Distinct synaptic mechanisms drive the behavioral response to acute stress and rapid correction by ketamine.
Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology – November 01, 2024
Source: PubMed
Summary
Ketamine's remarkable antidepressant effects work differently than previously thought. Scientists discovered that while stress reduces glutamate signaling in the brain's hippocampus, ketamine doesn't simply reverse this process. Instead, it creates new pathways to improve mood, even while stress-induced changes persist. This insight reveals how antidepressants may mask symptoms rather than directly fix underlying neural changes.
Abstract
Prevailing hypotheses on the mechanisms of antidepressant action posit that antidepressants directly counteract deficiencies in major neurotransmitter signaling systems that underlie depression. The rapidly acting antidepressant ketamine has been postulated to correct excess glutamatergic signaling via glutamatergic antagonism leading to the rescue of neuronal structural deficits and reversal of behavioral symptoms. We studied this premise using systemic administration of the acetylcholinesterase inhibitor physostigmine, which has been shown to rapidly elicit a shorter-term period of depressed mood in humans via cholinergic mechanisms. We observed that physostigmine induces acute stress in tandem with long term depression of glutamate release in the hippocampus of mice. However, ketamine rapidly acts to re-establish glutamatergic synaptic efficacy via postsynaptic signaling and behaviorally masks the reduction in passive coping induced by physostigmine. These results underscore the divergence of synaptic signaling mechanisms underlying mood changes and antidepressant action and highlight how distinct synaptic mechanisms may underlie neuropsychiatric disorders versus their treatment.