Oleylethanolamide: a lipid mediator involved in gut satiety mechanisms

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 microg/5 microl). 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 microg/5 microl, 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.

Diurnal variation of arachidonoylethanolamine, palmitoylethanolamide and oleoylethanolamide in the brain of the rat

The diurnal variations of the endocannabinoid arachidonoylethanolamine (anandamide, ANA) as well as palmitoylethanolamide (PEA) and oleoylethanolamide (OEA) were detected and quantified in cerebrospinal fluid (CSF), pons, hippocampus, and hypothalamus in the rat over 24 h using HPLC/MS. In CSF, the 3 compounds presented an increase in their concentration during the lights-on period and a remarkable decrease in their values during the lights-off period. In the pons, ANA, PEA and OEA showed the maximum values during the dark phase. On the other hand, we found that in the hippocampus, ANA increased its concentration during the lights-off period and PEA showed the highest peak at the beginning of the same period. OEA concentration showed no diurnal variations in the hippocampus. Finally, in the hypothalamus, ANA rose during the lights-on period whereas PEA and OEA presented the highest concentration at the end of the lights-off period. We postulate that all compounds are likely to be accumulated in parenchyma during the lights-off period (when animal is awake) and then, released into the CSF in order to reach target regions in turn to modulate diverse behaviors, such as feeding and sleep.