Anatomie und Histologie der Schwimmblase des Fluss�arsches (Perca fluviatilis) mit besonderer Ber�cksichtigung des Ovals

Ultrastructure and innervation of the swimbladder of Tetractenos glaber (Tetraodontidae)

The general structure, ultrastructure and innervation of the swimbladder of the smooth toadfish, Tetractenos glaber, were examined with light-microscopic, fluorescence-histochemical, and transmission electron-microscopic techniques. The structure of the swimbladder is similar to that of other euphysoclists. Fluorescence histochemistry showed adrenergic fibres in both the secretory and resorptive areas of the swimbladder. Transmission electron microscopy revealed two morphologically distinct axon profiles: type-I profiles containing many small, flattened vesicles; type-II profiles containing both large, granular vesicles and rounded, small clear vesicles in varying proportions. The gas-gland cells and surrounding muscularis mucosae are innervated by both type-I and type-II fibres. Type-I fibres also innervate pre-rete arteries. The rete- and gas-gland capillaries do not appear to be innervated. Arteries running to the resorptive area are innervated by type-I fibres. Both type-I and type-II profiles make contact with the muscularis mucosae in the resorptive area. Only type-I fibres innervate the radial dilator muscle in the oval sphincter region, whereas only type II fibres innervate the circular muscle of the oval sphincter. Type-I fibres took up alpha-methyl-noradrenaline, and could not be found after pre-treatment with 6-hydroxydopamine. They are, therefore, assumed to be adrenergic. Type-II fibres were tentatively identified, by exclusion, as cholinergic.

Layered membranes: a diffusion barrier to gases in teleostean swimbladders

Flattened cells are dispersed in an overlapping fashion within the submucosa of closed (physoclistous) swimbladders. Within the cells are located round platelets best seen by phase or interference type microscopy. At the electron microscope level the platelets are revealed as repeated, numerous layers of membranous discs. Each disc is a bilayer with an enlarged rim. The bilayer is strongly and preferentially reactive to osmium tetroxide. Swimbladder walls are known to be highly resistant to passage of gases. The randomly disposed platelets with the highly ordered layering of membranes may provide that physical resistance to gas movement.