Antinociceptive activities and mechanism of action of Cepharanthine.

Cepharanthine is an alkaloid that isolated from Stephania cepharantha Hayata, however，its analgesic properties are unclear and the molecular targets that mediating Cepharanthine-induced analgesia are not explored yet. In the current study, mice pain models including hot plate, acetic acid-induced writhing and formalin tests were conducted to evaluate the antinociceptive actions of Cepharanthine. [3H]-ligand competitive binding assay was applied to determine the binding affinity and selectivity of Cepharanthine at κ, µ and δ opioid receptors. Cepharanthine-induced constipation was investigated using the small intestinal transit test. The results showed that intraperitoneal injection of Cepharanthine produced potent antinociception with an ED50 value of 24.5 mg/kg in the acetic acid-induced writhing test. In the formalin test, Cepharanthine produced moderate antinociception with the maximum analgesic activity of 42.6 ± 11.3% in phase I and 60.1 ± 7.7% in phase Ⅱ, respectively. Cepharanthine had no effects in the hot plate test. In vitro radioligand binding assay, Cepharanthine exhibited a high affinity for µ opioid receptors with a Ki value of 80 nM, without binding to κ and δ opioid receptors. Correspondingly, Cepharanthine-mediated antinociceptive effects were antagonized by pretreatment with opioid receptor antagonist naloxone. Cepharanthine also decreased the small intestine propulsion rates in the small intestinal transit test. Together, this study firstly demonstrates that Cepharanthine produces potent antinociception in acetic acid-induced visceral pain and moderate antinociception in formalin-induced inflammatory pain, and its mechanism of action may be through activation of µ opioid receptors.

Alteration of twinfilin1 expression underlies opioid withdrawal-induced remodeling of actin cytoskeleton at synapses and formation of aversive memory.

Exposure to drugs of abuse induces alterations of dendritic spine morphology and density that has been proposed to be a cellular basis of long-lasting addictive memory and heavily depend on remodeling of its underlying actin cytoskeleton by the actin cytoskeleton regulators. However, the actin cytoskeleton regulators involved and the specific mechanisms whereby drugs of abuse alter their expression or function are largely unknown. Twinfilin (Twf1) is a highly conserved actin-depolymerizing factor that regulates actin dynamics in organisms from yeast to mammals. Despite abundant expression of Twf1 in mammalian brain, little is known about its importance for brain functions such as experience-dependent synaptic and behavioral plasticity. Here we show that conditioned morphine withdrawal (CMW)-induced synaptic structure and behavior plasticity depends on downregulation of Twf1 in the amygdala of rats. Genetically manipulating Twf1 expression in the amygdala bidirectionally regulates CMW-induced changes in actin polymerization, spine density and behavior. We further demonstrate that downregulation of Twf1 is due to upregulation of miR101a expression via a previously unrecognized mechanism involving CMW-induced increases in miR101a nuclear processing via phosphorylation of MeCP2 at Ser421. Our findings establish the importance of Twf1 in regulating opioid-induced synaptic and behavioral plasticity and demonstrate its value as a potential therapeutic target for the treatment of opioid addiction.