Changes of sensitivity to the cuing properties of narcotic drugs as evidenced by generalization and cross-generalization experiments.
With a discrete-trial, food-reward, two-lever procedure, rats were trained to discriminate 0.04 mg/kg fentanyl from saline. Individual threshold doses for generalization of fentanyl and for cross-generalization of morphine were determined repeatedly during a 17-week posttraining period. Threshold doses of both drugs almost continuously shifted in both the up- and downward direction. Shifts of fentanyl threshold doses covaried with those of morphine threshold doses. These shifts can best be described by a sustained oscillation, the mean amplitude of which amounts to a factor 3.65 of the dose-range for fentanyl, and to a factor 1.85 for morphine. The upper and lower limits of oscillation were symmetrical with respect to baseline. The oscillation can be described by a function expressing that the more distant a point along the function is from the baseline, the more it is susceptible to (positive/negative) acceleration along the intensity (i.e., dose) axis.
D000818:Animals; D003463:Cues; D004192:Discrimination, Psychological / Q000187:drug effects; D005283:Fentanyl / Q000494:pharmacology; D005795:Generalization, Stimulus / Q000187:drug effects*; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D051381:Rats; D013997:Time Factors
D009294:Narcotics; D009020:Morphine; D005283:Fentanyl