Chapter 22 : Probiotics in Neurology and Psychiatry

Abstract:

Probiotics are live nonpathogenic organisms that promote beneficial health effects when ingested. Increasing numbers of reports indicate that probiotics may have therapeutic potential in disorders ranging from atopic dermatitis to arthritis, highlighting the systemic impact of these organisms. While probiotics have been proposed as adjuvant therapy for depression, to date little is known of the ability of probiotic treatment to modulate brain function. The brain and the gut are engaged in constant bidirectional communication. Such communication becomes apparent when alterations in gastrointestinal (GI) function are communicated to the brain, bringing about the perception of visceral events such as nausea, satiety, and pain or when, in turn, stressful experiences lead to altered GI secretions and motility. This communication system involves neural pathways as well as immune and endocrine mechanisms. Consistent observations have suggested that patients with major depression who are otherwise healthy have activated inflammatory pathways, as indicated by increased proinflammatory cytokines, increased acute-phase proteins, and greater expression of chemokines and adhesion molecules. In addition to direct neural pathways, the gut also communicates to the brain utilizing hormonal signaling pathways that involve the release of gut peptides from enteroendocrine cells which can act directly on the brain at the area postrema, one of the circumventricular organs that lie outside the blood-brain barrier. Future research should be aimed at determining specific mechanisms involved in linking the human microbiota in general with central nervous system (CNS) homeostasis and function.