Ea. Mariathasan et Ip. Stolerman, FUNCTIONAL-RELATIONSHIPS, PREVIOUS HISTORY AND THE DISCRIMINATION OF A DRUG MIXTURE IN RATS, Drug and alcohol dependence, 35(2), 1994, pp. 117-125
These experiments aim to probe the role of different functional relati
onships between drugs, responses and reinforcers in studies on the dis
crimination of drug mixtures. Two-lever discriminations based on mixtu
res of (+)-amphetamine (0.4 mg/kg) plus pentobarbitone (10 mg/kg) have
been compared in three groups of rats (n = 8) trained to discriminate
: (i) the mixture from saline, called the AND-discrimination; (ii) eit
her the mixture, amphetamine or pentobarbitone from saline, the OR-dis
crimination; (iii) the mixture from either amphetamine or pentobarbito
ne, the AND-OR-discrimination. The rats were trained in a two-bar oper
ant conditioning procedure with a tandem schedule of food reinforcemen
t. The rats trained on the AND procedure acquired the discrimination m
ore rapidly than the rats trained on the other two procedures, but aft
er 60 training sessions, all discriminations were performed with simil
ar (90-94%) accuracy. In rats trained under the AND and the OR procedu
res, there was full generalization from the mixture to the largest dos
es used of either amphetamine or pentobarbitone. In contrast, in rats
trained under the AND-OR procedure, there was no generalization from t
he mixture to any dose of either drug separately. The training procedu
res for the OR and the AND-OR groups were changed to AND-discriminatio
n training; the effects of the different previous histories were found
to persist for a prolonged period, despite the fact that training con
ditions were now the same in all groups. The effects of the drugs on r
ates of responding were also influenced by the previous training histo
ry. Thus, using different training procedures to alter functional rela
tionships can substantially and persistently influence the major chara
cteristics of a discrimination based on a mixture of drugs.