ASTROGLIAL PATTERN IN THE SPINAL-CORD OF THE ADULT BARBEL (BARBUS-COMIZA)

The distribution and the structural, ultrastructural and immunohistoch emical characteristics of the astroglial cells in the spinal cord of t he adult barbel (Barbus comiza) have been studied by means of metallic impregnations (Golgi and gold-sublimate), immunohistochemical (GFAP a nd vimentin) and electron microscopic techniques. GFAP-positive cells were mainly distributed in the ependyma and in the periependymal regio n, but they have also been observed at subpial level in the anterior c olumn. The ependymocytes were heterogeneous cells because they showed different immunohistochemical characteristics: GFAP-positive, vimentin -positive or non-immunoreactive cells. The radial astrocytes showed on ly GFAP immunoreactivity, and their processes ended at the subpial zon e forming a continuous subpial glia limitans. Desmosomes and gap junct ions between somata and processes of radial astrocytes were numerous, and a relationship between radial astroglial processes and the nodes o f Ranvier was also described. The perivascular glia limitans was poorl y developed and it was not complete in the blood vessels of the periep endymal zone; in this case, the basal lamina was highly developed. An important characteristic in the barbel spinal cord was the existence o f a zone with an abundant extracellular space near the ependyma. The p resence of radial astroglial somata at subpial level, the existence of vimentin-positive ependymocytes and the abundant extra-cellular space in the periependymal zone is discussed in relation to the regeneratio n capacity and the continuous growth showed by fish. Moreover, the abu ndance of gliofilaments and desmosomes leads us to suggest that mechan ical support might be an important function for the astroglial cells i n the barbel spinal cord.