Drinking behavior is modulated by CNS administration of opioids in the rat

While opiate antagonists have been shown to reliably attenuate drinking following both central and peripheral administration, relatively few data exist on the effects of agonist agents on this behavior. To address this issue, two opiate agonists, morphine sulfate, a mu agonist, and [D-ala2, D-leu5]-enkephalin (DADLE), a semi-synthetic delta analog of a delta agonist, were administered into several CNS sites in rats. There was a dose-related, naloxone-reversible reduction of water intake following morphine injections into the lateral hypothalamus (LH) and preoptic area (POA). In addition, injections of DADLE also attenuated drinking when injected into LH and POA, but not following the ventral tegmental area or zona incerta administration. These data are discussed in view of a role for the endogenous opioid peptides in the regulation of drinking behavior.