Jessica Deslauriers

Combination of prenatal immune challenge and restraint stress affects prepulse inhibition and dopaminergic/GABAergic markers

Gestational immune challenge with the viral-like antigen poly I:C is a well-established neurodevelopmental model of schizophrenia. However, exposure to inflammation during early life may sensitize the developing brain to secondary insults and enhance the central nervous system vulnerability. To gain a better understanding of the pathophysiology of schizophrenia, we thus developed a two-hit animal model based on prenatal poly I:C immune challenge followed by restraint stress in juvenile mice. C57BL/6 gestational mice were intraperitoneally injected with poly I:C or saline at gestational day 12. Pups were then submitted or not, to restraint stress for 2h, for three consecutive days, from postnatal days 33 to 35. Prepulse inhibition (PPI) of acoustic startle response is commonly used to assess sensorimotor gating, a neural process severely disrupted in patients with schizophrenia. Our results revealed that the combination of prenatal immune challenge with poly I:C followed by a restraint stress period was able to induce a PPI disruption in 36-day-old pups, as opposed to each insult applied separately. PPI deficits were accompanied by dopaminergic and GABAergic abnormalities in the prefrontal cortex and striatum. Indeed, measurements of cortical and striatal dopamine D2 receptor (D2R) mRNA and protein levels revealed that the combination of gestational exposure to poly I:C and postnatal restraint stress induced an increase in D2R protein and mRNA levels. Likewise, the combination of both insults reduced the mRNA and protein expression levels of the 67 kDa form of glutamic acid decarboxylase (GAD67), in those two brain regions. To our knowledge, this two-hit animal model is the first in vivo model reporting PPI deficits at pubertal age. This two-hit animal model may also help in studying innovative therapies dedicated to the treatment of schizophrenia, especially in its early phase.

Antipsychotic-induced DRD2 upregulation and its prevention by α-lipoic acid in SH-SY5Y Neuroblastoma cells

Most antipsychotic (AP) drugs are dopamine (DA) D2 receptor (DRD2) antagonists and remain the main pharmacological treatment of schizophrenia. Long‐term AP use can give rise to tardive dyskinesia. It has been reported that chronic treatment with APs induces DRD2 upregulation and oxidative stress, which have been associated with tardive dyskinesia. We showed previously that H2O2‐induced oxidative stress increased DRD2 expression in human SH‐SY5Y neuroblastoma cells. We report here the effects of AP drugs on DRD2 expression levels in the same cell line and the effects of the inhibition of oxidative phenomena by (±)‐α‐lipoic acid treatment. Haloperidol, a first‐generation AP, induced an increase in DRD2 protein and mRNA levels, whereas amisulpride, a second‐generation AP, had no significant effect. (±)‐α‐Lipoic acid pretreatment reversed the haloperidol‐induced DRD2 upregulation in mRNA and protein levels. Furthermore, haloperidol induced a larger increase of oxidative stress biomarkers (protein carbonylation, lipid peroxidation, and superoxide anion production) than amisulpride. (±)‐α‐Lipoic acid also attenuated AP‐induced oxidative stress. Inhibition of catecholamine synthesis by α‐methyl‐DL‐tyrosine (AMPT) increased DRD2 expression and prevented further increase by APs. Our results suggest that haloperidol‐induced DRD2 upregulation is linked to oxidative stress and provide potential mechanisms by which (±)‐α‐lipoic acid can be considered as a therapeutic agent to prevent and treat side effects related to the use of first‐generation APs. Synapse, 2011.

Preventive effect of α-lipoic acid on prepulse inhibition deficits in a juvenile two-hit model of schizophrenia

Some pathophysiological models of schizophrenia posit that prenatal inflammation sensitizes the developing brain to second insults in early life and enhances brain vulnerability, thereby increasing the risk of developing the disorder during adulthood. We previously developed a two-hit animal model, based on the well-established prenatal immune challenge with poly-inosinic/cytidylic acid (polyI:C), followed by juvenile restraint stress (RS). We observed an additive disruption of prepulse inhibition (PPI) of acoustic startle in juvenile mice submitted to both insults. Previous studies have also reported that oxidative stress is associated with pathophysiological mechanisms of psychiatric disorders, including schizophrenia. We report here that PPI disruption in our two-hit animal model of schizophrenia is associated with an increase in oxidative stress. These findings led us to assess whether α-lipoic acid, an antioxidant, can prevent both increase in oxidative status and PPI deficits in our juvenile in vivo model of schizophrenia. In the offspring submitted to prenatal injection of polyI:C and to RS, treatment with α-lipoic acid prevented the development of PPI deficits 24h after the last period of RS. α-Lipoic acid also improved PPI performance in control mice. The reversal effect of α-lipoic acid pretreatment on these behavioral alterations was further accompanied by a normalization of the associated oxidative status and dopaminergic and GABAergic abnormalities in the prefrontal cortex. Based on our double insult paradigm, these results support the hypothesis that oxidative stress plays an important role in the development of PPI deficits, a well-known behavior associated with schizophrenia. These findings form the basis of future studies aiming to unravel mechanistic insights of the putative role of antioxidants in the treatment of schizophrenia, especially during the prodromal stage.

α-Lipoic Acid Interaction with Dopamine D2 Receptor-Dependent Activation of the Akt/GSK-3β Signaling Pathway Induced by Antipsychotics: Potential Relevance for the Treatment of Schizophrenia

Chronic administration of antipsychotics has been associated with dopamine D2 receptor (D2R) upregulation and tardive dyskinesia. We have previously shown that haloperidol, a first-generation antipsychotic (FGA), exerted an increase in D2R expression and oxidative stress and that (±)-α-lipoic acid reversed its effect. Previous studies have implicated the Akt/glycogen synthase kinase-3β (GSK-3β) signaling pathway in antipsychotic action. These findings led us to examine whether the Akt/GSK-3β pathway was involved in D2R upregulation and oxidative stress elicited by antipsychotics and, in (±)-α-lipoic acid-induced reversal of these phenomena, in SH-SY5Y cells. Antipsychotics increased phosphorylation of Akt and GSK-3β, and additive effects were observed with (±)-α-lipoic acid. GSK-3β inhibitors reversed haloperidol-induced overexpression of D2R mRNA levels but did not affect haloperidol-induced oxidative stress. Sustained antipsychotic treatment increased β-arrestin-2 and D2R receptor interaction. Regarding Akt/GSK-3β downstream targets, antipsychotics increased β-catenin levels, whereas (±)-α-lipoic acid induced an elevation of mTOR activation. These results suggest (1) that the effect of antipsychotics on the Akt/GSK-3β pathway in SH-SY5Y cells is reminiscent of their in vivo action, (2) that (±)-α-lipoic acid partially synergizes with antipsychotic drugs (APDs) on the same pathway, and (3) that the Akt/GSK-3β signaling cascade is not involved in the preventive effect of (±)-α-lipoic acid on antipsychotics-induced D2R upregulation.

A two-hit model of suicide-trait-related behaviors in the context of a schizophrenia-like phenotype: Distinct effects of lithium chloride and clozapine

Schizophrenia patients show a high rate of premature mortality due to suicide. The pathophysiological mechanisms of these suicidal behaviors in schizophrenia do not appear to involve serotonergic neurotransmission as found in the general population. Our aim was to develop an in vivo model of schizophrenia presenting suicide-trait-related behaviors such as aggressiveness, impulsivity, anxiety and helplessness. We opted for a two-hit model: C57BL/6 dams were injected with polyI:C on gestational day 12. The pups were submitted to social isolation for 4weeks after weaning. During the last week of social isolation and 30min before behavioral testing, the mice received vehicle, lithium chloride or clozapine. Lithium chloride is well known for its suicide preventive effects in the non-schizophrenic population, while clozapine is the antipsychotic with the best-established suicide preventive effect. The two-hit model induced several schizophrenia-related and suicide-trait-related behaviors in male, but not female, mice. Additionally, lithium chloride improved prepulse inhibition, aggressiveness, impulsivity and anxiety-like behavior in socially isolated mice only, whereas clozapine prevented behavioral abnormalities mainly in mice prenatally exposed to polyI:C and submitted to isolated rearing. The distinct effects of lithium chloride and clozapine suggested that mice prenatally exposed to polyI:C and submitted to social isolation presented a distinct phenotype from that of mice submitted to social isolation only. Because diagnosing suicidal risk in patients is a challenge for psychiatrists given the lack of specific clinical predictors, our in vivo model could help in gaining a better understanding of the mechanisms underlying suicidal behavior in the context of schizophrenia.

Implication of the ERK/MAPK Pathway in Antipsychotics-induced Dopamine D2 Receptor Upregulation and in the Preventive Effects of (±)-α-lipoic acid in SH-SY5Y Neuroblastoma Cells

Chronic administration of antipsychotics (APs) has been associated with dopamine D2 receptor (D2R) upregulation and tardive dyskinesia. We previously showed that haloperidol, a first-generation AP, exerted a more robust increase in D2R expression than amisulpride, a second-generation AP and that (±)-α-lipoic acid pre-treatment reversed the AP-induced D2R upregulation. We also demonstrated that the Akt/GSK-3β/β-catenin pathway is involved in the control of D2R expression levels, but is unlikely implicated in the preventive effects of (±)-α-lipoic acid since co-treatment with haloperidol and (±)-α-lipoic acid exerts synergistic effects on Akt/GSK-3β activation. These findings led us to examine whether the ERK/MAPK signaling pathway may be involved in D2R upregulation elicited by APs, and in its reversal by (±)-α-lipoic acid, in SH-SY5Y human neuroblastoma cells. Our results revealed that haloperidol, in parallel with an elevation in D2R mRNA levels, induced a larger increase of ERK (p42/p44) phosphorylation than amisulpride. Pre-treatment with the selective ERK inhibitor U0126 attenuated haloperidol-induced increase in D2R upregulation. Furthermore, (±)-α-lipoic acid prevented AP-induced ERK activation. These results show that (1) the ERK/MAPK pathway is involved in haloperidol-induced D2R upregulation; (2) the preventive effect of (±)-α-lipoic acid on haloperidol-induced D2R upregulation is in part mediated by an ERK/MAPK-dependent signaling cascade. Taken together, our data suggest that (±)-α-lipoic acid exerts synergistic effects with haloperidol on the Akt/GSK-3β pathway, potentially involved in the therapeutic effects of APs, and antagonism of ERK activation and D2R upregulation, potentially involved in tardive dyskinesia and treatment resistance.

Mitochondrial Dysfunction in Schizophrenia: Determination of Mitochondrial Respiratory Activity in a Two-Hit Mouse Model.

Schizophrenia is a chronic mental illness in which mitochondrial dysfunction has been suggested. Our laboratory recently developed a juvenile murine two-hit model (THM) of schizophrenia based on the combination of gestational inflammation, followed by juvenile restraint stress. We previously reported that relevant behaviors and neurochemical disturbances, including oxidative stress, were reversed by the antioxidant lipoic acid (LA), thereby pointing to the central role played by oxidative abnormalities and prompting us to investigate mitochondrial function. Mitochondrial activity was determined with the MitoXpress® commercial kit in two schizophrenia-relevant regions (prefrontal cortex (PFC) and striatum). Measurements were performed in state 3, with substrates for complex I- and complex II-induced respiratory activity (IRA). We observed an increase in complex I IRA in the PFC and striatum in both sexes but an increase in complex II activity only in males. LA treatment prevented this increase only in complex II IRA in males. Expression levels of the different respiratory chain complexes, as well as fission/fusion proteins and protein carbonylation, were unchanged. In conclusion, our juvenile schizophrenia THM shows an increase in mitochondrial activity reversed by LA, specifically in complex II IRA in males. Further investigations are required to determine the mechanisms of these modifications.

The Reciprocal Effects of Oxidative Stress and Glutamate Neurotransmission

The occurrence of oxidative phenomena during glutamatergic neurotransmission and its pathological correlate, excitotoxicity, was recognized early and is still the focus of active research. The present section will provide a brief overview of key components of glutamatergic transmission. The impact of redox status on glutamate release, reuptake, receptor expression, and function will be reviewed as well as some aspects of the complex neuroenergetics of the “tripartite synapse.” Symmetrically, we will also address how glutamate modulates redox status through effectors such as mitochondrial dynamics, NADPH oxidase stimulation, nitric oxide levels, and the redox modulating cystine glutamate exchanger.

The Impact of Oxidative Stress on Dopaminergic Neurotransmission

Dopamine neurotransmission has a demonstrated relevance for a number of neurodegenerative and movement disorders as well as psychiatric conditions such as bipolar affective disorder and schizophrenia. Apart from dopaminergic neuron loss in Parkinson’s disease and the involvement of dopamine therein, the striatum is inherently exposed to high levels of oxidative stress, which is increased in some of the pathological conditions mentioned above. In the present chapter, we will discuss how redox status impacts the key components of dopamine neurotransmission and evaluate the relevance of these modifications with respect to the recently revisited dopamine hypothesis of schizophrenia.

The Impact of Oxidative Stress on GAD67 Levels and Parvalbumin-Positive Neurons

GAD67, product of the GAD1 gene, and GAD65, product of GAD2, are critically involved in the control of GABA synthesis in the central nervous system. Since the initial report of decreased transcription levels of GAD67 in the prefrontal cortex of patients with schizophrenia, the finding of decreased GAD transcript and protein levels has been very generally replicated, making it the most consistent neurochemical abnormality in schizophrenia and to some extent in bipolar affective disorder. The concomitant decrease of the calcium-binding protein parvalbumin has been reported with similar regularity, and these neurochemical perturbations relate to the dysfunction of a network of cortical or hippocampal GABAergic interneurons, notably basket and chandelier cells. Among the potential mechanisms leading to this decrease, the hypofunction of the NMDA receptor has attracted the most attention and has been shown recently to involve increased oxidative stress, originating from NADPH oxidase activation. Lastly, a large preclinical and cognitive literature suggests that a dysfunctional frontal GABAergic network is associated to abnormal electroencephalographic spectra, which are thought to underlie higher cognitive functions and are known to be disturbed in schizophrenia.