Subcellular distribution of 5-HT(1B) and 5-HT(7) receptors in the mouse suprachiasmatic nucleus.
The suprachiasmatic nucleus (SCN), a circadian oscillator, receives glutamatergic afferents from the retina and serotonergic (5-HT) afferents from the median raphe. 5-HT(1B) and 5-HT(7) 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-HT(1B) and 5-HT(7) receptors in the SCN. 5-HT(1B) receptor immunostaining was associated with the plasma membrane of thin unmyelinated axons, preterminal axons, and terminals of optic and nonoptic origin. 5-HT(1B) receptor immunostaining in terminals was almost never observed at the synaptic active zone. To a much lesser extent, 5-HT(1B) immunoreaction product was noted in dendrites and somata of SCN neurons. 5-HT(7) receptor immunoreactivity in gamma-aminobutyric acid (GABA), vasoactive intestinal polypeptide (VIP), and vasopressin (VP) neuronal elements in the SCN was examined by using double-label procedures. 5-HT(7) receptor immunoreaction product was often observed in GABA-, VIP-, and VP-immunoreactive dendrites as postsynaptic receptors and in axonal terminals as presynaptic receptors. 5-HT(7) 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-HT(7) receptor immunoreaction product was distributed throughout the cytoplasm often in association with the endoplasmic reticulum and the Golgi complex. The distribution of 5-HT(1B) receptors in presynaptic afferent terminals and postsynaptic SCN processes, as well as the distribution of 5-HT(7) 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.
Department of Cell and Animal Biology, Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel.
M A
MA
Belenky
G E
GE
Pickard
D000818:Animals; D001253:Astrocytes / Q000378:metabolism; D008297:Male; D051379:Mice / Q000378:metabolism*; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D044302:Receptor, Serotonin, 5-HT1B; D011985:Receptors, Serotonin / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism*; D013493:Suprachiasmatic Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D014018:Tissue Distribution; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism; D014667:Vasopressins / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D044302:Receptor, Serotonin, 5-HT1B; D011985:Receptors, Serotonin; C104425:serotonin 7 receptor; D014667:Vasopressins; D014660:Vasoactive Intestinal Peptide; D005680:gamma-Aminobutyric Acid