Studies on serotonin-accumulating cells in rabbit retinal cultures

The serotonin-accumulating neurones in rabbit retinal cultures were studied, using immunohistochemistry to localize serotonin. Double-labelling experiments showed that serotonin-accumulating cells in culture and intact retinas react positively to antiserum PGP 9.5, which is neurone-specific. The uptake process of serotonin is very specific; known serotonergic blockers, such as chlorimipramine, abolished transport, while benztropine, a dopamine uptake blocker, was ineffectual. Analogues of serotonin such as tryptamine, tryptophan and 5-hydroxytryptophan at concentrations 100-fold those of exogenous serotonin did not appear to compete with the transport of the amine. Newly dissociated retinal cells from 1-5-day postnatal rabbits which lack processes have the capacity to take up exogenous serotonin; these cells when kept in culture grew processes and appeared to reach maximum development after 6-15 days. Dissociated retinal cells subjected to density centrifugation resulted in the production of an enriched (4-fold) population of serotonin-accumulating cells. Since most of the endogenous serotonin was associated with this fraction, it is concluded that the serotonin-accumulating cells contain serotonin.