GABA appears to be an inhibitory transmitter in the brain and spinal cord. Histidine is the precursor of histamine. Functions of histamine Histamine is a potent vasodilator and may be a neural transmitter. It is released during allergic reactions. Antihistamine drugs are compounds that bear a structural similarity to histamine and can prevent the physiologic changes that it normally produces.
Histidine decarboxylase catalyzes the formation of histamine from L-histidine.