Group I metabotropic glutamate receptors in the medial prefrontal cortex: role in mesocorticolimbic glutamate release in cocaine sensitization.

Cocaine sensitization is associated with increased excitability of pyramidal projection neurons in the medial prefrontal cortex. Such hyperexcitability is presumed to increase glutamatergic input to the nucleus accumbens and ventral tegmental area. This study examined the effects of medial prefrontal cortex Group I metabotropic glutamate receptor activation on glutamate levels in the medial prefrontal cortex, nucleus accumbens, and ventral tegmental area in sensitized and control animals. Male Sprague-Dawley rats received four daily injections of cocaine (15 mg/kg, i.p.) or saline (1 mL/kg i.p.). One, 7, or 21 days from the fourth injection, dual-probe microdialysis experiments were performed wherein Group I metabotropic glutamate receptor agonist DHPG was infused into the medial prefrontal cortex and glutamate levels in this region as well as the nucleus accumbens or ventral tegmental area were examined. Intra-mPFC DHPG infusion increased glutamate levels in the medial prefrontal cortex at 1 and 7 days withdrawal, and in the nucleus accumbens at 21 days withdrawal in sensitized rats. These results suggest Group I metabotropic glutamate receptor activation may contribute to the increased excitability of medial prefrontal cortex pyramidal neurons in sensitized animals.