Long-term withdrawal from repeated cocaine exposure during adolescence impairs spatial memory altering the glutamatergic receptors composition in the dorsal hippocampus

Background: Cocaine is a highly addictive psychostimulant whose abuse represents a widespread social and economic burden. Among individuals, cocaine abuse has a different impact on adolescent than adult users, inducing more profound long-lasting alterations in the brain of early-onset users. However, the neurobiological mechanisms that underpin the different age-of-onset changes induced by cocaine intake or withdrawal are poorly understood. Since the chronic cocaine exposure is associated with broad cognitive deficits, we here investigated the impact of developmental cocaine-withdrawal on spatial memory, one of the critical domain subserving essential memory processes during brain maturation. Moreover, we evaluated from a molecular standpoint the potential contribution of hippocampal glutamatergic adaptations induced by cocaine in altering the three-dimensional perceptions of adolescent rats. Methods: Adolescent male rats were treated subcutaneously with 5 mg/kg/day of cocaine or saline from post-natal day (PND) 28 to PND42. Following 2 weeks of drug withdrawal, rats were subjected to the spatial order object recogni on (SOOR) test, a hippocampal-dependent cogni vely demanding test. Then, immediately a er SOOR test, rats were sacrificed, and brains were collected and frozen. Western blot analyses were performed on glutamatergic receptor subunits and scaffolding proteins in the post synap c density (PSD) frac on of the dorsal hippocampus. Sta s cal significance was assessed by two-way ANOVA mul ple comparisons or unpaired t-test, as appropriate. Results: At behavioural level, we found that withdrawal from developmental cocaine affected the performance in the SOOR test (-0.1902, p=0.0189, t=2.525), indica ng an impairment in the spa al memory domain in cocaine-exposed rats. Interes ngly, in the PSD frac on of the dorsal hippocampus, we found that developmental exposure to cocaine increased GluN1 (+15 %, p=0.0054), GluN2A (+18 %, p=0.0071) and GluN2B (+19 %, p=0.0479) protein levels with respect to saline-treated rats. Conversely, in animals with a history of cocaine exposure, the SOOR test itself significantly reduced GluN1 (-26 %, p<0.0001), GluN2A (-36 %, p<0.0001), GluN2B (-27 %, p=0.0036) versus their not-tested counterparts. In parallel, also SAP102, which anchors NMDA receptors to the PSD, has been significantly reduced in cocaine-withdrawn rats a er the test performance (-29 %, p=0.0105). Of note, PSD95, an index of PSD integrity, was increased by cocaine (+18 %, p=0.0002) and the SOOR test (+32 %, p<0.0001), while unaltered a er the test performance in cocaine- treated rats. Conclusions: Our results revealed that animals with an history of cocaine exposure during adolescence failed the SOOR test performance. This deficit may be due to an overall increase of NMDA receptor subunits localization and retention in the PSD caused by cocaine, which, in turn, alters their capability to correctly process spatial information once exposed to the learning task. Together, these findings point to adolescence as a crucial developmental period of vulnerability for psychostimulant-induced cognitive impairment, here emphasized by long-term cocaine withdrawal that may have altered the fine-tuning mechanisms of memory formation.