The paraventricular organ of mormyrid fish: uptake or release of intraventricular biogenic amines?

The paraventricular organ of Gnathonemus petersii was investigated with light and electronmicroscopical techniques. It contains high concentrations of dopamine, noradrenaline and serotonin, but the synthesizing enzymes are not or hardly present. Consequently, the cerebrospinal fluid-contacting neurons might pick up their biogenic amines from the ventricular fluid. Dense subependymal axonal plexuses in the everted telencephalon probably release these substances into the ventricle. However, electronmicroscopical observations suggest release rather than uptake by the paraventricular organ. The possible significance of intraventricular release, transport and uptake of biogenic amines is discussed.