Effects of intrahypothalamic administration of opioid peptides selective for μ-, κ-, and δ-receptors on different schedules of water intake in the rat

Abstract

The effects of opioid peptides selective for μ-, κ-, and δ-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-Ala- 2-NMePhe 4-Gly(ol)-enkephalin, a μ-selective opioid agonist, tended to increase water intake in non-deprived rats, but 0.01 and 0.1 μg 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 κ-selective agonist, dynorphin A 1–13 (0.1, 0.3, 1.0 and 3.0 μg) and the δ-selective agonist, [ d-Pen 2, l-Pen 5]enkephalin (0.3 and 3.0 μg) did not affect spontaneous, deprivation or hypertonic saline-induced water intakes when injected into either the paraventricular or supraoptic hypothalamic nuclei. Thus, a μ-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.