Circadian rhythms in mammals are synchronized to the environmental light/dark cycle through photic cues perceived by the retina and reaching the time-keeper in the suprachiasmatic nucleus of the hypothalamus (SCN). We showed in rat that the photic synchronization process is associated with rearrangements of the SCN neuroglial architecture, presumably to permit adequate intercellular phasing of the multiple SCN cellular oscillators. In the SCN retinorecipient area, neurons synthesizing vasoactive intestinal peptide (VIP), a main target for retinal signals, contribute to such reorganizations through day/night changes in the extent of their membrane coverage by glial processes and axon terminals. Using confocal imaging and electron microscopy, we further provided evidence in rat that the daily changes in axonal coverage of the VIP neurons reflected synaptic reorganizations at their surface and involved both glutamatergic terminals, known to play major roles in conveying light environmental signals to the SCN, and nonglutamatergic terminals. However, although it appeared that the whole architecture of the SCN cellular assemblage reorganized over the 24-h cycle, the density of GABAergic synapses onto the VIP neurons did not change with time of day, at least on the dendritic compartment of these neurons as assessed by electron microscopy. Taken together, these data are interpreted on the basis of accumulated evidence that the VIP neurons exert major roles in communicating temporal cues through the SCN and in synchronizing SCN oscillating neurons with each other and with the environment. Data in adrenalectomized rats indicated that the daily plastic events in SCN are regulated by the daily secretory cycles of glucocorticoid hormones, known to act as temporal endocrine signals in the modulation of photic synchronization. Additional data supporting a role for PSA-NCAM, serotonin and BDNF as molecular actors of SCN day/night structural plasticity will be also highlighted
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.