κ-Opioid Receptor Agonists Modulate Visceral Nociception at a Novel, Peripheral Site of Action

Abstract

kappa-opioid receptor agonists (kappa-ORAs) have been shown to modulate visceral nociception through an interaction with a peripheral, possibly novel, kappa-opioid-like receptor. We used in the present experiments an antisense strategy to further explore the hypothesis that kappa-ORA effects in the colon are produced at a site different from the cloned kappa-opioid receptor (KOR). An antisense oligodeoxynucleotide (ODN) to the cloned rat KOR was administered intrathecally (12.5 microg, twice daily for 4 d) to specifically knock-down the cloned KOR. Efficacy of the KOR antisense ODN treatment was behaviorally evaluated by assessing the antinociceptive effects of peripherally administered kappa- (EMD 61, 753 and U 69,593), mu- (DAMGO) and delta- (deltorphin) ORAs in the formalin test. Intrathecal antisense, but not mismatch ODN blocked the actions of EMD 61,753 and U 69,593 without affecting the actions of DAMGO or deltorphin; a complete recovery of antinociceptive actions of the kappa-ORA EMD 61,753 was observed 10 d after the termination of antisense ODN treatment. In contrast, the ability of EMD 61,753 to dose-dependently attenuate responses of pelvic nerve afferent fibers to noxious colonic distension was unaffected in the same rats in which the antisense ODN effectively knocked-down the KOR as assessed in the formalin test. Additionally, Western blot analysis demonstrated a significant downregulation of KOR protein in the L4-S1 dorsal root ganglia of antisense, but not mismatch ODN-treated rats. The present results support the existence of a non-kappa-opioid receptor site of action localized in the colon.

The Expression of δ- and κ-Opioid Receptor Is Enhanced during Intestinal Inflammation in Mice

“…The band-size for the ␦-and -opioid receptor proteins is consistent with the results obtained in rodents by other investigators, which describe molecular masses of 43 to 125 kDa for the ␦-opioid receptor (Sá nchez-Blá zquez et al, 1997; Cahill et al, 2001;Cichewicz et al, 2001) and between 43 to 70 kDa for the -opioid receptor (Joshi et al, 2000;Cichewicz et al, 2001). In our experiments, the detected bands of 68 and 72 kDa could correspond to the monomeric receptors (␦ and ), which presumably represent different post-translational maturation forms (glycosylation) of these receptors.…”

Nonopioid Actions of U50,488 Enantiomers Contribute to Their Peripheral Cutaneous Antinociceptive Effects

“…Intrathecal (i.t.) administration of antisense, but not mismatch ODN has been previously shown by us to cause a peripheral down-regulation of the KOR and block peripheral -ORA-mediated antinociception in the formalin test, without affecting antinociception mediated at other opioid receptors (Joshi et al, 2000).…”

“…The synthesis and administration of the ODNs have been described previously (Joshi et al, 2000) and are only briefly summarized here. Antisense and mismatch ODNs had a phosphodiester backbone, derived from the 5Ј end of the coding sequence of the cloned rat KOR (nucleotides 6 -25) and were synthesized by Integrated DNA Technologies (Iowa City, IA) and reconstituted in sterile deionized water before use.…”

“…One strategy to circumvent the central nervous system side effects associated with opioids has been to take advantage of analgesia that can be produced by opioids at peripheral sites (Stein et al, 2001). Accordingly, -ORAs have been shown to be antinociceptive when restricted to peripheral cutaneous sites such as the tail (Kolesnikov et al, 1996) and hind paw (Joshi et al, 2000) as well as peripheral visceral sites such as the colon .…”

“…We have previously documented the ability of arylacetamide -ORAs to produce antinociception at peripheral sites (Joshi et al, 2000). However, it is not known whether -ORAs could produce such antinociception through nonopioid mechanisms, such as sodium channel blockade.…”