Synaptic structure of the lateral line lobe nucleus in mormyrid fish.

Electron microscopical observations reveal a complex synaptic structure (Fig. 1) in the nucleus of the lateral line lobe (nLLL). Different types of axosomatic and axoaxonic synapses are demonstrated to be in contact with the large cells. The results furnish morphological evidence for electrotonic transmission (by way of club endings with gap junctions) at this level of the electrosensory pathway of mormyrid fish. A new ultrastructural finding is the existence of presynaptic gap junctions on the unmyelinated surface area of the club endings.