Different drugs that activate the same serotonin receptor (5-HT2AR) can produce distinct patterns of gene expression in the brain, which correspond to different behavioral effects. The hallucinogens DOI and LSD triggered a head-twitch response in mice and produced similar changes in the somatosensory cortex transcriptome, while the nonhallucinogenic drug lisuride did not cause this behavior and generated a different transcriptome fingerprint. These effects were absent in mice lacking the 5-HT2AR, confirming the receptor's role. The findings suggest that drugs acting at the same receptor can induce unique cellular response patterns in the living brain, detectable through transcriptome analysis.
Indole agonists at the human serotonin 5-HT2A receptor achieve differing efficacies through specific hydrogen-bond interactions with serine residues in helices 3 and 5. Serotonin forms hydrogen bonds with Ser3.36 and Ser5.46; methyl-substitution of the cationic primary amine or the backbone N1-amine disrupts these bonds and reduces efficacy. Mutating Ser3.36 to alanine largely eliminates efficacy differences caused by cationic amine substitution, while mutating Ser5.46 to alanine reduces the efficacy loss from N1-amine substitution. Computational modeling shows these interactions shift the agonist's position in the binding pocket, and the indole ring's position correlates with agonist activity. The findings support a mechanism where agonist position, influenced by specific helix interactions, determines receptor activation, likely shared by other class A G-protein coupled receptors.