Thinking with your belly: microbes in the gut affect mental health

10/06/2020

Mental health, which consists of our emotional, psychic, and social well-being, affects the way we feel and deal with life's problems. Our emotional state is regulated by chemicals known as neurotransmitters, which are produced naturally in various parts of our body and travel through the bloodstream to the brain; their main function is to transmit information from one neuron to another.

Belly Thinking: Intestinal Microbes Affect Mental Health
Belly Thinking: Intestinal Microbes Affect Mental Health

One of the most important neurotransmitters is serotonin. Low levels of serotonin produce behavioral disorders such as depression, anger control problems, obsessive-compulsive disorders, sleep problems, and in extreme cases can lead to suicide.

Commonly used antidepressants, known as SSRIs (Selective Serotonin Reuptake Inhibitors), inhibit serotonin receptors to prevent serotonin from decreasing and failing to fulfill its mood control function in the brain.

The first known drug with these characteristics was fluoxetine or Prozac (its first brand name). It is used to treat depressive disorders, obsessive-compulsive disorders, bulimia nervosa, etc.

Another important neurotransmitter is gamma amino-butyric acid, also known as GABA, which inhibits other neurotransmitters that cause anxiety and, consequently, helps to maintain a relaxed state. Some painkillers such as diazepam (known by its trade name Valium) increase the effects of GABA.

When a person undergoing psychological treatment has consumed medication for a long time, he or she may have adverse reactions and develop resistance or dependence. Therefore, alternative treatments to conventional psychiatric medicine have been sought to regulate neurotransmitters, and it turns out that the link between microorganisms in the digestive system and the brain may be the key.

The intestinal flora and happiness

The human body is home to billions of microbes; most of them do not cause any harm and subsist in harmony with us. For example, the microorganisms that reside in our gastrointestinal tract are necessary for proper digestion and nutrition. Microbes have also been found to secrete neurotransmitters, such as serotonin, GABA, and catecholamines (which function similarly to serotonin), among others.

A study conducted at the Farncombe Institute for Family Digestive Health in Canada showed that mice with anxiety, depression, and abnormal stress response had low diversity in intestinal microbial composition. These behavioral alterations could be transferred to healthy mice through a fecal transplant.

If our intestines have low microbial diversity, it is likely that we suffer from depression and other mood disorders. The good news is that there are bacteria in the intestine that function as antidepressants. Especially some species of bacteria of the genera Lactobacillus and Bifidobacterium can cause organisms to have less depression and anxiety in model animal experiments. This was instrumental in the development of "psychobiotics", which have the potential to be used as psychological treatment.

An encouraging alternative

Tests have been conducted to find out if psychobiotics work better as a probiotic or as a prebiotic. Probiotics are living microorganisms that confer a health benefit when administered in adequate amounts, while prebiotics are selectively fermented ingredients that result in changes in the composition of the gastrointestinal flora, generating health benefits.

Psychobiotics administered as a probiotic do not work well, but their use as a prebiotic is encouraging. Influence on neurotransmitters in mice has been achieved with an effect on behavior through their feeding. In humans, it has been possible to positively modulate mood and anxiety through pre and probiotics, but in depressive patients, there are no published studies yet.

The use of probiotics for psychiatric treatment is encouraging, though still experimental, alternative. Despite advances in the characterization of bowel-brain relationships, much remains to be known.

The dream of consuming chocolate with a psychobiotic effect to prevent depression is still not scientifically substantiated.

This is a collaboration of Georgina Valdez Varela, who works with microbial genomics, mainly in the study of the obligatory essential genes of bacteria of the Vibrionaceae family. She studied a Master's degree in Science at CIAD, in the Mazatlán Regional Coordination.

This article was supervised by Dr. Beatriz Yáñez Rivera and Dr. Francisco Neptalí Morales Serna, professors at CIAD Mazatlán.