https://www.wired.com/story/lasers-highlight-ketamines-depression-fighting-secrets/

Last month, the FDA approved esketamine, the nose spray version of ketamine, for treatment-resistant depression. You probably know by now that ketamine is a party drug, but it actually finds far wider use as an anesthetic on the World Health Organization’s list of Essential Medicines. Scientists have a good idea of how exactly it brings about its anesthetic charms, on account of it interacting with certain receptors in the brain. But when it comes to ketamine’s antidepressant effects, researchers are still largely in the dark.

But here now, a bit of light. Today in Science, researchers report a peculiar finding in the brains of mice on ketamine. When first fed a stress hormone to mimic the effects of depression, the rodents lost dendritic spines, tiny protrusions that help neurons transmit signals. But when dosed with ketamine, after 12 hours, the mice began to grow back about half of those spines. Weirdly, the researchers noticed behavioral changes almost immediately after administering ketamine, some 9 hours before they saw the regrowth of spines. The finding can’t 100 percent explain ketamine’s antidepressant effects, but it could also lead scientists to even more effective ketamine treatments.