[The serotonergic fibers in the striatum. Ultrastructural characteristics (author's transl)]

This paper is a short review of serotonergic (5-HT) fibers in the striatum. Data concerning biochemical demonstrations of striatal 5-HT and tryptophan hydroxylase and of ascending serotonergic pathways are quickly reviewed. This study deals particularly with the morphology of striatal 5-HT fibers. Little information concerning these fibers is available in the literature. Fluorescence histochemistry of 5-HT in the striatum is difficulty used, and ultrastructural studies are rare. In our work (ARLUISON and DE LA MANCHE, 1980), using cerebro-ventricular injections of tritiated serotonin in the rat and autoradiography three types of nerve terminals are labelled along the ventricle. The first has spherical and clear synaptic vesicles and is characterized by rather numerous asymmetrical synaptic contacts. The second has particularly small, often granular, synaptic vesicles of ovoid or tubular shape and shows rare synaptic contacts. The third category of labelled nerve terminals is provides with both of the previously described types of synaptic vesicles and shows few synaptic contacts. The heterogeneity of serotonergic nerve terminals in the striatum is compared to that observed in other regions of the brain, and the possibility of their origin in different midbrain raphe nuclei is discussed.