Fine-tuning of dopamine receptor signaling with aripiprazole counteracts ketamine's dissociative action, but not its antidepressant effect.

Ketamine, a rapid-acting antidepressant, has undesirable psychotomimetic effects, including a dissociative effect. There is currently no effective strategy to suppress these side effects while preserving its antidepressant effect. Here, we investigated the effects of a D2/D3 receptor antagonist and partial agonists on the psychotomimetic and antidepressant effects of ketamine in mice and humans. Aripiprazole, a partial agonist, attenuated the psychotomimetic effect, but maintaining and even enhancing the antidepressant-like effect of ketamine in the forced swim test, whereas raclopride, an antagonist, suppressed both effects in mice. Brain-wide Fos mapping and its network analysis suggested the ventral tegmental area (VTA) as a critical region for distinguishing the effects of aripiprazole and raclopride. In the chronic stress model, local infusion of raclopride into the VTA inhibited ketamine's antidepressant-like effect, accompanied by activation of dopaminergic neurons, suggesting the inhibitory effect of VTA activation on the antidepressant-like effect of ketamine. Consistently, systemic injections of raclopride and brexpiprazole, a partial agonist similar to aripiprazole but closer to an antagonist (lower Emax), activated dopaminergic neurons in the VTA and suppressed ketamine's antidepressant-like effect in the model when co-administered with ketamine, whereas aripiprazole didn't. In line with these results, in a single-arm, double-blinded clinical study of sequential treatments in depressed patients (N = 9), co-administration of 12 mg of aripiprazole suppressed the dissociative symptoms induced by ketamine while maintaining its antidepressant effects. Together, these findings suggest that fine-tuning dopamine receptor signaling with aripiprazole allows selective suppression of ketamine-induced dissociation preserving its antidepressant effects, and that the combined use of aripiprazole and ketamine may be a preferred therapy for treatment-resistant depression.