The Clinical Research on the Relationship Between Depression and Gut Microbiota in TBI Patients

Neuroscientists are probing the connections between intestinal microbes and brain development. The general scaffolding of the brain-gut-enteric microbiota axis includes the central nervous system (CNS), the neuroendocrine and neuroimmune systems,the sympathetic and parasympathetic arms of the autonomic nervous system (ANS),the enteric nervous system (ENS), and of course the intestinal microbiota. These components interact to form a complex reflex network with afferent fibers that project to integrative CNS structures and efferent projections to the smooth muscle. Gut microbiota regulates intestinal and extraintestinal homeostasis. Accumulating evidence suggests that the gut microbiota may also regulate brain function and behavior. Results from animal models indicate that disturbances in the composition and functionality of some microbiota members are associated with neurophysiological disorders, strengthening the idea of a microbiota-gut-brain axis and the role of microbiota as a"peacekeeper" in the brain health. It is now clear that the gut-brain communication is bidirectional. On one hand, changes in the microbial community affect behavior. On the other hand, perturbations in behavior alter the composition of the gut microbiota. Since changes in the composition of the gut microbiota are associated with the behavioral and cognitive alterations, a healthy microbiota community is essential for a normal regulation of the microbiota-gut-brain axis. Among the potential factors regulating the axis, microbial metabolites may be the major mediators. Seven million traumatic brain injuries (TBIs) occur each year in the many countries. One of the most common sequelae in patients exposed to TBI is post-traumatic brain syndrome, which is especially common following mild TBI. And the common one is depression.Depression is governed by the intricate interplay between sleep wake homeostasis and circadian rhythms in the body. These rhythms are largely controlled by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. Clock genes form the molecular machinery of this circadian system, operating via autoregulatory feedback loops.

Among the vertebrate peripheral tissues that express circadian rhythms is the gastrointestinal system, which exhibit circadian rhythms in gene expression (including clock genes), motility and secretion in vivo and in vitro. These rhythms depend upon a patent molecular clock and they are also coordinated by SCN input via the sympathetic nervous system.

The emerging role of the gut microbiome as an important modulator of gastrointestinal function has recently included the role of circadian rhythms. Recent studies have suggested that microbial signaling plays a critical role in homeostatic maintenance of intestinal function along with the host circadian mechanism.