Development of tolerance to the antinociceptive effect of metergoline.
Metergoline given IP reduced the response to noxious stimulation in the mouse formalin test. Tolerance to this effect developed after a chronic treatment schedule consisting of ten daily injections of 5 mg/kg. Twenty four hours after the last injection a test dose of metergoline (2.5 mg/kg) reduced the licking time in the formalin test by 28% in the chronic metergoline group, compared to 68% reduction in the vehicle-treated animals. In addition, the antinociceptive effect of the 5-hydroxytryptamine releasing compound p-chloramphetamine (PCA) was reduced following chronic treatment with metergoline. The reduced effect of PCA may have been caused by down-regulation of 5-HT2 receptors. However, this finding is also compatible with the contention that metergoline may act as an agonist at postsynaptic serotonergic receptors.
D000818:Animals; D004361:Drug Tolerance; D004873:Ergolines / Q000494:pharmacology*; D008297:Male; D008711:Metergoline / Q000494:pharmacology*; D051379:Mice; D008815:Mice, Inbred Strains; D009619:Nociceptors / Q000187:drug effects*; D012684:Sensory Thresholds; D010133:p-Chloroamphetamine / Q000494:pharmacology
D004873:Ergolines; D008711:Metergoline; D010133:p-Chloroamphetamine