20.12.07

Domoic acid - How phytoplankton cause memory loss


  • phycotoxin (algal toxin) produced by marine diatoms of the wonderfully named genus Pseudo-nitzschia
    • diatoms are a type of phytoplankton, microscopic organisms that reside in the world's oceans and lakes and other bodies of water, and are technically classified as algae
  • nomenclature-wise, domoic acid is classified as a kainoid amino acid
    • kainoid amino acids, named after another phycotoxin called kainic acid, are agonists of AMPA/kainate (i.e. non-NMDA) glutamate receptors and exhibit highly potent neuroexcitatory activity
    • glutamate is an excitatory neurotransmitter in the brain, so a glut (ha ha) of domoic acid in the brain results in overexcitation of neurons, leading to neuronal damage
    • neurons in parts of the hippocampus and amygdala are preferentially damaged
  • first isolated from a variety of red algae in Japan in 1958, but not associated with human illness until it was recovered from a batch of mussels that were responsible for an outbreak of 'food poisoning' in eastern Canada in 1987 that affected over 150 people
    • many of the cases featured neurological symptoms including short-term memory loss, leading the illness to be named amnesic shellfish poisoning
    • the whole memory loss thing probably ties in with the fact that the hippocampus is associated with memory storage and is damaged by the toxin
    • marine creatures that consume phytoplankton, including shellfish (primarily filter-feeding molluscs such as mussels, clams, and oysters) and small fish (e.g. anchovies, sardines), can accumulate phycotoxins in their tissues
    • particularly high concentrations are found in these fish and shellfish when toxin-producing phytoplankton are present in high numbers (e.g. during a harmful algal bloom, better known as a red tide, so called due to pigments produced by the phytoplankton)
References
- Jeffery B, Barlow T, Moizer K, Paul S, Boyle C. Amnesic shellfish poison. Food Chem Toxicol. 2004 Apr;42(4):545-57.

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