DESCRIPTION (provided by applicant): A new class of pain-relieving drugs, derived from histamine antagonists, has recently been discovered. The prototype (named improgan) shows the following characteristics after direct injection into the brain: a) highly effective, morphine-like antinociception on thermal and mechanical tests, b) no impairment of motor coordination or locomotor activity, e) mechanism that is independent of known receptors for histamine and opioids, d) lack of tolerance with daily dosing, and e) unique structure-activity relationships among chemical congeners. Several impediments exist in the development of these agents: l) the mechanism of action is unknown, 2) high-potency congeners have not been discovered, 3) many have H2 or H3-blocking side effects (but do not produce analgesia through these receptors), and 4) the compounds do not penetrate the blood brain barrier after systemic dosing. The experiments below in rats and mice will discover new analgesic congeners of improgan with enhanced potency, reduced side effects and improved brain-penetrating properties: Aim l) Synthesize and test new improgan-like analgesics which lack H2 and H3 receptor side effects, and possess enhanced analgesic potency. Pilot results indicate that open chain; furan-containing congeners will show these properties. Aim 2) Synthesize and test brain-penetrating improgan-like analgesics. Pilot studies show the feasibility of discovering such compounds. Aim 3) Determine the in vitro actions of these new drugs on two new radioligand binding assays being developed to predict improgan analgesia. Aim 4) Study the activity of selected new compounds in vivo: a) classify their analgesic mechanism by treatments with transmitter agonists and antagonists, and b) assess their clinical potential in several different nociceptive tests and after various routes of administration. This project, which is a collaborative effort between medicinal chemists and pharmacologists, will produce new, brain-penetrating, non-opioid analgesics with the efficacy and potency of morphine. These experiments will help to discover the mechanism of action of this novel class of agents, and lead to the development of new pharmacotherapies for pain.