Investigating neuropsychiatric disorders through environmental and genetic animal models: exploring the role of the endocannabinoid system

Autism Spectrum disorders (ASD) are a complex group of neurodevelopmental disorders (NDDs) characterized by impairments in social interaction and communication, alongside stereotyped and repetitive behaviors. Psychotic disorders involve neurodevelopmental alterations and may occur as comorbid conditions in individuals with ASD, contributing to their onset and clinical manifestations. Together, these conditions represent a major global health challenge, accounting for a substantial proportion of disability and reduced quality of life. Emerging evidence highlights the involvement of the endocannabinoid system (ECS) in the regulation of neurodevelopmental processes, suggesting its potential as a therapeutic target in these disorders. Moreover, converging studies indicate that both redox imbalance and gut-brain axis dysfunction act as key contributors to the pathophysiology of these disorders. However, the mechanisms through which pharmacological modulation of the ECS influences neurotransmission, oxidative stress and the gut-brain communication remain poorly understood. This PhD thesis investigated the effects of pharmacological ECS modulation on behavioral, neurochemical and biomolecular alterations characterizing two preclinical models of the above mentioned neuropsychiatric disorders, i.e. the BTBR T+Itpr3tf/J (BTBR) mouse model of idiopathic ASD and the post-weaning social isolation (PSWI) rat model of psychosis. The results presented in the first part of this PhD thesis showed that the BTBR mouse model exhibited ASD-like core behaviors, including reduced sociability, increased repetitive behaviors and hyperlocomotion, associated with neurochemical alterations across key brain areas, including prefrontal cortex, hippocampus, amygdala and hypothalamus. Among these regions, amygdala displayed the most pronounced alterations, indicating its central role in ASD-like behaviors. Multiple pathogenic mechanisms have been proposed to underlie ASD-like behaviors, among which redox imbalance has emerged as a key contributor. In particular, the findings included in this PhD thesis showed that in BTBR mice oxidative stress was associated with impaired antioxidant defenses and elevated Reactive Oxygen Species (ROS) production in the hippocampus, a region critical for behavioral regulation. This ROS overproduction was mediated by NOX2, an isoform of the NADPH oxidase enzyme family that catalyzes the transfer of electrons from NADPH to molecular oxygen. Further, in the same animal model, β-caryophyllene (BCP), a naturally occurring sesquiterpene and selective CB2 receptor agonist, was administered due to its ability to downregulate proinflammatory cytokines and reduce gut inflammation, preventing disruption of gut-brain communication. The obtained findings showed that BCP administration improved social behaviors and hyperlocomotion and partially reduced repetitive behaviors in BTBR mice. These effects were accompanied by normalization of colonic serotonin and kynurenine levels and reduction of sympathetic hyperactivity, indicating that peripheral CB2 receptor activation could regulate enteric neurotransmission and tryptophan metabolism, which in turn may have influenced central ASD-like behaviors through the gut-brain axis. These findings underscored the critical role of gut-brain communication in ASD-like phenotypes and suggested that BCP, through CB2-mediated ECS modulation, represents a potential therapeutic strategy. In the second part of this PhD thesis, the PWSI model was employed to investigate the development of psychotic-like symptoms induced by the exposure to an early-life stressor, i.e social isolation, and its underlying mechanisms. The obtained results showed that isolated rats exhibited increased reactivity to environmental and social stimuli. Neurochemical profiling demonstrated alterations in monoaminergic and glutamatergic systems in prefrontal cortex, a brain area crucially involved in executive function and emotion regulation. Redox imbalance was observed in the same region, characterized by elevated ROS levels and a compensatory upregulation of SOD1, an endogenous antioxidant enzyme. Treatment with PF-3845, a selective inhibitor of fatty acid amide hydrolase (FAAH) that elevates endocannabinoid levels, partially normalized behavioral hypereactivity, attenuated monoaminergic alterations and reduced oxidative stress, without affecting glutamatergic alterations. These findings supported a homeostatic and neuroprotective role of ECS and highlighted a complex and dynamic interplay between neurotransmitter systems, oxidative stress and ECS signaling in psychosis-like alterations. Collectively, the findings obtained from the two considered animal models provide mechanistic insights into the role of the ECS in neurodevelopmental and psychosis-related disorders, highlighting its capacity to modulate both central and peripheral pathways. Moreover, they point towards the ECS as a promising therapeutic target for future preclinical and translational studies in ASD and psychosis-related conditions.