Effects of antisense oligonucleotides on brain delta-opioid receptor density and on SNC80-induced locomotor stimulation and colonic transit inhibition in rats

Abstract

1. To reduce the density of δ-opioid receptor protein, five antisense phosphorothioate oligodeoxynucleotides (aODN), targeting the three exons of rat δ-opioid receptor mRNA (DOR), were injected twice daily for 4 days or continuously infused for 7 days into brain lateral ventricles (i.c.v.) of Sprague-Dawley rats. Rats acting as controls were infused or injected with a mismatch sequence (mODN) of each aODN. The density of opioid receptors in rat brain membranes was measured by saturation binding experiments using selective ligands for δ, μ and κ opioid receptors. 2. aODh's injected twice a day for 4 days left rat brain δ-opioid receptor density unchanged. The ODN targeting the DOR nucleotide sequence 280-299 (aODN280-299, exon 2), decreased brain δ-opioid receptor density significantly more than aODNs targeting exon 1 (aODN239-258), exon 2 (aODN361-380), or exon 3 (aODN741-760) (to 52% vs 79, 72, and 68%). None of the aODNs to the DOR changed the brain density of μ- or k-opioid receptors. 3. When in a novel environment (but not when kept in their home cages), the locomotor activity of aODn280-299 treated rats was significantly lower than that of saline or mODN treated rats. The δ-opioid agonist SNC80 (5 mg kg-1, s.c.) significantly and potently stimulated locomotion and delayed colonic propulsion in saline- and mODN-infused rats, but left motor behaviour and colonic transit of δ-knockdown rats unchanged. 4. The baseline nociceptive threshold and the antinociceptive response to morphine were unchanged in δ-knockdown rats.