Effects of intrahypothalamic administration of opioid peptides selective for mu-, kappa, and delta-receptors on different schedules of water intake in the rat.

The effects of opioid peptides selective for mu, kappa, and delta-opioid receptors were investigated on 3 different schedules of water intake in the rat: spontaneous, deprivational (12 h), and hypertonic saline-induced drinking. Peptides were injected into the paraventricular and supraoptic hypothalamic nuclei, D-Ala2-NMePhe4-Gly(ol)-enkephalin, a mu-selective opioid agonist, tended to increase water intake in non-deprived rats, but 0.01 and 0.1 microgram significantly decreased water intake for 45 min in deprived rats, and for up to 60 min in hypertonic saline-injected rats when injected into the paraventricular hypothalamic nucleus. The kappa-selective agonist, dynorphin A1-13 (0.1, 0.3, 1.0 and 3.0 micrograms)and the delta-selective agonist, [D-Pen2,L-Pen5]enkephalin (0.3 and 3.0 micrograms) did not affect spontaneous, deprivational or hypertonic saline-induced water intakes when injected into either the paraventricular or supraoptic hypothalamic nuclei. Thus, a mu-selective opioid peptide produced dose- and time-dependent effects on drinking that were pharmacologically and anatomically specific, and dependent upon the schedule of water intake.