Altered dopamine D3 receptor gene expression in MAM model of schizophrenia is reversed by peripubertal cannabidiol treatment

Tibor Stark, Martina Di Bartolomeo, Roberta Di Marco, Eva Drazanova, Chiara Bianca Maria Platania, Fabio Arturo Iannotti, Jana Ruda-Kucerova, Claudio D’Addario, Lucie Kratka, Vladimir Pekarik, Fabiana Piscitelli, Zuzana Babinska, Julia Fedotova, Giovanni Giurdanella, Salvatore Salomone, Alexandra Sulcova, Claudio Bucolo, Carsten T.Wotjak, Zenon Starcuk Jr, Filippo Drago, Raphael Mechoulam, Vincenzo Di Marzo, Vincenzo Micale

Biochemical Pharmacology, April 2020, 1-12.

doi : 10.1016/j.bcp.2020.114004

 

 

Un excellent article international (République Tchèque, Allemagne, Italy, Russie, Israel, Canada), avec la plus grande plume de la recherche sur les cannabinoïdes (Mechoulam, Di Marzo…) qui devrait passionner les psychiatres travaillant sur les “psychoses émergentes” : “nos résultats démontrent que l’expression de l’ARNm des deux récepteurs à la dopamine (D2 et D3) sont altérés dans le modèle MAM (Gestational methylazoxymethanol acetate treatment who produces offspring with adult phenotype relevant to schizoprenia), que seul le niveau de transcription du récepteur D3 est affecté par le traitement au cannabidiol, ce qui suggère que ce gène ne fait pas que contribuer aux symptômes schizophréniques, mais représente également une “gachette” encore inexplorée en faveur de l’activité antipsychotique du cannabidiol.

Dr Christian Sueur

 

A B S T R A C T

Gestational methylazoxymethanol acetate (MAM) treatment produces offspring with adult phenotype relevant to schizophrenia, including positive- and negative-like symptoms, cognitive deficits, dopaminergic dysfunction, structural and functional abnormalities. Here we show that adult rats prenatally treated with MAM at gestational day 17 display significant increase in dopamine D3 receptor (D3) mRNA expression in prefrontal cortex (PFC), hippocampus and nucleus accumbens, accompanied by increased expression of dopamine D2 receptor (D2) mRNA exclusively in the PFC. Furthermore, a significant change in the blood perfusion at the level of the circle of Willis and hippocampus, paralleled by the enlargement of lateral ventricles, was also detected by magnetic resonance imaging (MRI) techniques. Peripubertal treatment with the non-euphoric phytocannabinoid cannabidiol (30 mg/kg) from postnatal day (PND) 19 to PND 39 was able to reverse in MAM exposed rats: i) the up-regulation of the dopamine D3 receptor mRNA (only partially prevented by haloperidol 0.6 mg/kg/day); and ii) the regional blood flow changes in MAM exposed rats. Molecular modelling predicted that cannabidiol could bind preferentially to dopamine D3 receptor, where it may act as a partial agonist according to conformation of ionic-lock, which is highly conserved in GPCRs. In summary, our results demonstrate that the mRNA expression of both dopamine D2 and D3 receptors is altered in the MAM model; however only the transcript levels of D3 are affected by cannabidiol treatment, likely suggesting that this gene might not only contribute to the schizophrenia symptoms but also represent an unexplored target for the antipsychotic activity of cannabidiol.

Keywords : Cannabidiol, Dopamine D3 receptor, Molecular Dynamics, Arterial Spine Labelling, MAM model, Schizophrenia

 

1. Introduction

Based on the neurodevelopmental hypothesis of schizophrenia (SCZ) [1], the administration of the DNA alkylating agent methylazoxymethanol acetate (MAM) at gestational day (GD) 17 in rodents (functionally equivalent to the human second trimester) induces in offspring at adulthood many of the SCZ-relevant neuropathological deficits including positive- and negative-like symptoms, cognitive deficits, hyperdopaminergic state, and functional and structural abnormalities, which are in part reversed by conventional and potential antiypsychotic drugs (APDs) [2–6]. Therefore, the MAM model represents a tool to reproduce the human condition in terms of construct, face and predictive validity and to further investigate potential APDs.

The dopaminergic (DAergic) dysfunction (in terms of both receptor expression and signalling alterations) represents a hallmark both in SCZ subjects and in neurodevelopmental animal models, which foster a great interest to develop new strategies to modulate the DAergic function for coping to unmet clinical needs [7]. Among new candidate compounds, accumulating evidence points towards cannabidiol (CBD), the most abundannt non-euphoric phytocannabinoid, endowed with a favourable pharmacological profile, as an alternative treatment option for those SCZ symptoms that are not satisfactorily ameliorated by current theraphies [8,9]. In agreement with the hypothesis that early intervention at a critical period (the so-called window of opportunity) may be effective in circumventing the transition to SCZ [10], it has been observed that peripubertal CBD treatment prevents the development of SCZ-like alterations in animal models at adulthood [11,12]. In particular, CBD regulates the mesolimbic DAergic system, which may, at least in part, underlie its behavioral effects [13]. However, the relationship between therapeutic effects of CBD and changes in DAergic system, particularly
in terms of dopamine D2-like receptor subtype expression, is currently unclear.

On this background, we tested the hypothesis that the development of a SCZ-related psychopathology induced by prenatal MAM exposure [4,12,14,15] involves changes in dopamine D2 (D2) and/or D3 (D3) receptor expression (in terms of mRNA and protein expression, and DNA methylation at the level of gene regulatory region) in SCZ-relevant brain regions (prefrontal cortex – PFC, hippocampus – HIP and nucleus accumbens – NAc) [3,8]. In addition, we explored whether these changes could be reversed by peripubertal treatment with CBD, as compared to the first-generation antipsychotic haloperidol (HAL), which is able to reduce the DAergic neuron activity in the MAM model [16]. We also assessed the enlargement of lateral ventricles and the changes in regional cerebral blood flow (rCBF) by magnetic resonance imaging (MRI), as index of structural impairments and functional abnormalities, respectively.
Both are known to be affected in psychosis [17] as well as in neurodevelopmental animal models [4,18], and might be reversed by pharmacological treatment. Finally, because recent studies suggest that
CBD could exert DAergic activity by binding to dopamine D2-like receptors [19,20], we explored the interaction of CBD with dopamine D2 and D3 receptors as compared to HAL, by means of molecular modelling approaches, i.e. molecular docking, molecular mechanics generalized born surface area (MM-GBSA) calculations and all-atom molecular dynamics (MD) simulations.

2. Material and methods

2.1. Animals and MAM model

Time-mated Sprague-Dawley dams (Charles River, Germany) were injected intraperitoneally (i.p.) with MAM (22 mg/kg; Midwest Research Institute, Kansas City, USA) or vehicle (CNT: 0.9% NaCl) on GD 17, as previously described [12,14,15,21,22]. Male pups were weaned on postnatal day (PND) 22 and housed in groups of 2–3 with littermates from the same treatment group until adulthood. From PND 100 they were used for neuroimaging and neurochemical experiments, with food and water available ad libitum and under constant environmental conditions: temperature 23 °C ± 1 °C, relative humidity 50–60%,
12-hour light–dark cycle (lights on at 6 a.m.). All the experiments were performed in agreement with EU Directive no. 2010/63/EU and approved by the Animal Care Committee of the Faculty of Medicine,
Masaryk University, Czech Republic, and Czech Governmental Animal Care Committee, in compliance with Czech Animal Protection Act No. 246/1992.

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