Specific enzymes for each amino acid called decarboxylases catalyze the release of $ CO_2 $:
The cadaverine produced can be revealed by colored indicators. The reaction is the basis of a medical test to detect bacteria causing cystitis, typhus, pneumonia or cholera.
The serotonin produced is a neurotransmitter. It is transformed in the pineal gland into melatonin that regulates sleep:
The tryptamine produced plays a role in nerve transmission by modulating the effect of serotonin.
The histamine produced plays a central role in the immune response. It makes the walls of capillary vessels permeable to white blood cells and pathogens.
The ethanolamine (2-aminoethane) produced occurs in the composition of most phospholipids that make up the cell walls.
The tyramine produced is widely present in animal or vegetable food. ($ \tau \upsilon \rho $ = cheese!).