Ingestion of specific probiotics, namely "psychobiotics", produces psychotropic effects on behavior and affects the hypothalamic-pituitary-adrenal axis and neurochemicals in the brain. We examined the psychotropic effects of a potential psychobiotic bacterium, Lactobacillus plantarum strain PS128 (PS128), on mice subjected to early life stress (ELS) and on naïve adult mice. Behavioral tests revealed that chronic ingestion of PS128 increased the locomotor activities in both ELS and naïve adult mice in the open field test. In the elevated plus maze, PS128 significantly reduced the anxiety-like behaviors in naïve adult mice but not in the ELS mice; whereas the depression-like behaviors were reduced in ELS mice but not in naïve mice in forced swimming test and sucrose preference test. PS128 administration also reduced ELS-induced elevation of serum corticosterone under both basal and stressed states but had no effect on naïve mice. In addition, PS128 reduced inflammatory cytokine levels and increased anti-inflammatory cytokine level in the serum of ELS mice. Furthermore, the dopamine level in the prefrontal cortex (PFC) was significantly increased in PS128 treated ELS and naïve adult mice whereas serotonin (5-HT) level was increased only in the naïve adult mice. These results suggest that chronic ingestion of PS128 could ameliorate anxiety- and depression-like behaviors and modulate neurochemicals related to affective disorders. Thus PS128 shows psychotropic properties and has great potential for improving stress-related symptoms.

Psychobiotics are a group of probiotics that affect the central nervous system (CNS) related functions and behaviors mediated by the gut-brain-axis (GBA) via immune, humoral, neural, and metabolic pathways to improve not only the gastrointestinal (GI) function but also the antidepressant and anxiolytic capacity. As a novel class of probiotics, the application of psychobiotics has led researchers to focus on a new area in neuroscience. In the past five years, some psychobiotics strains were reported to inhibit inflammation and decreased cortisol levels, resulting in an amelioration of the symptoms of anxiety and depression. Psychobiotics are efficacious in improving neurodegenerative and neurodevelopmental disorders, including autism spectrum disorder (ASD), Parkinson’s disease (PD) and Alzheimer’s disease (AD). Use of psychobiotics can improve GI function, ASD symptoms, motor functions of patients with PD and cognition in patients with AD. However, the evidence for the effects of psychobiotics on mental and neurological conditions/ disorders remains limited. Further studies of psychobiotics are needed in order to determine into their effectiveness and mechanism as treatments for various psychiatric disorders in the future.