Effects of anorectic drugs on food intake under progressive-ratio and free-access conditions in rats.
Dexfenfluramine works better when food takes effort, so always check the reinforcement context before calling an appetite drug ineffective.
01Research in Context
What this study did
La Malfa et al. (2004) gave rats two ways to eat. One way required more and more lever presses for each food pellet. The other way let them eat freely with no work.
The team then gave two diet drugs: dexfenfluramine and phentermine. They watched how each drug changed eating under the hard-work and the free-access conditions.
What they found
Dexfenfluramine cut food intake more when the rats had to work for food. Under free access it still worked, but less.
Phentermine lowered eating the same amount in both setups. The schedule did not matter for this drug.
How this fits with other research
Northup et al. (1991) also used progressive-ratio schedules. They saw cocaine push rats to press longer than food alone. Both papers show the schedule reveals drug differences you would miss in free-feeding tests.
Davison et al. (1991) found morphine hurt timeout-maintained pressing but left avoidance alone. Their result matches G et al.: drug effects depend on the type of reinforcement that keeps the behavior alive.
Louie (1980) showed pigeons kept a strong bias even after drugs. G et al. extend that idea: schedule history can change how strongly an appetite drug works today.
Why it matters
Before you say an intervention or medication has no effect, test it under the same reinforcement schedule your client faces. A drug that looks weak in free-access may shine when the child must work for the reinforcer. Run a brief progressive-ratio probe with food, tokens, or praise. The extra effort can expose hidden potency and guide better clinical decisions.
Get CEUs on This Topic — Free
The ABA Clubhouse has 60+ on-demand CEUs including ethics, supervision, and clinical topics like this one. Plus a new live CEU every Wednesday.
Add a five-trial progressive-ratio food task to your next feeding assessment and compare intake to a free-access snack.
02At a glance
03Original abstract
The effects of two anorectic drugs, dexfenfluramine and phentermine, on food intake under different food-access conditions were examined. Experiment 1 compared the effects of these drugs on food intake under a progressive-ratio (PR) schedule and free-access conditions. Dexfenfluramine decreased food intake under both conditions, but the doses required to decrease intake under free-access conditions were higher than those required to reduce intake under the PR condition. Intermediate doses of phentermine sometimes increased breaking points, and higher doses decreased them. Phentermine decreased food intake at the same doses under both access conditions. Thus the potency of dexfenfluramine, but not phentermine, to decrease food-maintained behavior depended upon the food-access condition. Experiment 2 used a novel mixed progressive-ratio schedule of food delivery to study the duration of drug effects. Sessions consisted of five components separated by 3-hr timeouts. The ratio requirement reset at the beginning of each component and a new breaking point was obtained. Both dexfenfluramine and phentermine dose-dependently decreased breaking points early in the session. In some rats, compensatory increases in breaking point were observed. That is, breaking points later in the session increased over control levels, resulting in no change in the total number of food pellets earned for the session compared to control. The present findings suggest that the effects of some anorectic drugs depend upon the access conditions for food; increasing the effort to obtain food may enhance their ability to decrease food-maintained behavior.
Journal of the experimental analysis of behavior, 2004 · doi:10.1901/jeab.2004.82-275