In-vivo studies on kappa opioid receptors

Abstract

The actions of opioids are mediated by multiple types of opioid receptor. As a result, ‘obtaining the right balance’ is the catchphrase most frequently heard these days in analgesic research laboratories throughout the pharmaceutical industry. Tomorrow's analgesics will feature a prominent κ component, a touch of δ, a tickle of μ, but not even a wisp of σ. New compounds are fashioned largely from structure-activity relationships involving bioassays and radioligand receptor binding. These in-vitro approaches have become well established over the past decade since they help to link receptor type to the analgesic under investigation. What about the complementary preclinical tests in-vivo? Specifically, how can the animal pharmacologist assist in characterizing κ opioid activity? In this article, Alan Cowan and Debra E. Gmerek present a survey of tests that are being used to detect and define κ activity in-vivo. Special emphasis is placed on the rat bombesin-scratch test, a new procedure in which several κ-preferring agents are selectively active.