Consequently it is not possible to ascertain whether or not a transporter redistribution was taking place when observing no decrease in radioligand binding in crude membrane preparations. We demonstrate that mephedrone, administered at doses that mimic a high exposure in humans, induced an important decrease in DA transporter density in mouse striatum and frontal cortex membranes that persisted 7 days after exposition. This effect was accompanied by a significant loss of 5-HT transporters in the hippocampus. However, at these high doses, acute cardiovascular toxicity of mephedrone is likely and probably outweighs neurotoxic effects. The subsequent experiments were carried out at a lower dose. Schedule 2 dosage schedule only elicited a transient decrease in cortical DA transporter, suggesting a temporary regulatory effect. Moreover, no significant loss of 5-HT transporter in the frontal cortex or the hippocampus was found. Schedule 3 can be considered the most representative because it is closest to the typical weekend consumption pattern. After this exposure, mephedrone induced loss of DA and 5-HT transporters that were especially apparent in the frontal cortex and the hippocampus respectively. The monoamine deficit induced by this schedule was also characterized by a significant decrease of each enzymatic marker that correlated with the decrease in radioligand binding. TH and TPH catalyze the first and rate-limiting step in the biosynthesis of DA and 5-HT respectively. The isoform TPH2 is responsible for 5-HT biosynthesis in the brain. Post-translational modifications have been shown to regulate the protein function. The enzyme is known to be phosphorylated on Ser-19 by both protein kinase A and calmodulin dependent protein kinase II in vitro. This modification results in increased stability and activity. The decrease in transporter binding and enzyme levels, jointly with astrogliosis, point to an injury at the nerve endings; the increase in Ser-19TPH2 in mephedrone-treated animals seems to reflect a compensatory mechanism in the undamaged 5-HT terminals The recovery of DA transporter levels in mouse striatum after 7 days of exposition raises the question on whether the decrease in WIN35428 binding observed 3 days after exposition is an effect of biochemical down-regulation in the absence of tissue damage rather than being reflective of an injury. The nonsignificant increase in astroglial activation observed in this area was consistent with the absence of terminal injury and suggests that the DA transporter gene expression may be negatively regulated by mephedrone exposure. This is consistent with previous results reporting that MDMA acts on 5-HT transporter gene expressions. Moreover, although DA transporter density returns to basal values in crude membrane preparations 7 days after exposition, results point to changes in DA levels in the striatal synapses, seeing as there is a significant redistribution of this transporter.