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Plasticity of μ and δ Opioid Receptors in the Superficial Dorsal Horn of the Adult Rat Spinal Cord Following Dorsal Rhizotomies: A Quantitative Autoradiographic Study

Authors

  • D. Besse,

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    1. Unité de Recherches de Physiopharmacologie du Système Nerveux (INSERM, U. 161) and Laboratoire de Physiopharmacologie de la Douleur, Ecole Pratique des Hautes Etudes, 2 rue d'Alésia 75014 Paris, France
      D. Besse, INSERM U. 161, 2 rue d'Alé, 75014 Paris, France
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  • M. C. Lombard,

    1. Unité de Recherches de Physiopharmacologie du Système Nerveux (INSERM, U. 161) and Laboratoire de Physiopharmacologie de la Douleur, Ecole Pratique des Hautes Etudes, 2 rue d'Alésia 75014 Paris, France
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  • J. M. Besson

    1. Unité de Recherches de Physiopharmacologie du Système Nerveux (INSERM, U. 161) and Laboratoire de Physiopharmacologie de la Douleur, Ecole Pratique des Hautes Etudes, 2 rue d'Alésia 75014 Paris, France
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D. Besse, INSERM U. 161, 2 rue d'Alé, 75014 Paris, France

Abstract

The aim was to study the regulation of μ and δ opioid binding sites in the superficial layers (laminae I–II) of the dorsal horn of the adult rat spinal cord 1, 2, 4 and 12 weeks after unilateral dorsal rhizotomies of various extents. Using quantitative autoradiography and highly selective tritiated opioid ligands, we have shown that the decrease in [3H]Tyr*-d-Ala-Gly-NMe-Phe-Gly-ol ([3H]DAMGO) (μ sites) and [3H]Tyr*-d-Thr-Gly-Phe-Leu-Thr ([3H]DTLET) (δ sites) binding in the side ipsilateral to the lesion as compared to the intact side is related to the number of dorsal roots cut. In the segment central to the lesion, 1 week after the lesion, ipsilateral/contralateral side binding ratios for [3H]DAMGO were 0.70, 0.49, 0.36 and 0.25 when 1, 3, 5 and 7 roots respectively were sectioned. For [3H]DTLET, the ratios were 0.71, 0.54, 0.42 and 0.39. The time-related analysis of binding ratios showed that, in partially deafferented spinal segments after long-term deafferentation (12 weeks postlesion) there were greater numbers of μ and δ binding sites than in cases of short-term deafferentation (1–2 weeks). By contrast, in spinal segments considered as completely deafferented, there was no difference in the remaining μ and δ binding sites at 12 weeks as compared to 1 week postlesion. Consequently, it is deduced that the partial recovery of μ and δ binding observed after long-term partial deafferentation could be associated with neuronal plasticity (probably collateral sprouting) of fine diameter primary afferent fibres arising from intact dorsal roots.

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