Gut Microbiome Depletion Lowers Baseline Oxytocin, Not MDMA Response, in Rats

The gut-brain axis is a complex communication network linking the intestinal microbiota with brain function, influencing various neurological and psychiatric conditions. Oxytocin, often called the 'love hormone,' plays a crucial role in social bonding, anxiety, and stress regulation, with its signaling primarily originating in the hypothalamus. While previous research suggests the microbiome can modulate neurochemical systems, the specific impact of antibiotic-induced microbiome depletion on both baseline and pharmacologically stimulated oxytocin signaling in the brain has remained unclear, particularly regarding differential effects. This study specifically aimed to investigate how microbiome depletion affects both basal hypothalamic oxytocin levels and the oxytocin response induced by MDMA.

The study demonstrated a significant impact of microbiome depletion on baseline oxytocin signaling. In antibiotic-treated rats, baseline hypothalamic oxytocin mRNA expression was reduced by 38% compared to controls (p<0.01), and oxytocin peptide levels showed a similar trend. However, the MDMA-induced oxytocin response remained unaffected by microbiome depletion. Both control and antibiotic-treated groups exhibited a robust 2.5-fold increase in hypothalamic oxytocin mRNA expression following MDMA administration (p<0.001), with no significant difference between the two groups. This suggests a selective modulation rather than a global suppression of the oxytocin system. > The most striking finding was that antibiotic-induced microbiome depletion selectively reduced baseline hypothalamic oxytocin signaling by 38% but did not impair the 2.5-fold increase in oxytocin response triggered by MDMA.