Ketamine-induced antidepressant effects: A role for postsynaptic supercomplexes revealed using mouse genetic models and synaptome mapping

S. A. Lemprière, Z. Qiu, N. H. Komiyama & S. G. N. Grant : Centre for Clinical Brain Sciences, University of Edinburgh J. Nithianantharajah : The Florey Institute of Neuroscience and Mental Health, Melbourne, Australia F. Zhu : Dept. of Neurodegenerative Disease, University College London

Ketamine is a widely-used anaesthetic and analgesic. At sub anaesthetic doses it causes a transient psychosis clinically indistinguishable from schizophrenia (Moore et al. 2011), this is followed by a long-lasting antidepressant response (Berman et al. 2000). Although it is known that ketamine is a non-competitive NMDA receptor antagonist (MacDonald et al. 1987), it is unclear how this receptor would mediate these different behavioural effects.

The NMDA receptor is assembled into supercomplexes with PSD95, Arc/Arg3.1 and other proteins via the critical role of the GluN2B cytoplasmic tail (Frank et al. 2016). Ketamine induces long-lasting (72hr) upregulation of PSD95 and Arc (Li et al. 2010), suggesting these molecules may be relevant to the dose- and time-dependent effects of ketamine.

To investigate the mechanisms used by the NMDA receptor to couple to PSD95 and Arc, we first examined ketamine-induced hyperlocomotion in mice carrying mutations in the cytoplasmic domains of GluN2A and GluN2B (Ryan et al. 2013) and knockouts of PSD95. Ketamine-induced hyperlocomotion was absent in mice lacking PSD95 and in mice with the cytoplasmic tail of the GluN2B NMDA receptor subtype replaced with that of the GluN2A receptor subtype.

Next we used a line of mice in which endogenous Arc was modified to express a fusion protein with Venus (Arc-Venus). These mice exhibit activity-dependent punctate postsynaptic labelling, which we quantified using high-throughput spinning-disk confocal microscopy in brain regions of adult mice. Since literature suggests that 10mg/kg ketamine induces a long-lasting (>24hr) antidepressant response (Ma et al. 2013), and 100mg/kg does not (Chatterjee et al. 2011), we treated Arc-Venus mice with these two doses. At 1hr the response of Arc to ketamine was the same for both doses: the density of Arc-Venus puncta was increased in dendritic sub-regions of hippocampus and in cortex. However, at 6hr post-ketamine the 100mg/kg dose produced a decrease in puncta number, while the earlier (1hr) increase was maintained in the 10mg/kg group.

These findings provide evidence for the involvement of the supercomplex formed by NMDA receptors, PSD95 and other proteins in the action of ketamine and the utility of genetically modified mice in dissecting signalling pathways in pharmacological studies.

References

1. Berman et al. (2000) Biol Psychiat, 47:351-354
2. Chatterjee et al. (2011) Behav Brain Res, 216:247-254
3. Frank et al. (2016) Nat Comms, 7:11264
4. Li et al. (2010) Science, 329:959-964
5. Ma et al. (2013) PLOS ONE, 8:e56053
6. MacDonald et al. (1987) J Neurophys, 58:2,251-266
7. Moore et al. (2011) Cogn Neuropsychol, 1464-0619
8. Ryan et al. (2013) Nat Neurosci, 16:25-32

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