Neuro-Signals from Gut Microbiota: Perspectives for Brain Glioma

SIMPLE SUMMARY: In the last few years, a lot of evidence demonstrated an unexpected bidirectional communication among the gut microbes and the brain. Gut microbiota derived molecules may affect the nervous system in physiological and pathological conditions, even modulating neurotransmitter levels. Here, we summarize the effects of neurotransmitters on the proliferation and differentiation of neuronal precursor cells in the adult brain, and in brain gliomas. Further, we discuss the hypothesis that modulation of neurotransmitters by gut microbiota might impact the development and progress of brain tumor, specifically glioma. Further investigation on the mechanisms involved in the bidirectional gut-brain communication is required to identify new molecular and cellular targets involved in the dysregulation of brain homeostasis occurring in glioma. ABSTRACT: Glioblastoma (GBM) is the most aggressive form of glioma tumor in adult brain. Among the numerous factors responsible for GBM cell proliferation and invasion, neurotransmitters such as dopamine, serotonin and glutamate can play key roles. Studies performed in mice housed in germ-free (GF) conditions demonstrated the relevance of the gut-brain axis in a number of physiological and pathological conditions. The gut–brain communication is made possible by vagal/nervous and blood/lymphatic routes and pave the way for reciprocal modulation of functions. The gut microbiota produces and consumes a wide range of molecules, including neurotransmitters (dopamine, norepinephrine, serotonin, gamma-aminobutyric acid [GABA], and glutamate) that reach their cellular targets through the bloodstream. Growing evidence in animals suggests that modulation of these neurotransmitters by the microbiota impacts host neurophysiology and behavior, and affects neural cell progenitors and glial cells, along with having effects on tumor cell growth. In this review we propose a new perspective connecting neurotransmitter modulation by gut microbiota to glioma progression.