Poop for thought: Can fecal microbiome transplantation improve cognitive function in aging dogs?

Abstract

Canine cognitive dysfunction (CCD) is the dog version of human Alzheimer's disease (AD), and it has strikingly similar pathological features to those of this neurodegenerative disorder. The gastrointestinal system is in constant communication with the brain via several conduits collectively termed the gut-brain axis. The microbial population of the gut, referred to as the microbiota, has a profound effect on the interactions that occur along this communication route. Recent evidence suggests that dysbiosis, an abnormal gastrointestinal microbial population, is linked to cognitive impairment in rodent AD models and human AD. There is also evidence from rodent AD models that correcting dysbiosis by transferring fecal material from healthy donors to the gastrointestinal tracts of cognitively impaired recipients [fecal microbiome transplantation (FMT)] reverses AD-associated brain pathology and improves cognitive function. Although limited, some clinical reports have described the improvement of cognitive function with FMT in human AD. The goals of this review article are to provide an overview of the mechanisms involved in dysbiosis- associated cognitive decline and the role of FMT in therapy for such decline. The potential role of FMT in CCD is also discussed.

Keywords: Alzheimer’s; Canine; Cognitive; Fecal; Gut–brain axis; Microbiota; Transplantation; dysfunction.

Fig. 1.. Schematic illustration of the IB. The first barrier is the mucosal (mucus) layer composed of water, glycoproteins, and antimicrobial proteins. The second or epithelial layer contains TJs between cells to prohibit the passage of potentially harmful substances and/or pathogens. The final layer is the lamina propria which contains immune cells such as plasma cells and macrophages.

Fig. 2.. Fig. 2. Illustration depicting the major components of the BBB. These components include endothelial cell TJs, astrocyte foot processes, and multifunctional cells called pericytes.

Fig. 3.. Schematic illustration of the GBA. This communication system is a bidirectional circuit composed of both humoral (blood and lymphatic vessels) and neural (primarily vagus nerve, with some contribution from sympathetic pathways) components. A third component (not pictured) is the HPA.