ULTRASTRUCTURAL CYTOCHEMISTRY AND PHARMACOLOGY OF 5-HYDROXYTRYPTAMINE IN ADRENERGIC NERVE ENDINGS. III. SELECTIVE INCREASE OF NOREPINEPHRINE IN THE RAT PINEAL GLAND CONSECUTIVE TO DEPLETION OF NEURONAL 5-HYDROXYTRYPTAMINE

¹ Instituto de Anatomía General y Embriología and Cátedra de Farmacologia, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, República Argentina

Pineal glands of rats treated with p-chlorophenylalanine and desmethylimipramine were studied with biochemical and electron microscopic cytochemical techniques. Both drugs deplete the pool of pineal 5-hydroxytryptamine (5-HT) localized in the adrenergic fibers which innervate the gland. The cores demonstrating a cytochemical reaction for 5-HT disappeared from the glands of treated rats. However, catecholamines were detected cytochemically in the nerves. After treatment with either drug there was an increase in pineal norepinephrine (NE) as determined fluorimetrically. This increase, which was well established 24 hours after the first injection, was maintained by prolonging the treatment and was not affected by decentralization of both superior cervical ganglia. Under conditions in which pineal NE was increased, no variations were observed in the content of NE of other sympathetically innervated organs. This increase is most probably the result of an enhancement of NE synthesis triggered by disappearance of 5-HT from the vesicles. The results obtained support the hypothesis that both NE and 5-HT coexist in the nerve vesicles of pineal adrenergic fibers.