Ketamine Self-Administration Elevates αCaMKII Autophosphorylation in Mood and Reward-Related Brain Regions in Rats

Abstract

Modulation of αCaMKII expression and phosphorylation is a feature shared by drugs of abuse with different mechanisms of action. Accordingly, we investigated whether αCaMKII expression and activation could be altered by self-administration of ketamine, a non-competitive antagonist of the NMDA glutamate receptor, with antidepressant and psychotomimetic as well as reinforcing properties. Rats self-administered ketamine at a sub-anesthetic dose for 43 days and were sacrificed 24 h after the last drug exposure; reward-related brain regions, such as medial prefrontal cortex (PFC), ventral striatum (vS), and hippocampus (Hip), were used for the measurement of αCaMKII-mediated signaling. αCaMKII phosphorylation was increased in these brain regions suggesting that ketamine, similarly to other reinforcers, activates this kinase. We next measured the two main targets of αCaMKII, i.e., GluN2B (S1303) and GluA1 (S831), and found increased activation of GluN2B (S1303) together with reduced phosphorylation of GluA1 (S831). Since GluN2B, via inhibition of ERK, regulates the membrane expression of GluA1, we measured ERK2 phosphorylation in the crude synaptosomal fraction of these brain regions, which was significantly reduced suggesting that ketamine-induced phosphorylation of αCaMKII promotes GluN2B (S1303) phosphorylation that, in turn, inhibits ERK 2 signaling, an effect that results in reduced membrane expression and phosphorylation of GluA1. Taken together, our findings point to αCaMKII autophosphorylation as a critical signature of ketamine self-administration providing an intracellular mechanism to explain the different effects caused by αCaMKII autophosphorylation on the post-synaptic GluN2B- and GluA1-mediated functions. These data add ketamine to the list of drugs of abuse converging on αCaMKII to sustain their addictive properties.

Neural Mechanisms Underlying the Rewarding and Therapeutic Effects of Ketamine as a Treatment for Alcohol Use Disorder

“…As with depression, AUD is a lifelong disorder and would require repeated ketamine infusions to maintain long term sobriety. This is significant given that repeated exposure to ketamine may have abuse potential as demonstrated by pre-clinical reports showing that rats will self-administer ketamine at doses as low as 0.1 mg/kg/infusion (De Luca and Badiani, 2011;Wright et al, 2017;Caffino et al, 2018). Furthermore, ketamine, a ''club drug'' known to be taken recreationally in combination with alcohol, has abuse potential in humans and is listed as a Schedule III drug.…”

On the safety of repeated ketamine infusions for the treatment of depression: Effects of sex and developmental periods

“…The reinforcing properties of ketamine at high doses is evident as demonstrated by adult male rodents’ propensity to self-administer ketamine (0.5 mg/kg/infusion, i.v.) under various schedules of reinforcement ( Caffino et al, 2016 , 2017 ; DeLuca and Badiani, 2011 ; van der Kam et al, 2007 ; Venniro et al, 2015 ). Escalation of ketamine self-administration is observed as the schedule of reinforcement is increased from fixed ratio 1 (FR1) to FR5 and occurs in a dose-dependent manner, as demonstrated by increased number of ketamine infusions at the highest dose (0.5 mg/kg, i.v.)…”

“…Studies examining ketamine self-administration at low doses have not yet examined the molecular mechanisms underlying ketamine's reinforcing effects. At high doses, ketamine self-administration in adult rats induces phosphorylation of calcium calmodulin kinase II alpha (CaMKIIα) in the nucleus accumbens (NAc), which leads to increased transcription and facilitation of AMPAR trafficking to the membrane ( Kristensen et al, 2011 ) and increased phosphorylation of the GluN2B subunit of the NMDAR ( Caffino et al, 2017 ), which has a higher sensitivity to calcium (Ca2+) than other NMDA subunits ( Evans et al, 2012 ). These molecular changes induce a hyperexcitable state in the NAc, which is also observed following chronic exposure to other drugs of abuse such as alcohol, another NMDAR-antagonist ( Ron and Barak, 2016 ).…”

“…A “switch” in expression levels of GluN2A and GluN2B occurs such that GluN2B expression peaks prenatally and declines over time whereas GluN2A expression gradually increases over time ( Sans et al, 2000 ; Laurie et al, 1997 ). Given the enhanced Ca2+-permeability of GluN2B ( Monyer et al, 1994 ; Paul and Connor, 2010 ) and its role in mediating the addictive properties of ketamine ( Caffino et al, 2017 ), repeated treatment with ketamine across different developmental periods could have differential effects given that its putative mechanism of action is through the blockade of NMDARs. As such, it is particularly important to examine the effects of repeated, low-dose ketamine can have on the developing brain.…”

Sex differences in sub-anesthetic ketamine's antidepressant effects and abuse liability

“…Akt signaling and subsequent phosphorylation of mTOR may be the critical mechanism by which ketamine exerts its effects in the prefrontal cortex and hippocampus, but this may be a sex- and region- specific effect, as ketamine's protracted effects on synaptic plasticity in the nucleus accumbens of males, a critical center of reward processing, occurs independently of mTOR activation (41). Additionally, differential nucleus accumbens phosphorylation of the glutamate receptor GluA1 has been observed with a single injection (increased (41)) vs chronic self-administration (decreased (42)). As the aforementioned studies only include males, it will be critical to characterize these effects in females as well.…”