Scientists have discovered a unique receptor in the adult brain that helps regulate moods. The receptor occurs in a region called the “medial habenula” which is also involved in nicotine addiction and pain.
N-methyl-D-aspartate (NMDA) receptors are involved in directing brain function and requires two different neurotransmitter molecules to bind to it and become activated, namely:
This particular receptor that was found only needs glycine to activate it. This may be a big reason why some react adversely to glycine and others not.