Foltin, R. W. (1999).
Food and cocaine self-administration by baboons: Effects of alternatives.
Journal of the Experimental Analysis of Behavior,
72, 215-234.
The effects of the availability of an alternative reinforcer on
responding maintained by food pellets or drug solutions were
examined in 8 adult male baboons (Papio hamadrayas
anubis). During daily 23-hr experimental sessions, baboons
had access to both food pellets and fluid under a two-choice
procedure, in which the response requirement, under a fixed-ratio
schedule, differed for the two commodities. There were no
restrictions on access to water, which was continuously available
from a spout at the rear of each cage. In Experiment 1, the
fixed- ratio requirement, or cost, for fluid delivery
remained constant while the fixed-ratio requirement for pellets
was changed every 2 or 3 days when (a) no fluid, (b) a dilute
dextrose vehicle, (c) 0.008 mg/kg per delivery cocaine, (d) 0.016
mg/kg per delivery cocaine, or (e) 0.032 mg/kg per delivery
cocaine was available concurrently. In Experiment 1,
progressively increasing the response requirement for pellets
decreased pellet intake, but for 4 baboons pellet intake at
maximum pellet cost was lower when cocaine, compared to the
vehicle, was available. Increasing the response requirement for
pellets had variable effects on vehicle intake. However,
increasing the response requirement for pellets increased intake
of at least one dose of cocaine to a greater extent than vehicle
in all 8 baboons. Thus, cocaine could be considered a more
effective economic substitute than vehicle for pellets.
Experiment 2 systematically varied the order in which the
response requirements for a pellet delivery were presented and
added a control condition in which cocaine doses, yoked to the
amount self-administered, were given three times during the
session by the experimenter. Again, pellet intake at maximal
pellet cost was lower when cocaine, compared to the vehicle, was
available. In contrast, experimenter-given cocaine doses did not
alter responding maintained by pellets. Thus, the effects of
self-administered cocaine on responding maintained by food
pellets differed from the effects of experimenter-given cocaine
on responding maintained by food pellets.
Key words: cocaine, food intake, ratio schedules,
self-administration, behavioral economics, lever pull, baboon