ULTRASTRUCTURAL CYTOCHEMISTRY AND PHARMACOLOGY OF 5-HYDROXYTRYPTAMINE IN ADRENERGIC NERVE ENDINGS. II. ACCUMULATION OF 5-HYDROXYTRYPTAMINE IN NERVE VESICLES CONTAINING NOREPINEPHRINE IN RAT VAS DEFERENS

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

To study the localization of 5-hydroxytryptamine:(5-HT) in the adrenergic nerve endings of rat vas deferens, biochemical and electron microscopic cytochemical techniques were applied to slices from the organ incubated in vitro with different concentrations of the amine. Exogenous 5-HT was detectable cytochemically within nerve fibers when its concentration in the medium was 5.6 x 10^-4M or higher. Cell fractionation studies indicated that the amine was concentrated in the microsomal fraction paralleling the distribution of endogenous norepinephrine. Moreover, norepinephrine was depleted from intact slices and from the microsomal fraction depending on the 5-HT accumulated, which in turn was a function of the exogenous 5-HT in the medium. The participation of adrenergic nerves in the process of 5-HT accumulation was confirmed by the reduction in this incorporation after chemical sympathectomy with 6-hydroxydopamine. These results indicate that under special conditions, exogenous 5-HT is incorporated into adrenergic nerves where it may be detected cytochemically without a significant depletion of endogenous norepinephrine. The existence of a "common vesicular storage" mechanism by which both amines are stored in the same morphologic entity in adrenergic postganglionic fibers is supported by these studies.