Antinociceptive effects of racemic AM1241 and its chirally synthesized enantiomers: lack of dependence upon opioid receptor activation.
Cannabinoid CB(2) receptors represent a therapeutic target that circumvents unwanted central side effects (e.g., psychoactivity and/or addiction) associated with activation of CB(1) receptors. One of the primary investigative tools used to study functions of the CB(2) receptor is the aminoalkylindole (R,S)-AM1241. However, (R,S)-AM1241 has been described as an atypical CB(2) agonist which produces antinociception mediated indirectly by opioid receptors. (R,S)-AM1241 and its enantiomers, (R)-AM1241 and (S)-AM1241, were evaluated for antinociception in response to thermal (Hargreaves) and mechanical (von Frey) stimulation. Pharmacological specificity was established using antagonists for CB(1) (rimonabant [SR141716]) and CB(2) (SR144528). The opioid antagonist naloxone was administered locally in the paw or systemically to evaluate the contribution of opioid receptors to CB(2)-mediated antinociception produced by (R,S)-AM1241, (R)-AM1241, and (S)-AM1241. Comparisons were made with the opioid analgesic morphine. (R,S)-AM1241, (R)-AM1241, and (S)-AM1241 (0.033-10 mg/kg i.p.) produced antinociception to thermal, but not mechanical, stimulation of the hindpaw in naive rats. Antinociception produced by (R,S)-AM1241 and (S)-AM1241 exhibited an inverted U-shaped dose response curve. (R)-AM1241 produced greater antinociception than either (S)-AM1241 or (R,S)-AM1241 at the lowest (0.033 and 0.1 mg/kg i.p.) and highest (10 mg/kg i.p.) doses. Similar levels of antinociception were observed at intermediate doses. (R,S)-AM1241, (R)-AM1241, and (S)-AM1241 each produced CB(2)-mediated antinociception that was blocked by SR144528 but not by rimonabant. Local and systemic naloxone blocked morphine-induced antinociception but did not block antinociceptive effects of (R,S)-AM1241, (R)-AM1241, or (S)-AM1241. The antinociceptive effects of the CB(2)-selective cannabinoid (R,S)-AM1241 and its enantiomers, (R)-AM1241 and (S)-AM1241, are not dependent upon opioid receptors.
Rahn
Elizabeth J
EJ
Neuroscience and Behavior Program, Department of Psychology, University of Georgia, Athens, Georgia 30602-3013, USA.
Zvonok
Alexander M
AM
Makriyannis
Alexandros
A
Hohmann
Andrea G
AG
D000700:Analgesics / Q000737:chemistry / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D002186:Cannabinoids / Q000737:chemistry / Q000494:pharmacology; D006358:Hot Temperature; D007536:Isomerism; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D043884:Receptor, Cannabinoid, CB1 / Q000037:antagonists & inhibitors; D043885:Receptor, Cannabinoid, CB2 / Q000819:agonists / Q000037:antagonists & inhibitors; D011957:Receptors, Opioid / Q000187:drug effects*; D013329:Structure-Activity Relationship
C439263:AM 1241; D000700:Analgesics; D000701:Analgesics, Opioid; D002186:Cannabinoids; D009292:Narcotic Antagonists; D043884:Receptor, Cannabinoid, CB1; D043885:Receptor, Cannabinoid, CB2; D011957:Receptors, Opioid; D009270:Naloxone; D009020:Morphine