceptor Na_v1.9 mediated currents were chronically potentiated following the 4 agent protocol but not following the 3 agent protocol. Muscarinic linkages to muscle nociceptor TRPA1 were also potentiated in the 4 agent but not the 3 agent, PB excluded, protocol. Although K_v7 activity changes diverged from the behavioral data, a K_v7 opener, retigabine, transiently reversed ambulation deficits. We concluded that PB played a critical role in the development of pain-like signs in a GWI rat model and that shifts in Na_v1.9 and TRPA1 activity were critical to the expression of these pain behaviors.

Ionic mechanisms in peripheral pain

Chronic pain constitutes an important and growing problem in society with large unmet needs with respect to treatment and clear implications for quality of life. Computational modeling is used to complement experimental studies to elucidate mechanisms involved in pain states. Models representing the peripheral nerve ending often address questions related to sensitization or reduction in pain detection threshold. In models of the axon or the cell body of the unmyelinated C-fiber, a large body of work concerns the role of particular sodium channels and mutations of these. Furthermore, in central structures: spinal cord or higher structures, sensitization often refers not only to enhanced synaptic efficacy but also to elevated intrinsic neuronal excitability. One of the recent developments in computational neuroscience is the emergence of computational neuropharmacology. In this area, computational modeling is used to study mechanisms of pathology with the objective of finding the means of restoring healthy function. This research has received increased attention from the pharmaceutical industry as ion channels have gained increased interest as drug targets. Computational modeling has several advantages, notably the ability to provide mechanistic links between molecular and cellular levels on the one hand and functions at the systems level on the other hand. These characteristics make computational modeling an additional tool to be used in the process of selecting pharmaceutical targets. Furthermore, large-scale simulations can provide a framework to systematically study the effects of several interacting disease parameters or effects from combinations of drugs.