Does naloxone suppress self-stimulation by decreasing reward or by increasing aversion?

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Neuropharmacology

Background:

• The ventrolateral midbrain central gray is a key area for reward and analgesia.
• Opiate receptors are implicated in both reward and pain modulation.

Purpose of the Study:

• To investigate the role of endorphins in self-stimulation reward and stimulation-produced analgesia.
• To determine if naloxone's effect on self-stimulation is mediated by analgesia.

Main Methods:

• Electrode implantation in the rat ventrolateral midbrain central gray.
• Assessment of self-stimulation and stimulation-produced analgesia.
• Administration of naloxone, an opiate receptor blocker.

Main Results:

• Naloxone significantly suppressed self-stimulation in rats by approximately 40%.
• This suppression occurred at both reward sites that produced analgesia and those that did not.
• Naloxone did not preferentially affect analgesic reward sites.

Conclusions:

• The findings do not support the hypothesis that naloxone suppresses self-stimulation by antagonizing endorphin-mediated analgesia.
• Data suggest naloxone suppresses self-stimulation by blocking endorphin-mediated reward pathways.