Assessing Gut‐Brain Interactions on Alcohol Consumption: The Role of Fecal Microbiota Transplantation

Abstract

Microbial representation in the gastrointestinal tract plays an important role in general health and illness. It is known that direct communication pathways exist between the gut and the brain, allowing for reciprocal influence via the gut-brain axis (GBA). The GBA can also be influenced on either side via interactions with the hypothalamic-pituitary-adrenal (HPA) axis and the immune system. Importantly, alcohol consumption has been correlated with changes in the HPA axis and can alter the levels of pro- and anti-inflammatory cytokines, though, the exact alterations are dependent upon the levels of alcohol administered. Additionally, research shows that alcohol consumption is correlated with dysbiosis of the gut microbiome, a condition that may be corrected via fecal microbiota transplantation (FMT). Therefore, this study was designed to assess the interconnected neurobiological impacts of FMT following a moderate alcohol consumption paradigm (drinking-in-the-dark; DID) on corticotropin releasing factor (CRF) and microglial reactivity. Adult male, Sprague-Dawley rats were exposed to alcohol following a repeated DID procedure in order to escalate voluntary consumption. After three rounds of DID, a proton pump inhibitor was provided in a suspension of Vanilla Ensure Plus for voluntary consumption prior to FMT. This was given in order to reduce gastric acid secretion and promote a successful FMT. FMT was administered via oral gavage using fecal samples obtained from either self-donations or those from healthy, non-experimental donor rats. Following FMT, the animals were exposed to a two-bottle choice paradigm with water and a 10% ethanol solution for 14 days to measure alcohol craving. Afterwards, brain tissue was collected, sliced, and stained using immunohistochemical techniques for either CRF as a marker of HPA activation or Iba1 as a marker of microglial reactivity indicative of immune activation. Initial results from a densitometric analysis of CRF expression in the paraventricular nucleus of the hypothalamus (PVN) failed to reveal any significant effects of FMT or alcohol consumption on this aspect of HPA axis activity. Additional quantification of CRF in the central nucleus of the amygdala also failed to demonstrate alterations to CRF levels following treatment. Quantification of Iba1 reactivity in the multiple brain regions and evaluation of the efficacy of FMT is ongoing. Although these initial results were non-significant, the complexity of the potential mechanisms underlying a role for gut health in contributing to excessive alcohol consumption warrants further investigation.