Several articles published near the end of 2011 examined the effects of mephedrone, compared to the similar drugs MDMA and amphetamine in the nucleus accumbens of rats, as well as examining the reinforcing potential of mephedrone. Dopamine and serotonin were collected using microdialysis, and increases in dopamine and serotonin were measured using HPLC. Reward and drug seeking are linked to increases in dopamine concentrations in the nucleus accumbens, and drug half-life plays a role in drug seeking, as well. Based on histological examination, most of the author's probes were in the nucleus accumbens shell. Mephedrone administration caused about a 500% increase in dopamine, and about a 950% increase in serotonin. They reached their peak concentrations at 40 minutes and 20 minutes, respectively, and returned to baseline by 120 minutes after injection. In comparison, MDMA caused a roughly 900% increase in serotonin at 40 minutes, with an insignificant increase in dopamine. Amphetamine administration resulted in about a 400% increase in dopamine, peaking at 40 minutes, with an insignificant increase in serotonin. Analysis of the ratio of the AUC for dopamine (DA) and serotonin (5-HT) indicated mephedrone was preferentially a serotonin releaser, with a ratio of 1.22:1 (serotonin vs. dopamine). Additionally, half-lives for the decrease in DA and 5-HT were calculated for each drug. Mephedrone had decay rates of 24.5 minutes and 25.5 minutes, respectively. MDMA had decay values of 302.5 minutes and 47.9 minutes, respectively, while amphetamine values were 51 minutes and 84.1 minutes, respectively. Taken together, these findings show mephedrone induces a massive increase in both DA and 5-HT, combined with rapid clearance. The rapid rise and subsequent fall of DA levels could explain some of the addictive properties mephedrone displays in some users.[46][47]