Ketamine decreases neuronally released glutamate via retrograde stimulation of presynaptic adenosine A1 receptors

Summary & key facts

This study in rodents and in neuronal cell cultures found that ketamine and its antidepressant metabolite (2R,6R)-HNK rapidly lower neuronally released glutamate in brain regions linked to depression. Using fast glutamate sensors (FAST), isolated synapses, and primary cortical neurons, the authors showed reduced depolarization-evoked glutamate release within 30 minutes after systemic dosing (15 mg/kg i.p.) and after local application (100 µM). The effect depended on AMPA receptor activity and on presynaptic adenosine A1 receptors, and was linked to decreased presynaptic signaling (P-T286-CaMKII and P-S9-synapsin) and reduced synaptic vesicle recycling. Blocking A1 receptors reversed the glut

Key facts:

• Ketamine and (2R,6R)-HNK reduced depolarization-evoked glutamate release in mouse prefrontal cortex and subiculum in vivo as measured with FAST.
• Systemic administration at an antidepressant dose (15 mg/kg, intraperitoneal) produced a reduction in evoked glutamate release detected within 30 minutes.
• Local application of ketamine or (2R,6R)-HNK was done at 100 µM and also caused a significant decrease in KCl-evoked glutamate release in both anesthetized and freely moving mice.
• The glutamate-lowering effect of ketamine and (2R,6R)-HNK could be blocked by AMPA receptor antagonists, indicating dependence on AMPA receptor activity.
• Antagonism of adenosine A1 receptors, which are mainly located at nerve terminals, counteracted ketamine’s reduction of glutamate release and presynaptic activity.
• Ketamine reduced levels of phosphorylated presynaptic proteins (P-T286-CaMKII and P-S9-synapsin) in primary neurons, and this correlated with decreased synaptic vesicle recycling measured ex vivo and in vitro.
• Giving an A1 receptor antagonist systemically lessened the antidepressant-like actions of ketamine and (2R,6R)-HNK in the mouse forced swim test.
• All experiments were performed in rodents or in neuronal cultures; the study does not show that the same mechanism occurs in humans.

Abstract

Ketamine produces a rapid antidepressant response in patients with major depressive disorder (MDD), but the underlying mechanisms appear multifaceted. One hypothesis, proposes that by antagonizing NMDA receptors on GABAergic interneurons, ketamine disinhibits afferens to glutamatergic principal neurons and increases extracellular glutamate levels. However, ketamine seems also to reduce rapid glutamate release at some synapses. Therefore, clinical studies in MDD patients have stressed the need to identify mechanisms whereby ketamine decreases presynaptic activity and glutamate release. In the present study, the effect of ketamine and its antidepressant metabolite, (2R,6R)-HNK, on neuronally derived glutamate release was examined in rodents. We used FAST methodology to measure depolarization-evoked extracellular glutamate levels in vivo in freely moving or anesthetized animals, synaptosomes to detect synaptic recycling ex vivo and primary cortical neurons to perform functional imaging and to examine intracellular signaling in vitro. In all these versatile approaches, ketamine and (2R,6R)-HNK reduced glutamate release in a manner which could be blocked by AMPA receptor antagonism. Antagonism of adenosine A1 receptors, which are almost exclusively expressed at nerve terminals, also counteracted ketamine's effect on glutamate release and presynaptic activity. Signal transduction studies in primary neuronal cultures demonstrated that ketamine reduced P-T286-CamKII and P-S9-Synapsin, which correlated with decreased synaptic vesicle recycling. Moreover, systemic administration of A1R antagonist counteracted the antidepressant-like actions of ketamine and (2R,6R)-HNK in the forced swim test. To conclude, by studying neuronally released glutamate, we identified a novel retrograde adenosinergic feedback mechanism that mediate inhibitory actions of ketamine on glutamate release that may contribute to its rapid antidepressant action.

Topics

Neuroscience and Neuropharmacology Research Treatment of Major Depression Tryptophan and brain disorders

Categories

Cellular and Molecular Neuroscience Life Sciences Neuroscience

Tags

Adenosine Adenosine A1 receptor Adenosine receptor Agonist AMPA receptor Biochemistry Biology Chemistry Endocrinology Glutamate receptor Glutamatergic Inhibitory postsynaptic potential Ketamine Neuroscience NMDA receptor Pharmacology Receptor