calcimycin and 8-bromoguanosino-3--5--cyclic-monophosphorothioate

Abstract Chemical synapses equipped with ribbons are tonically active, high-output synapses. The ribbons may play a role in the trafficking of synaptic vesicles. Recent findings in retinal rod cells of BALB/c mice indicate that ribbons are large and smooth in the dark phase, and, due to the formation and release of protrusions, small during the light phase. As a consequence of these changes, ribbons may traffick fewer vesicles in the light than in the dark phases. The aim of the present study was to find out whether the above ribbon changes in this mouse strain are strictly illumination-dependent and which signalling processes may be involved. Here, we show that ribbons form protrusions and release them into the cytoplasm within 30-60 min after lights on, the reverse occurring within 30 min after lights off. Under constant light or constant dark, no circadian rhythm of synaptic ribbon changes is observed. The illumination-dependence of ribbon structure is supported by in vitro experiments showing that in dark-adapted retinas, light induces the same morphological changes as in vivo. In vitro, the effect of light on the ribbons can be counteracted by cyclic guanosine monophosphate and melatonin. In dark-adapted retinas, light effects can be produced by decreasing the calcium ion concentrations in the incubation media. These results suggest that in retinal rod cells, the well known phototransduction signalling mechanisms may be responsible for the ribbon changes presently and previously reported.

Topics: Animals; Calcimycin; Calcium Chloride; Chelating Agents; Circadian Rhythm; Cyclic GMP; Dark Adaptation; Darkness; Drug Interactions; Egtazic Acid; Ionophores; Light; Lighting; Male; Melatonin; Mice; Mice, Inbred BALB C; Microscopy, Electron; Models, Biological; Organ Culture Techniques; Photic Stimulation; Photoreceptor Cells; Retina; Synapses; Thionucleotides; Time Factors

A significant fraction of the beta-amyloid precursor protein is proteolytically processed to yield large secreted forms (sAPP). These proteins have pleiotropic effects which potentially involve control of gene expression. We have investigated the influence of sAPP on the class of transcription factors which bind kappa B enhancer sequences. Transcription dependent on a kappa B element was enhanced by sAPP in several cell lines, as measured by expression of a transfected chloramphenicol acetyltransferase reporter gene. Secreted APP also induced an increase in kappa B DNA-binding activity in hippocampal neurons treated with sAPP. Both effects were mimicked by an analog of cyclic GMP and inhibited by an antagonist of cyclic GMP-dependent protein kinase. Such activation of kappa B-dependent transcription was correlated in two ways with the ability of sAPP to protect neuronal cells against calcium-mediated damage: (1) tumor necrosis factor beta also protected against calcium-mediated insults and induced kappa B-dependent transcription; (2) antisense oligonucleotide-mediated reduction of an endogenous inhibitor of NF-kappa B activated kappa B-binding activity and attenuated calcium-mediated toxicity in both a neuronal cell line and in primary neurons. These findings suggest that a kappa B-binding transcription factor can act as a coordinator of neuroprotective gene expression in response to cytokines.

Topics: Amyloid beta-Protein Precursor; Base Sequence; Calcimycin; Calcium; Cell Line; Cell Survival; Chloramphenicol O-Acetyltransferase; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; DNA-Binding Proteins; Enhancer Elements, Genetic; Glioma; Humans; I-kappa B Proteins; Kidney; Kinetics; Neuroblastoma; Neurons; NF-kappa B; NF-KappaB Inhibitor alpha; Oligonucleotides, Antisense; Recombinant Fusion Proteins; Thionucleotides; Transcription, Genetic; Transfection; Tumor Cells, Cultured