Ketamine, Stress Hormones, and the Female Brain: What a New Study Found and What It Doesn't Tell Us Yet
A study published this summer in Science Advances took an unexpected look at what happens in the brain while it recovers from ketamine anesthesia. The finding that caught attention: the answer looked different in female mice than in male ones.
Researchers in Austria gave mice a surgical anesthetic containing ketamine, then watched the living brain through a small glass window. About an hour after the injection, as the female mice began waking up, their microglia — the brain's resident immune cells, which spend most of their time quietly surveying their surroundings — started reaching out and touching neurons far more than usual. Male mice showed no consistent version of this. In the females, that contact was followed by a measurable increase in synaptic signaling, one of the fingerprints of neuroplasticity. When the researchers removed microglia from the equation, the increase disappeared with them.
The mechanism ran through the stress axis, which is the part I find most interesting. During recovery, the female mice released a surge of corticosterone, the rodent version of cortisol that the males didn't. That hormone switched on a gene called FKBP5 inside microglia, and FKBP5 in turn drove the cells' behavior. Blocking the protein, deleting the gene from microglia specifically, or removing the adrenal glands each shut the whole process down. Adding corticosterone back switched it on again. And here's the detail that reframes the story: when male mice were given corticosterone, their microglia responded the same way. So the sex difference wasn't in the immune cells at all. It was in how much stress hormone the body released in the first place.
I want to be straightforward about the limits, because this is exactly the kind of study that gets flattened into a headline. These were mice. The dose was full surgical anesthesia, many times what's used in psychiatric care and it was given alongside two other sedating drugs that act on the very stress and adrenaline systems being measured, so ketamine alone can't take credit for what happened. Only three to five animals were studied per group. One of the study's own headline observations, an increase in dendritic spines, didn't actually reach statistical significance. Nothing was measured about mood, memory, or behavior. And for most of the experiments, the researchers didn't track where the female mice were in their reproductive cycle a meaningful gap in a study whose entire argument is about sex differences.
So nothing here changes how ketamine or esketamine is used, and no one should read it as evidence that these treatments work differently in women. What it offers is a piece of biology worth watching. It suggests the stress hormone system and the brain's immune cells are in direct conversation with each other, and that this conversation may help set how much plasticity a brain produces after a given exposure. If that holds up in people, the useful variable probably isn't sex, it's an individual's own cortisol response, which is something we can actually measure. That's a hypothesis, not a finding about patients. But it's the kind of hypothesis that earns a human trial.
Venturino A, Alamalhoda M, Negrello T, et al. Corticosterone-linked microglial activity underpins sexually dimorphic neuroplasticity after ketamine anesthesia. Sci Adv. 2026;12(31):eadz6517. doi:10.1126/sciadv.adz6517
