Centrally administered [mu]- and [delta]-opioid agonists increase operant responding for saccharin

Abstract

In previous reports, ICV administration of selective [mu]- or [delta]-opioid receptor agonists was found to stimulate the intake of saccharin and salt solutions in nondeprived rats. In the present study, we measured the effects of selective [mu], [delta], and [kappa]-agonists on operant responding for saccharin. The selective [mu]-agonist [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) and the selective [delta]-agonist [D-Thr2]-leucine enkephalin-Thr (DTLET) increased responding, whereas the [kappa]-agonist dynorphin A analog [kappa] ligand (DAKLI) had no significant effect. These results agree with previous studies on saccharin and salt intake and are consistent with the possibility that the effects of opioids on the intake of these fluids are mediated via enhancement of activity in brain reward pathways.