Opioid-like discriminative stimulus properties of benzomorphans in the pigeon: stereospecificity and differential substitution patterns.
Pigeons were trained to discriminate the kappa-opioid agonist bremazocine (BREM) or the mu-opioid agonist fentanyl (FENT) from water. During tests of stimulus substitution, FENT and BREM failed to substitute for each other. The (-)-isomers of cyclazocine, pentazocine and ketocyclazocine substituted for the FENT but not the BREM stimulus. The (+)-isomers of these compounds, as well as the isomers of nallylnormetazocine, failed to substitute for either the FENT or BREM stimulus. In FENT- and BREM-trained pigeons, the (-)-isomers of cyclazocine, pentazocine, nallylnormetazocine and ketocyclazocine were more potent than their respective(+)-isomers in decreasing rates of responding. These results indicate that in the pigeon there is an isomeric separation of the discriminative stimulus properties of cyclazocine, pentazocine and ketocyclazocine and that the FENT-like stimulus effects of these drugs reside in their (-)-isomers. In addition, the present findings establish further that the classification of the discriminative stimulus effects of mu and kappa opioid compounds in the pigeon differ from those in rat and monkey.
Picker
M J
MJ
Department of Psychology, University of North Carolina, Chapel Hill 27599-3270.
Negus
S S
SS
Dykstra
L A
LA
D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D001575:Benzomorphans / Q000494:pharmacology*; D010856:Columbidae; D004193:Discrimination Learning; D005283:Fentanyl / Q000494:pharmacology; D009019:Morphinans / Q000494:pharmacology*; D019998:Racemases and Epimerases; D013237:Stereoisomerism; D014867:Water
D000700:Analgesics; D001575:Benzomorphans; D009019:Morphinans; D014867:Water; D019998:Racemases and Epimerases; C027248:bremazocine; D005283:Fentanyl