title: 5-HT1B receptor-mediated presynaptic inhibition of GABA release in the suprachiasmatic nucleus.
abstract: The suprachiasmatic nucleus (SCN) receives a dense serotonergic innervation that modulates photic input to the SCN via serotonin 1B (5-HT1B) presynaptic receptors on retinal glutamatergic terminals. However, the majority of 5-HT1B binding sites in the SCN are located on nonretinal terminals and most axonal terminals in the SCN are GABAergic. We therefore tested the hypothesis that 5-HT1B receptors might also be located on SCN GABAergic terminals by examining the effects of the highly selective 5-HT1B receptor agonist CP-93,129 on SCN miniature inhibitory postsynaptic currents (mIPSCs). Whole cell patch-clamp recordings of mIPSCs were obtained from rat and mouse SCN neurons in hypothalamic slices. Using CsCl-containing microelectrodes with QX314, we isolated mPSCs that were sensitive to the GABAA receptor antagonist, bicuculline. Bath application of CP-93,129 (1 microM) decreased the frequency of mIPSCs by an average of 22% (n = 7) in rat SCN neurons and by an average of 30% (n = 8) in mouse SCN neurons with no clear effect on mIPSC amplitude. In mice lacking functional 5-HT1B receptors, CP-93,129 (1 microM) had no clear effect on the frequency or the amplitude of mIPSCs recorded in any of the cells tested (n = 4). The decrease in the frequency of mIPSCs of SCN neurons produced by the selective 5-HT1B receptor agonist CP-93,129 is consistent with the interpretation that 5-HT1B receptors are located on GABA terminals in the SCN and that 5-HT inhibits GABA release via a 5-HT1B presynaptic receptor-mediated mechanism.
authors.affiliation: Dept. of Biomedical Sciences, Anatomy and Neurobiology Section, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Jayne R
authors.initials: JR
authors.lastname: Bramley
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Sollars
authors.forename: Gary E
authors.initials: GE
authors.lastname: Pickard
authors.forename: F Edward
authors.initials: FE
authors.lastname: Dudek
mesh_terms: D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D004347:Drug Interactions; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D009433:Neural Inhibition / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques / Q000379:methods; D017729:Presynaptic Terminals / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044302:Receptor, Serotonin, 5-HT1B / Q000172:deficiency / Q000378:metabolism*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014633:Valine / Q000031:analogs & derivatives* / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D011725:Pyridines; D011758:Pyrroles; D011810:Quinoxalines; D044302:Receptor, Serotonin, 5-HT1B; D017366:Serotonin Receptor Agonists; C065046:3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo(3,2-b)pyrid-5-one; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; C056723:FG 9041; C056639:2-amino-5-phosphopentanoic acid; D014633:Valine; D001640:Bicuculline