Tryptamine and Some Related Molecules Block the Accumulation of a Light-Sensitive Pool of Cyclic AMP in the Dark-Adapted, Dark-Incubated Mouse Retina

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Abstract
Dark-adapted retinas of mice (C57BL/6J) incubated in the dark in media containing 1 mM 3-isobutylmethylxanthine (IBMX) or 5 mM Co2+ accumulate cyclic AMP (cAMP). A portion of this pool is light sensitive, as light can prevent or reverse its accumulation. Similarly, tryptamine, serotonin, 5-methoxytryptamine, bufotenine, and 5-methoxydimethyltryptamine can block the accumulation of the light sensitive pool of cAMP, whereas tryptophan, melatonin, N-acetylserotonin, 5-methoxytryptophol, and tetrahydro-.beta.-carbolines are inactive. The phenomenon is not seen with mutant mouse retinas (rd/rd), which lack most photoreceptors, but persists in abnormal retinas containing photoreceptors but with extensive neuronal depletion in the inner retina. Tryptamine also inhibits cAMP accumulation in either dark or light-adapted retinas exposed to forskolin alone but not in media containing high levels of forskolin plus 1 mM IBMX. There is some suggestion that serotonin 5-HT antagonists can partially reverse the action of the tryptamines, but hitherto undescribed receptors may be involved. Current data suggest that photoreceptors are the target for the action of the tryptamines.