Date of Award

Fall 1980

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

Abstract

Toxic cyanobacteria bloom in eutrophic, freshwater lakes and ponds and may cause environmental, health and recreational problems during or after the massive growth of these microorganisms Microcystis aeruginosa is commonly involved in freshwater blooms and one of its toxins (microcystin) causes liver damage in birds and mammals. This study has determined the specific site of action of microcystin and characterized the hepatic damage at the ultrastructural level. Histological changes in centrilobular regions of liver tissue were noted after intraperitoneal administration in mice. Hepatic sinusoidal epithelial and hepatocyte plasma membranes ruptured with the release of cellular components that pooled with blood. Mitochondria appeared swollen but there were no obvious distortions of other organelles. Extensive vesiculation of membrane fragments was observed. Hepatic damage caused massive hemorrhaging into the liver where blood and cell debris accumulated and produced a significant increase in liver weight.

Primary cultures of hepatocyte microexplants from pre- and postnatal mice and rats were exposed to microcystin but in vitro effects were not observed. In vitro experiments demonstrated that young animals were not sensitive to the toxin but developed sensitivity as they matured.

Microcystin was shown to be very specific in its site of action since it had no antibiotic activity against green algae, yeast, or bacteria and was non-toxic to certain zooplanktors, crustacea, amphibians and teleosts. Electrical or mechanical activity in isolated nerve, nerve-muscle and cardiac preparations also was not effected. The toxins employed in this study came from cultured cells and naturally occurring blooms and gave identical results in all experiments.

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