Long T methamphetamine schedules produce circadian ensuing drug activity in rats

Norman Pecoraro, Ann E.K. Kosobud, George V. Rebec, William Timberlake

Research output: Contribution to journalArticle

12 Scopus citations


Eight female Sprague-Dawley rats were housed in isolated continuous 24-h/day environments under conditions of constant dim light and a rate-limited feeding schedule. Following 2 months of free-running activity, all animals were administered methamphetamine (MA) i.p. (2 mg/kg) once every 31 h for 24 injection cycles. Average wave forms of wheel-running activity showed that animals did not anticipate the 31-h schedule of MA injections, but rather displayed circadian ensuing drug activity (CEDA) between 24 and 28 h following the injections. Post-injection meals failed to meet reliably the threshold necessary to achieve food-engendered anticipatory or ensuing activity. Cosinor analysis showed that the intensity of CEDA was strongly influenced by the relative phase of the free-running rhythm. CEDA was moderately influenced by the size of the post-injection bout of activity. Because injection times rotated daily throughout local time without repeating a time of day, CEDA resulting from a long T schedule of MA administration appeared to be based on one-trial resetting of a circadian-related mechanism by a major drug of abuse.

Original languageEnglish (US)
Pages (from-to)95-106
Number of pages12
JournalPhysiology and Behavior
Issue number1-2
StatePublished - Jan 1 2000


  • Anticipatory activity
  • Circadian ensuing drug activity
  • Long T schedules
  • Methamphetamine
  • Type O resetting

ASJC Scopus subject areas

  • Behavioral Neuroscience
  • Physiology (medical)

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