Comparison of the effects of aging on 5-HT7 and 5-HT(1A) receptors in discrete regions of the circadian timing system in hamsters

Marilyn J. Duncan, Joshua Short, Deborah L. Wheeler

Research output: Contribution to journalArticlepeer-review

95 Scopus citations


The circadian timekeeping system exhibits many functional changes with aging, including a loss of sensitivity to time cues such as systemic injections of the serotonergic agonist, 8-hydroxy-2-(di-n- propylamino)tetralin (8-OH-DPAT). In order to elucidate the neurochemical mechanisms responsible for this age-related loss of sensitivity of the circadian pacemaker to serotonin agonists, the present study used quantitative autoradiography to determine whether aging decreases serotonin receptor populations in male Syrian hamsters. Four neuroanatomical regions that regulate circadian timekeeping were studied (the suprachiasmatic nuclei [SCN], the lateral geniculate nuclei [LGN], and the median raphe nucleus [MRN] and dorsal raphe nucleus [DRN]). The specific binding of [3H]8-OH- DPAT to serotonin7 (5-HT7) and serotonin(1A) (5-HT(1A)) receptors was investigated by competitive inhibition with ritanserin and pindolol, respectively. The results showed that the SCN, IGL, MRN, and DRN of the male Syrian hamster exhibited specific binding of [3H]8-OH-DPAT to both the 5- HT7 and 5-HT(1A) receptors, and that the latter receptor subtype is more abundant in all of these regions. At 17-19 months of age, a 50% decrease in 5-HT7 receptors was found in the DRN but not in any other regions. No significant age-related changes in 5-HT(1A) receptors were observed in any regions examined. The finding that a marked decrease in 5-HT7 receptors occurs in the DRN at the age previously characterized by loss of sensitivity to 8-OH-DPAT suggests that this region and this receptor subtype play important roles in 8-OH-DPAT induction of circadian phase shifts in vivo and that they constitute an important locus of aging in the circadian timing system.

Original languageEnglish
Pages (from-to)39-45
Number of pages7
JournalBrain Research
Issue number1-2
StatePublished - May 22 1999

Bibliographical note

Funding Information:
Supported by NIH Grant AG-13418.


  • Aging
  • Circadian rhythm
  • Intergeniculate leaflet
  • Lateral geniculate nucleus
  • Raphe nuclei
  • Serotonin receptor
  • Suprachiasmatic nucleus

ASJC Scopus subject areas

  • General Neuroscience
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology


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