Background and Purpose Mitragyna speciosa, more commonly known as kratom, is a plant that contains opioidergic alkaloids but is unregulated in most countries. Kratom is used in the self‐medication of chronic pain and to reduce illicit and prescription opioid dependence. Kratom may be less dangerous than typical opioids because of the stronger preference of kratom alkaloids to induce receptor interaction with G proteins over β‐arrestin proteins. We hypothesized that kratom (alkaloids) can also reduce alcohol intake. Experimental Approach We pharmacologically characterized kratom extracts, kratom alkaloids (mitragynine, 7‐hydroxymitragynine, paynantheine, and speciogynine) and synthetic carfentanil‐amide opioids for their ability to interact with G proteins and β‐arrestin at μ, δ, and κ opioid receptors in vitro. We used C57BL/6 mice to assess to which degree these opioids could reduce alcohol intake and whether they had rewarding properties. Key Results Kratom alkaloids were strongly G protein‐biased at all three opioid receptors and reduced alcohol intake, but kratom and 7‐hydroxymitragynine were rewarding. Several results indicated a key role for δ opioid receptors, including that the synthetic carfentanil‐amide opioid MP102—a G protein‐biased agonist with modest selectivity for δ opioid receptors—reduced alcohol intake, whereas the G protein‐biased μ opioid agonist TRV130 did not. Conclusion and Implications Our results suggest that kratom extracts can decrease alcohol intake but still carry significant risk upon prolonged use. Development of more δ opioid‐selective synthetic opioids may provide a safer option than kratom to treat alcohol use disorder with fewer side effects.

Autism spectrum disorder (ASD) is a group of pervasive developmental disorders with core symptoms such as sociability deficit, language impairment, and repetitive/restricted behaviors. Although worldwide prevalence of ASD has been increased continuously, therapeutic agents to ameliorate the core symptoms especially social deficits, are very limited. In this study, we investigated therapeutic potential of donepezil for ASD using valproic acid-induced autistic animal model (VPA animal model). We found that prenatal exposure of valproic acid (VPA) induced dysregulation of cholinergic neuronal development, most notably the up-regulation of acetylcholinesterase (AChE) in the prefrontal cortex of affected rat and mouse offspring. Similarly, differentiating cortical neural progenitor cell in culture treated with VPA showed increased expression of AChE in vitro. Chromatin precipitation experiments revealed that acetylation of histone H3 bound to AChE promoter region was increased by VPA. In addition, other histone deacetyalse inhibitors (HDACIs) such as trichostatin A and sodium butyrate also increased the expression of AChE in differentiating neural progenitor cells suggesting the essential role of HDACIs in the regulation of AChE expression. For behavioral analysis, we injected PBS or donepezil (0.3 mg/kg) intraperitoneally to control and VPA mice once daily from postnatal day 14 all throughout the experiment. Subchronic treatment of donepezil improved sociability and prevented repetitive behavior and hyperactivity of VPA-treated mice offspring. Taken together, these results provide evidence that dysregulation of ACh system represented by the up-regulation of AChE may serve as an effective pharmacological therapeutic target against autistic behaviors in VPA animal model of ASD, which should be subjected for further investigation to verify the clinical relevance.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder, featuring social communication deficit and repetitive/restricted behaviors as common symptoms. Its prevalence has continuously increased, but, till now, there are no therapeutic approaches to relieve the core symptoms, particularly social deficit. In previous studies, abnormal function of the glutamatergic neural system has been proposed as a critical mediator and therapeutic target of ASD-associated symptoms. Here, we investigated the possible roles of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) in autism symptoms using two well-known autistic animal models, Cntnap2 knockout (KO) mice and in utero valproic acid-exposed ICR (VPA) mice. We found that Cntnap2 KO mice displayed decreased glutamate receptor expression and transmission. Contrarily, VPA mice exhibited increased glutamate receptor expression and transmission. Next, we investigated whether AMPAR modulators (positive-allosteric-modulator for Cntnap2 KO mice and antagonist for VPA mice) can improve autistic symptoms by normalizing the aberrant excitatory transmission in the respective animal models. Interestingly, the AMPAR modulation specifically ameliorated social deficits in both animal models. These results indicated that AMPAR-derived excitatory neural transmission changes can affect normal social behavior. To validate this, we injected an AMPAR agonist or antagonist in control ICR mice and, interestingly, these treatments impaired only the social behavior, without affecting the repetitive and hyperactive behaviors. Collectively, these results provide insight into the role of AMPARs in the underlying pathophysiological mechanisms of ASD, and demonstrate that modulation of AMPAR can be a potential target for the treatment of social behavior deficits associated with ASD.

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