Serotonergic innervation of the hypothalamic suprachiasmatic nucleus and photic regulation of circadian rhythms

Gary E Pickard, Michael A. Rea

Research output: Contribution to journalReview article

74 Citations (Scopus)

Abstract

Converging lines of evidence have firmly established that the hypothalamic suprachiasmatic nucleus (SCN) is a light-entrainable circadian oscillator in mammals, critically important for the expression of behavioral and physiological circadian rhythms. Photic information essential for the daily phase resetting of the SCN circadian clock is conveyed directly to the SCN from retinal ganglion cells via the retinohypothalamic tract. The SCN also receives a dense serotonergic innervation arising from the mesencephalic raphe. The terminal fields of retinal and serotonergic afferents within the SCN are co-extensive, and serotonergic agonists can modify the response of the SCN circadian oscillator to light. However, the functional organization and subcellular localization of 5HT receptor subtypes in the SCN are just beginning to be clarified. This information is necessary to understand the role 5HT afferents play in modulating photic input to the SCN. In this paper, we review evidence suggesting that the serotonergic modulation of retinohypothalamic neurotransmission may be achieved via at least two different cellular mechanisms: 1) a postsynaptic mechanism mediated via 5HT(1A) or 5ht7 receptors located on SCN neurons; and 2) a presynaptic mechanism mediated via 5HT(1B) receptors located on retinal axon terminals in the SCN. Activation of either of these 5HT receptor mechanisms in the SCN by specific 5HT agonists inhibits the effects of light on circadian function. We hypothesize that 5HT modulation of photic input to the SCN may serve to set the gain of the SCN circadian system to light.

Original languageEnglish (US)
Pages (from-to)513-523
Number of pages11
JournalBiology of the Cell
Volume89
Issue number8
DOIs
StatePublished - Jan 1 1997

Fingerprint

Suprachiasmatic Nucleus
Circadian Rhythm
Light
Serotonin Receptor Agonists
Circadian Clocks
Retinal Ganglion Cells
Presynaptic Terminals
Synaptic Transmission
Mammals

Keywords

  • Circadian rhythm
  • Serotonin
  • Suprachiasmatic nucleus

ASJC Scopus subject areas

  • Cell Biology

Cite this

Serotonergic innervation of the hypothalamic suprachiasmatic nucleus and photic regulation of circadian rhythms. / Pickard, Gary E; Rea, Michael A.

In: Biology of the Cell, Vol. 89, No. 8, 01.01.1997, p. 513-523.

Research output: Contribution to journalReview article

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