title: Pre- and postsynaptic actions of serotonin on rat suprachiasmatic nucleus neurons.
abstract: Serotoninergic transmission is implicated in the photic and non-photic regulation of circadian rhythms. 5-HT (1-100 microM), carboxamidotryptamine (5-CT 0.1-10 microM) and (+)-8-hydroxy-dipropylaminotetraline (8-OH-DPAT, 1-30 microM) dose-dependently activated an outward current (5-100 pA) in 30% of neurons voltage-clamped at -60 mV in the suprachiasmatic nucleus (SCN) in vitro slice. EC(50) values were 7.0 microM for 5-HT and 0.2 microM for 5-CT. Serotonin-induced outward current was associated with an increase in input conductance, and the current was blocked by Ba(2+) (1 mM). The amplitude of the current was enhanced by depolarization, reduced by hyperpolarization, and reversed its polarity during a hyperpolarization beyond the potassium equilibrium potential. Mean amplitudes of the 5-HT outward current changed with time of the subjective circadian day. The value near CT2 (23.8 pA) was about 4 times greater than that around CT14 (6.7 pA). Cells that responded with an outward current showed four types of morphology: monopolar, simple bipolar, curly bipolar and radial shaped; they were localized in all parts of the SCN. The EPSC evoked by retino-hypothalamic-tract (RHT) stimulation was inhibited 26% but the inward current induced by exogenously applied glutamate or NMDA was not affected by serotonin agonists. Focal stimulation-induced and spontaneous IPSC but not the exogenous GABA-induced outward current were inhibited by 5-HT agonists in a subpopulation of cells. In conclusion, 5-HT regulates SCN neurons by both pre- and post-synaptic inhibitory mechanisms; the latter may play a key role in modulating SCN circadian rhythm by activation of 5-HT receptors and opening of a potassium channel.
authors.affiliation: Department of Physiology and Pharmacology, Oregon Health Sciences University, Portland, OR 97201-3098, USA. jiangz@ohsu.edu
authors.forename: Z G
authors.initials: ZG
authors.lastname: Jiang
authors.forename: K
authors.initials: K
authors.lastname: Teshima
authors.forename: Y
authors.initials: Y
authors.lastname: Yang
authors.forename: T
authors.initials: T
authors.lastname: Yoshioka
authors.forename: C N
authors.initials: CN
authors.lastname: Allen
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D013570:Synaptic Membranes / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D015221:Potassium Channels; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin