Neurotoxins in Marine Organisms

The presence of neurotoxins in marine animals, namely the presence of tetrodotoxin (TTX) in pufferfish, has been studied for a long time and is a cornerstone in our understanding of the function of sodium channels (Sasaki et al. 2007).  Without TTX, the properties of the sodium channel may have eluded scientists for many more years.  Though TTX has been a great asset to the field of neuroscience, we still do not know the mechanism for how the pufferfish acquires this neurotoxin.  Some have implicated it is the diet of the pufferfish that results in the accumulation of TTX (Noguchi et al. 2005).  Evidence to support this hypothesis was found when marine bacteria were found producing the compound (Miyazawa and Noguchi 2001).  It was also found that diet is necessary in order for the pufferfish to maintain its levels of TTX, or it will accumulate an analog (derivation of the same chemical) which has a lower toxicity (Kono et al. 2008; Fig 1).

Figure 1.  Pufferfish need to maintain TTX levels using their diet.  This is a representation of the findings in Kono et al. 2008.  Some pufferfish were injected with a stable analog and some with a pure form of TTX.  As time progressed, those injected with pure TTX could not maintain the level without the proper diet.

Pufferfish is considered a delicacy in nations such as Japan.  If it is not handled properly, there is a very serious risk of injury and death.  TTX inhibits the neurons’ ability to produce an action potential and communicate with each other.  Eating pufferfish should be done extremely cautiously, as once a neurotoxin is ingested it is very fast acting.