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The Journal of Neuroscience, November 1, 2002, 22(21):9210-9220

Changes in Spinal  and  Opioid Systems in Mice Deficient in the A_2A Receptor Gene

Alexis Bailey¹, Catherine Ledent², Mary Kelly¹, Susanna M. O. Hourani¹, and Ian Kitchen¹

¹ Pharmacology Group, School of Biomedical and Life Sciences, University of Surrey, Guildford, Surrey, GU2 7XH United Kingdom, and ² Institut de Recherche Interdisciplinaire en Biologie Humaine et Nucléaire, Université Libre de Bruxelles, B-1070 Brussels, Belgium

A large body of evidence indicates important interactions between the adenosine and opioid systems in regulating pain at both the spinal and supraspinal level. Mice lacking the A_2A receptor gene have been developed successfully, and these animals were shown to be hypoalgesic. To investigate whether there are any compensatory alterations in opioid systems in mutant animals, we have performed quantitative autoradiographic mapping of µ, , , and opioid receptor-like (ORL1) opioid receptors in the brains and spinal cords of wild-type and homozygous A_2A receptor knock-out mice. In addition, µ-, -, and mediated antinociception using the tail immersion test was tested in wild-type and homozygous A_2A receptor knock-out mice. A significant reduction in [³H]deltorphin-I binding to  receptors and a significant increase in [³H]CI-977 binding to  receptors was detected in the spinal cords but not in the brains of the knock-out mice. µ and ORL1 receptor expression were not altered significantly. Moreover, a significant reduction in -mediated antinociception and a significant increase in -mediated antinociception were detected in mutant mice, whereas µ-mediated antinociception was unaffected. Comparison of basal nociceptive latencies showed a significant hypoalgesia in knock-out mice when tested at 55°C but not at 52°C. The results suggest a functional interaction between the spinal  and  opioid and the peripheral adenosine system in the control of pain pathways.

Key words: A_2A knock-out; µ opioid receptor; opioid receptor; opioid receptor; ORL1 receptor; autoradiography; opioid-mediated antinociception

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Copyright © 2002 Society for Neuroscience  0270-6474/02/22219210-11$05.00/0

This article has been cited by other articles:

				O. M. Abo-Salem, A. M. Hayallah, A. Bilkei-Gorzo, B. Filipek, A. Zimmer, and C. E. Muller Antinociceptive Effects of Novel A2B Adenosine Receptor Antagonists J. Pharmacol. Exp. Ther., January 1, 2004; 308(1): 358 - 366. [Abstract] [Full Text] [PDF]

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