CB1 cannabinoid receptors mediate cognitive deficits and structural plasticity changes during nicotine withdrawal

BACKGROUND: Tobacco withdrawal is associated with deficits in cognitive function, including attention, working memory, and episodic memory. Understanding the neurobiological mechanisms involved in these effects is crucial because cognitive deficits during nicotine withdrawal may predict relapse in humans. METHODS: We investigated in mice the role of CB1 cannabinoid receptors (CB1Rs) in memory impairment and spine density changes induced by nicotine withdrawal precipitated by the nicotinic antagonist mecamylamine. Drugs acting on the endocannabinoid system and genetically modified mice were used. RESULTS: Memory impairment during nicotine withdrawal was blocked by the CB1R antagonist rimonabant or the genetic deletion of CB1R in forebrain gamma-aminobutyric acidergic (GABAergic) neurons (GABA-CB1R). An increase of 2-arachidonoylglycerol (2-AG), but not anandamide, was observed during nicotine withdrawal. The selective inhibitor of 2-AG biosynthesis O7460 abolished cognitive deficits of nicotine abstinence, whereas the inhibitor of 2-AG enzymatic degradation JZL184 did not produce any effect in cognitive impairment. Moreover, memory impairment was prevented by the selective mammalian target of rapamycin inhibitor temsirolimus and the protein synthesis inhibitor anisomycin. Mature dendritic spines on CA1 pyramidal hippocampal neurons decreased 4 days after the precipitation of nicotine withdrawal, when the cognitive deficits were still present. Indeed, a correlation between memory performance and mature spine density was found. Interestingly, these structural plasticity alterations were normalized in GABA-CB1R conditional knockout mice and after subchronic treatment with rimonabant. CONCLUSIONS: These findings underline the interest of CB1R as a target to improve cognitive performance during early nicotine withdrawal. Cognitive deficits in early abstinence are associated with increased relapse risk.This work was supported by the Ministerio de Economía y Competitividad-MINECO (Grant No. SAF2014-59648-P to RM and Grant Nos. BFU2012-33500 and BFU2015-68568-P to AO), the Instituto de Salud Carlos III (Grant No. PI13/00042 to FB and RETICS-RTA, Grant No. RD12/0028/0023 to RM), the Generalitat de Catalunya-AGAUR (Grant No. 2014-SGR-1547 to RM), Plan Nacional sobre Drogas (Grant No. 2014I019 to FB), the European Commission (NeuroPain, Grant No. HEALTH-F2-2013-602891 to RM), FP7-PEOPLE-2013-IEF-623638, and French State/Agence Nationale de la Recherche/IdEx (Grant No. ANR-10-IDEX-03-02 to AB-G