, Volume 62, Issue 3, pp 307–314 | Cite as

Naloxone effects on schedule-controlled behavior in morphine-pelleted rats

  • Alice M. Young
  • Travis Thompson
Original Investigations


The effects of morphine pellet implantation and naloxone administration were examined in rats lever pressing under inter-response time schedules of food presentation. Subcutaneous implantation of a morphine pellet initially decreased lever-pressing rates. Tolerance to this effect developed within 3–4 days. Naloxone (0.25–1.0 mg/kg) decreased response rates in morphine-pelleted rats in a dose-dependent and time-dependent manner. All doses of naloxone severely decreased rates of lever pressing on days four to nine post-pellet. This rate-decreasing effect persisted 7–17 days for 0.25 mg/kg naloxone, 9–22 days for 0.50 mg/kg, and 13–28 days for 1.0 mg/kg. Decreases in response rate were due to an increased frequency of long pauses and not to marked shifts in the temporal patterning of those lever presses that did occur. Changes in response rate after naloxone were accompanied by body weight loss. Area values summarizing the naloxone-induced changes in response rate or body weight over time after pellet implantation increased as a function of naloxone dose. Naloxone (0.25–1.0 mg/kg) did not alter performance by placebo-pelleted rats.

Key words

Morphine pellet Naloxone Schedule-controlled behaviors Precipitated abstinence Rats 


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Copyright information

© Springer-Verlag 1979

Authors and Affiliations

  • Alice M. Young
    • 1
  • Travis Thompson
    • 1
  1. 1.Department of PsychologyUniversity of MinnesotaMinneapolisUSA

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