Marijuana's interaction with brain reward systems: update 1991

Area of Science:

• Neuroscience
• Pharmacology
• Addiction Research

Background:

• Non-cannabinoid drugs of abuse commonly enhance brain reward circuits via dopamine.
• Cannabinoids were previously considered anomalous due to a perceived lack of interaction with these systems.

Purpose of the Study:

• To investigate the neurobiological mechanisms underlying marijuana's (cannabinoids) interaction with brain reward systems.
• To determine if delta 9-tetrahydrocannabinol (delta 9-THC) affects reward circuitry similarly to other drugs of abuse.

Main Methods:

• Review of existing data on delta 9-THC's effects on brain reward substrates.
• Examination of delta 9-THC's impact on medial forebrain bundle (MFB) electrical brain stimulation reward.
• Analysis of delta 9-THC's influence on dopamine release in MFB projection loci.
• Investigation of naloxone's effect on delta 9-THC's actions and modulation of opioid receptors.

Main Results:

• Delta 9-THC enhances MFB electrical brain stimulation reward.
• Delta 9-THC increases basal and stimulated dopamine release in reward-relevant MFB areas.
• These effects are naloxone-blockable and involve modulation of mu and delta opioid receptors.

Conclusions:

• Marijuana's (delta 9-THC) interaction with brain reward systems is fundamentally similar to non-cannabinoid drugs of abuse.
• Cannabinoids act on crucial drug-sensitive links in the brain's reward circuitry.
• A specific neural model for marijuana's abuse liability is proposed.