Nicotine has been indicated as a prevalent drug for substance abuse comorbidities in mental illness. Tobacco use is elevated in those suffering from psychiatric disorders, most notably in schizophrenia (SZ), where a three-to-five fold increase in usage compared to the general population is observed. Our laboratory has established a rodent model of psychosis. In this model, male and female rats are neonatally treated with quinpirole (NQ), a dopamine (DA) D2-like agonist for 21 days postpartum, resulting in lifelong supersensitization of the DAD2 receptor. Increases in dopamine D2 receptor sensitivity is a hallmark of psychosis. Interestingly, the dopamine D2 receptor forms a triple mutual inhibitor heteromer in the dorsal striatum with the adenosine A(2A) and metabotropic glutamate receptor type 5 (mGlu5), such that stimulation of the A(2A) or mGlu5 receptor results in decreased dopamine D2 signaling. The present study was designed to analyze the role of the mGlu5 receptor in a behavioral task involved in testing the associative aspects of rewarding drugs known as conditioned place preference (CPP). CPP is a behavioral task in which animals are conditioned with a reinforcing drug to prefer a particular environmental context. Male and female rats were neonatally treated with saline (NS) or quinpirole from postnatal day (P) 1 to 21. From P41-51, which is mid-adolescence in a rat, all rats were behaviorally tested on CPP. Results revealed that compared to NS rats, NQ animals administered nicotine demonstrated enhanced CPP, replicating our past work. Groups receiving a positive allosteric modulator to mGlu5, which results in stimulation of the mGlu5 receptor, reduced the enhanced rewarding effects of nicotine in CPP for NQ treated rats equal to control levels. Brain tissue was analyzed for brain-derived neurotropic factor (BDNF), a neurotrophin involved in cell growth, as well cell adhesion molecule cadherin-13 in the ventral tegmental area (VTA), which is a brain area rich in dopamine cell bodies. Results revealed elevations of BDNF in NQ-treated rats given nicotine compared to all other groups, and a sex difference in the increase in cadherin-13, with female NQ rats given nicotine demonstrating increases compared to all other groups. These effects were blocked by the mGlu5 receptor positive allosteric modulator. In addition, we analyzed phospho-p70S6 kinase in the nucleus accumbens (NAcc), which is the dopamine neuronal terminal region in the VTA mitigating drug reward. The NQ group given nicotine demonstrated significant increases in NAcc P70S6 kinase compared to all other groups, suggesting increased synaptic growth, which was also blocked by the positive allosteric modulator to mGlu5. Taken together, these results elucidate mGlu5 as a drug target for reducing the rewarding effects of nicotine via CDPPB administration in a model of substance abuse in psychosis.

Heritable and environmental factors contribute to an individual’s risk of substance abuse and psychosis. Individuals diagnosed with a mental disorder have greater vulnerability for substance abuse. Our laboratory established that neonatal treatment of rats with quinpirole (NQ), a dopamine (DA) D2-like agonist, results in a significant increase of DAD2 receptor sensitivity throughout the animal’s lifetime. An increase of DAD2 receptor sensitivity is relevant to a model of schizophrenia (SZ), although increases of DAD2 receptor activity also occur in a number of clinical disorders, including bipolar disorder, obsessive-compulsive disorder, panic disorder, and major depression. Common amongst these clinical conditions is a dramatic increase in cigarette smoking compared to the general population. We bred NQ-treated male and female rats with their NQ-treated or neonatal saline (NS)-treated counterparts once they reached adulthood to determine whether increases in DAD2 sensitivity were passed to the next generation. Offspring of these animals, regardless of whether one or both founders received NQ-treatment, also demonstrated increases of DAD2 receptor sensitivity both behaviorally and neurobiologically. RNASeq preliminary data revealed an increase in cortisol synthesis and release in F1 generation animals, demonstrating an enhanced response to stress, consistent with a model of drug abuse vulnerability. Consistent with this finding, F1 generation rats demonstrated enhanced nicotine conditioned place preference (CPP) and had an enhanced brain derived neurotrophic factor (BDNF) response to nicotine in the nucleus accumbens (NAcc), a brain area critical to drug reward. The DAD2 receptor forms a triple heteromer with the adenosine A(2A) and metabotropic glutamate type 5 (mGlu5) receptor, such that stimulation of either receptor results in a decrease of DAD2 activity. Therefore, we analyzed whether use of a positive allosteric modulator (PAM) of mGlu5 in the F1 generation would block nicotine CPP and improve sensorimotor gating deficits, which is a hallmark of psychosis. In both experiments, the mGlu5 PAM effectively blocked the enhanced rewarding effects of nicotine and also alleviated sensorimotor gating deficits in this model. In essence, we demonstrate in results reported here that there may be a common therapeutic target for the dual treatment of substance abuse and psychosis.

Alcohol use disorder (AUD) is the leading cause of substance use disorders among Veterans and 55 to 75% of the population that are diagnosed with PTSD also receive a comorbid diagnosis of AUD. The co-diagnosis of PTSD/AUD is associated with neurocognitive changes such as increased impulsivity and risk-taking behavior, especially among individuals with combat-related trauma. Furthermore, increased neuroinflammation in subregions of the prefrontal cortex (PFC) are suggested to contribute to these neurocognitive changes. To better understand the cognitive deficits associated with co-occurring PTSD/AUD we incorporated a probabilistic discounting task (PDT) to model risk-based decision-making in male and female Wistar rats that were exposed to restraint stress (RS) and chronic intermittent ethanol exposure (CIE). Following RS and CIE, rats underwent lever press training through a series of different training phases, in which one lever delivered a small reward 100% of the time, and the other a large reward, delivered with descending probability each trial block. Pressing the large-reward lever during the final two trial blocks when it is disadvantageous to do so is considered “risky” behavior. A week prior to PDT, rats were treated prophylactically with CDPPB, a positive allosteric modulator of the metabotropic glutamate type 5 (mGlu5) receptor, to determine if the cognitive deficits caused by stress and alcohol exposure could be prevented. Additionally, to determine if our model mimicked the neuroinflammatory mechanism seen in the human condition and the therapeutic effects of CDPPB, we assessed TNF-⍺ protein expression in a subset of rats. Our results indicated that male rats exposed to RS and CIE had significantly greater responding during the 3rd, 4th, and 5th risk blocks compared to all other groups. However, the administration of CDPPB reversed this effect. Females exposed to RS and CIE only displayed increased risky behavior at the highest risk block and this was also blocked with the administration of CDPPB. We also determined that RS and CIE significantly increased TNF-⍺ levels in the IfL cortex compared to either RS or CIE alone and the prophylactic administration of CDPPB reduced TNF-⍺ protein expression to control animal levels. In the present study, we demonstrate that exposure to stress and chronic alcohol leads to significant neurocognitive deficits resulting in increased risky decision-making, but these deficits can be attenuated through modulation of the mGlu5 receptor prior to behavioral testing. Additionally, these deficits could be due to deleterious neuroinflammation in subregions of the PFC.

Dans certaines aires cérébrales, l’action synergique du glutamate et de la dopamine est nécessaire pour induire et maintenir la plasticité synaptique. Un dialogue fonctionnel entre le récepteur métabotropique du glutamate mGlu5 et le récepteur de la dopamine D1 a été mise en évidence. Par ailleurs, de nombreuses études ont démontré que les récepteurs couplés aux protéines G ont la capacité de former des hétéromères créant ainsi de nouvelles entités fonctionnelles. En s’appuyant sur l’hypothèse d’une hétéromérisation des récepteurs, l’objectif de ce projet de thèse était d’étudier les mécanismes moléculaires qui sous-tendent une synergie fonctionnelle entre les récepteurs mGlu5 et D1. Dans la première partie de ce travail, j’ai caractérisé les bénéfices de la Nanoluciférase, une luciférase très lumineuse, pour améliorer la technique de BRET en imagerie (Bioluminescence Resonance Energy Transfer imaging) qui permet d’étudier la dynamique des interactions entre protéines dans les cellules vivantes. Les bénéfices mis en évidence en termes de résolution spatio-temporelle, de stabilité et de sensibilité du signal ont été exploités pour la suite de ce projet. Dans la seconde partie de ce travail, les améliorations techniques mentionnées ci-dessus ont permis de mettre en évidence pour la première fois des hétéromères mGlu5/D1 dans des neurones en culture. En outre, nous avons montré que la co-expression des récepteurs mGlu5 et D1 en système hétérologue favorise la signalisation calcique, d’une part en augmentant l'activité constitutive de mGlu5 et, d’autre part, en créant une voie de libération du calcium intracellulaire atypique induite par l'agoniste D1.Ces résultats apportent de nouveaux éléments de compréhension des bases moléculaires du dialogue fonctionnel glutamate/dopamine dans le contrôle de la communication neuronale en conditions physiologiques et ouvrent la voie à de nouvelles stratégies thérapeutiques capables de moduler sélectivement la fonction des hétéromères. / In some specific brain areas, synergism between glutamate and dopamine transmission is required to induce synaptic plasticity. Metabotropic glutamate receptor mGlu5 and dopamine receptor D1 are both known to control synaptic plasticity. Moreover, multiple lines of evidence converge toward the ability of G-protein coupled receptors to form dynamic heteromers thereby creating new entities with unique properties. Focusing on the hypothesis of receptor heteromerization, my PhD project aimed at investigating the molecular mechanisms underlying a functional interplay between mGlu5 and D1 receptors.To address this issue, a first part of this work consisted in improving single-cell Bioluminescent Resonance Energy Transfer (BRET) imaging, a technology enabling to study real time protein-protein interaction dynamics in living cells. Using the Nanoluciferase, an extremely bright luciferase, we characterized a faster and higher resolution single-cell BRET imaging technique with unprecedented performance in terms of temporal and spatial resolution, duration of signal stability and signal sensitivity. In the second part of this project, we showed that mGlu5 and D1 can form heteromers in heterologous expression system. The above-mentioned improvements of single-cell BRET imaging technique allowed to evidence the occurrence and the dynamics of mGlu5/D1 heteromers in cultured primary neurons. Furthermore, our results showed that the co-expression of mGlu5 and D1 receptors modifies single receptor properties to favor calcium signaling by increasing mGlu5 constitutive activity and creating a D1 agonist-induced activation of Ca2+ release from intracellular stores.These findings advance our knowledge about the molecular basis of the glutamate/dopamine functional dialogue to control neuronal communication in physiological conditions. Further investigation will help the dissection of the mGlu5/D1 heteromer specific signaling pathway with the hope of defining new therapeutics that may selectively modulate heteromer function and thus bypass undesirable side effects.

The present study used auditory fear conditioning to assess the impact of repeated binge-like episodes of alcohol exposure during adolescence on conditioned fear in adulthood. Male and female Long-Evans rats were subjected to adolescent intermittent ethanol (AIE) exposure by vapor inhalation between post-natal day 28 and 44. After aging into adulthood, rats then underwent fear conditioning by exposure to a series of tone-shock pairings. This was followed by cued-tone extinction training, and then testing of fear recovery. In male rats, AIE exposure enhanced conditioned freezing but did not alter the time-course of extinction of cued-tone freezing. During subsequent assessment of fear recovery, AIE exposed rats exhibited less freezing during contextual fear renewal, but greater freezing during extinction recall and spontaneous recovery. Compared to males, female rats exhibited significantly lower levels of freezing during fear conditioning, more rapid extinction of freezing behavior, and significantly lower levels of freezing during the tests of fear recovery. Unlike males that were all classified as high conditioners; female rats could be parsed into either a high or low conditioning group. However, irrespective of their level of conditioned freezing, both the high and low conditioning groups of female rats exhibited rapid extinction of conditioned freezing behavior and comparatively low levels of freezing in tests of fear recovery. Regardless of group classification, AIE had no effect on freezing behavior in female rats during acquisition, extinction, or fear recovery. Lastly, exposure of male rats to the mGlu5 positive allosteric modulator CDPPB prevented AIE-induced alterations in freezing. Taken together, these observations demonstrate sex-specific changes in conditioned fear behaviors that are reversible by pharmacological interventions that target mGlu5 receptor activation.

This study analyzed whether the positive allosteric modulator of metabotropic glutamate receptor type 5 (mGlu5) 3-Cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl) benzamide (CDPPB) would alleviate deficits in prepulse inhibition (PPI) and affect dopamine (DA) D2 signaling in the dorsal striatum and prefrontal cortex (PFC) in the neonatal quinpirole (NQ) model of schizophrenia (SZ). Male and female Sprague-Dawley rats were neonatally treated with either saline (NS) or quinpirole HCL (1 mg/kg; NQ), a DAD2 receptor agonist, from postnatal days (P) 1–21. Rats were raised to P44 and behaviorally tested on PPI from P44-P48. Before each trial, rats were subcutaneous (sc) administered saline or CDPPB (10 mg/kg or 30 mg/kg). On P50, rats were given a spontaneous locomotor activity test after CDPPB or saline administration. On P51, the dorsal striatum and PFC were evaluated for both arrestin-2 (βA-2) and phospho-AKT protein levels. NQ-treated rats demonstrated a significant deficit in PPI, which was alleviated to control levels by the 30 mg/kg dose of CDPPB. There were no significant effects of CDPPB on locomotor activity. NQ treatment increased βA-2 and decreased phospho-AKT in both the dorsal striatum and PFC, consistent with an increase DAD2 signaling. The 30 mg/kg dose of CDPPB significantly reversed changes in βA-2 in the dorsal striatum and PFC and phospho-AKT in the PFC equivalent to controls. Both doses of CDPPB produced a decrease of phospho-AKT in the PFC compared to controls. This study revealed that a mGlu5 positive allosteric modulator was effective to alleviate PPI deficits and striatal DAD2 signaling in the NQ model of SZ.