Morphine administration and abrupt cessation alter the behavioral diurnal activity pattern

Andrea M. Glaser, Cruz Reyes-Vázquez, Bertha Prieto-Gómez, Keith Burau, Nachum Dafny

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


In mammals, there is an underlying mechanism that dictates the organism's biological functions and daily activity schedule, known as circadian rhythms, which play a major role in maintaining steady metabolism, homeostasis, and immunity. Limited research has been done investigating the effects of continuous opiate administration on the circadian rhythm activity pattern. A change in circadian activity pattern is suggested as an experimental model to demonstrate long-term effect of the drug. The objective of this study was to investigate the effects of morphine treatment on the long term activity (24 h) of the animal as well as the activity after abrupt removal, since prescribed medication containing morphine is widely used and abused and its long term effects are not known. Male Sprague-Dawley rats were contained in stable conditions with a standard light/dark cycle recordings taken before, during and after morphine pellet implantation. Cosinor analysis was used to fit a 24-hour curve to the activity pattern. Results indicate that morphine pellet administration alters the mesor, amplitude, the day-time and night-time activity levels, and demonstrates a remarkable change in the maximal circadian rhythm timing during the withdrawal period. The question whether morphine changes the circadian rhythm or a change in circadian rhythm results in tolerance and withdrawal is discussed.

Original languageEnglish (US)
Pages (from-to)544-552
Number of pages9
JournalPharmacology Biochemistry and Behavior
Issue number4
StatePublished - Jun 2012
Externally publishedYes


  • Behavior
  • Circadian rhythm
  • Morphine pellet
  • Opioids
  • Tolerance
  • Withdrawal

ASJC Scopus subject areas

  • Biochemistry
  • Toxicology
  • Pharmacology
  • Clinical Biochemistry
  • Biological Psychiatry
  • Behavioral Neuroscience


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