Cannabidiol Improves Cognitive Impairment and Reverses Cortical Transcriptional Changes Induced by Ketamine, in Schizophrenia-Like Model in Rats
Ewa Kozela & Martyna Krawczyk & Tomasz Kos & Ana Juknat & Zvi Vogel & Piotr Popik
Molecular Neurobiology, 2019,
Doi : 10.1007/s12035-019-01831-2
Cannabidiol (CBD), a non-psychotropic cannabinoid, demonstrates antipsychotic-like and procognitive activities in humans and in animal models of schizophrenia. The mechanisms of these beneficial effects of CBD are unknown. Here, we examined behavioral effects of CBD in a pharmacological model of schizophrenia-like cognitive deficits induced by repeated ketamine (KET) administration. In parallel, we assessed transcriptional changes behind CBD activities in the prefrontal cortex (PFC), the main brain area linked to schizophrenia-like pathologies.Male Sprague-Dawley rats were injected for 10 days with KET followed by 6 days of CBD. The cognitive performance was evaluated in the novel object recognition test followed by PFC dissections for next-generation sequencing (RNA-Seq) analysis and bioinformatics. We observed that KET-induced learning deficits were rescued by CBD(7.5mg/kg). Similarly, CBD reversed transcriptional changes induced byKET. Themajority of the genes affected by KET and KET CBD were allocated to astroglial and microglial cells and associated with immune-like processes mediating synaptogenesis and neuronal plasticity. These genes include C1qc, C1qa, C1qb, C2, and C3 complement cascade elements, Irf8 factor and Gpr84, Gpr34, Cx3cr1, P2ry12, and P2ry6 receptors. The main pathway regulators predicted to be involved included TGFβ1 and IFNγ. In addition, CBD itself upregulated oxytocin mRNA in the PFC. The present data suggest that KET induces cognitive deficits and transcriptional changes in the PFC and that both effects are sensitive to a reversal by CBD treatment.
Keywords : Schizophrenia . Cognitive impairment . Cannabidiol . Ketamine . Gene expression . Oxytocin
Compelling evidence points to the involvement of the endocannabinoid system (ECB) and its modulators in the pathology of schizophrenia. The ECB comprises of endogenous ligands including N-arachidonoyl ethanolamide (anandamide, AEA, [1, 2]) and 2-arachidonoyl-glycerol (2-AG, ), G-protein coupled CB1 and CB2 receptors an enzymatic machinery controlling “on demand” synthesis and degradation of the endogenous ligands . The ECB system and its role in schizophrenia spectrum of disorders were described subsequent to the identification of Δ9-tetrahydrocannabinol (Δ9-THC, THC), the main psychotomimetic constituent of Cannabis plant binding to the CB1 and CB2 receptors, as well as of cannabidiol (CBD), the main non-psychotomimetic phytocannabinoid. Interestingly, THC and CBD exert opposite subjective effects in humans. The exposure to THC may induce a transient psychotic-like state in healthy individuals, including hallucinations, delusions, and cognitive impairment [5–7], may augment psychotic episodes, and may provoke relapses in schizophrenic patients [8–10]. On the contrary, CBD as early as in 1970s was shown to ameliorate schizophrenia-like symptoms in THC-intoxicated individuals, including healthy volunteers [11–14], revealing its antipsychotic activity. Moreover, it was observed that increased CBD content in Cannabis preparations has protective effects against THC-induced hallucinations or delusions [15–17]. In a case study, CBD reduced schizophrenia symptoms being superior to haloperidol, a typical antipsychotic drug with severe side effects  and decreased psychotic symptoms in openlabel study in Parkinsons patients . Double-blind controlled study in schizophrenia patients showed similar efficacy of CBD compared with amisulpride, one of the most effective antipsychotics in current use, in diminishing the disease symptoms. The same study revealed preferential side effect profile of CBD . More recently, however, Boggs et al.  reported that CBD did not improve cognitive impairments associated with schizophrenia in stable antipsychotic-treated outpatients.
In agreement with these observations in humans, CBD was shown to improve performance in various schizophrenia-like models in animals. CBD restored deficits in prepulse inhibition of startle response (PPI), a measure of impaired sensorimotor gating characteristic for schizophrenia. The PPI improvement
was reported in genetic  and pharmacologic schizophrenia-like approaches including inhibition of glutamatergic transmission/NMDA receptors [23, 24] or intraaccumbens amphetamine . Moreover, CBD diminished stereotyped behavior and hyperlocomotion induced by psychotomimetic drugs, the paradigms serving as behavioral equivalents of “positive” schizophrenia symptoms [23, 26, 27].
Interestingly, CBD has also been suggested to improve various cognitive deficits including spatial learning and memory, recognition and associative learning (reviewed by ). However, most of the data originate from animal models of neurodegenerative diseases, while data fromanimalmodels of
schizophrenia are limited. Only recently, the group of Guimaraes showed that CBD improves cognitive performance in the novel object recognition (NOR) test in mice, disturbed by NMDA receptor inhibition (with MK-801) . The mechanisms of the antipsychotic and possibly procognitive effects of CBD are unknown.
Here, we examined the effects of CBD in ketamine (KET)- induced schizophrenia-like cognitive impairment conditions. Sub-chronic, intermittent injections of KET, an NMDA receptor antagonist, at low, sub-anesthetic doses have been previously shown to produce a pattern of behavioral, neurochemical, metabolic, and transcriptional changes in rodents that reliably mirror those observed in schizophrenic brain [29–31]. To get an insight into the mechanisms of CBD and KET activities, we applied high-throughput transcription screening tools (next-generation sequencing [RNA-Seq] followed by bioinformatics) to reveal the transcriptional changes induced by both drugs in the prefrontal cortex (PFC). The PFC is considered the main brain region involved in the etiology of schizophrenia with various cellular, neurochemical, and functional changes suggested to contribute to the appearance of
positive, negative, and cognitive symptoms .
We report here that KET administration induces cognitive impairment and affects the transcription of a number of genes in the PFC of the tested rats and that these changes are rescued by the CBD treatment. The transcriptional activity of KETand CBD involves immune-like genes and pathways, suggesting a
dominant involvement of glial component (microglia and astroglia) in the beneficial, procognitive, and antipsychoticlike effects of CBD.