Myxophytes : Neurotoxic Manifestations

Blooms of blue-green algae are frequently associated with fatal episodes of aquatic fauna. Cyanobacteria produces two types of toxins : cytotoxins & biotoxins (neurotoxins and hepatotoxins). Neurotoxicity are, by and large, secreted by certain species of Anabaena, Aphanizomenon, Oscillatoria and Trichodesmium. Of these neurotoxins, saxitoxin (STX) and neosaxitoxin, also termed as 'aphantoxins' are produced by Aphanizomenon flos-aquae. Anatoxin-a (ANTX-a) is an alkaloid neurotoxin produced by Anabaena flos-aquae, A. spiroides and Oscillatoria. The LD50 in mice is about 200 µg/kg body weight as against 10 µg/kg dosages of aphantoxins. Mice injected intraperitoneally with lethal doses of ANTX-a die from respiratory arrest within some minutes showing symptoms like muscle fasciculation, heavy abdominal breath, cyanosis, convulsions and collapse. Another neurotoxin - Anatoxin-a(s) {ANTX-a(s)} has similar characteristics to an organophosphate insecticide, being a potent inhibitor of cholinesterase. On treatment with 20 µg/kg bw of dosage (LD50) animals show marked salivation, mucoid nasal emancipation, ataxia, diarrhea, dyspnea and cyanosis. Anatoxin-b (ANTX-b), a neurotoxin with acetocholinesterase activity; is more toxic than anatoxin-a and a(s). However, its exact nature and pharmacological action have yet to be worked out