Induction of Per1 expression following an experimentally induced epilepsy in the mouse hippocampus.

The Period1 (Per1) is a clock-oscillating gene product that plays an essential role in the generation and modulation of circadian rhythm in the suprachiasmatic nucleus (SCN) of hypothalamus. However, Per1 is also expressed in many other brain regions including cerebral cortex, hippocampus, and amygdala, suggesting that Per1 may be involved in the broader cellular functions in addition to the rhythm regulation. In this study, we found that chemical or electrical seizure-inducing stimulations regulate Per1 expression. Treatments with electric convulsive shock (ECS) or kainic acid (KA) robustly up-regulated the expressions of per1 mRNA and protein in the hippocampal formation and cerebral cortex. In consistent, we found that neuronal depolarization or KA treatment increased per1 mRNA expression in cultured primary cortical neurons. Because it has been demonstrated that Per family molecules contribute to the regulation of stress-induced cell death, we also explored the effect of Per1 overexpression on the survival of cultured neurons. However, neither basal, staurosporine- nor KA-induced neuronal death was affected by forced expression of Per1. Collectively, these results suggest that the Per1 expression is neuronal activity- and epileptogen-dependent, although its functional significance is remained to be explored.