THE STRUCTURE AND DEVELOPMENT OF DOPAMINERGIC INTERPLEXIFORM CELLS INTHE RETINA OF THE BROWN TROUT, SALMO-TRUTTA FARIO - A TYROSINE-HYDROXYLASE IMMUNOCYTOCHEMICAL STUDY

The organisation and development of the dopaminergic (DA) system in th e retina of the adult brown trout were studied with tyrosine hydroxyla se immunocytochemical techniques. Adult DA cells are rather homogeneou s in appearance and possess thick dendritic processes running to the g anglion cell layer and thinner axonal processes which run to the horiz ontal cell layer, where they form a rich plexus of varicose fibres clo sely associated with the surface of these cells. Contact of DA fibres with photoreceptor processes was not observed. We therefore consider t his DA population to consist mainly of interplexiform cells. These cel ls appear late in development, being first observed in prehatching (16 mm) embryos (after photoreceptors have begun to differentiate). DA ce lls increased in number throughout the fry and juvenile stages, but ev en in the largest juveniles studied (30-35 mm) the size of the DA cell population was only about 20% of that in adults. DA cells appear to a rise in the marginal retina. In developing stages (embryos and fry) on ly inner nuclear layer processes were observed, the horizontal cell la yer DA plexus appearing late in development (28 mm juveniles).