Regulation of neurons in the suprachiasmatic nucleus of Xenopus laevis

• Published in: Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology 2002-05, Vol.132 (1), p.269-274
• Main Authors: Kramer, Bianca M.R., Song, Ji-Ying, Westphal, Nicole J., Jenks, Bruce G., Roubos, Eric W.
• Format: Article
• Language: English
• Subjects: Animals; Background adaptation; Confocal laser scanning microscopy; Freshwater; Immunohistochemistry; Membrane Proteins - biosynthesis; Microscopy, Confocal; Microscopy, Electron; Models, Biological; Neurons - metabolism; Neurons - physiology; Neuropeptide Y - biosynthesis; NPY; Peptides - chemistry; R-SNARE Proteins; SMINs; Suprachiasmatic Nucleus - metabolism; Suprachiasmatic Nucleus - physiology; Suprachiasmatic Nucleus - ultrastructure; Symmetric synapses; Synapses - metabolism; Synapses - physiology; Synaptobrevin; Time Factors; Ultrastructure; Xenopus laevis
• ISSN: 1096-4959; 1879-1107
• DOI: 10.1016/S1096-4959(01)00539-5

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.