Localization of serotonin(5A) receptors in discrete regions of the circadian timing system in the Syrian hamster

Marilyn J. Duncan, Lothar Jennes, Jennifer B. Jefferson, Mark S. Brownfield

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


Endogenous serotonin and serotonergic drugs influence many aspects of circadian rhythms, including phase shifts, onset of locomotor activity, and period length and integrity of rhythms during exposure to constant light. The receptor subtype(s) mediating all of these circadian effects of serotonin has (have) not been identified. Immunoreactivity for the serotonin(5A) (5-HT(5A)) receptor has recently been identified in the rat suprachiasmatic nucleus (SCN). In this study, we investigated the distribution of the 5-HT(5A) receptors in four neural components of the circadian timing system (the SCN, the intergeniculate leaflet, and the median and dorsal raphe nuclei), in the Syrian hamster. Single and dual immunohistochemistry were conducted using an affinity-purified rabbit antibody generated against a peptide sequence unique to the 5-HT(5A) receptor, guinea pig anti-5-HT antisera and guinea pig anti-GABA antisera. For single labeling, immunoreactivity was visualized using DAB-nickel as the chromagen. All four regions showed strong, yet distinct, immunoreactivity for the 5-HT(5A) receptor. No specific labeling was present in the absorption or omission controls. For double labeling, immunoreactivity was visualized using immunofluorescence with Cy5- and FITC-labeled second antibodies followed by confocal microscopy. In the raphe nuclei, 5-HT-immunoreactivity and 5-HT(5A)-immunoreactivity were co-localized in cell bodies and axons. GABA-immunoreactive fibers surrounded some of the 5-HT(5A) receptor-immunoreactive cell bodies in the raphe nuclei. In conclusion, the 5-HT(5A) receptors are localized within several important neuroanatomical substrates of the circadian timekeeping system, and within the raphe nuclei, appear to be present on serotonin neurons. These findings suggest that some of the circadian effects of 5-HT may be mediated by the 5-HT(5A) receptor, which may function as a presynaptic autoreceptor. Theme: Neural basis of behaviour. Topic: Biological rhythms and sleep. Copyright (C) 2000 Elsevier Science B.V.

Original languageEnglish
Pages (from-to)178-185
Number of pages8
JournalBrain Research
Issue number1-2
StatePublished - Jun 30 2000

Bibliographical note

Funding Information:
This work was supported by NIH grant AG13418 (to MJD) and funds from DiaSorin Corporation (to MSB).


  • 5-HT(5A) receptor
  • Circadian rhythm
  • Dorsal raphe nucleus
  • Immunohistochemistry
  • Intergeniculate leaflet
  • Median raphe nucleus
  • Serotonin
  • Suprachiasmatic nucleus

ASJC Scopus subject areas

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


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