The morphology and DNA content of the electric lobe neurons in torpedoes (Torpedo marmorata Risso and Torpedo ocellata Rafinesque)

The neurons of the electric lobe of Torpedo (T. ocellata Risso and T. marmorata Risso ) are described at the light and the electron microscope as are the results of cytophotometric analyses of Feulgen-stained nuclei in order to measure the DNA content. The cells show a body with an average diameter of about 90 µm, many dendrites and one axon of about 4µm of diameter. The nucleus is vesicular with one or two nucleoli which can appear displaced into the cytoplasm as an artifact. The nuclear DNA content of the large neurons corresponds to that of red blood cells and therefore the neurons are not polyploid. The ultrastructural features of the electric lobe neurons are: the large number of pores in the nuclear envelope, the abundance of free polyribosomes, the numerous Golgi complexes which can reach the superficial cytoplasm, many neurofilaments and neurotubules, dense granules which can be distinguished in three classes: lipofuscinic granules, lysosomes and myelinic figures. It is suggested that the large size of the electric neurons depends on extention of axon synapse and on the considerable metabolic activity necessary to functionally synapse the neuron after discharge.