Microbial endocrinology in the microbiome-gut-brain axis: how bacterial production and utilization of neurochemicals influence behavior

In this series of studies, a low per oral dose of C. jejuni was able to induce anxiety-like behavior in mice through a vagal-mediated pathway in the absence of any immune activation [6]. Since these early reports in the 1990s, this microbial-gut-brain axis has been the subject of growing investigation and has even engendered the use of the term "mind-altering bugs" [7]. [...]investigators have shown that the neuroendocrine outflow from a host neurophysiology event such as stress-mediated release of flight-or-flight hormones can alter gene expression in a number of pathogens as well as conjugative transfer between enteric bacteria [13].\n As such, the number of reports demonstrating that bacteria within the gut can be detected by the brain with consequent changes in behavior has been increasing following the initial report utilizing C. jejuni [5] as described above and subsequent reports identifying the neural substrates both within the brain and vagal-mediated gut-to-brain pathway [6].