Catecholamine and serotonin in granulated vesicles of nerve endings in the pineal gland of the rat

p-Chloropherrylalaninc, a drug that selectively inhibits the synthesis of serotooin, has been used in order to invcstigate the localization of this amine in nerves of the pineal gland of rats. Glands of normal and treated rats were studied under the electron microscope, after fixing with osmium tetroxide and glutaraldehyde, and applying specific histochemistry for catechol and indolamines. Fluorometric determinations of scrotonin, noradrenalinc and dopaminc were also made in normal and treated glands. In normal glands about 35 % of granulated vesicles were observed in nerve endings fixed with osmium tetroxide or glutaraldehyde. After treatment with p-chlorophenylalanine the dense core of the granulated vesicles disappeared in glands fixed with glutaraldehyde but remained unchanged or increased in number in those fixed in osmium tetroxide. p-Chlorophcnylalanine produced an 87% decrease in serotonin content of the pineal gland while noradrenalinc and dopamine content did not diminish, The correlation between morphological and biochemical data suggests that both catechol and indolamines are stored in granulated vesicles in the pineal nerves of the rat. This assumption was confirmed with the specific histochemical technique of wood to differentiate catechol and indolamines.