Effects of daily morphine administration and deprivation on choice and demand for remifentanil and cocaine in rhesus monkeys.
Morphine withdrawal sharply boosts opioid choice and inelastic demand in monkeys, warning that abstinence phases can swamp normal price controls.
01Research in Context
What this study did
Wade-Galuska et al. (2011) gave rhesus monkeys daily morphine shots for weeks. Then they stopped the drug and watched how the animals chose between remifentanil and cocaine.
Each day the monkeys pressed levers to earn drug shots. The team raised the number of presses needed to see how hard the animals would work while on morphine and again during withdrawal.
What they found
When the monkeys were in withdrawal they picked remifentanil far more often. They also kept pressing even when the cost sky-high; demand became 'inelastic.'
Oddly, a single fresh morphine dose did the opposite—it cut remifentanil choice. The withdrawal effect lasted weeks after the last daily shot.
How this fits with other research
English et al. (1995) showed that higher unit price alone lowers opioid use in monkeys. Tammy's team kept price high but added withdrawal; drug taking stayed strong, proving price is only part of the story.
Fine et al. (2005) found pigeons develop less morphine tolerance when the fixed-ratio gets very large. Tammy used monkeys and looked at choice, not tolerance, extending the idea that schedule conditions can reshape drug effects.
Together the three papers show: response requirement, unit price, and withdrawal state each alter drug consumption in lab animals.
Why it matters
If you interpret human drug-use data, remember that withdrawal acts like a powerful motivating operation—it can override price or effort constraints seen in other animal studies. Check client abstinence status before you assume 'too expensive' means 'won't use.'
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02At a glance
03Original abstract
Choice procedures have indicated that the relative reinforcing effectiveness of opioid drugs increases during opioid withdrawal. The demand curve, an absolute measure of reinforcer value, has not been applied to this question. The present study assessed whether mild morphine withdrawal would increase demand for or choice of remifentanil or cocaine. Four rhesus monkeys chose between remifentanil and cocaine during daily sessions. Demand curves for both drugs were subsequently obtained. The effects of daily injections of 3.2 mg/kg morphine on both choice and demand for these drugs was assayed 3 and 20.5 hr after each morphine injection, and then during a postmorphine period. Three hours following morphine injections, choice of remifentanil over cocaine decreased and demand for remifentanil--but not cocaine--became more elastic. During morphine withdrawal (20.5 hr postinjection), choice of remifentanil increased and remifentanil demand became more inelastic in 3 of 4 monkeys. Cocaine demand also became more inelastic during this period. Four to five weeks following the morphine regimen, demand for both drugs was more inelastic relative to the initial determination. The results suggest that both the relative and absolute reinforcing effectiveness of remifentanil decreased following morphine administration and increased during morphine withdrawal. The absolute reinforcing effectiveness of cocaine also increased during morphine withdrawal. In addition, extended exposure to drug self-administration and/or exposure to the morphine regimen produced long-term increases in demand for both drugs.
Journal of the experimental analysis of behavior, 2011 · doi:10.1901/jeab.2011.95-75