Naltrexone reverses a long term depressive effect of a toxic lithium injection on saccharin preference

In 2 experiments, using female rats, we demonstrated that an injection of 2% body weight 150 mM lithium chloride (LiCl) reduced saccharin preference, measured 48 hr later. Furthermore, Experiment 1 showed that this effect of lithium was reversed by 10 mg/kg naltrexone injected immediately before lithium administration. Experiment 2 demonstrated that one injection of 10 mg/kg morphine also depressed saccharin preference 48 hr post-injection. Paradoxically, morphine given before lithium reversed the effects of lithium on saccharin preference. The experiments suggest the involvement of endogenous opioid peptides in the long term toxic effects of lithium on saccharin preference.