To gain a better understanding of symptoms experienced by California sea lions caused by the toxin domoic acid, we are studying the relationship between aggression and seizure behavior in laboratory rats exposed to domoic acid. Our results have shown increased aggression can be a symptom of domoic acid poisoning whether or not seizures are occurring, but the aggression is not permanent. Our ongoing work will provide a scientific basis for choosing the best possible rehabilitative measures.
Why We Care
Increasing numbers of California sea lions are becoming sick each year from ingesting domoic acid, a neurotoxin that accumulates in the fish and shellfish they consume. Domoic acid is produced by the algae Pseudo-nitzchia and causes vomiting, unusual behaviors, seizures, loss of pregnancy, and death in the sea lions and other organisms. The increase in sea lion cases may be indicative of an increasing threat to other marine species.
Strandings and symptoms occur even when domoic acid is not detected, which suggests previous exposure can cause long-term health problems. By recognizing abnormally aggressive behaviors as a symptom of domoic acid poisoning, wildlife veterinarians and staff can better understand the handling hazards that may come with these aggressive animals during rehabilitation and these animals may then get the most accurate diagnosis and treatment.
What We Are Doing
We are giving laboratory rats low levels of domoic acid similar to what California sea lions might experience in the wild. This amount of toxin has been enough to cause seizures, visible as muscle contractions, that lasted for several hours. After recovery and a seizure-free period of weeks to six months, 93 percent of the animals began to show spontaneous and recurrent seizures, a hallmark symptom of epilepsy. These results are similar to domoic aid poisoning symptoms seen in the California sea lions and in one human who had eaten contaminated mussels.
What We Found
Our research thus far indicates that:
- many of the rats became highly aggressive one month after domoic acid poisoning, similar to observations in some poisoned sea lions;
- aggression is neither a permanent behavioral change in rats, because it decreases to more normal levels after 2 months, nor is it always evident;
- some animals have had only seizures, some only aggression and some have had both;
- increased aggression can be one symptom of domoic acid poisoning whether or not seizures are occurring.
Our marine mammal-stranding network collaborators along the West Coast, such as the Marine Mammal Center in Sausalito, CA, are using the information to enhance diagnoses and provide the best treatment for helping all marine mammals with domoic acid poisoning. We are continuing work on our laboratory rat model by mapping specific areas of the brain damaged by domoic acid poisoning in epileptic and/or aggressive rats. We continue to monitor the effects of domoic acid on rats to help us understand the underlying cause of the disease in sea lions and provide a scientific basis for therapeutic and management approaches.