[Radioautographic study of "in vitro" incorporation of [3H]-hydroxyindoles and [3H]-melatonin into the pineal organ of the pigeon].

In the pigeon pineal organ studied in vitro, high resolution radioautography was used to visualize the sites of uptake and retention of [3H]-indoles: --incubation of the pineal organ with [3H]-5-hydroxytryptophan ([3H]-5-HTP) during the day and with [3H]-5-hydroxytryptamine ([3H]-5-HT) during the night led to strong selective labelling of the receptor line cells (RLC) which correspond to modified photoreceptor cells (rudimentary photoreceptor cells). No significant radioautographic reactions were found in other cell types. When the 20 min radioactive signal was followed by 20-100 min post-incubation in a cold medium, labelling was still restricted to RLC. The in vitro study of indole metabolism sites might be facilitated by this preparation. --labelling after [3H]-melatonin incorporation was found mainly in RLC but also in interstitial cells. Reactions were less intense than those obtained with [3H]-hydroxyindoles although some erythrocytes were strongly labelled. No definite conclusion can be drawn from the radioautographs, in which artefacts were apparent.