The Distribution of μ and δ Opioid Binding Sites Belonging to a Single Cervical Dorsal Root in the Superficial Dorsal Horn of the Rat Spinal Cord: A Quantitative Autoradiographic Study

Abstract

Numerous studies have demonstrated a dense concentration of opioid receptors in the superficial layers (laminae I - II) of the spinal cord. These receptors are located both pre- and postsynaptically at this level. The purpose of this study was to assess the distribution of opioid receptors belonging to a single (C7) dorsal root. Thus, quantitative autoradiography of &mgr; ([3H]Tyr-d-Ala-Gly-NMe-Phe-Gly-ol; [3H]DAMGO) and delta ([3H]Tyr-d-Thr-Gly-Phe-Leu-Thr; [3H]DTLET) opioid binding sites was performed for several experimental groups: control rats with intact dorsal roots and lesioned rats with a unilateral dorsal rhizotomy of (a) the C7 root alone, (b) the three successive roots rostral and caudal to the spared C7 root, and (c) the seven roots C4 - Th2. By subtracting results of the 'C7 cut' group from the 'intact' group or by subtracting results of the C4 - Th2 cut group from the C7 spaced group, it was possible to measure the distribution of &mgr; and delta opioid binding sites belonging to the C7 root. The combination of these two methods of calculation allowed us to demonstrate a significant distribution over two segments rostral and one segment caudal to the segment of entry. For [3H]DAMGO, the distribution was 10% (P < 0.05) in the C5, 27%, (P < 0.001) in the C6, 38% (P < 0.001) in the C7 and 14% (P < 0.05) in the C8 segment. For [3H]DTLET, the distribution was 11% (P=0.05) in the C5, 27%, (P < 0.01) in the C6, 37% (P < 0.001) in the C7 and 18% (P < 0.05) in the C8 segment. It is also noted that rostral distributions spread more densely and further than the caudal ones.

The Increased Trafficking of the Calcium Channel Subunit α2δ-1 to Presynaptic Terminals in Neuropathic Pain Is Inhibited by the α2δ Ligand Pregabalin

“…However, a proportion of afferents project in Lissauer's tract to up to two spinal segments rostrally and one spinal segment caudally. The L4 dorsal horn not only receives afferents from L4, but also from ligated L5/L6 dorsal roots (Besse et al, 1991;Shehab et al, 2008). This may contribute to the small, but statistically significant elevation of ␣ 2 ␦-1 in ipsilateral L4 after SNL.…”

Electrophysiological properties of spinal wide dynamic range neurons in neuropathic pain rats following spinal nerve ligation

“…As a result, the L4-L5 spinal segment received less afferent input [28,29] . This may induce a marked compensatory hyperexcitability within the spinal cord via NMDA receptor activation and/or spinal disinhibition, e.g., via reduced GABAergic inhibitory activity in the spinal cord [30] .…”

“…The L4 spinal segment would be likely to receive approximately 40% less fine fibers input as a result of L5 and L6 SNL [28] .…”

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

“…Although ipsilateral losses of opioid binding sites after a unilateral dorsal rhizotomy are well documented in the literature (Lamotte er al., 1976;Jessel et al, 1979;Ninkovic et al, 1981Ninkovic et al, , 1982Daval er al., 1987;Zajac et al, 1989;Besse et al, 1991;Stevens et al, 1991;Gouarderes er al., 1991), contralateral modifications have not, to our knowledge, been previously quantified and were a priori unexpected. The contralateral modifications in [3H]DAMG0 opioid binding were probably not due to direct contralateral projections crossing the midline, since such projections are not numerous in the rat spinal cord (Chung et al, 1989) and have not been described in laminae I -I1 of the cervical enlargement (Arvidsson and Pfaller, 1990).…”

“…In addition, we have recently proposed that, using selective tritiated ligands and autoradiography, the binding of opioid receptors is a useful technique to assess quantitatively the central projections of thin primary afferent fibres in the superficial layers of the rat dorsal horn (Besse et al, 1991). This hypothesis is based on several indirect pieces of Plasticity of opioid receptors following dorsal rhizotomy 955 evidence indicating that the major component of opioid receptors in laminae I -I1 is located on primary afferent fibres (Hiller et al , 1978;Fields et al, 1980;Young et al, 1980), and particularly on fine diameter fibres (Gamse et al, 1979;Nagy et al, 1980;Daval et af., 1987).…”