Oleoylethanolamide in the homeostatic and non-homeostatic control of eating

The goal of the present study is to evaluate the role of OEA as a potential novel pharmacological target for the treatment of obesity and eating disorders, two major health problems worldwide. OEA’s ability in inducing consistent and sustained food intake suppression in rats and mice, that is mediated by PPAR-α activation, has been well characterized over the last two decades from my laboratory and from other research groups. In fact, it is now well recognized that the pro-satiety effect of OEA is strictly dependent on the involvement of key brain hypothalamic and hindbrain areas. However, a crucial aspect remained to be fully elucidated, such as the way by which systemically administered OEA can reach the CNS from the periphery and whether it is able to permeate the brain parenchyma. In this background, circumventricular organs, such as the AP in the brainstem, are attracting a great deal of attention for their possible role in allowing the direct access to the brain for circulating peptides and other peripheral signals. Moreover, previous data showed that the i.p. administration of OEA, strongly activates neurons of the AP and significantly stimulates c-fos transcription in the subpostremal part of the NST, which is the closest sub nucleus to the AP. Based on these premises, in order to better delineate the mechanism underlying the eating-inhibitory effects of OEA, the aim of chapter II was to investigate the involvement of the AP in mediating OEA hypophagic action. To this purpose, in collaboration with Prof. Thomas Lutz at University of Zurich, we subjected rats to a surgical ablation of the AP and evaluated the effects of i.p. OEA administration (10 mg kg−1) on food intake, on Fos expression, on OXY immunoreactivity at both PVN and neurohypophysial level and on the expression of DBH within the brainstem and PVN. Further, we aimed to assess the phenotype of neuronal populations activated by OEA in the brainstem of controls and lesioned rats; to this aim, we assessed, also, whether OEA induced Fos expression co-localized with DBH as marker for noradrenergic neurons. Finally, as last step of our study, we investigated PPAR-alpha expression within the AP. Furthermore, since there are no observations demonstrating the ability of OEA to permeate the brain parenchyma, in the chapter III I aimed to investigate whether systemically administered OEA might directly reach and permeate the CNS through circumventricular organs devoid of a functional BBB, such as the AP and the ME. To this purpose, in collaboration with Prof. Lutz and Prof Giulio Muccioli at Université Catholique de Louvain, male Wistar rats were sacrificed at different time points (2.5, 5, 15, 30, 60 minutes) after acute administration of OEA (10 mg kg-1, i.p.). Plasma and different brain areas were collected for UPLC-MS/MS quantification of the main NAEs (including OEA, AEA, PEA, SEA, and LEA), and 2-arachidonoyl-glycerol (2-AG). In particular, in order to selectively investigate OEA concentrations within a variety of PPAR-α-expressing cerebral regions, selected brain areas of interest (AP, ME, NST, ventral and dorsal hippocampus (vHipp and dHipp)) were microdissected and used in this study. Finally, since current knowledge supports a relationship between neurobiological as well as psychological aspects of overeating, in chapter IV I also investigated the OEA’s pro-satiety action in a rat model of BED, which is a prototypical eating-related maladaptive behaviour that may determine fluctuations in body weight and in some instance may cause obesity. Among the different networks involved in the behavioural effect of OEA, it has been demonstrated that the systemic administration of OEA to obese rodents restores a “normal brain dopaminergic activity”, which resulted dampened by the excess of fat intake. Moreover, evidence suggests that OEA attenuates the effect of stress by dampening the hyperactivity of the HPA axis. Since both the abnormal dopaminergic transmission and the hyperactivation of HPA axis are considered mechanisms underlying the pathophysiology of BED, by acting at both the two deregulated conditions OEA might represent a potential novel pharmacological target for controlling aberrant eating patterns occurring in BED. Based on these premises, in order to test this hypothesis in collaboration with Prof. Carlo Cifani of University of Camerino we evaluated OEA effects in a BED model in which female rats with a history of intermittent food restriction show binge-like palatable food consumption after a 15-minute exposure to the sight of the palatable food (frustration stress). In this model, we investigated the anti-bingeing acute effects of OEA (2.5, 5 or 10 mg kg-1, i.p.) on HPF intake and analysed the neurobiological bases of these effects by focusing on the brain pattern of c-Fos expression, on DA release in the shell of the nucleus accumbens (AcbSh), on monoamine concentrations/turnovers in selected brain regions and on both CRF and OXY mRNA in hypothalamic and extra hypothalamic areas.