Effects of the fatty acid amide hydrolase inhibitor URB597 on the sleep-wake cycle, c-Fos expression and dopamine levels of the rat

Our group has described previously that the endogenous cannabinoid anandamide induces sleep. The hydrolysis of this lipid involves the activity of the fatty acid amide hydrolase (FAAH), which additionally catalyzes the degradation of the satiety factor oleoylethanolamide and the analgesic-inducing lipid palmitoylethanolamide. It has been demonstrated that the inhibition of the FAAH by URB597 increases levels of anandamide, oleoylethanolamide and palmitoylethanolamide in the brain of rats. In order to determinate the physiological properties of the FAAH inhibition on the sleep modulation, we report the pharmacological effects on the sleep-wake cycle of the rat after i.c.v. administrations of URB597, oleoylethanolamide or palmitoylethanolamide (10, 20 mu g/5 mu l). Separate unilateral i.c.v. injections of 3 compounds during the lights-on period, increased wakefulness and decreased slow wave (SW) sleep in rats in a dose-dependent fashion. We additionally found out that, compared to controls, c-Fos immunoreactivity in hypothalamus and dorsal raphe nucleus was increased in rats that received URB597, oleoylethanolamide or palmitoylethanolamide (10, 20 mu g/5 mu l, i.c.v.). Next, we found that after an injection of the compounds, levels of dopamine were increased whereas extracellular levels of levodopa (L-DOPA) were decreased. These findings indicate that that inhibition of the FAAH, via URB597, modulates waking. These effects were mimicked separately by the administration of oleoylethanolamide or palmitoylethanolamide. The alertness induced by the compounds tested here activated wake-promoting brain regions and they also induced the release of dopamine. Our results suggest that FAAH activity as well as two molecules that are catalyzed by this enzyme, oleoylethanolamide and palmitoylethanolamide, participate in the regulation of the waking state. Alternative approaches to treat sleep disorders such as excessive somnolence might consider the use of the URB597, oleoylethanolamide or palmitoylethanolamide since all compounds enhance waking. (c) 2007 Elsevier B.V. All rights reserved