Site-specific naloxone blockade of brain self-stimulation duration

Moderate doses of naloxone (1, 5, 10 mg/kg) did not reduce response rate measured by the initiation of intracranial self-stimulation bursts to the medial forebrain bundle or central gray, at several current intensities (30, 60, or 90 microA). Raising current intensity rates and duration of lever pressing at both sites. Naloxone produced a dose dependent reduction in self-selected current duration at both sites averaged over intensity. However, naloxone completely blocked the effect of intensity only at the gray site. In contrast to research showing effects of only high naloxone doses (e.g., 40 mg/kg) on self-stimulation at opiate-rich and opiate-poor receptor sites, this study indicates that endogenous opiates and opiate receptor mechanisms interact with aversive properties to modify central gray self-stimulation.