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Withdrawal from prescribed opioids results in increased pain sensitivity, which prolongs the treatment. This pain sensitivity is attributed to neuroplastic changes that converge at the spinal cord dorsal horn. We have recently reported that repeated morphine administration triggers an insertion of GluA2-lacking (Ca 2 þ -permeable) a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPAR) in the hippocampus. This finding together with the reported involvement of AMPAR in the mechanisms underlying inflammatory pain led us to hypothesize a role for spinal AMPAR in opioid-induced pain behavior. Mice treated with escalating doses of morphine showed hypersensitivity to mechanical stimulation. Intrathecal administration of a Ca 2 þ -permeable AMPAR selective blocker disrupted morphine-induced mechanical sensitivity. Analysis of the expression and phosphorylation levels of AMPAR subunits (GluA1/2/3/4) in homogenates and in postsynaptic density fractions from spinal cord dorsal horns showed an increase in GluA4 expression and phosphorylation in the postsynaptic density after morphine. Co-immunoprecipitation analyses suggested an increase in GluA4 homomers (Ca 2 þ -permeable AMPAR) and immunohistochemical staining localized the increase in GluA4 levels in laminae III-V. The excitatory postsynaptic currents (EPSCs) recorded in laminae III-V showed enhanced sensitivity to Ca 2 þ -permeable AMPAR blockers in morphinetreated mice. Furthermore, current-voltage relationships of AMPAR-mediated EPSCs showed that rectification index (an indicator of Ca 2 þ -permeable AMPAR contribution) is increased in morphine-treated but not in saline-treated mice. These effects could be reversed by infusion of GluA4 antibody through patch pipette. This is the first direct evidence for a role of GluA4-containing AMPAR in morphineinduced pain and highlights spinal GluA4-containing AMPAR as targets to prevent the morphine-induced pain sensitivity.

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The leaves of Mitragyna speciosa (kratom), a plant native to Southeast Asia, are increasingly used as a pain reliever and for attenuation of opioid withdrawal symptoms. Using the tools of natural products chemistry, chemical synthesis, and pharmacology, we provide a detailed in vitro and in vivo pharmacological characterization of the alkaloids in kratom. We report that metabolism of kratom’s major alkaloid, mitragynine, in mice leads to formation of (a) a potent mu opioid receptor agonist antinociceptive agent, 7-hydroxymitragynine, through a CYP3A-mediated pathway, which exhibits reinforcing properties, inhibition of gastrointestinal (GI) transit and reduced hyperlocomotion, (b) a multifunctional mu agonist/delta-kappa antagonist, mitragynine pseudoindoxyl, through a CYP3A-mediated skeletal rearrangement, displaying reduced hyperlocomotion, inhibition of GI transit and reinforcing properties, and (c) a potentially toxic metabolite, 3-dehydromitragynine, through a non-CYP oxidation pathway. Our results indicate that the oxidative metabolism of the mitragynine template beyond 7-hydroxymitragynine may have implications in its overall pharmacology in vivo.

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To compare aerosol clearance with and without negative pressure, the humidifier was turned off to simulate the end of an aerosol-generating procedure. Without negative pressure, 183 min was required for the particle count to decrease by 98%, compared with 5 min when negative pressure was applied (Supplementary Fig. 2). Whilst visual inspection correlated with the removal of large aerosolised particles (>10 mm), it was highly unreliable at determining the degree of removal of small aerosolised particles, as the hood appeared clear when particle count of particles greater than 0.5 mm was well above Access published on April 3 2020 3. Owen MK, Ensor DS, Sparks LE. Airborne particle sizes and sources found in indoor air. Atmos Environ Gen Top 1992; 26: 2149e62 4. Lindsley WG, Pearce TA, Hudnall JB, et al. Quantity and size distribution of cough-generated aerosol particles produced by influenza patients during and after illness. J Occup Environ Hyg 2012; 9: 443e9 5. Faulkner WB, Memarzadeh F, Riskowski GL, Kalbasi A, Chang AC. Effects of air exchange rate, particle size and injection place on particle concentrations within a reduced-scale room.

Circular RNAs (circRNAs) are a distinct category of singlestranded, covalently closed RNAs formed by backsplicing. The functions of circRNAs are incompletely known and are under active investigation. Here, we report that in addition to traditional linear mRNAs (linRNA), mouse, rat, and human opioid receptor genes generate exonic circRNA isoforms. Using standard molecular biologic methods, Oprm1 circRNAs (circOprm1) were detected in RNAs of rodent and human brains and spinal cords, as well as human neuroblastoma cells, suggesting evolutionary conservation. Sequencing confirmed backsplicing using canonical splice sites. Oprm1 circRNAs were sense-stranded circRNAs resistant to RNase R digestion. The relative abundance of Oprm1 circRNA to linRNA determined by quantitative reverse transcription polymerase chain reaction varied among mouse brain regions, with circRNA isoforms predominating in rostral structures and less abundant in brain stem. Chronic morphine exposure in mice increased brain circOprm1.e2.3 and circOprm1.e2.e3.e4(302) levels by 1.5-to 1.6-fold relative to linRNA. Sequence analysis predicted numerous microRNA binding sites within Oprm1 circRNA sequences, suggesting a potential role in microRNA sequestration through sponging. In addition, we observed that other opioid receptor genes including d, k, and nociceptin receptor genes produced similar circRNAs. In conclusion, all members of the opioid receptor gene family express circRNAs, with Oprm1 circRNA levels exceeding those of linear forms in some regions. SIGNIFICANCE STATEMENTThe modulation of Oprm1 circular RNA (circRNA) expression by morphine, coupled with the high abundance and existence of potential miRNA binding sites with circRNA sequences suggests the potential role of Oprm1 circRNAs in chronic opioid effects such as tolerance.

Involvement of the falx cerebri in infants with stage 4 neuroblastoma is thought to be rare. The falx is derived from the neural crest and thus may be a location for primary neuroblastoma. Its propensity for metastasis is unknown. Management of neuroblastoma in this location is potentially challenging. We describe two children less than 18 months of age who were successfully managed with chemotherapy alone (without radiation or surgery) for falx involvement with neuroblastoma.