This study used in vitro and ex vivo methods to investigate mechanisms of action for MDMA-induced monoamine release in rat brain synaptosomes (intended to mimic synapses) and brain tissue removed from MDMA-treated rats. The researchers assayed synaptosomal uptake via adding either MDMA (5 to 20 mcM) or the serotonin uptake inhibitor (SSRI) paroxetine (0.01 to 10 mcM), and then adding radioactively tagged neurotransmitters. Vesicular (cellular means of neurotransmitter transport) uptake was assessed by adding MDMA or paroxetine at preincubation, and then adding ATP and either 257 nM DA, 96 nM 5-HT or 1 nM glutamate. One ex vivo study used synaptosomes from brain tissue from rats given 3 s.c. injections 15 mg/kg MDMA every 2 h and then killed immediately after the last injection, and the other study used synaptosomes from rats killed 18, 42 or 66 h after receiving twice-daily injections of saline, 15 mg/kg MDMA or 5 mg/kg paroxetine on 4 consecutive days. 5 to 20 mcM MDMA reduced synaptosomal uptake of DA and 5-HT, and 1 to 10 nM paroxetine reduced synaptosomal uptake of 5HT. (MDMA affected DA uptake less strongly, and it did not reduce synaptosomal uptake of glutamate or GABA). MDMA (at 6 and 9 mcM) also reduced vesicular uptake of 5-HT and DA, but not glutamate or GABA. Paroxetine also reduced vesicular 5-HT and DA, but to a lesser degree. Ex vivo synaptosomes from rats killed immediately after 3 doses 15 mg/kg MDMA showed reduced DA uptake, and slightly but not significantly lower uptake of 5-HT and glutamate. Synaptosomes from rats exposed twice-daily 10 mg/kg MDMA for 4 days showed reduced uptake of 5-HT, but not DA. 5-HT uptake measured ex vivo in synaptosomes from rats killed 18, 42 and 66 h post-MDMA was at 75, 54 and 61% of control levels. (No data is presented on paroxetine-associated alterations of synaptosomal uptake). Vesicular uptake of 5-HT was reduced 66 h post-MDMA (65% of controls), but not at 18 or 42 h post-drug. Paroxetine did not affect vesicular 5-HT uptake at any point in time. The researchers concluded that inhibition of vesicular uptake, and not synaptosomal uptake, may be a marker for MDMA neurotoxicity. Their findings are somewhat similar to a previous report indicating that substituted amphetamines causing 5-HT and DA release in synaptosomes, and not just in vivo, were more likely to be neurotoxic (Gobbi et al. 2002). They also hypothesized that long-lasting changes in synaptosomal uptake of 5-HT after MDMA are indicative of serotonin neurotoxicity. While findings concerning acute effects of MDMA on monoamine release are not surprising, findings of a slight reduction in glutamate uptake have not been previously reported. This is also the first account of a potential difference in pharmacological profiles in high-dose repeated dose regimens, with greater dopamine release seen in the high-dose, frequent administration. With the recent retraction of findings of dopamine damage after MDMA in primates (Ricaurte et al. 2003, in reference to Ricaurte et al. 2002), it is unclear whether differences in neurotransmitter selectivity have significance in humans or non-human primates.