Augmentation of intracranial self-stimulation induced by amphetamine-like drugs in Period circadian regulator 2 knockout mice is associated with intracellular Ca²⁺ levels

Over the past decade, new psychoactive substances (NPS) have emerged in the illegal drug market and have continued to attract attention from the international community. Among these, amphetamine-like NPS, classified as stimulants, constitute a significant proportion. However, the pharmacological characteristics and mechanisms underlying addiction to amphetamine-like NPS remain poorly understood. Given that circadian rhythms are linked to the brain stimulation effects of methamphetamine (METH) and amphetamine, we investigated the effects of METH, 1-(4-methoxyphenyl)-N-methylpropan-2-amine (PMMA), and 1-(benzofuran-5-yl)-N-ethylpropan-2-amine (5-EAPB) on intracranial self-stimulation (ICSS) in wild-type (WT) or Period circadian regulator 2 knockout mice. Amphetamine-like drugs increase intracellular Ca²⁺ levels to provoke dopamine release, so we examined the impact of Per2 knockdown on intracellular Ca²⁺ levels in PC12 cells to elucidate a potential mechanism underlying NPS-induced ICSS enhancement. Our ICSS results showed that METH and PMMA significantly increased brain stimulation in Per2 knockout mice compared to WT mice. Similarly, METH and PMMA induced higher Ca²⁺ fluorescence intensity in Per2 knockdown PC12 cells than in control cells. In contrast, 5-EAPB did not produce significant changes in either ICSS or Ca²⁺ signaling. These findings suggest that Per2 plays a crucial role in the brain stimulation effects of amphetamine-like drugs through the regulation of intracellular Ca²⁺.