Biosemiotics as a theoretical framework to approach the human gut-microbiota-brain-axis
Rebeca Méndez-Veras & Òscar Castro
The human brain has approximately 86-100 billion neurons; however, the enteric nervous system has an estimated 200 million neurons, which is why our gut is called the “second brain”. Both systems connect through several sensors, microbes, and cells (Sarkar et al., 2018); host and microbiota interact continuously.
The gut-microbiota-brain-axis (GMBA) is a communication network which engages in a constant and complex dialogue. It connects the central nervous system (CNS) and the gastrointestinal tract. The brain, immune cells, and gut microbes communicate through signaling pathways and soluble factors such as cytokines, central lymphatic vessels, vagal connections, amino acids, neurotransmitters, hormones, and neuroactive metabolites (Sarkar et al., 2018). These communication elements can directly affect the gut, CNS, and immune system and indirectly affect the brain. Despite some disagreement, several studies have shown that the gut microbiota influences cognitive functions (Sarkar et al., 2018).
In this study, we present biosemiotics as a theoretical framework to explain the biocommunication occurring in the GMBA. We will use tryptophan-serotonin signaling as an example of neurotransmission and examine how Jesper Hoffmeyer´s semiotic scaffolding is one of the best ways to approach semiosis in this pathway. Do microbes communally work with host cells? Is their behavior part of a “shared agenda” (Hoffmeyer, 2014) or are they capable of making individual decisions? Is health, a continuous peaceful coexistence (as Hoffmeyer says) between the host homeostatic mechanisms and microbes? Is a disruption in this “blissful state” what leads to disease, to cognitive impairment? These are some of the questions that we pretend to answer, and that will lead us to reframe others as the ones proposed by those working on research regarding the use of pro(psycho)biotics as therapeutics.
As pointed out by Sharov and Vehkavaara (2015), “Biosemiotics should include both object-agent and meta-agent perspective in studying signs processes in living organisms” and “the importance of studying molecular interactions through biosemiotics terminology gives us a wider view of the problem” (Sharov & Vehkavaara, 2015). A holistic approach is the only path to truly understanding the human-microbiome interconnection, and biosemiotics is a wonderful framework to provide it.
References
Hoffmeyer, J. (2015). Semiotic Scaffolding of Multicellularity. Biosemiotics 8, 159–171. https://doi.org/10.1007/s12304-015-9231-6
Sarkar A, Harty S, Lehto SM, Moeller AH, Dinan TG, Dunbar RIM, Cryan JF, Burnet PWJ (2018). The Microbiome in Psychology and Cognitive Neuroscience. Trends Cogn Sci. Jul;22(7):611-636. doi: 10.1016/j.tics.2018.04.006. Epub 2018 Jun 12. PMID: 29907531.
Sharov, A.A., Vehkavaara, T. (2015). Protosemiosis: Agency with Reduced Representation Capacity. Biosemiotics 8, 103–123. https://doi.org/10.1007/s12304-014-92197