Indoleamines in the pineal complex of Lampetra planeri (Petromyzontidae). A fluorescence microscopic and microspectrofluorimetric study.

Using the technique of Falck and Hillarp, the pineal and parapineal organs of Lampetra planeri were found to exhibit a labile yellow fluorescence characteristic of indoleamines. Microspectrofluorimetric analysis of the yellow fluorophores yielded emission and excitation spectra very similar to those of the melatonin precursors serotonin (5-HT) or 5-hydroxytryptophan (5-HTP). 5-HT/5-HTP fluorophores are concentrated essentially in the region of the atrium, along the pineal tract and in the rostral part of the parapineal organ. The fluorescence is strong in early autumn, decreases in winter and is weak or absent in spring, implying a seasonal variation in indoleamine metabolism. Fluorescence intensity increases after injections of nialamide or nialamide and 5-HTP and is lowered by injection of reserpine. Indoleamine fluorescence is localized in the recently identified sensory-type cells: the photoneuroendocrine cells (Meiniel, 1980). The ependymal-like cells, the sensory neurons and the classical photoreceptor cells (Collin, 1969 a) do not appear to be involved in indole metabolism. The absence of catecholamine fibres in the perivascular spaces suggests that indole biosynthesis is regulated via the direct photosensitivity of the pineal complex.