Dietary N-3 PUFA plays a key role in brain maturation, development, stress response and cognitive abilities (Weiser et al., 2016; Devarshi et al., 2019). As adolescent’s prefrontal cortex is maturating, the period becomes sensitive to external factors such as environment, nutrition, and stress (Petrovich et al., 2001; Calabro et al., 2020). In this thesis, we aim to expand our knowledge of the influence of external factors, such as dietary omega-3 supplementation and enriched environment, during this critical maturation period. By designing four distinct studies, we tested the hypothesis that visible sex-specific alterations would arise from adolescence targeted diet n-3 PUFA supplementation and enriched environment, which would act to modify physiological and stress responses, as well as socio-emotional and cognitive performance. Our first study characterized the impact n-3 PUFA and n-6 PUFA regimen on corticosterone secretion and behavioural responses in adolescent male rodents. Additionally, it assessed the effects of delivery method (gavage versus restricted feeding) during this sensitive maturation period to ensure using a method with limited stress-mediated outcomes. This study highlighted gavage to induce reduced effects on corticosterone (CORT) secretion, regardless of the provided supplementation. On the last day of feeding, CORT secretion was diminished in fish oil (FO) fed rats exposed to restricted feeding, suggesting FO diet to promote physiological adjustments. Data also demonstrated that FO and soybean (CSO) rich diets were able to reduce anxiety-like behaviour compared to a high-fat diet intake (Hydrogenated Vegetal Fat - HVF), highlighting the role of n-3 PUFA dietary supplementation during adolescence on stress regulation. Our second study assessed sex-specific impact of adolescence targeted dietary supplementation on brain Docosahexaenoic Acid (DHA), Arachidonic Acid (AA) and Linolenic acid (LA) concentrations immediately following supplementation and during adulthood. Our findings demonstrated overall elevated DHA, AA and LA brain tissue concentrations in female compared to male rats, regardless of dietary supplementation. Benefit of supplementation were most apparent in adolescent males, where FO led to higher DHA concentrations compared to soybean oil supplementation, supporting a positive influence of FO dietary supplementation in males during intensive hormonal fluctuation and brain maturation. However, adolescent male rats showed reduced ability to extract nutrient essential fatty acids compared to female counterparts. Our third study characterized sex-specific coping strategies, socioemotional responses, and glucocorticoid regulation following an n-3 PUFA rich diet and enriched environment (EE) during the adolescent period. While basal CORT secretions were not significantly altered by supplementation in males, a gradual increase in CORT was observed during supplementation, peaking at DAY21. Passive coping strategies was preferred in the FST in RC (Regular Cage)- housed females exposed to FO while RC-housed CSO-fed males opted for an active climbing coping strategy. Increase locomotion and anxiolytic behaviour were observed in CSO-supplemented males (exposed to EE), while CSO by itself promoted social recognition in males. In contrast, sociability was improved in FO EE exposed females, indicating possible synergic effects. Adulthood hippocampal GR-ir expression was reduced at the hippocampal CA3 region in FO/RC and CSO/EE rat groups, which could have influenced memory consolidation and stress resilience. Overall, results from this study provided insights on positive effects associated with short-term adolescent n-3 PUFA supplementation in females, while male appeared to most benefited from soybean diet supplementation. Our fourth and last study assessed age- and sex-dependent influences of dietary supplementation on cognitive performance in the Barnes Maze Test. Our results showcase a gradual decrease in latencies to the escape box, as well as progressive decrease in working memory errors (WME) in adult compared to adolescent rats. Over the testing period, the FO females and CSO males showed improved performance through reduction of WMEs on specific days, which could subtend sex-related effects of dietary supplementations. However, while discrete effects of n-3 PUFA were more apparent in female rats, short-term supplementation appeared insufficient to promote consistent enhancement of visuospatial performance or cognitive flexibility that could be observed throughout the testing period. In conclusion, our findings support the importance of studying single and combined factors to understand overall impact. We were able to consistently demonstrate beneficial effects on coping strategies, stress reactivity, sociability, and cognitive performance of adolescence-targeted fish oil supplementation, especially in female rodents.

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