title: Regulation of neurons in the suprachiasmatic nucleus of Xenopus laevis.
abstract: In the amphibian Xenopus laevis, suprachiasmatic melanotrope-inhibiting neurons (SMINs) play an important role in the regulation of the background adaptation process. In this study, we investigated the innervation of the SMINs at the light- and electron- microscopical level. Immunocytochemistry in combination with confocal laser scanning microscopy revealed co-existence of neuropeptide Y (NPY) and synaptobrevin in spots in the direct vicinity of the SMINs, suggesting the existence of NPY-containing synapses on these cells. At the ultrastructural level, the SMINs showed a high degree of plasticity, containing more electron-dense vesicles and a larger extent of RER in white- than in black-adapted animals. In black-adapted animals, symmetric synapses (Gray type II) were observed on the soma of the SMINs, suggesting an inhibitory input to these cells. The synaptic profiles contained electron-lucent and electron-dense vesicles, indicating the involvement of both a classical neurotransmitter and a neuropeptide (possibly NPY) in this input. In white-adapted animals, synapses were only found at some distance from the SMIN somata. Our findings indicate a striking plasticity of the innervation of the SMINs in relation to background adaptation and support the hypothesis that the SMINs are innervated by NPY-containing interneurons that inhibit SMIN activity in black-adapted animals.
authors: Department of Cellular Animal Physiology, Nijmegen Institute for Neurosciences and Institute of Cellular Signalling, University of Nijmegen, Nijmegen, The Netherlands. bmkramer@sci.kun.nl
authors: Bianca M R
authors: BM
authors: Kramer
authors: Ji-Ying
authors: JY
authors: Song
authors: Nicole J
authors: NJ
authors: Westphal
authors: Bruce G
authors: BG
authors: Jenks
authors: Eric W
authors: EW
authors: Roubos
mesh_terms: D000818:Animals; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000096:biosynthesis; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008954:Models, Biological; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D009478:Neuropeptide Y / Q000096:biosynthesis; D010455:Peptides / Q000737:chemistry; D050683:R-SNARE Proteins; D013493:Suprachiasmatic Nucleus / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D013569:Synapses / Q000378:metabolism / Q000502:physiology; D013997:Time Factors; D014982:Xenopus laevis
chemical_list: D008565:Membrane Proteins; D009478:Neuropeptide Y; D010455:Peptides; D050683:R-SNARE Proteins