Repeated amphetamine administration alters AMPA receptor subunit expression in rat nucleus accumbens and medial prefrontal cortex

Abstract

Glutamate is critical for the induction and maintenance of behavioral sensitization and associated neuroadaptations in the mesocorticolimbic dopamine (DA) system. We have shown previously [Lu et al. (1997) Synapse 26:269-280] that repeated amphetamine administration alters AMPA receptor subunit mRNA levels in rat nucleus accumbens (NAc) and medial prefrontal cortex (PFC). The present study determined if amphetamine elicits corresponding changes in AMPA receptor subunit immunolabeling. Rats were injected with amphetamine sulphate (5 mg/kg/day) or saline for 5 days and perfused 3 or 14 days after the last injection. AMPA receptor subunit immunolabeling was quantified using autoradiographic immunocytochemistry. In the NAc, GluR1 and GluR2 immunolabeling were unchanged after 3 days of withdrawal, but both were decreased significantly after 14 days of withdrawal (GluR1, 85.5 ± 2,6% of control group, P < 0.01; GluR2, 79.2 ± 3.2%, P < 0.01). Analysis of core and shell subregions at the 14-day withdrawal time indicated that GluR1 immunolabeling decreased significantly in shell, while GluR2 immunolabeling decreased significantly in both core and shell. No changes in GluR2/3, GluR2/4, or GluR4 immunolabeling in NAc were found at either withdrawal time. In the PFC, GluR1 immunolabeling increased after 3 days of withdrawal (115.3 ± 7.0%, P < 0.01) but returned to control levels after 14 days. The present results correspond well with our previous findings at the mRNA level. These alterations in AMPA receptor expression may account for previously described changes in the electrophysiological responsiveness of NAc and PFC neurons to glutamate and AMPA. Along with alterations in DA function, they may contribute to drug-induced dysregulation of reward- related neurotransmission.