Fine structure of nerve-melanophore contacts in the angelfish Pterophyllum scalare.

Contacts between small unmyelinated nerve fibres and dermal melanophores of the angelfish, Pterophyllum scalare, exhibit several features characteristic of synapses, including small synpatic vesicles and dense core vesicles, a narrow synaptic cleft, electron-dense material at the postsynaptic membrane (cell membrane of the melanophore) and, occasionally, presynaptic densities. An analysis of serial thin sections shows that the synapses described here represent varicosities of an otherwise more or less straight nerve fibre. A single axon thereby may form several en passant synapses with a single melanophore. It is suggested that the synaptic contacts described here not only represent sites of transmitter release but also play a role as sites of firm attachment between nerves and melanophores which guarantee a stable arrangement of nerve fibres and melanophores.