Probing the function of 5-HT<inf>1B/1D</inf>receptors in psychiatric patients

Pharmacological challenge tests provide a method of assessing the functional responsiveness ofserotonin (5-HT) receptor subtypes in the human brain. A number of selective agonist ligandsfor the 5-HTjj receptor are available for human use; however, these compounds do not distinguish between 5-HT and 5-HTJ[} receptors, which is somewhat of a disadvantage. Acute administration ofsumatriptan, rizatriptan, and zolmilriptan all increase plasma growth hormone in healthy subjects, possibly via activation ofpostsynaptic 5-HT]D receptors. This response is blunted in major depression. Sumatriptan lowers plasma prolactin, perhaps via activation of presynaptic 5-HT1B receptors. This response is not altered during repeated treatment with selective serotonin reuptake inhibitors (SSRIs), suggesting that 5-HTlfi receptors retain the ability to restrain 5-HT outflow during short-term SSRI treatment.