Cl. Duvauchelle et al., THE SYNERGISTIC EFFECTS OF COMBINING COCAINE AND HEROIN (SPEEDBALL) USING A PROGRESSIVE-RATIO SCHEDULE OF DRUG REINFORCEMENT, Pharmacology, biochemistry and behavior, 61(3), 1998, pp. 297-302
The relative reinforcing value of cocaine/heroin combination (''speedb
all'') was compared in the rat using a progressive-ratio (PR) reinforc
ement schedule. The initial training for all rats was a combined dose
of 18 mu g/kg/inj of heroin (H) plus 300 mu g/kg/inj of cocaine (C). B
reak points for the training dose and individual component doses were
determined for half and double the training dose. Of the three doses o
f each treatment, only C yielded the expected monotonic increase in br
eak point as a function of dose. Also, break points for C (300 and 600
mu g/kg/inj) was greater than for the combination of C and H (18 H/30
0 C and 36 H/600 C mu g/kg/inj), suggesting a greater reward value for
C alone. The doses for these three drug treatments that produced sali
ne level break points were then determined. At these lower doses, sign
ificant break points were obtained with the H/C combination at which t
he respective doses of H or C had break points identical to those of s
aline. These lower dose results indicate that the combination is clear
ly synergistic and that the discrepancy with doses at the opposite end
of the dose response curve suggest that the PR schedule is vulnerable
to drug-induced motor effects. (C) 1998 Elsevier Science Inc.