Improved identification of endogenous peptides from murine nervous tissue by multiplexed peptide extraction methods and multiplexed mass spectrometric analysis

In recent years, mass spectrometry (MS) based techniques have made their entrance in the analysis of endogenous peptides extracted from nervous tissue. In this study, we introduce a novel peptide extraction procedure using 8 M urea, next to the more established extraction method that uses acetic acid. The extracted peptide mixtures are analyzed by both high-resolution nanoLC MS/MS using collision induced dissociation (CID) on an LTQ-Orbitrap and nanoLC electron transfer induced dissociation (ETD) on a linear ion trap. The combined use of the two extraction methods significantly increased the yield of identified endogenous neuropeptides. The multiplexed use of high mass accuracy mass spectrometry and the ETD fragmentation technique further increased the yield and confidence of peptide identifications. Furthermore, reduction of disulfide bridges during sample preparation was essential in the identification of several endogenous peptides containing cysteine disulfide bonds. Through this study, we identified in total 142 peptides in extracts of the mouse pituitary tissue, whereby 43 uniquely in the urea extract and 11 uniquely in the acetic acid extract. A large number of detected endogenous peptides were reported previously, but we confidently identified 22 unreported peptides that possess characteristics of endogenous peptides and are thus interesting targets to be explored further.

Aspects of the neuroendocrine cerebellum: expression of secretogranin II, chromogranin A and chromogranin B in mouse cerebellar unipolar brush cells

Morphologically distinct neuron classes can be subdivided in sublineages by differential chemical phenotypes that correlate with functional diversity. Here we show by immunocytochemistry that chromogranin A (CgA) chromogranin B (CgB) and secretogranin II (SgII), the principal granins situated in neuronal secretory granules and large dense-core vesicles, are widely but differentially expressed in cells of the mouse cerebellum and terminals of cerebellar afferents. While CgA and CgB were nearly panneuronal, SgII was more restricted in distribution. The cells most intensely immunoreactive for SgII were a class of small, excitatory interneurons enriched in the granular layer of the vestibulocerebellum, the unipolar brush cells (UBCs), although larger neurons likely to be a subset of the Golgi-Lugaro-globular cell population were also distinctly immunopositive; by contrast, Purkinje cells and granule cells were, at best, faintly stained and, stellate, basket cells were unstained. SgII was also present in subsets of mossy fibers, climbing fibers and varicose fibers. Neurons in the cerebellar nuclei and inferior olive were distinctly positive for the three granins. Double-labeling with subset-specific cell class markers indicated that, while both CgA and CgB were present in most UBCs, SgII immunoreactivity was present in the calretinin (CR)-expressing subset, but lacked in metabotropic glutamate receptor 1alpha (mGluR1alpha)-expressing UBCs. Thus, we have identified an additional cell class marker, SgII, which serves to study subtype properties in the UBC population. The abundance of SgII in only one of the two known subsets of UBCs is remarkable, as its expression in other neurons of the cortex was moderate or altogether lacking. The data suggest that the CR-positive UBCs represent a unique neuroendocrine component of the mammalian cerebellar cortex, presumably endowed with transynaptically regulated autocrine or paracrine action/s. Because of the well-known organization of the cerebellar system, several of its neuron classes may represent valuable cellular models to analyze granin functions in situ, in acute slices and in dissociated cell and organotypic slice cultures.

Peripheral projections of NESP55 containing neurons in the rat sympathetic ganglia

The peripheral projections of neurons expressing neuroendocrine secretory protein 55 (NESP55), a novel member of the chromogranin family, were studied by retrograde tracing technique. It was found that NESP55 positive neurons in the rat superior cervical ganglion projected to a number of targets including the submandibular gland, the cervical lymph nodes, the forehead skin, the iris, but not to the thyroid. Among these NESP55 positive target-projecting neurons, a subpopulation contained neuropeptide Y (NPY), a vasoconstrictor. Forepaw pad projecting neurons were found exclusively in the stellate ganglion, almost all of which (approximately 90%) were immunoreactive to NESP55. Colocalization of NESP55 and calcitonin gene-related peptide (CGRP), a peptide involved in sudomotor effects, was observed in a subpopulation of these paw pad projecting neurons, as was colocalization of NESP55 and NPY. The data suggest that NESP55 may have a functional role in some populations of sympathetic neurons.