Characterization of a novel effect of serotonin 5-HT_1A and 5-HT_2A receptors: Increasing cGMP levels in rat frontal cortex

Elucidating the mechanisms of action of hallucinogens has become an increasingly important area of research as their abuse has grown in recent years. Although serotonin receptors appear to play a role in the behavioral effects of the phenethylamine and indoleamine hallucinogens, the signaling pathways activated by these agents are unclear. Here it is shown that administration of serotonin (5-hydroxytryptamine, 5-HT) increased cyclic guanosine monophosphate (cGMP) production in frontal cortical slices of rat brain. The effect of 5-HT was greater than that of N-methyl-D-aspartate (NMDA), a stimulant of cGMP formation in the central nervous system. The 5-HT _2A/2C receptor phenethylamine agonist, 2,5-dimethoxy-4- methylamphetamine (DOM), increased cGMP content in the slices. Additionally 8-hydroxy-2-(di-n-propylamino)tetralin (DPAT), a 5-_HT1A/7 receptor agonist also increased cGMP production. Stimulation of cGMP formation by DOM was prevented by a 5-HT_2A/2C receptor antagonist, pirenperone, as well as by a 5-HT_2A receptor selective antagonist, MDL100907. A 5-HT_2C receptor antagonist, SB242084, did not block the effect of DOM. Stimulation of cGMP production by DPAT was blocked by the 5-HT _1A receptor antagonist, WAY100635. Stimulation of cGMP formation by serotonin could be prevented by pirenperone orWAY100635. In summary, activation of serotonin 5-HT_1A and 5-HT_2A receptors increase brain cGMP levels.