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.
Belenky
M A
MA
Department of Cell and Animal Biology, Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Pickard
G E
GE
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