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Caffeine, the most widely used psychoactive compound, is an adenosine receptor antagonist. It promotes wakefulness by blocking adenosine A2A receptors (A2ARs) in the brain, but the specific neurons on which caffeine acts to produce arousal have not been identified. Using selective gene deletion strategies based on the Cre/loxP technology in mice and focal RNA interference to silence the expression of A2ARs in rats by local infection with adeno-associated virus carrying short-hairpin RNA, we report that the A2ARs in the shell region of the nucleus accumbens (NAc) are responsible for the effect of caffeine on wakefulness. Caffeine-induced arousal was not affected in rats when A2ARs were focally removed from the NAc core or other A2AR-positive areas of the basal ganglia. Our observations suggest that caffeine promotes arousal by activating pathways that traditionally have been associated with motivational and motor responses in the brain. [ABSTRACT FROM AUTHOR]

Dopamine (DA) and its D2 receptor (R) are involved in cognition, reward processing, and drug addiction. However, their roles in sleep-wake regulation remain unclear. Herein we investigated the role of D2R in sleep-wake regulation by using D2R knock-out (KO) mice and pharmacological manipulation. Compared with WT mice, D2R KO mice exhibited a significant decrease in wakefulness, with a concomitant increase in non-rapid eye movement (non-REM, NREM) and REM sleep and a drastic decrease in the low-frequency (0.75-2 Hz) electroencephalogram delta power of NREM sleep, especially during the first 4 h after lights off. The KO mice had decreased mean episode duration and increased episode numbers of wake and NREM sleep, many stage transitions between wakefulness and NREM sleep during the dark period, suggesting the instability of the wake stage in these D2R KO mice. When the KO mice were subjected to a cage change or an intraperitoneal saline injection, the latency to sleep in the KO mice decreased to half of the level for WT mice. The D2R antagonist raclopride mimicked these effects in WT mice. When GBR12909, a dopamine transport inhibitor, was administered intraperitoneally, it induced wakefulness in WT mice in a dose-dependent manner, but its arousal effect was attenuated to one-third in the D2R KO mice. However, these 2 genotypes showed an identical response in terms of sleep rebound after 2, 4, and 6 h of sleep deprivation. These results indicate that D2R plays an essential role in the maintenance of wakefulness, but not in homeostatic regulation of NREM sleep. [ABSTRACT FROM AUTHOR]

Modafinil is a wake-promoting compound with low abuse potential used in the treatment of narcolepsy. Although the compound is reported to affect multiple neurotransmitter systems such as catecholamines, serotonin, glutamate, GABA, orexin, and histamine, however, the molecular mechanism by which modafinil increases wakefulness is debated. Herein we used dopamine (DA) D2 receptor (D2R)-deficient mice combined with D1R- and D2R-specific antagonists to clarify the role of DA receptors in the arousal effects of modafinil. In wild-type mice, intraperitoneal modafinil induced wakefulness in a dose-dependent manner. Pretreatment with eitherD1R antagonist SCH23390 [R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine] at 30 μg/kg or D2R antagonist raclopride at 2 mg/kg blocked the arousal effects of low-dose modafinil at 22.5 and 45 mg/kg. When modafinil was given at 90 and 180 mg/kg, pretreatment of D1R antagonist did not affect the wakefulness at all, whereas D2R antagonist significantly attenuated the wakefulness to the half level compared with vehicle control. Similarly,D2R knock-out (KO) mice exhibited attenuated modafinil-induced wakefulness. However, pretreatment of D2R KO mice with D1R antagonist completely abolished arousal effects of modafinil. These findings strongly indicate that dopaminergic D1R and D2R are essential for the wakefulness induced by modafinil. [ABSTRACT FROM AUTHOR]

Presents a study which examined the effect of prostaglandin E[sub2] (PGE[sub2]) on the activity of the histaminergic system and the involvement of PGE[sub2] receptor subtypes in the wakefulness response of rats. Materials and methods; Results; Discussion and findings.