Intermittent ethanol exposure during adolescence impairs cannabinoid type 1 receptor-dependent long-term depression and recognition memory in adult mice

Penasco S, Rico-Barrio I, Puente N, Fontaine CJ, Ramos A, Reguero L, Gerrikagoitia I, de Fonseca FR, Suarez J, Barrondo S, Aretxabala X, Garcia Del Cano G, Salles J, Elezgarai I, Nahirney PC, Christie BR and Grandes P

Neuropsychopharmacology (2020) 45: 309-318

Link to abstract

Binge drinking is a significant problem in adolescent populations, and because of the reciprocal interactions between ethanol (EtOH) consumption and the endocannabinoid (eCB) system, we sought to determine if adolescent EtOH intake altered the localization and function of the cannabinoid 1 (CB₁) receptors in the adult brain. Adolescent mice were exposed to a 4-day-per week drinking in the dark (DID) procedure for a total of 4 weeks and then tested after a 2-week withdrawal period. Field excitatory postsynaptic potentials (fEPSPs), evoked by medial perforant path (MPP) stimulation in the dentate gyrus molecular layer (DGML), were significantly smaller. Furthermore, unlike control animals, CB₁ receptor activation did not depress fEPSPs in the EtOH-exposed animals. We also examined a form of excitatory long-term depression that is dependent on CB₁ receptors (eCB-eLTD) and found that it was completely lacking in the animals that consumed EtOH during adolescence. Histological analyses indicated that adolescent EtOH intake significantly reduced the CB₁ receptor distribution and proportion of immunopositive excitatory synaptic terminals in the medial DGML. Furthermore, there was decreased binding of [³⁵S]guanosine-5*-O-(3-thiotriphosphate) ([³⁵S] GTPγS) and the guanine nucleotide-binding (G) protein Gαi2 subunit in the EtOH-exposed animals. Associated with this, there was a significant increase in monoacylglycerol lipase (MAGL) mRNA and protein in the hippocampus of EtOH-exposed animals. Conversely, deficits in eCB-eLTD and recognition memory could be rescued by inhibiting MAGL with JZL184. These findings indicate that repeated exposure to EtOH during adolescence leads to long-term deficits in CB₁ receptor expression, eCB-eLTD, and reduced recognition memory, but that these functional deficits can be restored by treatments that increase endogenous 2-arachidonoylglycerol.