Repeated cocaine administration increases N-methyl-d-aspartate NR1 subunit, extracellular signal-regulated kinase and cyclic AMP response element-binding protein phosphorylation and glutamate release in the rat dorsal striatum

Key transcription factors mediating cocaine-induced plasticity in the nucleus accumbens

Repeated cocaine use induces coordinated changes in gene expression that drive plasticity in the nucleus accumbens (NAc), an important component of the brain's reward circuitry, and promote the development of maladaptive, addiction-like behaviors. Studies on the molecular basis of cocaine action identify transcription factors, a class of proteins that bind to specific DNA sequences and regulate transcription, as critical mediators of this cocaine-induced plasticity. Early methods to identify and study transcription factors involved in addiction pathophysiology primarily relied on quantifying the expression of candidate genes in bulk brain tissue after chronic cocaine treatment, as well as conventional overexpression and knockdown techniques. More recently, advances in next generation sequencing, bioinformatics, cell-type-specific targeting, and locus-specific neuroepigenomic editing offer a more powerful, unbiased toolbox to identify the most important transcription factors that drive drug-induced plasticity and to causally define their downstream molecular mechanisms. Here, we synthesize the literature on transcription factors mediating cocaine action in the NAc, discuss the advancements and remaining limitations of current experimental approaches, and emphasize recent work leveraging bioinformatic tools and neuroepigenomic editing to study transcription factors involved in cocaine addiction.

Conducting polymer-based electrochemical biosensors for neurotransmitters: A review

Neurotransmitters are important biochemical molecules that control behavioral and physiological functions in central and peripheral nervous system. Therefore, the analysis of neurotransmitters in biological samples has a great clinical and pharmaceutical importance. To date, various methods have been developed for their assay. Of the various methods, the electrochemical sensors demonstrated the potential of being robust, selective, sensitive, and real time measurements. Recently, conducting polymers (CPs) and their composites have been widely employed in the fabrication of various electrochemical sensors for the determination of neurotransmitters. Hence, this review presents a brief introduction to the electrochemical biosensors, with the detailed discussion on recent trends in the development and applications of electrochemical neurotransmitter sensors based on CPs and their composites. The review covers the sensing principle of prime neurotransmitters, including glutamate, aspartate, tyrosine, epinephrine, norepinephrine, dopamine, serotonin, histamine, choline, acetylcholine, nitrogen monoxide, and hydrogen sulfide. In addition, the combination with other analytical techniques was also highlighted. Detection challenges and future prospective of the neurotransmitter sensors were discussed for the development of biomedical and healthcare applications.

Withdrawal from cocaine self-administration and yoked cocaine delivery dysregulates glutamatergic mGlu5 and NMDA receptors in the rat brain

In human addicts and in animal models, chronic cocaine use leads to numerous alterations in glutamatergic transmission, including its receptors. The present study focused on metabotropic glutamatergic receptors type 5 (mGluR₅) and N-methyl-D-aspartate receptor subunits (NMDAR: GluN1, GluN2A, GluN2B) proteins during cocaine self-administration and after 10-day of extinction training in rats. To discriminate the contingent from the non-contingent cocaine delivery, we employed the “yoked”-triad control procedure. Protein expression in rat prefrontal cortex, nucleus accumbens, hippocampus, and dorsal striatum was determined. We also examined the Homer1b/c protein, a member of the postsynaptic density protein family that links NMDAR to mGluR₅. Our results revealed that cocaine self-administration selectively increased GluN1 and GluN2A subunit in the rat hippocampus and dorsal striatum, respectively, while mGluR₅ protein expression was similarly increased in the dorsal striatum of both experimental groups. Withdrawal from both contingent and non-contingent cocaine delivery induced parallel increases in prefrontal cortical GluN2A protein expression, hippocampal mGluR₅, and GluN1 protein expression as well as in accumbal GluN1 subunit expression, while the mGluR₅ expression was reduced in the prefrontal cortex. Extinction training in animals with a history of cocaine self-administration resulted in an elevation of the hippocampal GluN2A/GluN2B subunits and accumbal mGluR₅, and in a 50 % decrease of mGluR₅ protein expression in the dorsal striatum. The latter reduction was associated with Homer1b/1c protein level decrease. Our results showed that both contingent and non-contingent cocaine administration produces numerous, brain region specific, alterations in the mGluR₅, NMDA, and Homer1b/1c protein expression which are dependent on the modality of cocaine administration.

The effect of active and passive intravenous cocaine administration on the extracellular signal-regulated kinase (ERK) activity in the rat brain

According to a current hypothesis of learning processes, recent papers pointed out to an important role of the extracellular signal-regulated kinase (ERK), in drug addiction. We employed the Western blotting techniques to examine the ERK activity immediately after cocaine iv self-administration and in different drug-free withdrawal periods in rats. To distinguish motivational vs. pharmacological effects of the psychostimulant intake, a "yoked" procedure was used. Animals were decapitated after 14 daily cocaine self-administration sessions or on the 1st, 3rd or 10th extinction days. At each time point the activity of the ERK was assessed in several brain structures, including the prefrontal cortex, hippocampus, dorsal striatum and nucleus accumbens. Passive, repeated iv cocaine administration resulted in a 45% increase in ERK phosphorylation in the hippocampus while cocaine self-administration did not change brain ERK activity. On the 1st day of extinction, the activity of the ERK in the prefrontal cortex was decreased in rats with a history of cocaine chronic intake: by 66% for "active" cocaine group and by 35% for "yoked" cocaine group. On the 3rd day the reduction in the ERK activity (25-34%) was observed in the hippocampus for both cocaine-treated groups, and also in the nucleus accumbens for "yoked" cocaine group (40%). On the 10th day of extinction there was no significant alteration in ERK activity in any group of rats. Our findings suggest that cortical ERK is involved in cocaine seeking behavior in rats. They also indicate the time and regional adaptations in this enzyme activity after cocaine withdrawal.

Imaging glutamate homeostasis in cocaine addiction with the metabotropic glutamate receptor 5 positron emission tomography radiotracer [(11)C]ABP688 and magnetic resonance spectroscopy

BACKGROUND

Preclinical studies demonstrate that glutamate homeostasis in the striatum is disrupted following cocaine exposure, including a decrease in metabotropic glutamate receptor type 5 (mGluR5) expression and reduced glutamate turnover. The goal of this study was to use imaging of the human brain to investigate alterations in the glutamate signaling in cocaine addiction.

METHODS

Positron emission tomography imaging with the radiotracer [(11)C]ABP688 was used to measure mGluR5 binding and magnetic resonance spectroscopy was used to measure glutamate-glutamine levels in the striatum of cocaine-addicted participants (n = 15) compared with healthy control subjects (n = 15). Following the scans, the cocaine-addicted volunteers performed cocaine self-administration sessions to investigate the correlation between cocaine-seeking behavior and mGluR5 receptor binding.

RESULTS

The results of the study showed that cocaine addiction was associated with a 20% to 22% reduction in [(11)C]ABP688 binding in the striatum. A secondary analysis of cortical and subcortical regions other than the striatum showed a similar reduction in [(11)C]ABP688 binding, suggesting that the decrease was widespread. No between-group differences were seen in the magnetic resonance spectroscopy measures of glutamate-glutamine in the left striatum. In addition, no correlation was seen between [(11)C]ABP688 binding in the striatum and the choice to self-administer cocaine.

CONCLUSIONS

Overall, these results show that long-term cocaine use is associated with a decrease in mGluR5 availability compared with matched healthy control subjects and suggests that this receptor may serve as a viable target for treatment development for this disorder.

Activation of glycine site and GluN2B subunit of NMDA receptors is necessary for ERK/CREB signaling cascade in rostral anterior cingulate cortex in rats: implications for affective pain

OBJECTIVE

The rostral anterior cingulate cortex (rACC) is implicated in processing the emotional component of pain. N-methyl-D-aspartate receptors (NMDARs) are highly expressed in the rACC and mediate pain-related affect by activating a signaling pathway that involves cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) and/or extracellular regulated kinase (ERK)/cAMP-response element-binding protein (CREB). The present study investigated the contributions of the NMDAR glycine site and GluN2B subunit to the activation of ERK and CREB both in vitro and in vivo in rat rACC.

METHODS

Immunohistochemistry and Western blot analysis were used to separately assess the expression of phospho-ERK (pERK) and phospho-CREB (pCREB) in vitro and in vivo. Double immunostaining was also used to determine the colocalization of pERK and pCREB.

RESULTS

Both bath application of NMDA in brain slices in vitro and intraplantar injection of formalin into the rat hindpaw in vivo induced significant up-regulation of pERK and pCREB in the rACC, which was inhibited by the NMDAR antagonist DL-2-amino-5-phospho-novaleric acid. Selective blockade of the NMDAR GluN2B subunit and the glycine-binding site, or degradation of endogenous D-serine, a co-agonist for the glycine site, significantly decreased the up-regulation of pERK and pCREB expression in the rACC. Further, the activated ERK predominantly colocalized with CREB.

CONCLUSION

Either the glycine site or the GluN2B subunit of NMDARs participates in the phosphorylation of ERK and CREB induced by bath application of NMDA in brain slices or hindpaw injection of 5% formalin in rats, and these might be fundamental molecular mechanisms underlying pain affect.

Chronic cocaine exposure induces putamen glutamate and glutamine metabolite abnormalities in squirrel monkeys

RATIONALE

Chronic cocaine exposure has been associated with progressive brain structural and functional changes. Clarifying mechanisms underlying cocaine's progressive brain effects may help in the development of effective cocaine abuse treatments.

OBJECTIVES

We used a controlled squirrel monkey model of chronic cocaine exposure (45 mg/kg/week for 9 months) combined with ultra-high magnetic field (9.4 T) proton magnetic resonance spectroscopy to prospectively measure putamen metabolite changes.

METHODS

Proton metabolites were measured with a STEAM sequence, quantified with LCModel using a simulated basis set, and expressed as metabolite/total creatine (tCr) ratios.

RESULTS

We found cocaine-induced time-dependent changes in putamen glutamate/tCr and glutamine/tCr metabolite ratios suggestive of altered glutamate compartmentalization, neurotransmission, and metabolism. By contrast, saline-treated monkeys exhibited no metabolite changes over time. The time course of cocaine-induced metabolite abnormalities we detected is consistent with the apparent time course of glutamate abnormalities identified in a cross-sectional study in human cocaine users, as well as with microdialysis findings in rodent models of repeated cocaine exposure.

CONCLUSIONS

Together, these findings suggests that this squirrel monkey model may be useful for characterizing glutamatergic changes associated with cocaine exposure and for determining efficacies of treatments designed to mitigate cocaine-induced glutamatergic system dysfunction.

Interactions of Dopamine D1 and N-methyl-D-Aspartate Receptors are Required for Acute Cocaine-Evoked Nitric Oxide Efflux in the Dorsal Striatum

Alterations in nitric oxide (NO) release in response to psychostimulants in the striatum cause a plastic change contributing to the development and expression of addiction. In this study, regulation of NO efflux evoked by acute cocaine in the dorsal striatum was investigated using real-time detection of NO in vivo. We found that acute systemic injection of cocaine (20 mg/kg) increased NO efflux, which was reduced by the intrastriatal infusion of the dopamine D1 receptor antagonist, SCH23390 (7.5 nmol), and the dopamine D2 receptor agonist, quinpirole (5 nmol). Increased levels of NO efflux by acute cocaine were also reduced by the intrastriatal infusion of the N-methyl-D-aspartate (NMDA) receptor antagonists, MK801 (2 nmol) and AP5 (2 nmol). These findings suggest that interactions of dopamine D1 receptors and NMDA receptors after acute exposure to cocaine participate in the upregulation of NO efflux in the dorsal striatum.

The role of striatal NMDA receptors in drug addiction

The past decade has witnessed an impressive accumulation of evidence indicating that the excitatory amino acid glutamate and its receptors, in particular the N-methyl-D-aspartate (NMDA) receptor subtype, play an important role in drug addiction. Various lines of research using animal models of drug addiction have demonstrated that drug-induced craving is accompanied by significant upregulation of NR2B subunit expression. Furthermore, selective blockade of NR2B-containing NMDA receptors in the striatum, especially in the nucleus accumbens (NAc) can inhibit drug craving and reinstatement. The purpose of this review is to examine the role of striatal NMDA receptors in drug addiction. After a brief description of glutamatergic innervation and NMDA receptor subunit distribution in the striatum, we discuss potential mechanisms to explain the role of striatal NMDA receptors in drug addiction by elucidating signaling cascades involved in the regulation of subunit expression and redistribution, phosphorylation of receptor subunits, as well as activation of intracellular signals triggered by drug experience. Understanding the mechanisms regulating striatal NMDA receptor changes in drug addiction will provide more specific and rational targets to counteract the deleterious effects of drug addiction.

Repeated cocaine administration increases cleaved poly(ADP-ribose) polymerase-1 expression in the rat dorsal striatum

Poly(ADP-ribose) polymerase-1 (PARP-1) expression is associated with the endoplasmic reticulum (ER) stress response in neurons. In this study, the regulation of PARP-1 activation by repeated cocaine administration in the rat dorsal striatum was investigated in vivo. Our results demonstrated that repeated systemic injections of cocaine (20 mg/kg) once a day for 7 days increased cleaved PARP-1 expression. This increase was reduced by blocking dopamine D1, but not dopamine D2, receptors. The blocking of group I metabotropic glutamate receptors (mGluRs), mGluR1 subtype, and N-methyl-D-aspartate receptors also reduced cocaine-stimulated cleaved PARP-1 expression. Taken together, these findings suggest that PARP-1 activation is upregulated by repeated cocaine administration, and that interactions between dopamine D1 and glutamate receptors may be involved in this upregulation.

Molecular and genetic substrates linking stress and addiction

Drug addiction is one of the top three health concerns in the United States in terms of economic and health care costs. Despite this, there are very few effective treatment options available. Therefore, understanding the causes and molecular mechanisms underlying the transition from casual drug use to compulsive drug addiction could aid in the development of treatment options. Studies in humans and animal models indicate that stress can lead to both vulnerability to develop addiction, and increased drug taking and relapse in addicted individuals. Exposure to stress or drugs of abuse results in long-term adaptations in the brain that are likely to involve persistent alterations in gene expression or activation of transcription factors, such as the cAMP Response Element Binding (CREB) protein. The signaling pathways controlled by CREB have been strongly implicated in drug addiction and stress. Many potential CREB target genes have been identified based on the presence of a CRE element in promoter DNA sequences. These include, but are not limited to CRF, BDNF, and dynorphin. These genes have been associated with initiation or reinstatement of drug reward and are altered in one direction or the other following stress. While many reviews have examined the interactions between stress and addiction, the goal of this review was to focus on specific molecules that play key roles in both stress and addiction and are therefore posed to mediate the interaction between the two. Focus on these molecules could provide us with new targets for pharmacological treatments for addiction.

Cocaine effects on dopamine and NMDA receptors interactions in the striatum of Fischer rats

Numerous studies have shown that biochemical and behavioral effects of cocaine are mediated by dopamine D1 receptor (D1R) and NMDA R1 receptor (NR1)-mediated transmission. In this study, we investigated the physical interactions between D1R and NR1 in response to acute cocaine administration in a time course of 5-60 min. In the caudate-putamen (CPu) of male Fischer rats, a single cocaine injection (30 mg/kg) reduced D1R-NR1 protein-protein interactions 30 min after treatment. In addition, activation or blockade of the NMDA receptor using NMDA (25mg/kg) or MK-801 (0.25mg/kg), respectively, also reduced the D1R-NR1 physical interactions. Acute cocaine administration did not alter total D1R or NR1 protein levels in our time course of study. These results indicate that D1R-NR1 physical interaction rather than total protein levels may regulate the intracellular signaling after acute cocaine administration.