Bromovalerylurea modulates GABA_A receptor-mediated inhibitory neurotransmission while inducing sleep

Bromovalerylurea (BU), an acyl urea derivative, was originally developed as a hypnotic/sedative. We recently reported that BU at a dose of 50 mg/kg ameliorates sepsis, Parkinson's disease, and traumatic brain injury in Wistar rat models through its anti-inflammatory actions on microglia and macrophages. However, since BU was developed more than 100 years ago, its hypnotic mechanism and characteristics are poorly understood. Herein, we conducted an electroencephalogram (EEG) study and found that BU, when administered at a dose of more than 125 mg/kg but not at a dose of 50 mg/kg in Wistar rats, significantly increased non-rapid eye movement (NREM) sleep duration and dose-dependently decreased rapid eye movement (REM) sleep duration. This characteristic of sleep induced by BU is similar to the effect of compounds such as barbiturate, benzodiazepine, and z-drugs, all of which require γ-aminobutyric acid _A receptors (GABA_AR) for hypnotic/sedative activity. To investigate whether BU could potentiate GABA_Aergic neurotransmission, we conducted a whole-cell patch-clamp recording from pyramidal neurons in rat cortical slices to detect spontaneous GABA_AR-mediated inhibitory postsynaptic currents (IPSCs). We found that BU dose-dependently prolonged IPSCs. Importantly, the prolonged IPSCs were not attenuated by flumazenil, a benzodiazepine receptor antagonist, suggesting that modulation of IPSCs by BU is mediated by different mechanisms from that of benzodiazepine. Taken together, these data elucidate the basic characteristics of the hypnotic effects of BU and suggest that the enhancement of GABA_AR-mediated Cl^- flux may be a possible mechanism that contributes to its hypnotic/sedative activity.