The Effects of Human Milk Oligosaccharide Supplementation During Critical Periods of Development on the Mesolimbic Dopamine System

•Human milk oligosaccharide supplementation sex-dependently affects mesolimbic dopamine system gene expression.•In females, 3′SL + 2′FL diet fortification decreased DAT expression in the VTA and increased leptin expression in the NAc.•Overall expression of NAc D2, VTA ghrelinR, and VTA leptin is lower is females.•Exploring sex differences may uncover different critical periods of development to add translational value to future studies. Human milk oligosaccharides (HMO)s are a key component in human milk and represent an important dietary modulator of infant gut microbiota composition and associated gut-brain axis development and homeostasis. The brain reward system, specifically the mesolimbic dopamine (DA) projections from the ventral tegmental area (VTA) to nucleus accumbens (NAc) is involved in the motivation and preference for food. The objective of the present study was to determine if HMO fortified diets given during the critical period of reward system development (p21) could affect the structure of the reward system. At weaning (p21), Sprague-Dawley rats were randomized to one of four fortified diet groups: Control, 3′sialyllactose (3′FL), 2′-fucosyllactose (2′FL), or a combination of 3′SL and 2′FL (3′SL + 2′FL). Messenger RNA (mRNA) expression was quantified for DA and appetite associated markers in the VTA and NAc and western blots measured the immediate early gene FosB and its isoform ΔFosB. Females fed the 3′SL + 2′FL fortified diet displayed a decrease in DAT expression in the VTA and an increase in leptin expression in the NAc. Females displayed an overall lower expression of NAc D2, VTA ghrelinR, and VTA leptin. In males, VTA DAT and FosB were negatively correlated with body weight and systemic leptin. Sex differences in the expression of DA markers underscore the need to investigate this phenomenon and understand the functional significance in preventing or treating obesity. This study highlights sex differences in response to HMO supplementation and the need for further investigations into the functional significance of nutritional interventions during DA system development.