Enduring effects of an unhealthy diet during adolescence on systemic but not neurobehavioural measures in adult rats

Introduction: Adolescence is an important stage of maturation for various brain structures. It is during this time therefore that the brain may be more vulnerable to environmental factors such as diet that may influence mood and memory. Diets high in fat and sugar (termed a cafeteria diet) during adolescence have been shown to negatively impact upon cognitive performance, which may be reversed by switching to a standard diet during adulthood. Consumption of a cafeteria diet increases both peripheral and central levels of interleukin-1β (IL-1β), a pro-inflammatory cytokine which is also implicated in cognitive impairment during the ageing process. It is unknown whether adolescent exposure to a cafeteria diet potentiates the negative effects of IL-1β on cognitive function during adulthood. Methods: Male Sprague-Dawley rats consumed a cafeteria diet during adolescence after which time they received a lentivirus injection in the hippocampus to induce chronic low-grade overexpression of IL-1β. After viral integration, metabolic parameters, circulating and central pro-inflammatory cytokine levels, and cognitive behaviours were assessed. Results: Our data demonstrate that rats fed the cafeteria diet exhibit metabolic dysregulations in adulthood, which were concomitant with low-grade peripheral and central inflammation. Overexpression of hippocampal IL-1β in adulthood impaired spatial working memory. However, adolescent exposure to a cafeteria diet, combined with or without hippocampal IL-1β in adulthood did not induce any lasting cognitive deficits when the diet was replaced with a standard diet in adulthood. Discussion: These data demonstrate that cafeteria diet consumption during adolescence induces metabolic and inflammatory changes, but not behavioural changes in adulthood