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Front Mol Neurosci. 2012 Jun 27;5:72. doi: 10.3389/fnmol.2012.00072. eCollection 2012.

Calcium-permeable AMPA receptors in the VTA and nucleus accumbens after cocaine exposure: when, how, and why?

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  • 1Department of Neuroscience, Rosalind Franklin University of Medicine and Science, North Chicago IL, USA.

Abstract

In animal models of drug addiction, cocaine exposure has been shown to increase levels of calcium-permeable AMPA receptors (CP-AMPARs) in two brain regions that are critical for motivation and reward-the ventral tegmental area (VTA) and the nucleus accumbens (NAc). This review compares CP-AMPAR plasticity in the two brain regions and addresses its functional significance. In VTA dopamine neurons, cocaine exposure results in synaptic insertion of high conductance CP-AMPARs in exchange for lower conductance calcium-impermeable AMPARs (CI-AMPARs). This plasticity is rapid in onset (hours), GluA2-dependent, and can be observed with a single cocaine injection. Whereas it is short-lived after experimenter-administered cocaine, it persists for months after cocaine self-administration. In addition to strengthening synapses and altering Ca(2+) signaling, CP-AMPAR insertion alters subsequent induction of plasticity at VTA synapses. However, CP-AMPAR insertion is unlikely to mediate the increased DA cell activity that occurs during early withdrawal from cocaine exposure. Metabotropic glutamate receptor 1 (mGluR1) exerts a negative influence on CP-AMPAR accumulation in the VTA. Acutely, mGluR1 stimulation elicits a form of LTD resulting from CP-AMPAR removal and CI-AMPAR insertion. In medium spiny neurons (MSNs) of the NAc, extended access cocaine self-administration is required to increase CP-AMPAR levels. This is first detected after approximately a month of withdrawal and then persists. Once present in NAc synapses, CP-AMPARs mediate the expression of incubation of cue-induced cocaine craving. The mechanism of their accumulation may be GluA1-dependent, which differs from that observed in the VTA. However, similar to VTA, mGluR1 stimulation removes CP-AMPARs from MSN synapses. Loss of mGluR1 tone during cocaine withdrawal may contribute to CP-AMPAR accumulation in the NAc. Thus, results in both brain regions point to the possibility of using positive modulators of mGluR1 as treatments for cocaine addiction.

KEYWORDS:

addiction; calcium-permeable AMPA receptor; cocaine; nucleus accumbens; ventral tegmental area

PMID:
22754497
[PubMed]
PMCID:
PMC3384237
Free PMC Article

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