Maternal high-fat diet drives sex-specific microglia remodeling of serotonergic reward circuitry

Maternal nutrition shapes offspring brain development and influences neurodevelopmental disorder risk, but the underlying mechanisms remain unclear. In mice, maternal high-fat diet exposure disrupted microglia-serotonin interactions during a critical postnatal period, producing persistent, sex-specific mesolimbic alterations. Male but not female offspring showed increased serotonergic fiber density in the nucleus accumbens (NAc), coincident with reduced microglial phagocytosis of serotonergic projections. Microglial 5-HT2C receptor signaling is a key regulator of this process. Viral over expression in microglia, mimicking diet-induced upregulation, was sufficient to cause serotonergic hyperinnervation. By adulthood, male offspring displayed increased NAc serotonin release and projection-specific changes in dorsal raphe physiology. These circuit alterations accelerated reward-motivated learning, a phenotype reproduced by chemogenetic activation of NAc-projecting serotonergic neurons. Together, these findings reveal a novel mechanism by which maternal diet programs serotonergic circuit assembly and behavior in a sex-specific manner, providing a potential link between early-life metabolic inflammation and lifelong serotonergic dysfunction.