The Effect of Microbiota on Behaviour.

There is currently enormous interest in the impact of the intestinal microbiota on the development and function of the brain via activity of the microbiota-gut-brain axis. It has long been recognised that symbiotic microorganisms influence host behaviour, but in recent years evidence has accumulated that this can, in fact, be beneficial to the host. Indeed, substantial research has now demonstrated an influence of the intestinal microbiota on a wide range of mammalian behaviours. Here, we review what is currently known about the influence of intestinal microbiota on learning and memory, olfaction, social behaviours, and circadian processes. While work in animal models is compelling, further work is required to elucidate mechanisms whereby bacterial influence is occurring, as well as to determine the extent to which gut microbiota can influence similar phenotypes in humans.

Experimental Pulmonary Tuberculosis in the Absence of Detectable Brain Infection Induces Neuroinflammation and Behavioural Abnormalities in Male BALB/c Mice.

Tuberculosis (TB) is a chronic infectious disease in which prolonged, non-resolutive inflammation of the lung may lead to metabolic and neuroendocrine dysfunction. Previous studies have reported that individuals coursing pulmonary TB experience cognitive or behavioural changes; however, the pathogenic substrate of such manifestations have remained unknown. Here, using a mouse model of progressive pulmonary TB, we report that, even in the absence of brain infection, TB is associated with marked increased synthesis of both inflammatory and anti-inflammatory cytokines in discrete brain areas such as the hypothalamus, the hippocampal formation and cerebellum accompanied by substantial changes in the synthesis of neurotransmitters. Moreover, histopathological findings of neurodegeneration and neuronal death were found as infection progressed with activation of p38, JNK and reduction in the BDNF levels. Finally, we perform behavioural analysis in infected mice throughout the infection, and our data show that the cytokine and neurochemical changes were associated with a marked onset of cognitive impairment as well as depressive- and anxiety-like behaviour. Altogether, our results suggest that besides pulmonary damage, TB is accompanied by an extensive neuroinflammatory and neurodegenerative state which explains some of the behavioural abnormalities found in TB patients.

Behavioural change: a rare presentation of leptospirosis.

Neurological manifestations of leptospirosis without severe multiorgan involvement are a rare clinical entity. Despite the increasing prevalence of the disease in many tropical countries, its protean clinical presentations make its timely diagnosis challenging. We report the case of a 44-year-old Filipino man presenting with fever, myalgia, behavioural changes and altered sensorium. Neurological examination did not show any focal neurological deficits or clear signs of meningoencephalitis. Lumbar tap, cranial CT scan and cranial MRI were inconclusive. The diagnosis of leptospirosis with acute encephalitis relied heavily on the patient's clinical clues, appropriate exposure history and patterns in ancillary laboratory tests. Empiric antibiotic therapy with ceftriaxone was initiated. Seroconversion and fourfold increase in serological antibody titres by leptospirosis microagglutination test later confirmed the diagnosis. The patient was successfully treated, and all neurological complications were reversed.

Human Gut Microbiota from Autism Spectrum Disorder Promote Behavioral Symptoms in Mice.

Autism spectrum disorder (ASD) manifests as alterations in complex human behaviors including social communication and stereotypies. In addition to genetic risks, the gut microbiome differs between typically developing (TD) and ASD individuals, though it remains unclear whether the microbiome contributes to symptoms. We transplanted gut microbiota from human donors with ASD or TD controls into germ-free mice and reveal that colonization with ASD microbiota is sufficient to induce hallmark autistic behaviors. The brains of mice colonized with ASD microbiota display alternative splicing of ASD-relevant genes. Microbiome and metabolome profiles of mice harboring human microbiota predict that specific bacterial taxa and their metabolites modulate ASD behaviors. Indeed, treatment of an ASD mouse model with candidate microbial metabolites improves behavioral abnormalities and modulates neuronal excitability in the brain. We propose that the gut microbiota regulates behaviors in mice via production of neuroactive metabolites, suggesting that gut-brain connections contribute to the pathophysiology of ASD.

The mind-body-microbial continuum.

Our understanding of the vast collection of microbes that live on and inside us (microbiota) and their collective genes (microbiome) has been revolutionized by culture-independent "metagenomic" techniques and DNA sequencing technologies. Most of our microbes live in our gut, where they function as a metabolic organ and provide attributes not encoded in our human genome. Metagenomic studies are revealing shared and distinctive features of microbial communities inhabiting different humans. A central question in psychiatry is the relative role of genes and environment in shaping behavior. The human microbiome serves as the interface between our genes and our history of environmental exposures; explorations of our microbiomes thus offer the possibility of providing new insights into our neurodevelopment and our behavioral phenotypes by affecting complex processes such as inter- and intra personal variations in cognition, personality, mood, sleep, and eating behavior, and perhaps even a variety of neuropsychiatric diseases ranging from affective disorders to autism. Better understanding of microbiome-encoded pathways for xenobiotic metabolism also has important implications for improving the efficacy of pharmacologic interventions with neuromodulatory agents.

Does group A beta-hemolytic streptococcal infection increase risk for behavioral and neuropsychiatric symptoms in children?

OBJECTIVE: To determine whether group A beta-hemolytic streptococcal infections increase the risk of developing symptoms characteristic of the diagnosis pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS). DESIGN: Prospective cohort study. METHODS: Children (N = 814) aged 4 to 11 years seen for sore throat or well-child care in a large pediatric practice in Rochester, NY, were enrolled from October 2001 to June 2002 (group A beta-hemolytic streptococcal [GAS] infected, n = 411; GAS uninfected, n = 403, of whom 207 had a sore throat of presumed viral etiology and 196 were well children). Symptomatic children with GAS infection (n = 399) were treated with antibiotics. At baseline and 2 and 12 weeks following baseline, all parents completed a 20-item questionnaire about the presence/absence of recent PANDAS symptoms in their children, and capable children answered 10 items about worries, obsessions, and compulsions. The relative risk of developing a "mild PANDAS variant" (> or = 2 new PANDAS symptoms) by illness type (GAS positive, presumed viral, or well child) and by parent and child report was determined and adjusted for potential covariates. RESULTS: By parent report, ill children more frequently manifested several PANDAS symptoms at baseline than well children. However, neither new symptoms nor the risk of developing a mild PANDAS variant developed during the subsequent 12 weeks more commonly in children with GAS infection than in those with presumed viral illness or in well children by parent or child report. CONCLUSIONS: Ill children with GAS infection, treated for their GAS infection, were not at increased risk for developing PANDAS symptoms or a mild PANDAS variant compared with children with presumed viral illness or well children. The role of antibiotics in the prevention or treatment of PANDAS as well as the investigation of PANDAS in the asymptomatic, infectious host deserves future research.