Differential role of dose and environment in initiating and intensifying neurotoxicity caused by MDMA in rats

BACKGROUND

MDMA causes serotonin (5-HT) syndrome immediately after administration and serotonergic injury in a few days or weeks. However, a serotonin syndrome is not always followed by serotonergic injury, indicating different mechanisms responsible for two adverse effects. The goal of present study was to determine causes for two adverse events and further test that dose and environment have a differential role in initiating and intensifying MDMA neurotoxicity.

METHODS

Initiation and intensification were examined by comparing neurotoxic effects of a high-dose (10 mg/kg × 3 at 2 h intervals) with a low-dose (2 mg/kg × 3) under controlled-environmental conditions. Initiation of a serotonin syndrome was estimated by measuring extracellular 5-HT, body-core temperature, electroencephalogram and MDMA concentrations in the cerebrospinal fluid, while intensification determined in rats examined under modified environment. Initiation and intensification of the serotonergic injury were assessed in rats by measuring tissue 5-HT content, SERT density and functional integrity of serotonergic retrograde transportation.

RESULTS

Both low- and high-dose could cause increases in extracellular 5-HT to elicit a serotonin syndrome at the same intensity. Modification of environmental conditions, which had no impact on MDMA-elicited increases in 5-HT levels, markedly intensified the syndrome intensity. Although either dose would cause the severe syndrome under modified environments, only the high-dose that resulted in high MDMA concentrations in the brain could cause serotonergic injury.

CONCLUSION

Our results reveal that extracellular 5-HT is the cause of a syndrome and activity of postsynaptic receptors critical for the course of syndrome intensification. Although the high-dose has the potential to initiate serotonergic injury due to high MDMA concentrations present in the brain, whether an injury is observed depends upon the drug environment via the levels of reactive oxygen species generated. This suggests that brain MDMA concentration is the determinant in the injury initiation while reactive oxygen species generation associated with the injury intensification. It is concluded that the two adverse events utilize distinctly different mediating molecules during the toxic initiation and intensification.

Environment Influencing Serotonin Syndrome Induced by Ecstasy Abuse

Ecstasy is a recreational drug containing 3,4-methylenedioxymethamphetamine (MDMA). In the U.S., there are several millions of lifetime users, and millions each year added to the list as new users. Only several thousand every year show signs of severe toxicity and require emergency intervention. The illness is known as serotonin (5-HT) syndrome, which can be mild, moderate or severe. The relationship between mild, moderate and severe syndromes appears to be interchangeable, but the severe syndrome is life-threatening. The serotonergic mechanisms of how the mild or moderate syndrome becomes severe and life-threatening have attracted considerable attention in the last few years as an effort to explore new treatments potentially to manage illness and prevent death of patients. High levels of extracellular 5-HT in the brain produced by large doses of MDMA are not always necessary to cause a severe serotonin syndrome. Additional mechanisms may be more important. Recent research has demonstrated that environmental conditions (i.e., non-drug factors) are more critical in determining the severity of MDMA-induced serotonin syndrome than the drug dose. The purpose of the current article was to review available evidence regarding the effect of non-drug factors on serotonergic extrasynaptic receptor responsivity and the severity of MDMA-induced serotonin syndrome.