Metergoline elevates or reduces nociceptive thresholds in mice depending on test method and route of administration.
Intrathecal injection of metergoline reduced the response latencies in the tail-flick and hot-plate tests, supporting the contention that descending 5-hydroxytryptamine (5-HT) pathways tonically inhibit pain sensitivity. Elevated latencies were, however, observed after both intraperitoneal (IP) and intracerebroventricular (ICV) injections in the hot-plate test, when hindpaw lick was used as the response criterion. These findings may indicate that supraspinal 5-HT pathways tonically increase pain responsiveness in certain test situations . Alternative hypotheses are that metergoline in supraspinal structures acts as an agonist at post-synaptic 5-HT receptors mediating antinociception, or as an antagonist at pre-synaptic 5-HT receptors. Recording of first reaction latencies on the hot-plate showed increased thresholds after IP, but not after ICV injections. This may indicate an action on 5-HT receptors in the brain not accessible after ICV injections, or that the effect is mediated by blockade of peripheral 5-HT receptors.
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004873:Ergolines / Q000494:pharmacology*; D007274:Injections, Intraperitoneal; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008297:Male; D008711:Metergoline / Q000008:administration & dosage / Q000494:pharmacology*; D051379:Mice; D009619:Nociceptors / Q000187:drug effects*; D011930:Reaction Time / Q000187:drug effects
D004873:Ergolines; D008711:Metergoline