Daily changes in synaptic innervation of VIP neurons in the rat suprachiasmatic nucleus: contribution of glutamatergic afferents.
The daily temporal organization of rhythmic functions in mammals, which requires synchronization of the circadian clock to the 24-h light-dark cycle, is believed to involve adjustments of the mutual phasing of the cellular oscillators that comprise the time-keeper within the suprachiasmatic nucleus of the hypothalamus (SCN). Following from a previous study showing that the SCN undergoes day/night rearrangements of its neuronal-glial network that may be crucial for intercellular phasing, we investigated the contribution of glutamatergic synapses, known to play major roles in SCN functioning, to such rhythmic plastic events. Neither expression levels of the vesicular glutamate transporters nor numbers of glutamatergic terminals showed nycthemeral variations in the SCN. However, using quantitative imaging after combined immunolabelling, the density of synapses on neurons expressing vasoactive intestinal peptide, known as targets of the retinal input, increased during the day and both glutamatergic and non-glutamatergic synapses contributed to the increase (+36%). This was not the case for synapses made on vasopressin-containing neurons, the other major source of SCN efferents in the non-retinorecipient region. Together with electron microscope observations showing no differences in the morphometric features of glutamatergic terminals during the day and night, these data show that the light synchronization process in the SCN involves a selective remodelling of synapses at sites of photic integration. They provide a further illustration of how the adult brain may rapidly and reversibly adapt its synaptic architecture to functional needs.
Girardet
Clémence
C
Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille (CRN2M), CNRS-UMR 6231, Université de la Méditerranée, Faculté de Médecine Nord, Marseille, France.
Blanchard
Marie-Pierre
MP
Ferracci
Géraldine
G
Lévêque
Christian
C
Moreno
Mathias
M
François-Bellan
Anne-Marie
AM
Becquet
Denis
D
Bosler
Olivier
O
D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism; D001683:Biological Clocks / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism*; D008297:Male; D009412:Nerve Fibers / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013493:Suprachiasmatic Nucleus / Q000166:cytology* / Q000378:metabolism; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism*; D050598:Vesicular Glutamate Transport Protein 1 / Q000378:metabolism; D050599:Vesicular Glutamate Transport Protein 2 / Q000378:metabolism
C113688:Bsn protein, rat; D009419:Nerve Tissue Proteins; C493475:Slc17a6 protein, rat; C493466:Slc17a7 protein, rat; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D001127:Arginine Vasopressin; D014660:Vasoactive Intestinal Peptide; D018698:Glutamic Acid