Dantrolene sodium fails to reverse robust brain hyperthermia induced by MDMA and methamphetamine in rats

RATIONALE

Hyperthermia induced by psychomotor stimulants may cause leakage of the blood-brain barrier, vasogenic edema, and lethality in extreme cases. Current treatments such as whole-body cooling are only symptomatic and a clear need to develop pharmacological interventions exists. Dantrolene sodium, a peripheral muscle relaxant used in the treatment of malignant hyperthermia, has been proposed as potentially effective to treat MDMA-hyperthermia in emergency rooms. However, debate around its efficacy for this indication persists.

OBJECTIVES

To investigate dantrolene as a treatment for illicit hyperthermia induced by psychomotor stimulant drugs, we examined how Ryanodex®, a concentrated formulation of dantrolene sodium produced by Eagle Pharmaceuticals, influences 3,4-methylenedioxymethamphetamine (MDMA)- and methamphetamine (METH)-induced hyperthermia in awake freely moving rats. We injected rats with moderate doses of MDMA (9 mg/kg) and METH (9 mg/kg) and administered Ryanodex® intravenously (6 mg/kg) after the development of robust hyperthermia (>2.5 °C) mimicking clinical acute intoxication. We conducted simultaneous temperature recordings in the brain, temporal muscle, and skin to determine the basic mechanisms underlying temperature responses. To assess the efficacy of dantrolene in attenuating severe hyperthermia, we administered MDMA to rats maintained in a warm ambient environment (29 °C), conditions which produce robust brain and body hyperthermia (>40 °C) and lethality.

RESULTS

Dantrolene failed to attenuate MDMA- and METH-induced hyperthermia, though locomotor activity was significantly reduced. All animals maintained at warm ambient temperatures that received dantrolene during severe drug-induced hyperthermia died within or soon after the recording session.

CONCLUSIONS

Our results suggest that dantrolene sodium formulations are not mechanistically suited to treat MDMA- and METH-induced hyperthermia.

Persistent gene expression changes in NAc, mPFC, and OFC associated with previous nicotine or amphetamine exposure

Highly addictive drugs like nicotine and amphetamine not only change an individual's behaviour in the short and long-term, they also induce persistent changes in neuronal excitability and morphology. Although research has started to examine the epigenetic changes that occur immediately after drug exposure, there has been little investigation into the persistent modifications to the epigenome that likely moderate the stable maintenance of the neurological changes. Male Long-Evans rats were administered amphetamine, nicotine, or saline for 14 consecutive days, given a 14 day withdrawal period, and then sacrificed. DNA from the mPFC, OFC, and nucleus accumbens (NAc) was used for global DNA methylation analysis and RNA from the same brain regions was used for gene expression analysis. Following the two-week withdrawal period, exposure to amphetamine or nicotine was associated with a decrease in global DNA methylation in each brain region examined. Previous exposure to nicotine was associated with changes in expression of 16 genes (NAc:6, mPFC:5, OFC:5) whereas exposure to amphetamine was associated with changes in expression of 25 genes (NAc:13, OFC:8, mPFC:4). The persistent epigenetic changes associated with exposure to amphetamine and nicotine were region and drug dependent, and differ from the latent epigenetic changes that occur immediately after drug exposure. The changes in DNA methylation are consistent with the gene expression results and provide further support to the notion that DNA methylation is the key regulatory mechanism for experience dependent changes.