DOMOIC ACID TOXICOSIS

Domoic acid toxicosis is a disorder caused by domoic acid, a toxin produced by diatoms, namely, Pseudo-nitzschia. Domoic acid moves up the food chain and accumulates in other organisms, and unfortunately, results in adverse neurological effects.

Diatoms thrive in warm water, and with global warming, their populations have bloomed and now pose even more of a problem than in years prior. While this does affect humans, measures have been taken to ensure that we are safe, including screening shellfish and other measures for fishing. In humans, domoic acid toxicosis is often called amnesiac shellfish poisoning, but in nonhuman organisms, it is more frequently called domoic acid toxicosis. Marine mammals, specifically pinnipeds, are frequently affected by domoic acid toxicosis. On the California shores, California sea lions are primarily affected in what is considered an epidemic. These sea lions experience seizures, confusion, and head bobbing patterns. Sea lions under the influence of domoic acid have been known to attack people and are, just, generally more aggressive. Something currently being explored is the specific mechanism with how domoic acid works. We understand for the most part the biochemical pathway of domoic acid, but we haven't made proper connections between that and the symptoms, a necessary step to treat this disorder. Currently, our default mechanism of treatment is gabapentin and phenobarbital, but these medications, rather than solve the issue, treat just the symptoms. Domoic acid mimics the structure of kainic acid and glutamate, and has high affinity for glutamate receptors. Domoic acid "disguises" itself as glutamate, resulting in activation of glutamate receptors, (specifically the kainic acid receptors and AMPA receptors), by domoic acid rather than glutamate. As a result, a phenomenon known as excitotoxicity occurs. Those glutamate receptors are overstimulated, and calcium ion channels are unblocked, causing an excess of calcium within the cell. These calcium ions result in interference with metabolism, cell structure, and more. For starters, the calcium ions result in an opening of the mitochondrial permeability transition pore, ultimately leading to cell apoptosis and hydrolysis of ATP by ATP synthase. Furthermore, calcium influxes can directly lead to activation of caspases. Caspases are the primary agents of apoptosis.

The cell death provoked by domoic acid occurs in two regions of the brain that are crucial for complex processing: the hippocampus and amygdala. The hippocampus consolidates short term memory into long term memory, and also has functions in spatial memory. The amygdala works with complex processing and emotional processing. The amygdala has two sides: the right and the left. The left side of the amygdala is typically associated with negative and positive emotions, whereas the right side of the amygdala is confined to only negative emotions. Our knowledge of how these regions of the brain work is extremely limited, even more so in sea lions. This is Torple, a California sea lion who was admitted to the Marine Mammal Center in September 2022. Torple had domoic acid toxicosis, and was among the many sea lions admitted that summer for the same ailment.

Ultimately, Torple was able to recover, but a cure for domoic acid toxicosis is essential: as sea temperatures rise, the problem will worsen for pinnipeds and other marine mammals. As someone really interested in pinnipeds and veterinary science, this is something I'm personally very passionate about and very interested in!