The supraependymal fibres (SEF) of the mouse brain. as visualized by the Golgi method

The well-known Golgi method, which impregnates, among other elements, unmyelinated fibres, has been proved suitable to visualize a dense plexus of very winding and smooth axonal processes lying all over the ventricular surface of the mouse brain. Comparisons with other cytochemical studies correlate quite well the pattern of distribution of these supraependymal fibres (SEF), and allow the characterization of most of these axons as serotoninergic. Combining thick sections, selective impregnation and well-defined plane of section, a restricted exit zone of the SEF in the fourth ventricle has been found over the raphe dorsalis region, which is known from previous studies to represent the main site of origin of serotoninergic fibres in the brain. However, this fact does not exclude the possibility of other pathways, yet to be discovered.