Experimental and structural analysis of the function of saccus vasculosus in rainbow trout, Salmo gairdneri (Richardson)

Summary

Injection of a saccus vasculosus homogenate from sea water adapted rainbow trout into the third brain ventricle of fresh-water rainbow trout increased the survival time of the latter in sea water of high salinity. This indicated an active role of saccus vasculosus in osmoregulation.

Autoradiographic analysis of brains from injected fish that had received a saccus vasculosus homogenate from sea water adapted specimens, in which the coronet cells of saccus vasculosus had previously been labelled with ³H-glucoseamine, revealed actual incorporation of labelled material into brain cells, especially in the hypothalamic region. The intracellular distribution of labelled material in the coronet cells of rainbow trout labelled with ³H-glucoseamine strongly indicates that such material represents a secretory product; it is therefore probable that the observed incorporation of label into brain cells of injected fish actually reflects normal processing of material secreted from the coronet cells.

In the scanning electron microscope, the inside wall of the third brain ventricle of the rainbow trout was in many areas found to be covered with cilia. These apparently serve to keep liquor in circulation. The observation, both in injected and control animals, of free globules among these cilia supports the idea of an intra-ventricular transport of detached coronet cell material to the infundibular recess, as indicated by the autoradiographic analysis.