Five toxins (T1-T5) have been isolated from a crude acidified ether extract of unialgal cultures of the dinoflagellate Gymnodinium breve Davis using techniques of column, liquid and thin layer chromatography. Electrophysiological studies using the spontaneously active ventral nerve cord preparation of the crayfish showed that two of the fractions, T2 and T4 caused excitation to more than 250% of control levels at a concentration of 0·05 ng/ml. A blockage of firing occurred at higher concentrations. Fractions T1, T3 and T5 produced gradual excitation only at the higher concentrations. T2 and T4 at a concentration of 250 ng/ml also produced excitation and irregular firing in central neurons from Aplysia californica. Studies on the effect of purified toxins on total choline incorporation in C61A rat glia clone cultures indicate that toxins T2-T5 increase lipid vs nonlipid choline metabolites, presumably by base exchange stimulation. Only T2 stimulated choline uptake in this system.
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