A Conserved Role for Serotonergic Neurotransmission in Mediating Social Behavior in Octopus
https://www.cell.com/current-biology/fulltext/S0960-9822(18)30991-6


[Dolen] and her colleague Eric Edsinger put five Californian two-spot octopuses individually into the middle of three connected chambers and gave them free rein to explore. One of the adjacent chambers housed a second octopus, confined inside an overturned plastic basket. The other contained an unfamiliar object, such as a plastic flower or a Chewbacca figurine. Dolen and Edsinger measured how long the main animal spent in the company of its peer, and how long with the random toy. The free-moving individuals thoroughly explored the chambers, and from their movements, Dolen realized that individuals of any sex gravitate toward females, but avoid males. Next, she dosed the animals with ecstasy. Again, there's no precedent for this, but researchers often anesthetize octopuses by dunking them in ethanol -- a humane procedure with no lasting side effects. So Dolen and Edsinger submerged their octopuses in an MDMA solution, allowing them to absorb the drug through their gills. At first they used too high a dose, and the animals "freaked out and did all these color changes," Dolen says. But once the team found a more suitable dose, the animals behaved more calmly -- and more sociably.