Müller (glial) cells in the retina of urodeles and anurans reveal different morphology by means of freeze-fracturing.

Müller (glial) cells of the retina of various species of amphibia (urodeles and anurans) were investigated by means of the freeze-fracture technique. This was done because Müller cells in anamniotes were believed to differ from those in mammals in that they should lack the so-called orthogonal arrays of particles (OAP) which are a characteristic feature of Müller cells in mammalian retina. However, as we could demonstrate previously (Berg-von der Emde and Wolburg, Glia, 2 (1989) 458), fish retinal Müller cells also contain OAP in their membranes suggesting that OAP are a general marker of Müller cells in all vertebrates. As demonstrated in this study, Müller cells of urodeles (Batrachoseps attenuatus and Pleurodeles waltlii) are OAP-positive, whereas two anurans (Rana esculenta and Xenopus laevis) do not reveal any OAP in their Müller cell membranes. Under phylogenetic aspects, it appears very interesting that frogs are as yet the only vertebrate group that deviates from all other vertebrates in terms of Müller cell membrane morphology.