Non-aminergic effects of amphetamine on the NMDA receptor in primary cultured cortical cells

Activation of metabotropic glutamate receptor 5 is associated with effect of amphetamine on brain neurons

The role of metabotropic glutamate receptor 5 (mGluR5) was explored in mechanisms underlying the action of amphetamine (AMPH). The activity of mGluR5 was monitored by measuring the level of [3H]inositol monophosphates in brain neurons, in response to stimulation of 2-choloro-5-hydroxyphenylglycine (CHPG), a selective agonist of mGluR5. Treatment with 1 microM of AMPH for 1 h or 7 days increased the CHPG (1 mM, 30 min)-evoked phosphoinositide turnover by 46% or 92% and 26% or 84% in cultured cortical and hippocampal neurons, respectively, from that of CHPG-only treated cells. When AMPH was present during CHPG application post-1 h or 7 day AMPH incubation, the rate of phosphoinositide hydrolysis in cortical neurons became 121% or 142% higher than that treated with CHPG only. The postnatal day (P) 21 (juvenile) and P60 (adult) rats received three intraperitoneal injections of 5 mg/kg of AMPH or saline daily for 6 days. They were challenged on the eighth day with one dosage and sacrificed 3 h later. Reversible 3H-glutamate binding detected increases of 22-89% in the binding levels of cortex and hippocampus of both ages following the AMPH injections. Increases of 13-18% in the levels of mGluR5 mRNA were seen in the juvenile pyramidal neurons of hippocampal CA1-4, granular cells of dentate gyrus, and ventral thalamic nuclei, as shown by in situ hybridization. The AMPH-induced altered activity of mGluR5 is probably associated with changes in the expression of the glutamate receptors, including mGluR5. AMPH may modify the sensitivity of mGluR5 or interact with the receptor itself.

Amphetamine induces differential changes in the gene expression of metabotropic glutamate receptor 5 in cultured cortical and hippocampal neurons

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.

Methamphetamine causes differential regulation of pro-death and anti-death Bcl-2 genes in the mouse neocortex

Bcl-2, an inner mitochondrial membrane protein, inhibits apoptotic neuronal cell death. Expression of Bcl-2 inhibits cell death by decreasing the net cellular generation of reactive oxygen species. Studies by different investigators have provided unimpeachable evidence of a role for oxygen-based free radicals in methamphetamine (METH) -induced neurotoxicity. In addition, studies from our laboratory have shown that immortalized rat neuronal cells that overexpress Bcl-2 are protected against METH-induced apoptosis in vitro. Moreover, the amphetamines can cause differential changes in the expression of Bcl-X splice variants in primary cortical cell cultures. These observations suggested that METH might also cause perturbations of Bcl-2-related genes when administered to rodents. Thus, the present study was conducted to determine whether the use of METH might indeed be associated with transcriptional and translational changes in the expression of Bcl-2-related genes in the mouse brain. Here we report that a toxic regimen of METH did cause significant increases in the pro-death Bcl-2 family genes BAD, BAX, and BID. Concomitantly, there were significant decreases in the anti-death genes Bcl-2 and Bcl-XL. These results thus support the notion that injections of toxic doses of METH trigger the activation of the programmed death pathway in the mammalian brain.

Amphetamines induce apoptosis and regulation of bcl-x splice variants in neocortical neurons

Amphetamineanalogs have emerged as popular recreational drugs of abuse. The number of reports of these substances producing severe acute toxicity and death is increasing. In 'Ecstasy' -associated deaths, focal necrosis in the liver and individual myocytic necrosis has been reported. Furthermore, serotonergic and dopaminergic neuronal cell damage has been observed in experimental amphetamine intoxication in laboratory animals. Here we demonstrate that subchronic exposure to D-amphetamine, methamphetamine, methylenedioxyamphetamine, and methylenedioxymethamphetamine ('Ecstasy') results in significant neurotoxicity in rat neocortical neurons in vitro. This neuronal cell death is accompanied by endonucleosomal DNA cleavage and differential expression of anti- and proapoptotic bcl-xL/S splice variants. In addition, we observed pronounced induction of cell stress-associated transcription factor c-jun and translation initiation inhibitor p97 after amphetamine treatment. These data support that the neurotoxic effects of different amphetamines are extended to rat neocortical neurons and that apoptotic pathways are involved in amphetamine-induced neurotoxicity.