[Epiphyseal epithelium of pigeons under natural conditions and in vitro. Ultrastructure and histochemical evidence of hydroxyindoles in the receptor line cells].

An electron microscopic study of the pineal organ of the pigeon was conducted under natural conditions and after short in vitro incubation or culture. Two cell types could be identified in the epithelium: receptor line cells (RLC) and interstitial cells of the ependymal type. Good preservation of the cells' fine structure could be observed whatever the different incubation times used. RLC display cytological features reflecting the existence of a protein secretory process and of regression of the photoreceptor structures (secretory rudimentary photoreceptor cells). The use of the Falck-Hillarp technique together with specific inhibition of tryptophan hydroxylase enabled to demonstration of the storage of 5-hydroxytryptophan/serotonin in RLC. In contrast with other birds, no catecholamine containing nerve fibers could be observed by histofluorescence.