Dopamine D2-receptor knockout mice are protected against dopaminergic neurotoxicity induced by methamphetamine or MDMA

The dopamine D2 receptor is necessary for the neurotoxic effects of methamphetamine and MDMA (ecstasy) in mice. In wild-type mice, both drugs caused hyperthermia, loss of dopamine markers (tyrosine hydroxylase and dopamine transporter) in the striatum, inflammation, and dopaminergic cell death in the substantia nigra pars compacta. In mice lacking the D2 receptor (D2R−/−), all these effects were blocked, including the loss of dopaminergic neurons. The neuroprotective effect of D2R inactivation was not solely due to preventing hyperthermia, as reserpine lowered body temperature in both genotypes but potentiated toxicity only in wild-type mice. These results indicate that D2R is essential for methamphetamine and MDMA neurotoxicity, independent of body temperature.

Study at a glance

Abstract

Methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA), amphetamine derivatives widely used as recreational drugs, induce similar neurotoxic effects in mice, including a marked loss of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the striatum. Although the role of dopamine in these neurotoxic effects is well established and pharmacological studies suggest involvement of a dopamine D2-like receptor, the specific dopamine receptor subtype involved has not been determined. In this study, we used dopamine D2 receptor knock-out mice (D2R−/−) to determine whether D2R is involved in METH- and MDMA-induced hyperthermia and neurotoxicity. In wild type animals, both drugs induced marked hyperthermia, decreased striatal dopamine content and TH- and DAT-immunoreactivity and increased striatal GFAP and Mac-1 expression as well as iNOS and interleukin 15 at 1 and 7 days after drug exposure. They also caused dopaminergic cell loss in the SNpc. Inactivation of D2R blocked all these effects. Remarkably, D2R inactivation prevented METH-induced loss of dopaminergic neurons in the SNpc. In addition, striatal dopamine overflow, measured by fast scan cyclic voltammetry in the presence of METH, was significantly reduced in D2R−/− mice. Pre-treatment with reserpine indicated that the neuroprotective effect of D2R inactivation cannot be explained solely by its ability to prevent METH-induced hyperthermia: reserpine lowered body temperature in both genotypes, and potentiated METH toxicity in WT, but not D2R−/− mice. Our results demonstrate that the D2R is necessary for METH and MDMA neurotoxicity and that the neuroprotective effect of D2R inactivation is independent of its effect on body temperature.