[Asymmetrical gap junctions in the fish brain (author's transl)]

Morphologically asymmetrical or symmetrical gap junctions are to be distinguished from each other by two features, first, by the distribution of amorphous electron dense cytoplasmic material and, second, by the presence or absence of vesicles. Morphologically asymmetrical gap junctions are therefore characterized by the presence of submembranous material only on one side of the contact. The distribution of this material along the synaptic membrane reveals different forms. In vertebrates, vesicles if present occur only on the opposite side of the junction. Comparing morphologically symmetrical and asymmetrical gap junctions with electrophysiologically rectifying or non-rectifying synapses it has to be stated that a correlation is not possible at this time. In a topografic sense it can be noted that dendrodentritic electric synapses are always symmetrically built, whereas axosomatic and axodendritic junctions are often asymmetrically formed.