Circadian 5-HT production regulated by adrenergic signaling.
Using on-line microdialysis, we have characterized in vivo dynamics of pineal 5-hydroxytryptamine (5-HT; serotonin) release. Daily pineal 5-HT output is triphasic: (i) 5-HT levels are constant and high during the day; (ii) early in the night, there is a novel sharp rise in 5-HT synthesis and release, which precedes the nocturnal rise in melatonin synthesis; and (iii) late in the night, levels are low. This triphasic 5-HT production persists in constant darkness and is influenced strongly by intrusion of light at night. We demonstrate that both diurnal 5-HT synthesis and 5-HT release are activated by sympathetic innervation from the superior cervical ganglion and show that these processes are controlled by distinct receptors. The increase in 5-HT synthesis is controlled by beta-adrenergic receptors, whereas the increase in 5-HT release is mediated by alpha-adrenergic signaling. On the other hand, the marked decrease in 5-HT content and release late at night is a passive process, influenced by the extent of melatonin synthesis. In the absence of melatonin synthesis, the late-night decline in 5-HT release is prevented, reaching levels roughly twice as high as that of the day value. In summary, our results demonstrate that 5-HT levels display marked circadian rhythms that depend on adrenergic signaling.
Sun
Xing
X
Department of Embryology, Carnegie Institution of Washington, Baltimore, MD 21210, USA.
Deng
Jie
J
Liu
Tiecheng
T
Borjigin
Jimo
J
D000818:Animals; D002940:Circadian Rhythm; D008297:Male; D008550:Melatonin / Q000096:biosynthesis; D017551:Microdialysis; D010870:Pineal Gland / Q000294:innervation / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D012701:Serotonin / Q000032:analysis / Q000096:biosynthesis*; D017783:Superior Cervical Ganglion / Q000502:physiology
D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D012701:Serotonin; D008550:Melatonin