Evidence For Cannabidiol Modulation of Serotonergic Transmission in a Model of Osteoarthritis via in vivo PET Imaging and Behavioral Assessment.

Background: Preclinical studies indicate that cannabidiol (CBD), the primary nonaddictive component of cannabis, has a wide range of reported pharmacological effects such as analgesic and anxiolytic actions; however, the exact mechanisms of action for these effects have not been examined in chronic osteoarthritis (OA). Similar to other chronic pain syndromes, OA pain can have a significant affective component characterized by mood changes. Serotonin (5-HT) is a neurotransmitter implicated in pain, depression, and anxiety. Pain is often in comorbidity with mood and anxiety disorders in patients with OA. Since primary actions of CBD are analgesic and anxiolytic, in this first in vivo positron emission tomography (PET) imaging study, we investigate the interaction of CBD with serotonin 5-HT1A receptor via a combination of in vivo neuroimaging and behavioral studies in a well-validated OA animal model. Methods: The first aim of this study was to evaluate the target involvement, including the evaluation of modulation by acute administration of CBD, or a specific target antagonist/agonist intervention, in control animals. The brain 5-HT1A activity/availability was assessed via in vivo dynamic PET imaging (up to 60 min) using a selective 5-HT1A radioligand ([18F]MeFWAY). Tracer bindings of 17 ROIs were evaluated based on averaged SUVR values over the last 10 min using CB as the reference region. We subsequently examined the neurochemical and behavioral alterations in OA animals (induction with monosodium iodoacetate (MIA) injection), as compared to control animals, via neuroimaging and behavioral assessment. Further, we examined the effects of repeated low-dose CBD treatment on mechanical allodynia (von Frey tests) and anxiety-like (light/dark box tests, L/D), depressive-like (forced swim tests, FST) behaviors in OA animals, as compared to after vehicle treatment. Results: The tracer binding was significantly reduced in control animals after an acute dose of CBD administered intravenously (1.0 mg/kg, i.v.), as compared to that for baseline. This binding specificity to 5-HT1A was further confirmed by a similar reduction of tracer binding when a specific 5-HT1A antagonist WAY1006235 was used (0.3 mg/kg, i.v.). Mice subjected to the MIA-induced OA for 13-20 days showed a decreased 5-HT1A tracer binding (25% to 41%), consistent with the notion that 5-HT1A plays a role in the modulation of pain in OA. Repeated treatment with CBD administered subcutaneously (5 mg/kg/day, s.c., for 16 days after OA induction) increased 5-HT1A tracer binding, while no significant improvement was observed after vehicle. A trend of increased anxiety or depressive-like behavior in the light/dark box or forced swim tests after OA induction, and a decrease in those behaviors after repeated low-dose CBD treatment, are consistent with the anxiolytic action of CBD through 5HT1A receptor activation. There appeared to be a sex difference: females seem to be less responsive at the baseline towards pain stimuli, while being more sensitive to CBD treatment. Conclusion: This first in vivo PET imaging study in an OA animal model has provided evidence for the interaction of CBD with the serotonin 5-HT1A receptor. Behavioral studies with more pharmacological interventions to support the target involvement are needed to further confirm these critical findings.

Effect of Housing Condition and Diet on the Gut Microbiota of Weanling Immunocompromised Mice.

Gastrointestinal microbiota are affected by a wide variety of extrinsic and intrinsic factors. In the husbandry of laboratory mice and design of experiments, controlling these factors where possible provides more reproducible results. However, the microbiome is dynamic, particularly in the weeks immediately after weaning. In this study, we characterized the baseline gastrointestinal microbiota of immunocompromised mice housed under standard conditions for our facility for 6 weeks after weaning, with housing either in an isolator or in individually ventilated cages and a common antibiotic diet (trimethoprim sulfamethoxazole). We compared these conditions to a group fed a standard diet and a group that was weaned to a standard diet then switched to antibiotic diet after 2 weeks. We found no clear effect of diet on richness and α diversity of the gastrointestinal microbiota. However, diet did affect which taxa were enriched at the end of the experiment. The change to antibiotic diet during the experiment did not convert the gastrointestinal microbiome to a state similar to mice consistently fed antibiotic diet, which may highlight the importance of the initial post-weaning period in the establishment of the gastrointestinal microbiome. We also observed a strong effect of housing type (isolator compared with individually ventilated cage) on the richness, α diversity, ß diversity, and taxa enriched over the course of the experiment. Investigating whether the diet or microbiome affects a certain strain's phenotype is warranted in some cases. However, our findings do not suggest that maintaining immunocompromised mice on antibiotic feed has a clinical benefit when potential pathogens are operationally excluded, nor does it result in a more consistent or controlled microbiome in the post-weaning period.

Expression of glial CBP in steroid mediated neuroprotection in male and female zebra finches.

Under neurodegenerative conditions, reactive astrocytes upregulate both aromatase (estrogen synthase) as well as estrogen and androgen receptors. This increased steroidogenic signal promotes neuroprotection and repair by promoting neurogenesis and decreasing cell death, but also by modulating the release of inflammatory molecules. Thus, endocrine - immune cross-talk is an essential component of estrogen mediated neuroprotection following brain injury. However, the exact mechanisms underlying this cross-talk remains unknown. cAMP response element-binding protein-binding protein (CBP) may be involved in the modulation of both the endocrine and inflammatory response following injury. CBP acts as both an estrogen receptor (ER) coactivator and as a promotor for NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) target genes and previous data suggests that ER and NF-κB compete for CBP. When CBP is displaced, target genes for NF-κB are repressed and inflammation is decreased. To test the role of CBP following injury, we examined CBP expression following penetrating injury in adult male and female zebra finches. Using immunohistochemistry, we were able to specifically examine glial CBP expression, as glial cells are important mediators of the neuroendocrine response to damage. Male but not female zebra finches upregulated glial CBP following damage to the brain. To determine if this upregulation was estrogen dependent, we decreased local estrogen levels with fadrozole (aromatase inhibitor) and reexamined glial CBP expression following injury. Aromatase inhibition resulted in no change in overall glial CBP expression suggesting that circulating estrogens do not mediate the upregulation of glial CBP following injury. Thus CBP may play a role in the both the estrogen and immune response to injury.