Methylenedioxypyrovalerone (MDPV) is an abused synthetic cathinone, commonly referred to as a "bath salt." Because the dopamine (DA) transporter (DAT) and vesicular monoamine transporter-2 (VMAT-2) are key regulators of both the abuse and neurotoxic potential of structurally and behaviorally related agents, the impact of MDPV on these transporters was investigated. Results revealed that a single in vivo MDPV administration rapidly (within 1 hour) and reversibly increased both rat striatal DAT and VMAT-2 activity, as assessed via [ 3 H]DA uptake in synaptosomes and synaptic vesicles, respectively, prepared from treated rats. There was no evidence of an MDPV-induced increase in plasmalemmal membrane DAT surface expression. Plasma concentrations of MDPV increased dose-dependently as assessed 1 hour after 2.5 and 5.0 mg/kg (s.c.) administration and returned to levels less than 10 ng/ml by 18 hours after 2.5 mg/kg (s.c.). Neither pretreatment with a D1 receptor (SCH23390), a D2 receptor (eticlopride), nor a nicotinic receptor (mecamylamine) antagonist attenuated the MDPV-induced increase in DAT activity. In contrast, eticlopride pretreatment attenuated both the MDPV-induced increase in VMAT-2-mediated DA uptake and an associated increase in cytoplasmic-associated vesicle VMAT-2 immunoreactivity. SCH23390 did not attenuate the MDPV-induced increase in VMAT-2 activity. Repeated MDPV injections did not cause persistent DAergic deficits, as assessed 7 to 8 days later. The impact of MDPV on striatal and hippocampal serotonergic assessments was minimal. Taken together, these data contribute to a growing pharmacological rubric for evaluating the ever-growing list of designer cathinone-related stimulants. The profile of MDPV compared with related psychostimulants is discussed. SIGNIFICANCE STATEMENTPharmacological characterization of the synthetic cathinone, 3,4-methylenedioxypyrovalerone (MDPV; commonly referred to as a "bath salt"), is critical for understanding the abuse liability and neurotoxic potential of this and related agents. Accordingly, the impact of MDPV on monoaminergic neurons is described and compared with that of related psychostimulants.

Methylenedioxypyrovalerone (MDPV) is a synthetic cathinone designer drug primarily abused for its psychostimulant properties. Rapid dysregulation of central monoamine neurotransmitter transport into presynaptic terminals and synaptic vesicles are principal mechanisms of psychostimulant action, and contribute to the development of persistent monoaminergic deficits. Still, the impact of in vivo MDPV administration on the function of central monoamine transporters is not fully elucidated. Consequently, this study examined the response of the striatal dopamine transporter (DAT) and vesicular monoamine transporter‐2 (VMAT2) to a single MDPV exposure in adult male rats. A single in vivo MDPV administration rapidly (within 1 h) and reversibly (effect diminishes after 6 h) increased both DAT and VMAT2 function when assessed ex vivo in striatal synaptosomes and non‐membrane‐associated (presumably cytoplasmic) synaptic vesicles, respectively. MDPV treatment did not increase VMAT2 immunoreactivity within the cytoplasmic synaptic vesicle fraction, suggesting increased VMAT2 activity is unlikely due to intracellular trafficking increasing the number of available cytoplasmic VMAT2‐associated synaptic vesicles. In contrast to other psychostimulants, most notably methamphetamine and methylphenidate, MDPV acutely increases both DAT and VMAT2 function, and increased VMAT2 function is likely independent of vesicular trafficking‐mediated mechanisms. Together, these data suggest that MDPV has a unique and undescribed mechanism of action on striatal dopaminergic neurons.Support or Funding InformationThis work was supported by National Institutes of Health grants DA039145 and DA031883.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

β‐Ketoamphetamines such as methylenedioxypyrovalerone (MDPV) and mephedrone (MEPH) are synthetic cathinones with a structural similarity to methamphetamine (METH) that may account for some similarities in behavioral effects. However, the persistent effects of repeated high‐dose MDPV exposures on striatal dopaminergic and hippocampal serotonergic systems remain to be fully elucidated. Accordingly, the persistent effects of repeated high‐dose MPDV administrations were investigated. Results revealed that MDPV treatment did not alter striatal dopaminergic or hippocampal serotonergic systems as assessed 7 days later in synaptosomes prepared from treated rats. Further, MDPV did not alter hippocampal serotonin or 5‐hydroxyindoleacetic acid content at this time point. These data stand in contrast to our previous report that repeated high‐dose MEPH administrations cause persistent hippocampal serotonergic deficits. These data also stand in contrast to effects of repeated high‐dose METH administrations that include persistent striatal dopaminergic and hippocampal serotonergic deficits. Noteworthy, in these studies MDPV did not induce hyperthermia to the degree reported in previous studies of MEPH and METH. Further, the impact of MDPV on the dopamine transporter and vesicular monoamine transporter‐2 appears distinct from that of MEPH and METH. Taken together, these latter findings may contribute to the differential impact of MDPV, MEPH, and METH on dopaminergic and serotonergic systems.Support or Funding InformationDA039145 and DA031883This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Methcathinone (MCAT) is a psychostimulant of abuse that can cause both persistent striatal dopaminergic and serotonergic, as well as hippocampal serotonergic, deficits. Evidence suggests that the rapid effects of stimulants that are structurally and mechanistically similar to MCAT on monoamine transporter function may contribute to the abuse liability and/or persistent monoaminergic deficits caused by these agents. Thus, effects of MCAT on 1) striatal dopamine (DA) transporter (DAT); and 2) striatal and hippocampal serotonin transporter (SERT) function, as determined in tissues from adult male rats, were assessed. As reported previously, a single administration of MCAT rapidly (within 1 hr) decreases striatal [3H]DA uptake. Similarly, incubation of rat synaptosomes with MCAT at 37℃ (but not 4˚C) decreased striatal [3H]DA uptake. Incubation with MCAT likewise decreased [3H]5HT but not vesicular [3H]DA uptake. MCAT incubation in vitro was without effect on [3H]DA uptake in striatal synaptosomes prepared from MCAT‐treated rats. The decrease in [3H]DA uptake caused by MCAT incubation: (a) reflected a decrease in Vmax, with minimal change in Km, and (b) was attenuated by co‐incubation with the cell‐permeable calcium chelator, N,N'‐[1,2‐ethanediylbis(oxy‐2,1‐phenylene)]bis[N‐[2‐[(acetyloxy)methoxy]‐2‐oxoethyl]‐1,1'‐bis[(acetyloxy)methyl] ester‐glycine (BAPTA‐AM), as well as the non‐selective protein kinase‐C (PKC) inhibitors bisindolylmaleimide‐1 (BIM‐1) and 2‐[1‐3(Aminopropyl)indol‐3‐yl]‐3(1‐methyl‐1H‐indol‐3‐yl)maleimide (or Bisindolylmaleimide VIII; Ro‐31‐7549). Taken together, these results suggest that in vitro MCAT incubation may model important aspects of MCAT administration in vivo, and that calcium and PKC contribute to the in vitro effects of MCAT on DAT.

Methcathinone (MCAT) is a synthetic cathinone that causes both persistent striatal dopaminergic as well as striatal and hippocampal serotonergic deficits. It has been demonstrated that the rapid effects of similar stimulants on dopamine (DA) transporter (DAT) function contribute to persistent monoaminergic deficits. Thus, the effect of MCAT on DAT was assessed. Results revealed that MCAT self‐administration (SA) decreased striatal [3H]DA uptake, as assessed ex vivo in synaptosomes prepared from male rats 1 h after the final MCAT SA session. In vitro co‐incubation of synaptosomes with MCAT (1, 10, 100 μM) at 37°C likewise decreased striatal [3H]DA uptake. There was no effect of in vitro co‐incubation with MCAT at 4°C, suggesting that decreases in [3H]DA uptake are not due to residual drug. These effects were not limited to DAT as MCAT SA decreased hippocampal [3H]serotonin uptake. Further, in vitro co‐incubation of synaptosomes with MCAT decreased both striatal and hippocampal [3H]serotonin uptake. The in vitro effect on DAT function was attenuated by co‐incubation with the cell‐permeable calcium chelator, 1,2‐bis (2‐aminophenoxy) ethane‐N, N, N, N‐tetraacetic acid acetoxymethyl ester (BAPTA‐AM), as well as with the structurally related non‐specific protein kinase C (PKC) inhibitors bisindolylmaleimide I and Ro‐31‐7549. In contrast, this in vitro decrease in DAT function was not attenuated by co‐incubation with other non‐specific PKC inhibitors (NPC‐15437 and Go6976), nor with the PKC‐β inhibitor ruboxistaurin. Neither co‐incubation with the Ca2+/calmodulin‐dependent protein kinase II inhibitor, KN‐93, nor the glycogen synthase kinase 3β inhibitor, SB‐216763, attenuated the MCAT‐induced decrease in [3H]DA uptake. Taken together, these results suggest that MCAT self‐administration and in vitro MCAT exposure have comparable effects to investigator administered MCAT on DAT and SERT function in the striatum and hippocampus; further, in vitro data suggest that the MCAT‐induced effect on DAT is dependent upon calcium and some, but not all, PKC isoforms. Support or Funding Information R01‐DA039145