Not just that. In mice, SSRIs stop having any anti-depressant effects if the vagus nerve is severed: https://www.nature.com/articles/s41598-019-50807-8 https:

Not just that. In mice, SSRIs stop having any anti-depressant effects if the vagus nerve is severed: https://www.nature.com/articles/s41598-019-50807-8 https://www.nature.com/articles/s41598-019-50807-8 So they also seem to be effective via the enteric nervous system!