Behavioral effects of KOR activation typically oppose effects observed with other opioid receptors. Whereas activation of mu opioid receptors is highly reinforcing, resulting in conditioned place preference and increased dopamine release in the nucleus accumbens, KOR activation produces aversive or dysphoric states, resulting in conditioned place aversion and reduced dopamine release in the nucleus accumbens (Mucha and Herz, 1985; Di Chiara and Imperato, 1988). KOR agonists have also been shown to increase reward thresholds in intracranial self-stimulation procedures, suggesting an anhedonic effect (decreased sensitivity to rewarding stimuli) (Todtenkopf et al., 2004). In addition to inducing negative affective states, KOR activation also influences locomotor, feeding, and sexual behavior (Bruijnzeel, 2009).
