Cannabinoid dependence induces sustained changes in GABA release in the globus pallidus without affecting dopamine release in the dorsal striatum: A dual microdialysis probe study

Region-Specific Impact of Repeated Synthetic Cannabinoid Exposure and Withdrawal on Endocannabinoid Signaling, Gliosis, and Inflammatory Markers in the Prefrontal Cortex and Hippocampus

Synthetic cannabinoid use raises concerns about its neuroinflammatory effects, including molecular adaptations of the endocannabinoid system (ECS) in the brain. This study investigates the pharmacological effects of 14-day repeated intraperitoneal administration, as well as 14-day administration followed by a 7-day withdrawal period of two synthetic cannabinoids: WIN55,212-2 and HU-210. The study assessed gene expression and protein markers related to the ECS, gliosis, and inflammation in two brain regions critical for cognitive processes and memory-key components of addiction pathways-the prefrontal cortex (PFC) and the hippocampus of rats. Our findings showed that repeated WIN55,212-2 administration induced adaptations in the ECS and reduced IBA1, a glial protein marker, along with inflammatory responses likely mediated through CB2 activity. Notably, regional differences emerged in the hippocampus, where repeated administration of WIN55,212-2 and HU-210 increased IBA1 and inflammatory markers, effects unrelated to CB2 activity. Withdrawal from WIN55,212-2 in the PFC, as well as from both compounds in the hippocampus, decreased IBA1 levels. This was associated with altered protein expression of cannabinoid-synthesizing and degrading enzymes, favoring acylethanolamide synthesis. These findings highlight region-specific effects of synthetic cannabinoids on cannabinoid signaling, gliosis, and inflammation. Further research is needed to elucidate the long-term neurobiological consequences of synthetic cannabinoid use and withdrawal.

Chronic cannabinoid exposure produces tolerance to the dopamine releasing effects of WIN 55,212-2 and heroin in adult male rats

Synthetic cannabinoids were introduced into recreational drug culture in 2008 and quickly became one of the most commonly abused drugs in the United States. The neurobiological consequences resulting from synthetic cannabinoid repeated exposure remain poorly understood. It is possible that a blunted dopamine (DA) response may lead drug users to consume larger quantities to compensate for this form of neurochemical tolerance. Because the endogenous cannabinoid and opioid systems exhibit considerable cross-talk and cross-tolerance frequently develops following repeated exposure to either opioids or cannabinoids, there is interest in investigating whether a history of synthetic cannabinoid exposure influences the ability of heroin to increase DA release. To test the effects of chronic cannabinoid exposure on cannabinoid- and heroin-evoked DA release, male adult rats were treated with either vehicle or a synthetic cannabinoid (WIN55-212-2; WIN) using an intravenous (IV) dose escalation regimen (0.2-0.8 mg/kg IV over 9 treatments). As predicted, WIN-treated rats showed a rightward shift in the dose-response relationship across all behavioral/physiological measures when compared to vehicle-treated controls. Then, using fast-scan cyclic voltammetry to measure changes in the frequency of transient DA events in the nucleus accumbens shell of awake and freely-moving rats, it was observed that the DA releasing effects of both WIN and heroin were significantly reduced in male rats with a pharmacological history of cannabinoid exposure. These results demonstrate that repeated exposure to the synthetic cannabinoid WIN can produce tolerance to its DA releasing effects and cross-tolerance to the DA releasing effects of heroin.

GPCR-Based Dopamine Sensors-A Detailed Guide to Inform Sensor Choice for In vivo Imaging

Understanding how dopamine (DA) encodes behavior depends on technologies that can reliably monitor DA release in freely-behaving animals. Recently, red and green genetically encoded sensors for DA (dLight, GRAB-DA) were developed and now provide the ability to track release dynamics at a subsecond resolution, with submicromolar affinity and high molecular specificity. Combined with rapid developments in in vivo imaging, these sensors have the potential to transform the field of DA sensing and DA-based drug discovery. When implementing these tools in the laboratory, it is important to consider there is not a 'one-size-fits-all' sensor. Sensor properties, most importantly their affinity and dynamic range, must be carefully chosen to match local DA levels. Molecular specificity, sensor kinetics, spectral properties, brightness, sensor scaffold and pharmacology can further influence sensor choice depending on the experimental question. In this review, we use DA as an example; we briefly summarize old and new techniques to monitor DA release, including DA biosensors. We then outline a map of DA heterogeneity across the brain and provide a guide for optimal sensor choice and implementation based on local DA levels and other experimental parameters. Altogether this review should act as a tool to guide DA sensor choice for end-users.