High affinity binding of red tide neurotoxins to marine mammal brain

During a period of several weeks in the spring of 1996, over 200 manatees ( Trichechus manatus latirostris) were found dead or dying in coastal waters or on beaches of the Florida west coast. Concurrent with this event, high d ensities of Gymnodinium breve, the dinoflagellate which produces the potent neurotoxin called brevetoxin, were observed in the same coastal areas. Our study demonstrates that brevetoxin binds to isolated nerve preparations fr om manatee brain with similar affinity as that reported for a number of ter restrial mammals. Analysis of receptor binding of tritiated brevetoxin to m anatee brain, illustrates saturable specific binding, competition of specif ic binding by a non-radioactive toxin of the same structure, and temperatur e dependence of binding. Complementary studies with the red tide neurotoxin , saxitoxin, which is responsible for the intoxication syndrome paralytic s hellfish poisoning, show high affinity and specific binding of this toxin t o isolated nerve preparations from several marine mammals, including manate e, gray whale (Eschrichtius robustus), humpback whale (Megaptera novaeangli ae), and sea lion (Zalophus californianus). These results demonstrate the s pecific binding of brevetoxin and saxitoxin to excitable brain tissue of ma rine mammals and support the hypothesis that the exposure of manatees to br evetoxin in the spring of 1996 was a factor in their stranding and death. ( C) 1999 Elsevier Science B.V. All rights reserved.