title: Ultrastructural plasticity in the rat suprachiasmatic nucleus. Possible involvement in clock entrainment.
abstract: Circadian rhythms in mammals are synchronized to the light (L)/dark (D) cycle through messages relaying in the master clock, the suprachiasmatic nucleus of the hypothalamus (SCN). Here, we provide evidence that the SCN undergoes rhythmic ultrastructural rearrangements over the 24-h cycle characterized by day/night changes of the glial, axon terminal, and/or somato-dendritic coverage of neurons expressing arginine vasopressin (AVP) or vasoactive intestinal peptide (VIP), the two main sources of SCN efferents. At nighttime, we noted an increase in the glial coverage of the dendrites of the VIP neurons (+29%) that was concomitant with a decrease in the mean coverage of the somata (-36%) and dendrites (-43%) of these neurons by axon terminals. Conversely, glial coverage of the dendrites of AVP neurons decreased (-19%) with parallel increase in the extent of somatal (+96%) and dendritic (+52%) membrane appositions involving these neurons. These plastic events were concomitant with daily fluctuations in quantitative expression of glial fibrillary acidic protein (GFAP), which were then used as an index of structural plasticity. The GFAP rhythm appeared to be strictly dependent on light entrainment, indicating that structural reorganization of the SCN may subserve synchronization of the clock to the L/D cycle. Other results presented reinforced this view while showing that circulating glucocorticoid hormones, which are known to modulate photic entrainment, were required to maintain amplitude of the GFAP rhythm to normal values.
authors: CNRS-UMR 6544, IFR Jean-Roche, Faculté de médecine, Université de la Méditerranée, Marseille, France.
authors: Denis
authors: D
authors: Becquet
authors: Clémence
authors: C
authors: Girardet
authors: Fabienne
authors: F
authors: Guillaumond
authors: Anne-Marie
authors: AM
authors: François-Bellan
authors: Olivier
authors: O
authors: Bosler
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D005786:Gene Expression Regulation / Q000502:physiology; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D008297:Male; D046529:Microscopy, Electron, Transmission / Q000379:methods; D009457:Neuroglia / Q000378:metabolism / Q000648:ultrastructure; D009473:Neuronal Plasticity / Q000502:physiology*; D009474:Neurons / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013493:Suprachiasmatic Nucleus / Q000166:cytology* / Q000378:metabolism; D014660:Vasoactive Intestinal Peptide
chemical_list: D005904:Glial Fibrillary Acidic Protein; D001127:Arginine Vasopressin; D014660:Vasoactive Intestinal Peptide