3,4-Methylenedioxypyrovalerone: Neuropharmacological Impact of a Designer Stimulant of Abuse on Monoamine Transporters

Abstract

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 [³H]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 STATEMENT: Pharmacological 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.

Fig. 1.

MDPV is self-administered by male Sprague-Dawley rats. Rats self-administered MDPV (0.0175 mg/infusion; FR1; n = 5) or saline (10 µl/infusion; n = 5) for 7 days (90 minutes/day). Values represent means, and vertical lines represent 1 S.E.M.

Fig. 2.

MDPV administration rapidly and reversibly increases striatal vesicular [³H]DA uptake. (A) Rats received a single injection (s.c.) of MDPV (2.5 or 5.0 mg/kg) or saline vehicle (1 ml/kg) and were sacrificed 1 hour later. Values/columns represent means, and vertical lines represent 1 S.E.M. (n = 6–8). (B) Rats received a single injection (s.c.) of MDPV (2.5 mg/kg) or saline (1 ml/kg; zero-time value) and were sacrificed 1–18 hours later. Values/columns represent means, and vertical lines represent 1 S.E.M. from two combined independent experiments (n = 11–14). *P < 0.05 from saline.

Fig. 3.

VMAT-2 immunoreactivity decreases in the (A) membrane-associated fraction and increases in the (B) non-membrane–associated fraction in rats that received a single injection (s.c.) of MDPV (2.5 mg/kg) compared with rats that received a single injection (s.c.) of saline (1 ml/kg) and were sacrificed 1 hour later. Western blots display band localization prior to normalization to protein content. Bar graphs represent data normalized to protein content (see Materials and Methods). Columns represent means, and vertical lines represent 1 S.E.M. (n = 8). *P < 0.05 from saline.

Fig. 4.

D1 receptor antagonist pretreatment is without effect on the MDPV-induced increase in striatal vesicular [³H]DA uptake, whereas D2 receptor antagonist pretreatment attenuates the MDPV-induced increases in striatal vesicular [³H]DA uptake and associated VMAT-2 redistribution. Rats received a single intraperitoneal injection of (A) SCH23390 (0.5 mg/kg) and (B and C) eticlopride (0.5 mg/kg) or saline (1 ml/kg), followed by a single injection (s.c.) of MDPV (2.5 mg/kg) or saline (1 ml/kg) 15 minutes later. Rats were sacrificed 1 hour after second injection. (A) [³H]DA uptake, (B) [³H]DA uptake, and (C) representative Western blot of VMAT-2 immunoreactivity in the vesicle-enriched fraction as described in Materials and Methods and associated quantification. Columns represent means, and vertical lines represent 1 S.E.M. (n = 6–8). *P < 0.05 from saline.

Fig. 5.

MDPV administration rapidly and reversibly increases striatal plasmalemmal [³H]DA uptake. Rats received a single injection (s.c.) of MDPV (2.5 mg/kg) or saline (1 ml/kg; zero-time value) and were sacrificed 1–18 hours later. Symbols represent means, and vertical lines represent 1 S.E.M. (n = 7 to 8). *P < 0.05 from saline.

Fig. 6.

MDPV administration does not affect DAT localization in synaptosome subcellular fractions. Representative image of Western blots as described in Materials and Methods, and quantification of DAT in P3 and S3 obtained from rats that received a single injection (s.c.) of MDPV (2.5 mg/kg) or saline (1 ml/kg) and were sacrificed 1 hour later. Values represent means, and vertical lines represent 1 S.E.M. (n = 8).

Fig. 7.

Neither D1, D2, nor nACh receptor antagonist pretreatment attenuates the MDPV-induced increase in striatal plasmalemmal [³H]DA uptake. Rats received a single injection of (A) SCH23390 (0.5 mg/kg, i.p.) or saline (1 ml/kg, i.p.), (B) eticlopride (0.5 mg/kg, i.p.) or saline (1 ml/kg, i.p.), or (C) mecamylamine (3 mg/kg, s.c.) or saline (1 ml/kg, s.c.) followed by a single injection (s.c.) of MDPV (2.5 mg/kg) or saline vehicle (1 ml/kg) 15 or 10 minutes later for SCH23390/eticlopride or mecamylamine, respectively. Rats were sacrificed 1 hour after the second injection. Columns represent means, and vertical lines represent 1 S.E.M. (n = 8). *P < 0.05 from respective saline control.

Fig. 8.

MDPV, unlike METH, does not alter plasmalemmal [³H]DA uptake as assessed 7 days after treatment, despite causing hyperthermia. Male rats received multiple injections (s.c.; 2-hour intervals) of either MDPV (3 × 2.5 or 5.0 mg/kg/injection) or saline vehicle (3 × 1 ml/kg per injection). (A) [³H]DA uptake as assessed 7 days after MDPV treatment. (B) Core body temperatures were assessed at times indicated by arrows. Values/columns represent means, and vertical lines represent 1 S.E.M. (n = 11–14).