Naloxone-precipitated withdrawal causes an increase in impulsivity in morphine-dependent rats

Opiate dependence is associated with increased impulsivity in both humans and animals. Although the state of withdrawal appears to contribute to this effect, a causal relationship has not been shown. Here, we test whether precipitating withdrawal in morphine-dependent rats through naloxone can cause increased impulsivity. Rats were trained on a delay discounting task and then randomly assigned to either a dependent group that received a nightly 30 mg/kg subcutaneous dose of morphine or a naive group that received nightly saline. Once dependence was established, 2-day test delay discounting curves were determined 1 h after three doses of naloxone (0, 0.25, 0.5 mg/kg). In dependent rats both doses of naloxone caused increased preference for the small reward at short delays. Naloxone had no effect on delay discounting in naive rats. We conclude that precipitating withdrawal in dependent rats can cause increased impulsivity.