Mechanisms underlying the short-term effects of amphetamine (AMPH) were examined by monitoring the expression of metabotropic glutamate receptor 5 (mGluR5) in cultured rat neurons. The cortical and hippocampal neurons were incubated with 0.1-100 microM of AMPH for 1 h or 1 microM of AMPH for 10 min to 3 h. Immunocytochemical and in situ hybridization (ISH) analyses revealed that the levels of mGluR5 immunoreactivity and mRNA in the cortical neurons were initially increased with the treatment time and dosage, to reach maximal elevations of 34 and 53% from control values following 1 h incubation of 1 microM, and then returned toward the controls. When the cortical neurons were preincubated with the antagonist, alpha-methyl-4-carboxyphenylglycine (MCPG) to mGluRs, before treated with 1 M of AMPH for 1 h, the levels of mGluR5 protein and mRNA became 120 and 116% of control values. In hippocampal neurons, the AMPH treatment persistently upregulated the mGluR5 protein by 50-62%; however, the mRNA responded with the bell-shaped pattern to the treatment times and doses, with 20-43% increases from controls. These modifications of the receptor were reversible, since removal of AMPH resulted in regular levels of the receptor. Notably, the AMPH-generated increases in mGluR5 protein and mRNA were completely blocked by the pretreatment with cycloheximide and actinomycin D, respectively. The data indicate differential responsive patterns of mGluR5 in the cortical and hippocampal neurons to the drug perturbation. The action of AMPH may involve regulation to transcriptional and translational events in the neurons, and the activation of the MCPG-sensitive receptors.
