Retention of indoles in the pineal organ of the bird (Melopsittacus undulatus, Shaw) during its preparation for radioautographic study

Since high-resolution radioautography (dipping technique) might be very useful for the study of indole metabolism in the pineal cells, the retention of 3H]-indoles has to be examined during the preparation of specimens for electron microscopy (EM). The pineal organ of the parakeet (Melopsittacus undulatus) was used in the present work. 1) Indole metabolism: following uptake of 3H]-5-hydroxytryptophan (3H]-HW) in vivo and 3H]-5-hydroxytryptamine (3H]-HT) in vitro in similar seasonal and nycthemeral conditions--all the known pineal indolic metabolites were recovered by thin layer chromatography. 3H]-5-methoxyindoles were also formed from 3H]-melatonin (3H]-aMT). 2) The radioactivity of fluids used in the processing of pineal organs in EM was determined by liquid scintillation counting: (a) no exogenous 3H]-indoles could be revealed in EM solutions after 3H]-HW in vivo uptake. (b) 8.8 to 13.4% of 3H]-indoles were washed out by glutaraldehyde after 3H]-HT in vitro uptake. (c) most of the 5-methoxyindoles after in vitro uptake of 3H]-aMT were lost in glutaraldehyde. Our chromatography procedures did not permit the identification of 3H]-indoles extracted by the glutaraldehyde fixative. In previous experiments, 3H]-HW and 3H]-HT uptake showed the presence of selective radioautographic reactions in the cells of the receptor line; however, silver grains were scarce and diffusely distributed in the pineal parenchyma after 3H]-aMT uptake.