Endogenous Regulation of Serotonin Release in the Hamster Suprachiasmatic Nucleus

• Published in: The Journal of neuroscience Vol. 18; no. 13; pp. 5045 - 5052
• Main Authors: Dudley, Thomas E, DiNardo, Lisa A, Glass, J. David
• Format: Journal Article
• Language: English
• Published: United States Soc Neuroscience 01-07-1998; Society for Neuroscience
• Subjects: Animals; Autoreceptors - agonists; Circadian Rhythm - physiology; Cricetinae; Male; Mesocricetus; Microdialysis; Motor Activity - physiology; Piperazines - pharmacology; Receptors, Serotonin - physiology; Receptors, Serotonin, 5-HT1; Serotonin - metabolism; Suprachiasmatic Nucleus - chemistry; Suprachiasmatic Nucleus - drug effects; Suprachiasmatic Nucleus - metabolism
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/jneurosci.18-13-05045.1998

Serotonin (5-HT) has been strongly implicated in the regulation of the mammalian circadian clock located in the suprachiasmatic nuclei (SCN). However, little is known of the pattern of neuronal 5-HT release in the SCN or of the factors involved in regulating its release. Using in vivo microdialysis, we demonstrated the existence of a daily rhythm in the output of 5-HT in the SCN of freely behaving hamsters. This rhythm was characterized by a sharp increase in release from a nadir during late midday to peak levels at the light/dark transition. Output declined to basal levels throughout the remainder of the night. A similar pattern also was evident under constant darkness, with increased 5-HT output occurring at the onset of subjective night. Locomotor activity induced by exposure to a novel running wheel had a pronounced phase-dependent effect on 5-HT release in the SCN, with stimulation during the light phase and suppression during the late dark phase. Systemic application of the somatodendritic 5-HT1A agonist BMY 7378 had a significantly greater suppressive effect on 5-HT release in the SCN during the late dark phase compared with mid light phase, indicating that a variation in raphe autoreceptor response may underlie the time-dependent effects of wheel running on 5-HT release. Collectively, these results show that the daily rhythm in output of 5-HT in the SCN is generated endogenously, and that behavioral state can strongly influence serotonergic activity in the circadian clock in a phase-dependent manner.