The suprachiasmatic nuclei: Two circadian clocks?

Gary E. Pickard, Fred W. Turek

Research output: Contribution to journalArticlepeer-review

63 Scopus citations


Unilateral lesions of the bilaterally paired suprachiasmatic nuclei of the hypothalamus were made in golden hamsters maintained in constant light (LL). Prior to surgery, the circadian rhythm of locomotor activity had dissociated or 'split' into two distinct components in 19 out of 30 hamsters, while in the remaining 11 animals (i.e. non-splitters) a normal rhythm with a single bout of activity was maintained. Following destruction of a major portion (i.e. 50-100%) of a single suprachiasmatic nucleus (SCN) in 6 'split' and 5 'nonsplit' hamsters, a single circadian bout of activity was observed in all animals. In 9 of these 11 animals, the circadian period of the activity rhythm was altered following unilateral SCN lesions. In two split animals sustaining lesions which missed the SCN, but disrupted efferents caudal to the SCN, the split condition was also abolished. Lesions which destroyed less than 50% of a single SCN did not abolish the split condition (n = 6) and had little effecy on the circadian pattern of the non-splitters (n = 5). In contrast, bilateral destruction of the suprachiasmatic nuclei eliminated the circadian pattern of activity in both 'split' (n = 5) and 'non-split' (n = 1) animals. These results demonstrate that each SCN is capable by itself of maintaining circadian rhythmicity and that at least two circadian oscillators, or oscillating systems, reside within the suprachiasmatic nuclei.

Original languageEnglish (US)
Pages (from-to)201-210
Number of pages10
JournalBrain Research
Issue number2
StatePublished - Jun 6 1983
Externally publishedYes


  • acticity rhythm
  • circadian clocks
  • retinohypothalamic tract
  • suprachiasmatic nucleus

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology


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