Motivational Effects of Cannabinoids Are Mediated by µ-Opioid and [kappa ]-Opioid Receptors. This study by a Spanish-French research team using a ‘knockout’ mouse model (in which mice are genetically engineered to lack a class of neuroreceptors) produced the surprising finding that the modulation of reward pathways produced by THC is mediated by opiate receptors. J. Neurosci. — Abstracts: 22 (3): 1146