Sea lions, those endearing creatures seen frolicking in San Francisco Bay area waters and beyond, are under threat from an unlikely source. The new foe is domoic acid, a neurotoxin that can cause memory loss, tremors, convulsions and death. The toxin is carried in algae that has been proliferating along the coast in recent years; sea lions ingest it by feeding on small, contaminated fish.
As a result of the exposure, the sea lions develop a form of epilepsy that is very similar to that in humans, according to a new Stanford-led study. The sea lions suffer brain damage in the hippocampus - the brain's memory center - that mimics the damage in humans with temporal lobe epilepsy, said Paul Buckmaster, PhD, DVM, a Stanford veterinarian and expert in epilepsy in animals.
"We found there was a loss of neurons in specific patterns that closely matched what is found in people," said Buckmaster, the study's lead author. Moreover, the researchers noticed a pattern of rewiring in the brains of the animals that resembled that in humans with epilepsy, he said.
He said sea lions could serve as good models for studying the disease and developing much-needed treatments. Until now, scientists have been using rodent models for epilepsy, but rodent brains don't exhibit the same kind of damage as that seen in sea lions and humans, he said.
The Marine Mammal Center in Sausalito rescues a few hundred sea lions every year that have washed ashore in the throes of seizure as a result of domoic acid poisoning. About half are effectively treated with anti-convulsive therapy, but the other half are beyond help and have to be euthanized, said Frances Gulland, PhD, DVM, senior scientist and co-author on the recent paper. Many more sea lions, as well as other sea animals, are believed to die in the open ocean of untreated seizures, she said.
The hope is that the new findings will help lead to interventions to prevent seizures in the animals and lead to better treatments for them, as well as their human counterparts, Buckmaster said.
"What we need is an interventional treatment - both in humans and sea lions," he said. "You'd give the treatment right after the brain injury, and that would prevent them from developing epilepsy. That's the dream, but we are not there yet."
The new study appears in the Journal of Comparative Neurology.
Photo courtesy of Marine Mammal Center