Subcellular distribution of 5-HT1B and 5-HT7 receptors in the mouse suprachiasmatic nucleus

Michael A. Belenky, Gary E. Pickard

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The suprachiasmatic nucleus (SCN), a circadian oscillator, receives glutamatergic afferents from the retina and serotonergic (5-HT) afferents from the median raphe. 5-HT1B and 5-HT7 receptor agonists inhibit the effects of light on SCN circadian activity, Electron microscopic (EM) immunocytochemical procedures were used to determine the subcellular localization of 5-HT1B and 5-HT7 receptors in the SCN. 5-HT1B receptor immunostaining was associated with the plasma membrane of thin unmyelinated axons, preterminal axons, and terminals of optic and nonoptic origin, 5-HT1B receptor immunostaining in terminals was almost never observed at the synaptic active zone. To a much lesser extent, 5-HT1B immunoreaction product was noted in dendrites and somata of SCN neurons. 5-HT7 receptor immunoreactivity in γ-aminobutyric acid (GABA), vasoactive intestinal polypeptide (VIP), and vasopressin (VP) neuronal elements in the SCN was examined by using double-label procedures. 5-HT7 receptor immunoreaction product was often observed in GABA-, VIP-, and VP-immunoreactive dendrites as postsynaptic receptors and in axonal terminals as presynaptic receptors. 5-HT7 receptor immunoreactivity in terminals and dendrites was often associated with the plasma membrane but very seldom at the active zone. In GABA-, VIP-, and VP-immunoreactive perikarya, 5-HT7 receptor immunoreaction product was distributed throughout the cytoplasm often in association with the endoplasmic reticulum and the Golgi complex. The distribution of 5-HT1B receptors in presynaptic afferent terminals and postsynaptic SCN processes, as well as the distribution of 5-HT7 receptors in both pre- and postsynaptic GABA, VIP, and VP SCN processes, suggests that serotonin plays a significant role in the regulation of circadian rhythms by modulating SCN synaptic activity.

Original languageEnglish
Pages (from-to)371-388
Number of pages18
JournalJournal of Comparative Neurology
Issue number3
StatePublished - 9 Apr 2001
Externally publishedYes


FundersFunder number
National Institute of Neurological Disorders and StrokeR01NS035615


    • 5-HT receptor subtypes
    • Circadian rhythms
    • Intergeniculate leaflet
    • Retinal ganglion cells
    • Retinohypothalamic tract
    • Serotonin


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