 it acts as an inhibitory heteroreceptor) including, but probably not limited to dopamine, GABA, acetylcholine, noradrenaline, histamine and serotonin.The gene sequence for H3 receptors expresses only about 22% and 20% homology with both H1 and H2 receptors respectively.There is much interest in the histamine H3 receptor as a potential therapeutic target because of its involvement in the neuronal mechanism behind many cognitive H3R-disorders and especially its location in the central nervous system.