Octopuses on ecstasy: The party drug leads to eight-armed hugs

Octopuses and humans are very different, but scientists have found that octopuses respond to MDMA — the mood-altering drug popularly known as ecstasy — in a very similar way to us. Normally octopuses are solitary creatures. But after taking MDMA, they suddenly become much more social, reaching out to be near their fellow octopuses.

"Most octopuses are not social. They can be very aggressive to other octopuses," neuroscientist Gul Dolen of Johns Hopkins University told Bob McDonald, host of Quirks & Quarks.

But once the animals had been exposed to MDMA, they showed a marked preference for spending time near other octopuses, Dolen and her colleague Eric Edsinger found. There was also a qualitative change in their behaviour, which was suddenly "much more social than we'd normally see," Dolen said, adding it would be fair to call them more "touchy-feely."

The molecular roots of sociality

The finding is a little surprising because octopuses and humans are very different both in terms of their anatomy and their evolutionary history. Their lineages diverged some 500 million years ago. However, the molecular systems that control the response to drugs such as MDMA appear to be very similar in both animals.

"What this is telling us is that these social behaviours are evolutionarily very old — and they're encoded by a molecular signalling system that's also very old," Dolen said.

The underlying molecular system likely dates back to a time before vertebrates and invertebrates split off, she added. That split happened during the "Cambrian explosion," when the diversity of creatures living on our planet shot up dramatically.

Reach out and touch someone

Dolen and Edsinger studied the California two-spot octopus (Octopus bimaculoides). In their experiment, an octopus was allowed to choose which of three chambers to spend time in: an empty chamber; one containing a plastic toy; or one containing another octopus. The other octopus was inside an upside-down mesh flowerpot, to prevent the octopuses from harming each other.

Without the drug, octopuses showed a preference for the chamber with the plastic toy, but with the drug, they preferred the chamber with the other octopus. They could be seen "hugging the flowerpot containing the other octopus," Dolen said. They would even expose their undersides — a highly atypical behaviour for these animals.

Scientists knew that octopuses aren't solitary every moment of their lives. Whatever system causes them to stay clear of their fellow octopuses, it is clearly disabled when they seek out sex partners. But it was still unclear what triggers that change in behaviour. Now scientists have a better understanding of the underlying molecular process, and how its regulated.

Controlling the flow of serotonin 

A key discovery is that the protein to which MDMA bonds, known as a serotonin transporter, is present in both humans and octopuses, and has a similar structure.

MDMA works by triggering neurons to release serotonin, a mood-regulating chemical associated with feelings of well-being. MDMA has previously been studied in mice and rats. They too show what scientists call "prosocial" behaviour when on the drug, but this is the first time its effects have been studied on an animal so different from humans.

One possible application of this research is in drug studies, because it suggests that even animals not closely related to humans can experience similar drug responses.

In particular, it could potentially lead to new insights into the treatment of conditions such as depression and post-traumatic stress disorder. According to Dolen, "I think having mechanistic perspectives from evolutionary biology, from synaptic neurophysiology, from learning and memory — these will inform us and give us a better idea of how and why these drugs are working."

The research was published Thursday in the journal Current Biology.