Gut-Brain Axis, Part II – Nausea
By: Brooklyn A. Bradley, BS; Medically edited by Dr. Deena Kuruvilla, MD
The gut-brain axis is a communication network that links the enteric and central nervous systems. The components linking the gut and the brain include the autonomic nervous system, hypothalamic-pituitary-adrenal (HPA) axis, and nerves within the gastrointestinal (GI) tract [1]. Nausea is a common complaint of GI conditions, and can often accompany migraine. In today’s blog post, we will dive deeper into the gut-brain axis, and how it is connected to nausea.
The autonomic nervous system is a part of the peripheral nervous system, and regulates involuntary physiologic processes including heart rate, blood pressure, digestion, and respiration [2]. There are three divisions of the autonomic nervous system: sympathetic, parasympathetic, and enteric. The enteric nervous system is responsible for the regulation of digestive processes, and is responsible for some of the bidirectional communication that occurs in the gut-brain axis [2]. Feedback from the autonomic nervous system occurs at a subconscious level, which then leads to other actions in the visceral (internal organs and blood vessels) or somatic (muscles, bones, and soft tissue) portions of the body [2]. The autonomic nervous system has a major role in nausea and vomiting [3]. The GI vagus nerve afferent fibers are considered the first-line defense when the body encounters a stimulus [4]. When the neurons involved in this vagus pathway detect toxins in the GI tract, they transmit this information to the brain which leads to nausea and vomiting [4].
The HPA axis is a system of neuroendocrine (makes hormones and releases them into the bloodstream) pathways that functions to maintain physiological homeostasis, which is the body’s way of maintaining stability by adjusting to conditions that are best for its survival. To maintain this, the body may adjust its blood glucose level or core temperature, for example [5]. The HPA axis regulates metabolism, immune responses, and the autonomic nervous system. The HPA axis is involved in the hormonal changes associated with nausea [3]. When there is dysfunction in the HPA axis, it can lead to symptoms including pain, headache, stomach pain, nausea, and vomiting [6].
In conclusion, changes to the communication between the autonomic nervous system, HPA axis, and nerves within the GI tract can lead to not only functional GI disruptions, but also psychological comorbidities. When there are alterations in the composition of gut bacteria, it can also impact cognitive function. Thus, there are many factors that can affect the bidirectional communication between the brain and the gut, leading to symptoms such as nausea and vomiting.
References:
- Appleton J (2018) The Gut-Brain Axis: Influence of Microbiota on Mood and Mental Health. Integr Med (Encinitas) 17:28–32
- Waxenbaum JA, Reddy V, Varacallo M (2023) Anatomy, Autonomic Nervous System. In: StatPearls. StatPearls Publishing, Treasure Island (FL)
- Abell TL, Parajuli D (2017) Nausea and Vomiting Related to Autonomic Nervous System Disorders. In: Koch KL, Hasler WL (eds) Nausea and Vomiting: Diagnosis and Treatment. Springer International Publishing, Cham, pp 89–107
- Horn CC (2014) The medical implications of gastrointestinal vagal afferent pathways in nausea and vomiting. Curr Pharm Des 20:2703–2712. https://doi.org/10.2174/13816128113199990568
- Sheng JA, Bales NJ, Myers SA, et al (2021) The Hypothalamic-Pituitary-Adrenal Axis: Development, Programming Actions of Hormones, and Maternal-Fetal Interactions. Front Behav Neurosci 14:601939. https://doi.org/10.3389/fnbeh.2020.601939
- Kozlowska K, Scher S, Helgeland H (2020) The HPA Axis and Functional Somatic Symptoms. In: Kozlowska K, Scher S, Helgeland H (eds) Functional Somatic Symptoms in Children and Adolescents: A Stress-System Approach to Assessment and Treatment. Springer International Publishing, Cham, pp 161–173