Changes in the Phase Response Curve of the Circadian Clock to a Phase-Shifting Stimulus

Olivier Van Reeth, Fred W. Turek

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Experiments were conducted in hamsters to determine whether the phase response curve (PRC) to injections of the short-acting benzodiazepine triazolam is a fixed or a labile property of the circadian clock. The results indicated that (1) both the shape and the amplitude of the PRC to triazolam generated on the first day of transfer from a light-dark cycle (LD 14:10) to constant darkness (DD) (i.e., PRCLD) were different from those of the PRC generated after many days in DD (PRCDD); and (2) the phase-shifting effects of triazolam on the activity rhythms of hamsters transferred from LD 14:10 or 12:12 to DD changed dramatically within the fist 8-9 days spent in DD. In an attempt to accelerate the resynchronization of the circadian clock of hamsters subjected to an 8-hr advance in the LD cycle, triazolam was given to the animals at a time selected on the basis of the characteristics of PRCLD. The activity rhythms of five of eight triazolam-treated animals were resynchronized to the new LD cycle within 2-4 days after the shift, whereas those of most of the control animals were resynchronized 21-29 days after the shift. These findings suggest that attempts to use pharmacological or nonpharmacological tools to phase-shift circadian clocks under entrained conditions should take into account information derived from PRCs generated at the time of transition from entrained to free-running conditions.

Original languageEnglish (US)
Pages (from-to)137-147
Number of pages11
JournalJournal of biological rhythms
Issue number2
StatePublished - Jul 1992


  • activity
  • arousal
  • benzodiazepines
  • circadian
  • clock
  • period
  • phase
  • rhythm
  • triazolam

ASJC Scopus subject areas

  • Physiology (medical)
  • Physiology


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