Morphological, cytochemical, and cytofluorimetric features of supramedullary neurons of the fish Solea ocellata

Various teleost species belonging to different orders possess a particular neuronal system, formed by giant supramedullary neurons (SNs). In some species SNs are scattered along the spinal cord, while in others SNs are organized in a compacted and well-defined cluster located at the boundary between the medulla oblongata and spinal cord. Besides many morphological, physiological and histochemical studies performed both in vivo and in vitro by several authors since the end of the 19th century, quantitative microfluorometric evaluation of the DNA content of SNs showed that clustered SNs but not aligned SNs have a DNA content much greater than normal 2C. Such a high DNA content is exceptional for vertebrate neurons. In the present study, we extend this analysis of SNs to the fish Solea ocellata. Our results show that the organization of SNs of S. ocellata are neither strictly aligned or clustered SNs, but somewhere in between, in both their morphological characteristics and DNA content values. Interspecific differences in the distribution and morphology of SNs may reflect functional differences, possibly related to environmental and/or behavioral differences among species. Furthermore, some possible functional significance of endoreplication in SNs is discussed.