Ketamine Rapidly Enhances Glutamate-Evoked Dendritic Spinogenesis in Medial Prefrontal Cortex Through Dopaminergic Mechanisms.

Summary

Ketamine rapidly enhances the formation of new dendritic spines in the mouse medial prefrontal cortex when glutamate uncaging triggers local plasticity, and this effect occurs within minutes—matching the drug's rapid antidepressant onset and preceding any overall increase in spine density. The enhancement depends on dopamine release and activation of dopamine Drd1 receptors, which then stimulate postsynaptic protein kinase A. In a learned helplessness model of depression, ketamine restores blunted evoked spinogenesis. Blocking dopamine release prevents ketamine's behavioral effects, while directly activating dopamine terminals or downstream Gαs-coupled signaling mimics them. Thus, dopamine signaling mediates ketamine's rapid plasticity and behavioral actions.

Study at a glance

Abstract

BACKGROUND Ketamine elicits rapid onset antidepressant effects in patients with clinical depression through mechanisms hypothesized to involve the genesis of neocortical dendritic spines and synapses. Yet, the observed changes in dendritic spine morphology usually emerge well after ketamine clearance, raising questions about the link between rapid behavioral effects of ketamine and plasticity. METHODS Here, we used two-photon glutamate uncaging/imaging to focally induce spinogenesis in the medial prefrontal cortex, directly interrogating baseline and ketamine-associated plasticity of deep layer pyramidal neurons in C57BL/6 mice. We combined pharmacological, genetic, optogenetic, and chemogenetic manipulations to interrogate dopaminergic mechanisms underlying ketamine-induced rapid enhancement in evoked plasticity and associated behavioral changes. RESULTS We found that ketamine rapidly enhances glutamate-evoked spinogenesis in the medial prefrontal cortex, with timing that matches the onset of its behavioral efficacy and precedes changes in dendritic spine density. Ketamine increases evoked cortical spinogenesis through dopamine Drd1 receptor (Drd1) activation that requires dopamine release, compensating blunted plasticity in a learned helplessness paradigm. The enhancement in evoked spinogenesis after Drd1 activation or ketamine treatment depends on postsynaptic protein kinase A activity. Furthermore, ketamine's behavioral effects are blocked by chemogenetic inhibition of dopamine release and mimicked by activating presynaptic dopaminergic terminals or postsynaptic Gαs-coupled cascades in the medial prefrontal cortex. CONCLUSIONS Our findings highlight dopaminergic mediation of rapid enhancement in activity-dependent dendritic spinogenesis and behavioral effects induced by ketamine.