Opioids and food intake: distributed functional neural pathways?

Agonists of the mu, delta, kappa and ORL(1)opioid receptors increase food intake while opioid receptor blockade decreases food intake. The majority of the collected data related to opioids and feeding has led to the speculation that opioids are involved in meal maintenance and orosensory reward; however, some data suggest that opioids may impact feeding associated with energy needs. Based on the wide distribution of CNS opioid receptors and the presence of other neuropeptides in the vicinity of opioidergic pathways, it seems likely that opioids affect multiple feeding systems. For example, opioids in the hindbrain might be involved in both sensory and metabolic aspects of food intake, those in the amygdala in processing of 'emotional' properties of foods, and those in the hypothalamus in energy needs. In this review we present data which support functional diversity of opioids in feeding behavior.