title: GABAergic synapses of the suprachiasmatic nucleus exhibit a diurnal rhythm of short-term synaptic plasticity.
abstract: We examined synaptic plasticity at intrasuprachiasmatic nucleus (SCN) gamma-aminobutyric acid (GABA)ergic synapses by measuring the paired-pulse ratio between pairs of evoked inhibitory postsynaptic currents (IPSCs). Interstimulus intervals were chosen to represent the range of spontaneous action potential firing frequencies found in SCN neurons. A majority of synapses studied during the day exhibited paired-pulse depression (PPD), whereas a majority of synapses studied during the night showed no PPD. Two types of PPD were found. Type 1 PPD expresses the greatest inhibition at shorter interstimulus intervals, is predominant in the early morning and is likely to be a result of vesicle depletion. Type 2 showed the greatest inhibition at interstimulus intervals between 175 and 225 ms, is found throughout the day yet rarely at night and is likely to be a result of a Ca(2+)-dependent mechanism that is independent of pertussis toxin-sensitive G-proteins. Thus, multiple mechanisms of synaptic plasticity modulate intra-SCN communication throughout the diurnal cycle.
authors.affiliation: Department of Physiology and Pharmacology and Centre for Research on Occupational and Environmental Toxicology, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.
authors.forename: Heinrich S
authors.initials: HS
authors.lastname: Gompf
authors.forename: Charles N
authors.initials: CN
authors.lastname: Allen
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018756:GABA Antagonists; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008959:Models, Neurological; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D013493:Suprachiasmatic Nucleus / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D005680:gamma-Aminobutyric Acid; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D001418:Baclofen; D008274:Magnesium; C080629:saclofen; D005033:Ethylmaleimide; D002118:Calcium