Old and new synthetic cannabinoids: lessons from animal models.

Synthetic cannabinoids have long been studied for their therapeutic potentials. However, during the last decade, new generations of synthetic cannabinoid agonists appeared on the drug market. These new psychoactive substances are currently sold as 'marijuana-like' products as they claim to mimic the effects of the psychoactive component of cannabis, delta-9-tetrahydrocannabinol (THC). Yet, their effects are more intense and potent than THC, typically last longer and are often associated to serious psychiatric consequences. Animal models of drug addiction are frequently used in preclinical research to assess the abuse potential of new compounds, evaluate drug positive reinforcing effects and analyze drug-induced behaviors. Some of these protocols have been used recently to study the newly synthesized cannabinoid agonists and have started elucidating their pharmacology and actions in the brain. The aim of this review is to summarize the major findings reported by animal studies that tested synthetic cannabinoids of first, second, and third generation by using self-administration and reinstatement models, drug discrimination and conditioned place preference procedures. Altogether, behavioral studies clearly indicate that synthetic cannabinoids possess abuse liability, are likely to activate the brain reward circuit and induce positive subjective and reinforcing effects.