PT  - JOURNAL ARTICLE
AU  - Jan Rodriguez Parkitna
AU  - Ilona Obara
AU  - Agnieszka Wawrzczak-Bargiela
AU  - Wioletta Makuch
AU  - Barbara Przewlocka
AU  - Ryszard Przewlocki
TI  - Effects of Glycogen Synthase Kinase 3β and Cyclin-Dependent Kinase 5 Inhibitors on Morphine-Induced Analgesia and Tolerance in Rats
AID  - 10.1124/jpet.106.107581
DP  - 2006 Nov 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 832--839
VI  - 319
IP  - 2
4099  - http://jpet.aspetjournals.org/content/319/2/832.short
4100  - http://jpet.aspetjournals.org/content/319/2/832.full
SO  - J Pharmacol Exp Ther2006 Nov 01; 319
AB  - Repeated administration of morphine is associated with the development of tolerance, yet the mechanism underlying this phenomenon is still poorly understood. Recent evidence implicating glycogen synthase kinase 3 (GSK3) in opioid receptor signaling pathways has prompted us to investigate its role in morphine tolerance. Administration of 10 mg/kg morphine i.p. to Wistar rats twice daily for 8 days resulted in complete tolerance to its analgesic effects as measured by the tail-flick test. When injections of morphine were preceded by intrathecal (i.t.) administration of either an inhibitor of GSK3 [(3-(2,4-dichlorophenyl)-4-(1-methyl-1H-indol-3-yl)-1H-pyrrole-2,5-dione (SB216763) or 6-bromoindirubin-3′oxime] or an inhibitor of cyclin-dependent kinase (Cdk), roscovitine, development of tolerance to morphine analgesia was completely abolished. In addition, a single i.t. injection of either kinase inhibitor was able to restore in a dose-dependent manner the analgesic effect of morphine in morphine-tolerant rats. None of the inhibitors in doses used in the present study had analgesic effects of their own nor an effect on the analgesic potency of morphine. Repeated i.t. administration of either inhibitor had caused an increase in abundance of GSK-3β phosphorylated at Ser9 in the dorsal lumbar part of the spinal cord of rats that were chronically treated with morphine. Furthermore, reversal of morphine tolerance by a single injection of either inhibitor was always associated with increased abundance of phospho-GSK3β. In conclusion, our data indicate that chronic morphine treatment activates a highly efficient pathway by means of which Cdk5 regulates GSK3β activity. The American Society for Pharmacology and Experimental Therapeutics