Opioid receptors in the human cerebellum: evidence from [C-11]diprenorphine PET, mRNA expression and autoradiography

LITTLE is known regarding opioid receptors in the human cerebellum. The pre sent [C-11]diprenorphine PET study investigated opioid receptor binding in the human cerebellum in vivo, and showed a differential binding level in ce rebellar cortex, vermis and dentate nuclei. The additional study in vitro o f opioid receptors in human cerebellar cortex and rat brain corroborated th e presence of opioidergic mechanisms in the human cerebellum in contrast to the rat. A differential cellular distribution pattern was detected for the three major opioid receptors investigated. For the mu-receptor, and at a l ower level for the K-receptor, mRNA expression was mainly observed over gra nule cells. Binding sites were most prominent in the molecular layer. For t he delta-receptor no signal was detected. The consideration of cerebellar o pioidergic mechanisms and the distribution patterns of the various opioid r eceptors may promote the understanding of cerebellar function and of opioid ergic pharmacology in the human. (C) 1999 Lippincott Williams & Wilkins.