the agonists serotonin , 5-methoxytryptamine , bufotenine , and tryptamine display threefold lower affinities for s2 serotonin receptors in the presence of 10 ( -4 ) m gtp or gpp ( nh ) p than in the absence of the nucleotides .
C0036751
serotonin
C0000589
5-methoxytryptamine