Nerve Cells Associated with the Endocrine Pancreas in Young Mice: an Ultrastructural Analysis of the Neuroinsular Complex Type I

The neuroinsular complex type 1 is composed of pancreatic endocrine islet cells and nerve cell bodies intrinsic to the islet. The details of the relation between nerve cells and between endocrine cells and nerve cells in the complex are unknown. Pancreata from newborn and 18-day-old mice were analysed by electron microscopy to establish the ultrastructural morphology of the neuroinsular complex. Immunohistochemical staining for protein gene-product 9.5 was also performed. The study showed that nerve cell bodies were closely associated to each other in the periphery of the islets with no connective tissue separating the cells. The nerve cells were closely associated to both beta-cells and alpha-cells. Direct intercellular contacts were observed between nerve cells and endocrine cells and between Schwann cells and endocrine cells. Varicose nerve endings were frequently observed in the neuroinsular complex. In the peripheral parts the varicosities were mostly being associated to the nerve cell bodies. The varicosities contained small clear or small clear and larger dense cored vesicles, suggesting cholinergic and peptidergic contents. The varicosities made specialized synaptic connections with adjacently located nerve cells. The study shows that the neuronal part of the neuroinsular complex is closely associated to the endocrine islet cells and that it is richly innervated, indicating an important regulatory function of the nerve cell component in the neuroinsular complex.