INTRAVENOUS SELF-ADMINISTRATION OF THE SYNTHETIC CANNABINOID RECEPTOR AGONIST JWH-018 IN ADOLESCENT MICE: NEUROBIOLOGICAL SEQUELAE IN ADULTHOOD

Synthetic cannabinoids (SCs) are currently the most frequently used novel psychoactive substances worldwide. Typically sprayed on herbal mixtures, SCs are commonly known as Spice or K2, usually marketed as marijuana-like drugs and perceived as risk free by naive users. SCs use is growing, particularly among adolescents, and is posing major medical and psychiatric risk. The first generation SC JWH-018 is frequently detected in Spice/K2 drugs and represents the reference/prototypal compound in SC-containing products. This study was performed to evaluate for the first time the long-term neurochemical and behavioral consequences of adolescent voluntary consumption of JWH-018 in the intravenous self-administration (IVSA) animal model of addiction. To investigate the enduring consequences of adolescent exposure to JWH-018, we measured the levels of specific markers of neuroinflammation, such as glial fibrillary acidic protein (GFAP) and ionized calcium binding adapter molecule 1 (IBA-1), in the prefrontal cortex (PFC), nucleus accumbens (NAc) shell and core, and caudate-putamen (CPu) of adult mice that underwent JWH-018 IVSA during adolescence. In addition, we evaluated the enduring consequences related to the alteration of CB1 receptor (CB1R) in several brain areas. Finally, since CB1Rs are expressed also in mitochondrial membrane (mtCB1), possible alterations of mitochondrial activity were investigated using markers such as citrate synthase (CS) activity and expression of complex I proteins. Results showed that male adolescent mice post-natal day (PND) 30-53 acquired lever-pressing behavior under different fixed ratio schedules of reinforcement (FR-1 and FR-3) when JWH-018 was made available at the dose of 7.5 µg/kg/inf, and maintained a stable responding over the training sessions. Importantly, operant behavior was specifically directed at obtaining JWH-018 since the responding rate increased under the PR schedule of reinforcement and was not present in the vehicle (Veh) group. However, active lever-pressing did not decrease during extinction training, in spite of the absence of drug reward and associate cues. Moreover, cannabinoid IVSA was reduced by pretreatment with the CB1R antagonist AM251 (0.7 and 1 mg/kg), but not the CB2 receptor CB2R antagonist AM630 (0.5 and 1mg/kg), administered intraperitoneally (i.p.) 30 minutes before starting the session. Moreover, adult mice that self-administered JWH-018 during adolescence displayed increased microglia in the CPu and NAc, decreased GFAP-positive astrocytes in the CPu and a decreased expression of CB1Rs in the hippocampus. Finally, a decrease of CS activity was observed in all the areas studied (cortex, hippocampus and striatum) along with an increase of NADH dehydrogenase iron-sulfur mitochondrial protein 4, (NDUFS4) in the cortex and hippocampus. The operant behavior of adolescent mice and the neurochemical and mitochondrial long-lasting alterations observed in the same animals during adulthood suggest that consumption of SC during adolescence can induce persistent alterations in specific brain areas and that further studies are urgently needed to fully elucidate the behavioral, neurochemical and molecular changes associated to the use of SCs by adolescents.