Foltin, R. W. (1997).
Food and amphetamine self-administration by baboons: Effects of alternatives.
Journal of the Experimental Analysis of Behavior,
68, 47-66.
The effects of the availability of an alternative reinforcer on
responding maintained by food pellets or fluid solutions were
examined in 6 adult male baboons (Papio cynocephalus
anubis). During daily 23-hr experimental sessions, baboons
had concurrent access to both food pellets and fluid, with
responding maintained under fixed-ratio schedules of
reinforcement that varied between the two commodities. The
fixed-ratio requirement, or cost, for pellets was increased when
(a) no fluid, (b) a dilute dextrose vehicle, (c) 0.002 mg/kg
d-amphetamine, or (d) 0.004 mg/kg d-amphetamine was
available. When given nonrestricted concurrent access to food
pellets and amphetamine at minimal cost (FR 2), baboons
self-administered sufficient amphetamine to decrease pellet
intake. Increasing the response requirement for pellets decreased
pellet intake at a similar rate regardless of the available fluid
and increased fluid intake in a variable manner among baboons
such that there were no statistically significant increases in
fluid intake. In contrast, when access to pellets was restricted
to 70% of maximal intake under nonrestricted conditions,
increasing pellet cost decreased pellet intake and increased
fluid intake more rapidly when the high amphetamine dose was
available. Thus, amphetamine was more effective as an economic
substitute for pellets when access to pellets was restricted. The
response cost for vehicle and both amphetamine concentrations was
increased when baboons had nonrestricted and restricted access to
pellets. Increasing the response requirement for fluid delivery
decreased intake of all three fluids similarly under both
pellet-access conditions. The results indicate that substitution
between commodities with minimal commonalities can be studied
under controlled laboratory conditions and is dependent upon
reinforcement schedule and commodity restrictions.
Key words: food intake, amphetamine, ratio schedules,
self-administration, behavioral economics, demand, baboon