The following characteristics of the adenosine triphosphatases (ATPase) in the saccus vasculosus were studied in Salmo gairdneri Richardson: 1) distributional pattern, 2) cytochemical properties in relation to different substrates, inhibitors, pH and bivalent metal ions, and 3) ultrastructural localization. Ultracytochemical studies using modifications of the Washstein-Meisel technique showed that within the pH range 7.1-8.0 several Mg++ or Ca++-activated ATPase are localized on the intracellular surface of membranes and in the cytoplasm of ependymal coronet cells and tanycytes ("supporting cells", "Zwischenzellen", glial cells"). The high ATPase activity at the level of the specialized luminal plasma membranes of coronet cell globules and of tanycyte microvilli is discussed in relation to phenomena of active transport and a possible resulting transfer of low-molecular weight substances into and/or from the cerebrospinal fluid (CSF). The localization of ATPase on the specialized membranes of primary vesicles is considered in connection with available structural and enzyme-cytochemical data on a possible function of these cell organelles in storage and release of substances (including Ca++ ions?). The cytoplasmic ATPase activity in coronet cells is ascribed to microtubules and/or possible existing contractile proteins/filaments, presumably concerned with internal transport or motility processes. In tanycytes ATPase activity is believed to be associated with the characteristic microfilamentous system of still unknown function. The ATPase activity in the (9 + 0) ciliary apparatus of globules could not be interpreted in terms of motility. The present study provides further support to the proposed hypothesis of the transport function of the saccus vasculosus, and an extension of the concept in the sense that not only the principal coronet cells, but also the tanycytes of this circumventricular organ are involved in CSF-homeostasis.
The recent idea that fish, like all vertebrates, have emotional brains is based on new evidence about the evolution of the brains of vertebrates, and about homologies between behavioural, neurohormonal and neurostructural features of fish and mammals (humans). Therefore it is now assumed that fish are liable to suffer, and should be slaughtered by methods that induce insensibility by the fastest way, as is required for mammals. Two commercial methods for slaughtering eel, decapitation and brining, were experimentally tested and found inadequate: severed eel heads showed signs of life for up to 8 h; after the brining procedure eels remained alive for up to 18 h. It has been too readily assumed that, like a mammal, a fish is killed immediately by decapitation. The so‐called isolated gill preparation, a standard method for studying various gill functions, but actually involving part of a severed fish head, is one further example of this shallow generalization.
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