Butorphanol Suppression of Histamine Itch Is Mediated by Nucleus Accumbens and Septal Nuclei: A Pharmacological fMRI Study

Abstract

Opioid receptors in the central nervous system are important modulators of itch transmission. In this study, we examined the effect of mixed-action opioid butorphanol on histamine itch, cowhage itch and heat pain in healthy volunteers. Using functional MRI, we investigated significant changes in cerebral perfusion to identify the critical brain centers mediating the antipruritic effect of butorphanol. Butorphanol suppressed the itch induced experimentally with histamine, reduced the intensity of cowhage itch by approximately 35%, and did not affect heat pain sensitivity. In comparison with the placebo, butorphanol produced a bilateral deactivation of claustrum, insula and putamen, areas activated during itch processing. Analysis of cerebral perfusion patterns of brain processing of itch vs. itch inhibition under the effect of the drug, revealed that the reduction of cowhage itch by butorphanol was correlated with changes in cerebral perfusion in the midbrain, thalamus, S1, insula and cerebellum. The suppression of histamine itch by butorphanol was paralleled by the activation of nucleus accumbens and septal nuclei, structures expressing high levels of kappa opioid receptors. In conclusion, important relays of the mesolimbic circuit were involved in the inhibition of itch by butorphanol and could represent potential targets for the development of antipruritic therapy.