NMDAR dependent intracellular responses associated with cocaine conditioned place preference behavior

Hypoxia-inducible factor upregulation by roxadustat attenuates drug reward by altering brain iron homoeostasis

Substance use disorder remains a major challenge, with an enduring need to identify and evaluate new, translational targets for effective treatment. Here, we report the upregulation of Hypoxia-inducible factor-1α (HIF-1α) expression by roxadustat (Rox), a drug developed for renal anemia that inhibits HIF prolyl hydroxylase to prevent degradation of HIF-1α, administered either systemically or locally into selected brain regions, suppressed morphine (Mor)-induced conditioned place preference (CPP). A similar effect was observed with methamphetamine (METH). Moreover, Rox also inhibited the expression of both established and reinstated Mor-CPP and promoted the extinction of Mor-CPP. Additionally, the elevation of HIF-1α enhanced hepcidin/ferroportin 1 (FPN1)-mediated iron efflux and resulted in cellular iron deficiency, which led to the functional accumulation of the dopamine transporter (DAT) in plasma membranes due to iron deficiency-impaired ubiquitin degradation. Notably, iron-deficient mice generated via a low iron diet mimicked the effect of Rox on the prevention of Mor- or METH-CPP formation, without affecting other types of memory. These data reveal a novel mechanism for HIF-1α and iron involvement in substance use disorder, which may represent a potential novel therapeutic strategy for the treatment of drug abuse. The findings also repurpose Rox by suggesting a potential new indication for the treatment of substance use disorder.

Datumetine Preferentially Upregulates N-methyl-D-aspartate Receptor Signalling Pathways in Different Brain Regions of Mice

Introduction

We previously reported that datumetine possesses binding affinity with N-methyl-D-aspartate receptor (NMDAR) and that 14-day exposure to datumetine altered NMDAR signaling by mimicking glutamate toxicity. Here, we investigated the potential neuroprotective effect of a single shot of a low dose of datumetine administration in BALB/c mice.

Methods

30 male adult BALB/c mice were used for the study. The mice were randomly divided into three groups of ten mice each with an intraperitoneal injection of 0.1 mL of 10% DMSO for the Vehicle group, Datumetine group were administered 0.1 mg/kg body weight (bw) of datumetine and MK-801+Datumetine group were administered 0.5 mg/kg bw of MK-801 (to block NMDAR) followed by 0.1 mg/kg bw of datumetine after 30 minutes. 24 hours after administration, mice were euthanized in an isoflurane chamber followed by perfusion with 1X PBS. Brains were excised and stored at -20°C till further processing. Mice designated for IHC were further perfused with 4% PFA and brain excised and stored in 4% PFA till further processing. NMDAR signalling molecules expression was evaluated in frozen brain samples and the fixed brain samples were stained for neuron, vGlut and NMDAR subtypes.

Results

Relative to vehicle (Veh), datumetine downregulate calcium calmodulin kinase II alpha (CamKIIα) expression in the hippocampus and prefrontal cortex (PFC) but not in the cerebellum, cyclic AMP response element binding protein (CREB) was also upregulated only in the PFC but phosphorylated CREB (pCREB) was also upregulated in three brain regions observed, while brain-derived neurotrophic factor (BDNF) was only upregulated in hippocampus and PFC of Datumetine relative to vehicle (Veh). On the other hand, dizocilpine (MK-801) reversed some of the effects of datumetine in the observed brain regions. No major histological alterations were observed in the different brain regions immunohistochemically.

Conclusion

We conclude that a low dose of datumetine moderately enhances NMDAR activity. This showed the neuroprotective potentials of low datumetine exposure.

Protein kinases in natural versus drug reward

Natural and drug rewards act on the same neural pathway, the mesolimbic dopaminergic system. In brain regions such as the nucleus accumbens and ventral tegmental area, drugs of abuse-induced stimulation of signaling pathways can lead to synaptic reshaping within this system. This is believed to be underlying the maladaptive alterations in behaviors associated with addiction. In this review, we discuss animal studies disclosing the implication of several protein kinases, namely protein kinase A (PKA), extracellular signal regulated kinase (ERK) mitogen-activated protein kinases (MAPK), p38 MAPK, and calcium/calmodulin-dependent kinase II (CaMKII), in reward-related brain regions in drug and natural reward. Furthermore, we refer to studies that helped pave the way toward a better understanding of the neurobiology underlying non-drug and drug reward through genetic deletion or brain region-specific pharmacological inhibition of these kinases. Whereas the role of kinases in drug reward has been extensively studied, their implication in natural reward, such as positive social interaction, is less investigated. Discovering molecular candidates, recruited specifically by drug versus natural rewards, can promote the identification of novel targets for the pharmacological treatment of addiction with less off-target effects and being effective when used combined with behavioral-based therapies.

Implication of Extracellular Signal-Regulated Kinase in the Expression of Natural Reward: Evidence Not Found

Many studies have implicated extracellular signal-regulated kinase (ERK) in drug-rewarding properties. Yet, only few investigated whether ERK also mediates the naturally rewarding stimuli. In this study, we compared ERK activation in the nucleus accumbens (NAc) after cocaine reward and after positive social interaction (SI) with a partner-reward in male rats. With our protocol, ERK phosphorylation in the NAc was not increased after cocaine reward. In addition, the interaction with a social partner did not alter ERK activation in the NAc. These results suggest that ERK in the NAc may not be involved in natural reward learning. SI in an alternative context to the one associated with drugs of abuse can abolish drug preference. Given that intra-NAc core ERK inhibition impaired the expression of cocaine preference, we wanted to investigate whether the protective effects of SI when an individual is allowed to interact with a social partner in an alternative context to the one associated with drugs during the learning phase are enhanced by ERK inhibition. For that, U0126 was bilaterally infused into the NAc core of rats conditioned with cocaine in one context and with SI in the opposite context before assessing the expression of reward-related learning. Intra-NAc core ERK inhibition was ineffective to impair the expression of drug reward as previously demonstrated, when a social partner was available in an alternative context. Thus, the effects of the pharmacological manipulations based on decreasing ERK activity are not cumulative to other treatments for drug addiction based on SI.

CBD Effects on Motor Profile and Neurobiological Indices Related to Glutamatergic Function Induced by Repeated Ketamine Pre-Administration

Clinical evidence and experimental studies have shown the psychotomimetic properties induced by ketamine. Moreover, acute or chronic ketamine (KET) administration has been widely used for modeling schizophrenia-like symptomatology and pathophysiology. Several studies have reported the antipsychotic potential of cannabidiol (CBD), while there is limited information on the cannabidiol effect on KET-induced schizophrenia-like impairments. Therefore, the goal of the present study was to evaluate neuroplastic changes induced by repeated KET administration, which is used as an experimental model of schizophrenia—with a behavioral focus on positive-like symptomatology– and to assess the modulatory role of CBD treatment. The present findings have shown a robust increase in motor activity in KET-treated rats, following a 10-day period of chronic administration at the sub-anesthetic dose of 30 mg/kg (i.p), that was reversed to normal by subsequent chronic CBD treatment. Concerning the expression of glutamate receptors, the current findings have shown region-dependent KET-induced constitutional alterations in NMDA and AMPA receptors that were modified by subsequent CBD treatment. Additionally, repeated KET administration increased ERK1/2 phosphorylation state in all regions examined, apart from the ventral hippocampus that was modulated by subsequent CBD treatment. The present results show, for the first time, a stimulated motor output coupled with a specific glutamatergic-related status and ERK1/2 activation following chronic KET administration that were attenuated by CBD treatment, in a region-dependent manner. These findings provide novel information concerning the antipsychotic potential of CBD using a specific design of chronic KET administration, thus contributing to experimental approaches that mirror the symptomatology and pathophysiology of schizophrenia.

Cannabidiol Modulates the Motor Profile and NMDA Receptor-related Alterations Induced by Ketamine

Cannabidiol (CBD) is a non-addictive ingredient of cannabis with antipsychotic potential, while ketamine (KET), an uncompetitive NMDA receptor inhibitor, has been extensively used as a psychotomimetic. Only few studies have focused on the role of CBD on the KET-induced motor profile, while no study has investigated the impact of CBD on KET-induced alterations in NMDA receptor subunit expression and ERK phosphorylation state, in brain regions related to the neurobiology and treatment of schizophrenia. Therefore, the aim of the present study is to evaluate the role of CBD on KET-induced motor response and relevant glutamatergic signaling in the prefrontal cortex, the nucleus accumbens, the dorsal and ventral hippocampus. The present study demonstrated that CBD pre-administration did not reverse KET-induced short-lasting hyperactivity, but it prolonged it over time. CBD alone decreased motor activity at the highest dose tested (30 mg/kg) while KET increased motor activity at the higher doses (30, 60 mg/kg). Moreover, KET induced regionally-dependent alterations in NR1 and NR2B expression and ERK phosphorylation that were reversed by CBD pre-administration. Interestingly, in the nucleus accumbens KET per se reduced NR2B and p-ERK levels, while the CBD/KET combination increased NR2B and p-ERK levels, as compared to control. This study is the first to show that CBD prolongs KET-induced motor stimulation and restores KET-induced effects on glutamatergic signaling and neuroplasticity-related markers. These findings contribute to the understanding of CBD effects on the behavioral and neurobiological profiles of psychotogenic KET.

CREB transcription in the medial prefrontal cortex regulates the formation of long-term associative recognition memory

The medial prefrontal cortex (mPFC) is known to be critical for specific forms of long-term recognition memory, however the cellular mechanisms in the mPFC that underpin memory maintenance have not been well characterized. This study examined the importance of phosphorylation of cAMP responsive element binding protein (CREB) in the mPFC for different forms of long-term recognition memory in the rat. Adenoviral transduction of the mPFC with a dominant-negative inhibitor of CREB impaired object-in-place memory following a 6 or 24 h retention delay, but no impairment was observed following delays of 5 min or 3 h. Long-term object temporal order memory and spatial temporal order memory was also impaired. In contrast, there were no impairments in novel object recognition or object location memory. These results establish, for the first time, the importance of CREB phosphorylation within the mPFC for memory of associative and temporal information crucial to recognition.

The role of neuronal nitric oxide synthase in cocaine place preference and mu opioid receptor expression in the nucleus accumbens

RATIONALE

There is evidence that central mu opioid receptors (MORs) are implicated in several aspects of cocaine addiction, and that MOR expression is elevated by cocaine in vitro and in the nucleus accumbens (NAc) when administered in vivo.

OBJECTIVE

To understand the cellular mechanisms involved in regulating MOR expression, this study explored whether neuronal nitric oxide synthase (nNOS) modulates the neurochemical and behavioral effects of acute and repeated cocaine administration.

METHODS

Male Sprague-Dawley rats received a single cocaine injection (20 mg/kg, i.p.) in combination with the selective nNOS inhibitor 7-nitroindazole (7-NI) (0, 25, or 50 mg/kg, i.p.), and the expression of MOR and nNOS messenger RNA (mRNA) and protein levels in the NAc were measured. In a separate conditioned place preference (CPP) experiment, 7-NI (0, 25, or 50 mg/kg, i.p.) was administered prior to cocaine (0 or 20 mg/kg, i.p.) conditioning sessions, and levels of MOR and nNOS mRNA and protein in the NAc were measured following CPP test.

RESULTS

Acute cocaine administration significantly enhanced nNOS and MOR mRNA and protein expression in the NAc, and this increase in MOR expression was blocked by 7-NI. Furthermore, in 7-NI pre-treated rats, cocaine-induced CPP was not statistically significant and the increase in MOR mRNA expression in the NAc in these animals was attenuated.

CONCLUSIONS

These findings suggest that nNOS modulates MOR expression following acute cocaine administration, and that cocaine CPP and associated upregulation of MOR expression involve both nNOS-dependent and independent mechanisms. Elucidation of these molecular events may identify useful therapeutic target for cocaine addiction.

NMDA receptor dependent changes in c-fos and p-CREB signaling following extinction and reinstatement of morphine place preference

Neural circuitry comprising the ventral tegmental area, nucleus accumbens (NAc), prefrontal cortex (PFC) and hippocampus (HIP) has a main role in reward phenomena. Previous behavioral studies indicated that intracerebroventricular administration of AP5 (NMDA glutamate receptor antagonist) and CNQX (AMPA/kainate glutamate receptor antagonist) during the extinction and before reinstatement of morphine-induced conditioned place preference (CPP) reduced the extinction period and reinstatement of morphine-CPP. Therefore, in the present study, we tried to evaluate the effect of antagonism of NMDA glutamate receptors on the p-CREB/CREB ratio and c-fos expression in the NAc, PFC and HIP during these two phases of morphine-CPP in male adult albino Wistar rats. The p-CREB/CREB ratio and c-fos levels were estimated by Western blot analysis. The results revealed that these two factors decreased by antagonism of NMDA glutamate receptors (different doses of AP5) compared to saline-control group in aforementioned regions. The reduction of molecular markers, especially the p-CREB/CREB ratio, after AP5 administration was more during the extinction period. Therefore, it can be assumed that consolidation and reconsolidation of morphine memory via intra-PFC, -NAc and -HIP NMDA glutamate receptors are in accordance with changes in p-CREB/CREB ratio and c-fos levels.