[Endogenous opiates, palatability and control of food intake]

Endogenous opiate or opioïds are peptidic neuromodulators which bind with specific receptors (mu, kappa, delta, etc), and thus control numerous physiological process, mainly pain and food intake (FI). Endogenous or exogenous agonists of opioïd receptors increase FI. Antagonists decrease it. However several results indicate discrepancies. The anorectic activity of antagonists is different of the activity of classical anorexigenic drugs since inhibition of opioïd receptors did not induce long term change of body weight. The analysis of the neurophysiological action of the opioïd system on FI can explain this apparent discrepancy. Opioïds act on the short term control of FI modulating the rewarding properties of alimentary stimuli: agonist increase and antagonists decrease it. Such an action correspond to a control of food palatability or, in human, to a control of the sensory pleasure/displeasure associated with food stimuli. Opioïd system does not seem to directly act on body weigh regulation.