The etiological roles of miRNAs, lncRNAs, and circRNAs in neuropathic pain: A narrative review.

BACKGROUND: Non-coding RNAs (ncRNAs) are involved in neuropathic pain development. Herein, we systematically searched for neuropathic pain-related ncRNAs expression changes, including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular non-coding RNAs (circRNAs). METHODS: We searched two databases, PubMed and GeenMedical, for relevant studies. RESULTS: Peripheral nerve injury or noxious stimuli can induce extensive changes in the expression of ncRNAs. For example, higher serum miR-132-3p, -146b-5p, and -384 was observed in neuropathic pain patients. Either sciatic nerve ligation, dorsal root ganglion (DRG) transaction, or ventral root transection (VRT) could upregulate miR-21 and miR-31 while downregulating miR-668 and miR-672 in the injured DRG. lncRNAs, such as early growth response 2-antisense-RNA (Egr2-AS-RNA) and Kcna2-AS-RNA, were upregulated in Schwann cells and inflicted DRG after nerve injury, respectively. Dysregulated circRNA homeodomain-interacting protein kinase 3 (circHIPK3) in serum and the DRG, abnormally expressed lncRNAs X-inactive specific transcript (XIST), nuclear enriched abundant transcript 1 (NEAT1), small nucleolar RNA host gene 1 (SNHG1), as well as ciRS-7, zinc finger protein 609 (cirZNF609), circ_0005075, and circAnks1a in the spinal cord were suggested to participate in neuropathic pain development. Dysregulated miRNAs contribute to neuropathic pain via neuroinflammation, autophagy, abnormal ion channel expression, regulating pain-related mediators, protein kinases, structural proteins, neurotransmission excitatory-inhibitory imbalances, or exosome miRNA-mediated neuron-glia communication. In addition, lncRNAs and circRNAs are essential in neuropathic pain by acting as antisense RNA and miRNA sponges, epigenetically regulating pain-related molecules expression, or modulating miRNA processing. CONCLUSIONS: Numerous dysregulated ncRNAs have been suggested to participate in neuropathic pain development. However, there is much work to be done before ncRNA-based analgesics can be clinically used for various reasons such as conservation among species, proper delivery, stability, and off-target effects.

Cascaded effect in a high-peak-power terahertz-wave parametric generator.

We demonstrate megawatt-level terahertz (THz)-wave generation via a Stokes-seed-injected THz-wave parametric generator and study the cascaded effect. The optical-to-THz conversion efficiency was 1.72 × 10-3, and the peak power was conservatively estimated to be 1.09 MW using the pulse width of the pump. More than 80% of the THz-wave energy came from primary parametric generation, with the rest coming from high-order parametric amplification. Clear cascaded Stokes spots of second to fourth order were observed, and the factors affecting the high-order parametric process are discussed. The cascaded parametric effect is beneficial for achieving a higher optical-to-THz conversion efficiency, thereby improving the performance of high-peak-power THz-wave parametric sources.

Cascaded difference frequency generation in organic crystal 4'-dimethylamino-N-methyl-4-stilbazolium tosylate.

In this Letter, we verified, for the first time to the best of our knowledge, an efficient cascaded difference frequency generation (DFG) with multi-order red shift. The experiment was performed with homemade organic crystals pumped by an optical parametric oscillator. The characteristics of energy conversion during DFG were investigated comprehensively at different frequencies and crystal thicknesses. Theoretical explanations were provided, based on the coupled-wave equations. The calculations predicted that the cascading effect contributed to a sustained growth of the DFG output (free from the saturation and shrinkage), especially in thick crystals. By measuring the optical spectrum, remarkable cascading processes of at least seven orders were observed. This effect shows the potential to overcome the quantum defect of the terahertz-wave DFG and fundamentally improve the conversion efficiency.

Sedimentation of short cylindrical pollutants with mechanical contacts.

Lattice Boltzmann method and elastic particle collision model were used to investigate the sedimentation of short cylindrical pollutant particles with mechanical contacts for varying bulk number density epsilon and terminal Reynolds number ReT. The corresponding experiments were performed as a comparison. The clusters of pollutant particles with an inverted "T" structure were observed, the pollutant particles for high epsilon and large ReT scattered wider than that for low epsilon and small ReT. The sedimentation velocities increased suddenly at the initial stage, then decreased drastically, after that swayed around and approached to a steady value. The time to steady state did not depend on epsilon and ReT. The effect of particle interactions was to hinder the average sedimentation velocity, and hindrance was directly proportional to epsilon. The orientation distributions of pollutant particles depended on ReT and epsilon, especially on the former. Both the standard deviations of vertical and horizontal velocity, the former was larger than the latter, were nearly independent on epsilon and ReT.

Numerical simulation of the sedimentation of cylindrical pollutant particles in fluid.

The sedimentation of cylindrical pollutant particles which fall through a fluid is investigated. Differing from previous research work, particle oscillation and effect of particle on the fluid are considered, and the torque exerted on a particle when viscous fluid flow around a particle is got through experiment and included in the numerical simulation. The computational results showed that the sedimentation velocities of particle increase slowly with the increase of particle aspect ratio phi. For disk-like particle, when the motion direction of particle is parallel to axis of particle, particle falls more slowly than the case of perpendicular to axis of particle; while for rod-like particle, it is inverse. For sedimentation of a crowd of high-frequency oscillating cylindrical particles with arbitrary initial orientation, both vertical velocity and horizontal velocity oscillate dramatically, the degree of oscillation of the former is stronger than the later. A crowd of particles fall more quickly than an isolated particle. Particles tend to strongly align in the direction of gravity. The computational results agreed well with the experimental ones and helpful for controlling of pollutant particles.