Stereoselective discriminative stimulus effects of zopiclone in rhesus monkeys.
BACKGROUND
The behavioral effects of racemic zopiclone are similar to those of benzodiazepines that positively modulate GABA at the GABA(A) receptor complex; however, it is not clear how enantiomers or metabolites of zopiclone contribute to the benzodiazepine-like behavioral effects of racemic zopiclone.


OBJECTIVE
Racemic zopiclone, its ( R)- and ( S)- enantiomers, and the ( S)-N-desmethyl metabolite, were evaluated for discriminative stimulus effects in untreated and diazepam treated rhesus monkeys.


METHODS
One group of monkeys discriminated the benzodiazepine midazolam and another group, treated daily with the benzodiazepine diazepam (5.6 mg/kg, PO), discriminated the benzodiazepine antagonist flumazenil.


RESULTS
( RS)-Zopiclone (0.32-17.8 mg/kg) and ( S)-zopiclone (0.1-10 mg/kg) substituted with similar potencies for midazolam (>/=80% midazolam-appropriate responding). The midazolam-like discriminative stimulus effects of ( RS)-zopiclone were antagonized by flumazenil (p K(B)=7.52). ( R)-Zopiclone occasioned a maximum 45% midazolam-appropriate responding at a dose of 100 mg/kg; ( S)-desmethylzopiclone produced saline-appropriate responding up to a dose of 100 mg/kg. All four test compounds occasioned predominantly vehicle-appropriate responding in diazepam treated monkeys discriminating flumazenil. ( RS)-Zopiclone (10 mg/kg) attenuated the discriminative stimulus effects of flumazenil in diazepam treated monkeys.


CONCLUSIONS
These results clearly demonstrate that in rhesus monkeys the discriminative stimulus effects of zopiclone are stereoselective and qualitatively similar to those of midazolam. These results fail to show any benzodiazepine-like or benzodiazepine antagonist-like discriminative stimulus effects for ( S)- N-desmethylzopiclone, suggesting that any behavioral (e.g. anxiolytic) effects of this compound are not the result of actions at benzodiazepine receptors.
McMahon
Lance R
LR
Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
Jerussi
Thomas P
TP
France
Charles P
CP
D000284:Administration, Oral; D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology; D053961:Azabicyclo Compounds; D003975:Diazepam / Q000009:adverse effects / Q000037:antagonists & inhibitors; D004193:Discrimination Learning / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005442:Flumazenil / Q000494:pharmacology; D018757:GABA Modulators / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology*; D058787:GABA-A Receptor Antagonists; D008253:Macaca mulatta; D008297:Male; D008874:Midazolam / Q000494:pharmacology; D010879:Piperazines / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology*; D013237:Stereoisomerism; D013375:Substance Withdrawal Syndrome / Q000523:psychology
D014151:Anti-Anxiety Agents; D053961:Azabicyclo Compounds; D018757:GABA Modulators; D058787:GABA-A Receptor Antagonists; D010879:Piperazines; C515050:zopiclone; D005442:Flumazenil; C053229:N-desmethylzopiclone; D003975:Diazepam; D008874:Midazolam