Circadian tryptophan hydroxylase levels and serotonin release in the suprachiasmatic nucleus of the rat.
Serotonin (5-HT) plays an important role in the regulation of the time-keeping system in rodents. In the present study, we have investigated the interplay between the rhythms of 5-HT synthesis and release in the suprachiasmatic nuclei (SCN) of the rat. The quantitative distribution of tryptophan hydroxylase (TpH) protein was used as an index of 5-HT synthesis, in perikarya and terminals areas. In the raphe medianus, the maximal levels of TpH was reached in the early daytime period, followed by a decrease before the onset of darkness. Conversely, in the axon terminals of the SCN the highest levels of TpH were found before the onset of the dark-period. Furthermore, TpH amount in SCN displays variations depending on the anatomical area of the SCN. Extracellular 5-HT peaked at the beginning of the night, as evidenced by in vivo microdialysis in the SCN. The 5-HT metabolite, 5-HIAA, presented a similar pattern, but the acrophase occurred in the middle of the dark period. These results suggest that TpH is transported from the soma to the nerve terminals in which 5-HT is synthesized during daytime. This would fill the intracellular stores of 5-HT to provide for its nocturnal release.
Barassin
Stéphane
S
Neurobiologie des Rythmes, UMR 7518, Université Louis Pasteur, Strasbourg, France.
Raison
Sylvie
S
Saboureau
Michel
M
Bienvenu
Christèle
C
Maître
Michel
M
Malan
André
A
Pévet
Paul
P
D000818:Animals; D001345:Autoradiography; D002940:Circadian Rhythm / Q000502:physiology*; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D009434:Neural Pathways / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D017729:Presynaptic Terminals / Q000201:enzymology* / Q000378:metabolism / Q000648:ultrastructure; D011903:Raphe Nuclei / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000096:biosynthesis* / Q000378:metabolism; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D014365:Tryptophan Hydroxylase / Q000378:metabolism*
D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D014365:Tryptophan Hydroxylase