Giving rats and squirrel monkeys a drug called Ro 61-8048, which increases the levels of kynurenic acid (KYNA) in the brain and in turn reduces dopamine levels, seems to have reduced the rewarding aspect of both THC and a synthetic variant of the cannabinoid. The rats stopped pushing their levers to self-administer the synthetic cannabinoid. In monkeys trained to self-administer food and cocaine as well as THC, the drug kept them from pushing the THC lever. It also reduced THC-seeking behavior when abstinent, formerly-dependent rats and monkeys were re-introduced to the drug. The researchers hypothesize that this is because the increase in KYNA blocked THC-induced dopamine elevation in the shell of the nucleus accumbens. The brain may not have been getting the same reward, so the animals stopped wanting THC.