Effects of the new generation α-pyrrolidinophenones on spontaneous locomotor activities in mice, and on extracellular dopamine and serotonin levels in the mouse striatum.

Purpose: Pyrovalerone derivatives (α-pyrrolidinophenones) form a distinct branch of synthetic cathinones, a popular group of novel psychoactive substances, and exert strong psychostimulatory effects resulting from their high potency to inhibit dopamine (DA) and norepinephrine transporters, with negligible activity at the serotonin (5-HT) transporter. In contrast to the old generation α-pyrrolidinophenones, 3,4-MDPV and α-PVP, there is limited data on the pharmacology and toxicology of the novel analogs. Therefore, the present study assesses the in vivo effects of two new pyrovalerones, PV8 and PV9, along with those of α-PVP, on spontaneous locomotor activities of mice and extracellular DA and 5-HT levels in the mouse striatum.

Methods: Spontaneous locomotor activity was measured using Opto-Varimex Auto-Track. Effects of tested compounds on extracellular levels of DA and 5-HT in the striatum were studied by an in vivo microdialysis technique; their concentrations in dialysate fractions were analyzed by high-performance liquid chromatography with electrochemical detection.

Results: α-PVP, PV8 and PV9 stimulated mice locomotor activity (an effect being blocked by D-dopamine receptor antagonist, SCH 23390), and increased extracellular levels of DA and 5-HT in the striatum. Observed effects depend on dose, time and compound under investigation, with α-PVP being more potent than PV8 and PV9. When used at the same dose, the pyrovalerones produced effects significantly weaker than a model, old generation psychostimulant, methamphetamine.

Conclusions: Enhancement of dopaminergic neurotransmission plays a dominant role in the psychomotor stimulation caused by α-PVP, PV8 and PV9. Extending an aliphatic side chain beyond a certain point leads to the decrease in their potency in vivo.