An effect of castration and testosterone replacement on a circadian pacemaker in mice (Mus musculus)

Serge Daan, David Damassa, Colin S. Pittendrigh, Erla R. Smith

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Castration of mice in freerunning conditions (total darkness, DD) causes a reduction of running wheel activity in the beginning of the active period (α) and stimulates activity at the end of α. Simultaneously, the period (τ) of the freerunning rhythm is increased. Both effects are abolished by implantation of a Silastic capsule from which a physiological dose of testosterone is released at a constant rate. The results are tentatively explained by differential endocrine influences on two oscillating components in the pacemaker of the circadian activity rhythm.
Original languageEnglish
Pages (from-to)3744-3747
Number of pages4
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number9
Publication statusPublished - 1975


  • activity
  • circadian rhythm

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