Localization of 5-hydroxytryptamine and protein(s) in the secretion granules of the rudimentary photoreceptor cells in the pineal of Lacerta.

In order to localize 5-hydroxytryptamine (5-HT) stores, the pineal organ of Lacerta was examined by electron microscopy following argentaffin and chromaffin reactions. The results obtained with these ultracytochemical reactions were correlated with those obtained previously using the Falck and Hillarp method and electron microscopic radioautography. The secretion granules (diameter: 60-340 nm) of the secretory rudimentary photoreceptor (SRP) cells are the locus of the argentaffin and chromaffin reactions. The reactivity of the granules disappeared after p-CPA or reserpine administration and increased after nialamide injection. From the previous and present results it can be concluded that 5-HT in the pineal organ of Lacerta is stored in the secretion granules of SRP cells and coexists with a proteinaceous and/or possibly a glycoproteinaceous component. Whether this secretion is neurohormonal in nature is still not clear.