Gap junctions and septate-like junctions between neurons of the opisthobranch mollusc Navanax inermis

The buccal ganglia of Navanax inermis were studied by thin section, lanthanum infiltration and freeze fracture. Freeze fracture clearly demonstrates small gap junctions between neuronal processes in the neuropil, many of which are known to be electrotonically coupled. Junctional particles cleave with the P-face. In thin section, gap junctions appeared as small blurred contacts, presumably because of the small size of the junctions. Lanthanum infiltration was poor and failed to aid in identifying gap junctions. However, it did reveal septate-like junctions whose septa were not osmiophilic. Corresponding E-face grooves and ridges were seen in freeze fracture, sometimes adjacent to gap junctions. The septate-like junctions have parallel membranes and may have been mistaken for gap junctions in several other thin section studies of invertebrate neurons.