Elevation of Extracellular Glutamate by Blockade of Astrocyte Glutamate Transporters Inhibits Cocaine Reinforcement in Rats via a NMDA-GluN2B Receptor Mechanism

Study authors Hong-Ju Yang and Briana J Hempel

Featured Paper of the Month – August 2022

Published in The Journal of Neuroscience by Hong-Ju Yang, Briana J Hempel and Zheng-Xiong Xi, et al. of the NIDA IRP Addiction Biology Unit.

Summary

It is well known that glutamate plays an important role in relapse to drug seeking. However, the role of glutamate in drug reward is unclear. In this report, we found that elevating extracellular glutamate level in the nucleus accumbens (NAc) by TFB-TBOA, a selective astrocyte glutamate transporter inhibitor, dose-dependently inhibits cocaine self-administration and brain-stimulation reward. Mechanistic assays indicate that prolonged cocaine self-administration selectively upregulates NMDA-GluN2B receptor subtype expression in striatal dopaminoceptive neurons. Transgenic downregulation or pharmacological blockade of GluN2B in the NAc blocked TFB-TBOA or glutamate-induced reduction in cocaine self-administration, suggesting a GluN2B receptor mechanism underlying glutamate modulation of drug reward. In contrast, elevating extracellular glutamate levels in the NAc, ventral tegmental area (VTA), or ventral pallidum (VP) by TFB-TBOA reinstates extinguished cocaine-seeking behavior. These findings demonstrate that glutamate plays an opposite role in drug reward versus relapse – reducing cocaine reward, while potentiating relapse to cocaine seeking.

Publication Information

Yang, Hong-Ju; Hempel, Briana J; Bi, Guo-Hua; He, Yi; Zhang, Hai-Ying; Gardner, Eliot L; Xi, Zheng-Xiong

Elevation of Extracellular Glutamate by Blockade of Astrocyte Glutamate Transporters Inhibits Cocaine Reinforcement in Rats via a NMDA-GluN2B Receptor Mechanism Journal Article

In: J Neurosci, vol. 42, no. 11, pp. 2327–2343, 2022, ISSN: 1529-2401.

Abstract | Links

@article{pmid35091501,

title = {Elevation of Extracellular Glutamate by Blockade of Astrocyte Glutamate Transporters Inhibits Cocaine Reinforcement in Rats via a NMDA-GluN2B Receptor Mechanism},

author = {Hong-Ju Yang and Briana J Hempel and Guo-Hua Bi and Yi He and Hai-Ying Zhang and Eliot L Gardner and Zheng-Xiong Xi},

url = {https://pubmed.ncbi.nlm.nih.gov/35091501/},

doi = {10.1523/JNEUROSCI.1432-21.2022},

issn = {1529-2401},

year  = {2022},

date = {2022-01-01},

urldate = {2022-01-01},

journal = {J Neurosci},

volume = {42},

number = {11},

pages = {2327--2343},

abstract = {It is well established that glutamate plays an important role in drug-induced and cue-induced reinstatement of drug seeking. However, the role of glutamate in drug reward is unclear. In this study, we systemically evaluated the effects of multiple glutamate transporter (GLT) inhibitors on extracellular glutamate and dopamine (DA) in the nucleus accumbens (NAc), intravenous cocaine self-administration, intracranial brain-stimulation reward (BSR), and reinstatement of cocaine seeking in male and female rats. Among the five GLT inhibitors we tested, TFB-TBOA was the most potent. Microinjections of TFB-TBOA into the NAc, but not the ventral tegmental area (VTA), or dorsal striatum (DS), dose-dependently inhibited cocaine self-administration under fixed-ratio and progressive-ratio (PR) reinforcement schedules, shifted the cocaine dose-response curve downward, and inhibited intracranial BSR. Selective downregulation of astrocytic GLT-1 expression in the NAc by GLT-1 antisense oligonucleotides also inhibited cocaine self-administration. The reduction in cocaine self-administration following TFB-TBOA administration was NMDA GluN2B receptor dependent, and rats self-administering cocaine showed upregulation of GluN2B expression in NAc DA- and cAMP-regulated phosphoprotein 32 (DARPP-32)-positive medium-spiny neurons (MSNs). In contrast, TFB-TBOA, when locally administered into the NAc, VTA, or ventral pallidum (VP), dose-dependently reinstated cocaine-seeking behavior. Intra-NAc TFB-TBOA-evoked drug-seeking was long-lasting and NMDA/AMPA receptor dependent. These findings, for the first time, indicate that glutamate in the NAc negatively regulates cocaine's rewarding effects, while an excess of glutamate in multiple brain regions can trigger reinstatement of drug-seeking behavior. It is well known that glutamate plays an important role in relapse to drug seeking. However, the role of glutamate in drug reward is less clear. Here, we report that TFB-TBOA, a highly potent glutamate transporter (GLT) inhibitor, dose-dependently elevates extracellular glutamate and inhibits cocaine self-administration and brain-stimulation reward (BSR), when administered locally into the nucleus accumbens (NAc), but not other brain regions. Mechanistic assays indicate that cocaine self-administration upregulates NMDA-GluN2B receptor subtype expression in striatal dopaminoceptive neurons and activation of GluN2B by TFB-TBOA-enhanced glutamate inhibits cocaine self-administration. TFB-TBOA also reinstates cocaine-seeking behavior when administered into the NAc, ventral tegmental area (VTA), and ventral pallidum (VP). These findings demonstrate that glutamate differentially regulates cocaine reward versus relapse, reducing cocaine reward, while potentiating relapse to cocaine seeking.},

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pubstate = {published},

tppubtype = {article}

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It is well established that glutamate plays an important role in drug-induced and cue-induced reinstatement of drug seeking. However, the role of glutamate in drug reward is unclear. In this study, we systemically evaluated the effects of multiple glutamate transporter (GLT) inhibitors on extracellular glutamate and dopamine (DA) in the nucleus accumbens (NAc), intravenous cocaine self-administration, intracranial brain-stimulation reward (BSR), and reinstatement of cocaine seeking in male and female rats. Among the five GLT inhibitors we tested, TFB-TBOA was the most potent. Microinjections of TFB-TBOA into the NAc, but not the ventral tegmental area (VTA), or dorsal striatum (DS), dose-dependently inhibited cocaine self-administration under fixed-ratio and progressive-ratio (PR) reinforcement schedules, shifted the cocaine dose-response curve downward, and inhibited intracranial BSR. Selective downregulation of astrocytic GLT-1 expression in the NAc by GLT-1 antisense oligonucleotides also inhibited cocaine self-administration. The reduction in cocaine self-administration following TFB-TBOA administration was NMDA GluN2B receptor dependent, and rats self-administering cocaine showed upregulation of GluN2B expression in NAc DA- and cAMP-regulated phosphoprotein 32 (DARPP-32)-positive medium-spiny neurons (MSNs). In contrast, TFB-TBOA, when locally administered into the NAc, VTA, or ventral pallidum (VP), dose-dependently reinstated cocaine-seeking behavior. Intra-NAc TFB-TBOA-evoked drug-seeking was long-lasting and NMDA/AMPA receptor dependent. These findings, for the first time, indicate that glutamate in the NAc negatively regulates cocaine's rewarding effects, while an excess of glutamate in multiple brain regions can trigger reinstatement of drug-seeking behavior. It is well known that glutamate plays an important role in relapse to drug seeking. However, the role of glutamate in drug reward is less clear. Here, we report that TFB-TBOA, a highly potent glutamate transporter (GLT) inhibitor, dose-dependently elevates extracellular glutamate and inhibits cocaine self-administration and brain-stimulation reward (BSR), when administered locally into the nucleus accumbens (NAc), but not other brain regions. Mechanistic assays indicate that cocaine self-administration upregulates NMDA-GluN2B receptor subtype expression in striatal dopaminoceptive neurons and activation of GluN2B by TFB-TBOA-enhanced glutamate inhibits cocaine self-administration. TFB-TBOA also reinstates cocaine-seeking behavior when administered into the NAc, ventral tegmental area (VTA), and ventral pallidum (VP). These findings demonstrate that glutamate differentially regulates cocaine reward versus relapse, reducing cocaine reward, while potentiating relapse to cocaine seeking.