Effects of preferential delta and kappa opioid receptor agonists on the intake of hypotonic saline

A previous study has implicated central mu opioid receptors in the preference for salt solutions. Because mu, kappa and delta receptors are all thought to play a role in food intake and/or the mediation of palatability, we performed a series of experiments to determine whether preferential agonists at kappa and delta receptors might also stimulate the intake of salt solutions. When injected centrally into nondeprived rats, two selective agonists at delta receptors caused increases in the intake of 0.6% saline; the intake of concurrently available water was either unchanged or slightly increased. The selective kappa agonist U-50, 488H had no effect on water or saline intake, whereas the preferential kappa agonist DAFPHEDYN caused a delayed increase in saline intake. These results indicate a role for central delta receptors in the preference for salt solutions, and are consistent with the suggestion that opioids play a role in the mediation of palatability.