2. Molecular Toxicology of Marine Toxins A. Specific Receptor Site Interaction: Physiologic Biomarkers of Susceptibility The naturally-occurring marine toxins responsible for Paralytic Shellfish Poisoning, Neurotoxic Shellfish Poisoning, Amnesic Shellfish Poisoning, Diarrheic Shellfish Poisoning, Fugu Poisoning, and Ciguatera exert their effects in the nanomole to picomole per kg body weight ranges (Yasumoto and Murata 1993). By virtue of their highly specific and potent deleterious effects on living systems, specific receptor-ligands were postulated as the pharmacologically significant event in the onset of toxicity even before the chemical identity of the toxin(s) were known (see Baden, 1983 for a review). Of those toxins now known to the seafood safety regulators, four types are known to interact with specific orphan receptors located on nerve membrane glycoproteins, one type is a potent muscle enzyme inhibitor, and one interacts specifically with a central nervous system neurotransmitter receptor site