Serotonergic transmission plays differentiated roles in the rapid and sustained antidepressant-like effects of ketamine.

Ketamine produces rapid antidepressant-like effects in mice within 60 minutes and increases brain serotonin levels. The sustained effects at 24 hours require an intact serotonin system: depleting serotonin or knocking out the serotonin synthesis enzyme Tph2 eliminated the 24-hour but not the 60-minute effects. Blocking AMPA receptors with NBQX also prevented the rise in serotonin and abolished the sustained antidepressant-like effects. Serotonergic neurotransmission is necessary for ketamine's lasting antidepressant action, and this mechanism involves AMPA receptors.

Study at a glance

Abstract

The emerging antidepressant effects of ketamine have inspired tremendous interest in its underlying neurobiological mechanisms, although the involvement of 5-HT in the antidepressant effects of ketamine remains unclear. The chronic restraint stress procedure was performed to induce depression-like behaviours in mice. OFT, FST, TST, and NSFT tests were used to evaluate the antidepressant-like effects of ketamine. Tph2 knockout or depletion of 5-HT by PCPA and 5,7-DHT were used to manipulate the brain 5-HT system. ELISA and fibre photometry recordings were used to measure extracellular 5-HT levels in the brain. 60 min after injection, ketamine (10 mg·kg-1, i.p.) produced rapid antidepressant-like effects and increased brain 5-HT levels. After 24 h, ketamine significantly reduced immobility time in TST and FST tests and increased brain 5-HT levels, as measured by ELISA and fibre photometry recordings. The sustained (24 h) but not rapid (60 min) antidepressant-like effects of ketamine were abrogated by PCPA and 5,7-DHT, or by Tph2 knockout. Importantly, NBQX (10 mg·kg-1, i.p.), an AMPA receptor antagonist, significantly inhibited the effect of ketamine on brain 5-HT levels and abolished the sustained antidepressant-like effects of ketamine in naïve or CRS-treated mice. This study confirms the requirement of serotonergic neurotransmission for the sustained antidepressant-like effects of ketamine, which appears to involve AMPA receptors, and provides avenues to search for antidepressant pharmacological targets.