Effects of Repeated Nicotine Treatment on the Changes in Glutamate Receptor Subunits Levels in Mesocorticolimbic Dopamine Areas

ABSTRACT

Recent studies suggest that alterations in glutamate receptor subunit levels in mesocorticolimbic dopamine areas could account for neural adaptations in response to psychostimulant drugs. Although many drugs of abuse induce changes in ionotropic glutamate receptor subunits in mesocorticolimbic dopamine areas, the changes of ionotropic glutamate receptor subunits by repeated nicotine treatment in these areas are not known. To answer this question, we injected male Sprague-Dawley rats twice daily with nicotine (0.4 mg/kg) or saline (1 ml/kg) for 10 days. The immunoreactivity of NR1, GluR1, and GluR2 glutamate receptor subunits was examined 16~18 h after the last injection of saline or nicotine. Repeated nicotine treatment significantly increased NR1 levels in the ventral tegmental area (VTA). In addition, repeated nicotine treatment showed a tendency towards an increase in GluR1 levels in the VTA as well as in striatum. However, there was no significant change in glutamate receptor subunits in other areas including nucleus accumbens (NAc). These results demonstrate that repeated nicotine treatment increases NR1 levels in VTA similarly to other drugs of abuse, suggesting that elevated glutamate receptor subunits in the VTA, but not NAc may be involved in the excitation of mesocorticolimbic dopamine neurons by nicotine.