Endomorphin-1 and Endomorphin-2 Show Differences in Their Activation of μ Opioid Receptor-Regulated G Proteins in Supraspinal Antinociception in Mice1
- Neurofarmacologı́a, Instituto de Neurobiologı́a Santiago Ramón y Cajal, Consejo Superior de Investigaciones Cientı́ficas, Madrid, Spain
Abstract
Endomorphin-1 and endomorphin-2 are tetrapeptides of the brain whose binding profiles and analgesic activities indicate that they are endogenous ligands at μ opioid receptors. To analyze the classes of G transducer proteins activated by these opioids in the production of supraspinal antinociception, the expression of α subunits of the Gi protein class, Gi1, Gi2, Gi3, Go1, Go2, and Gz, and those of the Gq protein family, Gq and G11, was reduced by administration of antisense oligodeoxynucleotides (ODNs) complementary to sequences in their respective mRNAs. The ODN treatments promoted differences in the analgesic effects displayed by morphine, [d-Ala2,N-MePhe4,Gly-ol5]enkephalin (DAMGO), and the novel opioids endomorphin-1 and endomorphin-2. The impairment of Gi1α and Gi3α function led to a weaker analgesic response to the endomorphins and to the α2-adrenoceptor agonist clonidine, whereas the effects of morphine and DAMGO were not affected. An antisense probe targeting Gi2α blocked the antinociceptive effects of endomorphin-2, morphine, DAMGO, and clonidine but was without effect on the activity of endomorphin-1. Mice receiving the ODN to Gzα subunits showed impaired response to all agonists. The knockdown of either Go1α, Go2α, Gqα, or G11α had little or no influence on the antinociception induced by any of the opioids in the study. Thus, agonists exhibit differences in activating the variety of GTP-binding proteins regulated by μ opioid receptors.
Footnotes
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Send reprint requests to: Dr. Pilar Sánchez-Blázquez, Instituto Cajal, CSIC, Avenida Doctor Arce 37, E-28002, Madrid, Spain. E-mail: jgarzon{at}cajal.csic.es
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↵1 This work was supported by Comisión Interministerial de Ciencia y Tecnologı́a Grant CICYT SAF98-0057, Comunidad Autónoma de Madrid (CAM) Grant 08.8/0011/1998, and Fondo de Investigaciones Sanitarias (FIS) Grant FIS97/0506. M.R.-D. is supported by CAM. I.D. is supported by FIS. A preliminary report of this work was presented at the 29th International Narcotic Research Conference, Gasmisch-Partenkirchen, July 1998.
- Abbreviations:
- G protein
- GTP-binding protein
- i.c.v.
- intracerebroventricular
- ODN
- oligodeoxynucleotide
- MAE
- maximum analgesic effect
- RD
- random sequence
- DAMGO
- [d-Ala2,N-MePhe4,Gly-ol5]enkephalin
- ICI 174,864
- N,N-diallyl-Tyr-Aib-Aib-Phe-Leu
- CTOP
- Cys2,Tyr3,Orn5,Pen7-amide (somatostatin analog)
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- Received February 23, 1999.
- Accepted May 28, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
