Glycoproteins are molecules composed of carbohydrates and proteins. Mucin, for example, is a type of glycoprotein that gives the mucus layer a gel-like consistency.

The term “gnotobiotic” refers to the study of organisms inoculated in a carefully controlled environment containing one or a few types of organisms to observe their influence on the body or brain (Williams, 2014). For example, germ-free (GF) animals become gnotobiotic after being inoculated with one or more specific bacterial strains. This method assists researchers in studying the interactions between microbes and hosts.

Gram-staining is a traditional laboratory technique used to rapidly classify bacterial species into two broad categories: gram-positive and gram-negative, according to their type of cell wall.

Gram-negative bacteria contain outer and inner cell membranes and create pink color colonies upon gram-staining. Most of the gram-negative bacterial species are pathogenic due to the presence of lipopolysaccharides (LPS) on their cell membrane. For instance, E.coli is a gram-negative bacteria in our gut and expresses LPS molecules that participate in the MGBA mechanism.

Gram-positive bacteria do not express LPS and have no outer lipid layer except the thick peptidoglycan layer, which gives purple colonies upon gram-staining. Gram-positive bacteria reside in our gut and carry out essential bodily functions. For instance, Lactobacillus and Bifidobacterium are true probiotics.

Gray matter is a type of neural tissue found in the brain and spinal cord that appears grayish in color. It primarily consists of the cell bodies of neurons and their associated dendrites and synapses. Gray matter is crucial in information processing, decision-making, and sensory perception. In contrast, its counterpart, white matter, consists of myelinated nerve fibers that facilitate communication between different parts of the nervous system.

The theory proposed in the late 1970s and early 1980s by Jeffrey Gray postulates that people differ in how sensitive they are to rewards and punishments. It is one of the major theories of personality proposing that three systems called behavioral activation system, behavioral inhibition system, and the fight-flight-or-freeze systems determine a wide range of human behavior.

Green spaces refer to areas within urban or rural environments that are primarily covered by vegetation, such as parks, gardens, forests, and natural reserves. These spaces provide numerous environmental, social, and economic benefits, including biodiversity conservation, air and water purification, recreational opportunities, and mental health benefits.

A short-hand way of referring to the gastrointestinal system. In this course, this term most commonly refers to the large intestine and the microbiota inhabiting it.

Dysbiosis is an imbalance in the normal composition and diversity of microorganisms within the gut, which can affect physical health, mental health, and various bodily functions.