Emerging microbiota-gut-brain axis research demonstrates an important role of gut microbes in the establishment and treatment of nervous system disorders, including depression. An estimated 300 million or nearly 4% of the human population suffers from depression globally. Depression is a complex multifactorial disease and recent epidemiological studies indicate that antibiotic treatment predisposes humans to the development of neuropsychiatric disorders, including depression. One proposed mechanism is that antibiotic administration alters gut microbiome structure and function as well as hinders gut-brain communication through decreased synthesis of neuroactive compounds. However, the mechanisms by which antibiotics induce depression remain unclear. We are using a novel nonhuman primate model, the common marmoset (Callithrix jacchus), to investigate the mechanisms by which antibiotics induce depression.