In vivo brain levels of acetylcholine and 5-hydroxytryptamine after oleoylethanolamide or palmitoylethanolamide administrations are mediated by PPARα engagement.

The peroxisome proliferator-activated receptor alpha (PPARα) is a nuclear receptor that has been linked to the modulation of several physiological functions, including the sleep-wake cycle. The PPARα recognizes as endogenous ligands the lipids oleoylethanolamide (OEA) and palmitoylethanolamide (PEA), which in turn, if systemically injected, they exert wake-promoting effects. Moreover, the activation of PPARα by the administration of OEA or PEA increases the extracellular contents of neurotransmitters linked to the control of wakefulness; however, the role of PPARα activated by OEA or PEA on additional biochemicals related to waking regulation, such as acetylcholine (ACh) and 5-hydroxytryptamine (5-HT), has not been fully studied. Here, we have investigated the effects of treatments of OEA or PEA on the contents of ACh and 5-HT by using in vivo microdialysis techniques coupled to HPLC means. For this purpose, OEA or PEA were systemically injected (5, 10 or 30 mg/kg; i.p.), and the levels of ACh and 5-HT were collected from the basal forebrain, a wake-related brain area. These pharmacological treatments significantly increased the contents of ACh and 5-HT as determined by HPLC procedures. Interestingly, PPARα antagonist MK-886 (30 mg/kg; i.p.) injected before the treatments of OEA or PEA blocked these outcomes. Our data suggest that the activation of PPARα by OEA or PEA produces significant changes on ACh and 5-HT levels measured from the basal forebrain and support the conclusion that PPARα is a suitable molecular element involved in the regulation of wake-related neurotransmitters.

The Role of Nuclear Receptor PPARα in the Sleep-wake Cycle Modulation. A Tentative Approach for Treatment of Sleep Disorders.

BACKGROUND: There is a general consensus that sleep-wake cycle is controlled by neuroanatomical, neurochemical and molecular systems as well as by homeostatic and circadian complex networks. The research has shown that a molecular element that could be displaying a relevant role in the modulation of sleep is the peroxisome proliferator-activated receptor alpha (PPARα), which belongs to the family of nuclear receptor ligand-activated transcription factors that includes PPARß/δ and PPARγ. A growing body of evidence supports the notion that PPARα is activated by natural ligands such as the anorexic lipid mediator oleoylethanolamide (OEA) or synthetic compounds including Wy14643 whereas antagonists like MK-886 block the neurobiological outcomes of PPARα. More recently, studies have reported the permissive role of PPARα by modulating diverse neurobiological functions such as inflammation, metabolic disorders, learning, degenerative diseases and sleep. Remarkably, this nuclear receptor has been described in sleep-related brain regions leading to the hypothesis that PPARα might be involved in sleep modulation inasmuch as activation of this protein promotes a robust enhancement of wakefulness while reduces sleep. OBJECTIVE: In this mini review, the emerging evidence of the putative role of PPARα in sleep control is highlighted. Even though the data are derived from new areas of research, there are many reasons to believe that understanding and appreciation of PPARα functions may provide knowledge of possible mechanisms of action activated by this nuclear receptor in sleep modulation. CONCLUSION: Novel insights of therapeutic intervention for sleep disorders might be visualized targeting the function of PPARα in sleep abnormalities.