Modulation of the cGMP signaling pathway by melatonin in pancreatic beta-cells.

Melatonin influences the second messenger cyclic guanosine 3',5'-monophosphate (cGMP) signaling pathway in pancreatic beta-cells via a receptor-mediated mechanism. In the present study, it was determined how the regulation of cGMP concentrations by melatonin proceeds. The results provide evidence that melatonin acts via the soluble guanylate cyclase (sGC), as molecular investigations demonstrated that long-term incubation with melatonin significantly reduced the expression levels of the sGC mRNA in rat insulinoma beta-cells (INS1) cells, whereas mRNA expression of membrane guanylate cyclases was unaffected.

Increased melatonin synthesis in pineal glands of rats in streptozotocin induced type 1 diabetes.

It is well-documented that melatonin influences insulin secretion. The effects are mediated by specific, high-affinity, pertussis-toxin-sensitive, G protein-coupled membrane receptors (MT(1) as well MT(2)), which are present in both the pancreatic tissue and islets of rats and humans, as well as in rat insulinoma cells (INS1). Via the Gi-protein-adenylatecyclase-3',5'-cyclic adenosine monophosphate (cAMP) and, possibly, the guanylatecyclase-cGMP pathways, melatonin decreases insulin secretion, whereas, by activating the Gq-protein-phospholipase C-IP(3) pathway, it has the opposite effect.

Melatonin and type 2 diabetes - a possible link?

The aim of the present study was to determine the existence of melatonin membrane receptors and to examine the mRNA expression of nuclear orphan receptors in human pancreatic tissue, in an effort to explain differences between type 2 diabetic and metabolically healthy patients. Molecular and immunocytochemical investigations established the presence of the melatonin membrane receptors MT1 and MT2 in human pancreatic tissue and, notably, also in the islets of Langerhans. Results of a calculation model to determine mRNA expression ratios, as well as subjective analysis of immunoreactions, showed elevated MT1 receptor expression in comparison with MT2 expression.

Characterization of the rhesus monkey superior olivary complex by calcium binding proteins and synaptophysin.

This study was performed in order to characterize the main nuclei of the rhesus monkey superior olivary complex by means of antibodies against the calcium binding proteins parvalbumin, calbindin and calretinin and the synaptic vesicle protein synaptophysin. These markers revealed the neuronal morphology and organization of nuclei located within the rhesus monkey superior olivary complex. The architectural details included the distribution of axonal terminals on neurons.

Characterization of the human superior olivary complex by calcium binding proteins and neurofilament H (SMI-32).

This study provides a morphologic characterization of the human superior olivary complex as revealed by immunohistochemistry by using antibodies against the calcium binding proteins parvalbumin, calbindin, calretinin, and the nonphosphorylated neurofilament H SMI-32. By combining these markers, it was possible to establish the neuronal architecture and details of the morphologic organization (including axonal terminals) of the different nuclei. The medial superior olivary nucleus is formed by a sheet of parallel-oriented cells.