Role of the area postrema in the hypophagic effects of oleoylethanolamide.

The satiety-promoting action of oleoylethanolamide (OEA) has been associated to the indirect activation of selected brain areas, such as the nucleus of the solitary tract (NST) in the brainstem and the tuberomammillary (TMN) and paraventricular (PVN) nuclei in the hypothalamus, where noradrenergic, histaminergic and oxytocinergic neurons play a necessary role. Visceral ascending fibers were hypothesized to mediate such effects. However, our previous findings demonstrated that the hypophagic action of peripherally administered OEA does not require intact vagal afferents and is associated to a strong activation of the area postrema (AP). Therefore, we hypothesized that OEA may exert its central effects through the direct activation of this circumventricular organ. To test this hypothesis, we subjected rats to the surgical ablation of the AP (APX rats) and evaluated the effects of OEA (10mgkg-1 i.p.) on food intake, Fos expression, hypothalamic oxytocin (OXY) immunoreactivity and on the expression of dopamine beta hydroxylase (DBH) in the brainstem and hypothalamus. We found that the AP lesion completely prevented OEA's behavioral and neurochemical effects in the brainstem and the hypothalamus. Moreover OEA increased DBH expression in AP and NST neurons of SHAM rats while the effect in the NST was absent in APX rats, thus suggesting the possible involvement of noradrenergic AP neurons. These results support the hypothesis of a necessary role of the AP in mediating OEA's central effects that sustain its pro-satiety action.

Fats for thoughts: An update on brain fatty acid metabolism.

Brain fatty acid (FA) metabolism deserves a close attention not only for its energetic aspects but also because FAs and their metabolites/derivatives are able to influence many neural functions, contributing to brain pathologies or representing potential targets for pharmacological and/or nutritional interventions. Glucose is the preferred energy substrate for the brain, whereas the role of FAs is more marginal. In conditions of decreased glucose supply, ketone bodies, mainly formed by FA oxidation, are the alternative main energy source. Ketogenic diets or medium-chain fatty acid supplementations were shown to produce therapeutic effects in several brain pathologies. Moreover, the positive effects exerted on brain functions by short-chain FAs and the consideration that they can be produced by intestinal flora metabolism contributed to the better understanding of the link between "gut-health" and "brain-health". Finally, attention was paid also to the regulatory role of essential polyunsaturated FAs and their derivatives on brain homeostasis.