Vol. 303, Issue 2, 867-873, November 2002

Spinal Pretreatment with Antisense Oligodeoxynucleotides against Exon-1, -4, or -8 of µ-Opioid Receptor Clone Leads to Differential Loss of Spinal Endomorphin-1-and Endomorphin-2-Induced Antinociception in the Mouse

Hsiang-en Wu, Hirokazu Mizoguchi, Maia Terashvili, Randy J. Leitermann, Kuei-chun Hung, James M. Fujimoto and Leon F. Tseng

Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin

Intrathecal (i.t.) pretreatments with antisense oligodeoxynucleotides (AS ODNs) against exon-1, -4, or -8 of µ-opioid receptor clone (MOR-1) to knockdown different variants of MOR-1 on the antinociception induced by endomorphin-1, enomorphin-2, or [D-Ala²,N-Me-Phe⁴,Gly⁵-ol]-enkephalin (DAMGO) given i.t. were investigated in male CD-1 mice. The antinociception was measured with the tail-flick test. AS ODNs against exon-1 (5 µg) given i.t. once daily for 3 days attenuated the antinociception induced by endomorphin-1 and endomorphin-2 with the dose-response curves shifted to the right by 4.5- and 5.3-fold, respectively. AS ODNs against exon-4 (5 µg) attenuated the antinociception induced by endomorphin-1 and endomorphin-2 with the dose-response curves shifted to the right by 2.4- and 5.3-fold, respectively. However, AS ODNs against exon-8 (5 µg) attenuated only the antinociception induced by endomorphin-1, but not endomorphin-2 with the dose-response curves shifted to the right by 3.9- and 1.3-fold, respectively. One more day of pretreatment with antisense probes failed to further reduce the antinociception. The antinociception induced by DAMGO was attenuated by i.t. pretreatment with AS ODNs directed against exon-1, and, to a lesser extent, by AS ODNs directed against exon-8. The mismatch AS ODNs against respective exon-1, -4, and -8 failed to exert significant effects. The selective actions of antisense probes directed against different exons of the MOR-1 in attenuating the antinociception induced by endomorphin-1, endomorphin-2, and DAMGO suggest that multiple splice variants of the MOR-1 exist and support the view that different subtypes of µ-opioid receptors are involved in antinociception induced by endomorphin-1, endomorphin-2, and DAMGO.