Auditory event-related signals in mouse ERG recordings.

PURPOSE: In murine disease models, particularly in cases when retinal electrical activity is reduced, an event-related component becomes apparent that does not change with the stimulus intensity in electroretinogram (ERG) recordings. In this work, we show that this electric component is evoked by the sound of the flash discharge rather than the light flash itself. METHODS: Wild-type mice (C57BL/6), mice with rod function only (Cnga3 (-/-)), mice lacking any photoreceptor function (Cnga3 (-/-) rho (-/-)), and mice with no auditory function (Cdh23 (vAlb/vAlb) ) were examined with Xenon flash ERG systems. An acoustic noise generator was used to mask discharge sounds. RESULTS: ERG recording modalities were identified where usually no discernible response can be elicited. These include photopic conditions in Cnga3 (-/-) mice, photopic conditions together with very low stimulus intensities in C57BL/6 mice, and both scotopic and photopic conditions in Cnga3 (-/-) rho (-/-) mice. However, in all of these cases, small signals, featuring an initial a-wave like deflection at about 20 ms and a subsequent b-wave like deflection peaking at about 40 ms after the flash, were detected. In contrast, such signals could not be detected in deaf Cdh23 (vAlb/vAlb) mice. Furthermore, masking the Xenon discharge sound by continuous acoustic noise led to a loss of the event-related signals in a reversible manner. CONCLUSIONS: We could identify an auditory event-related component, presumably resembling auditory evoked potentials, as a major source of ERG signals of non-visual origin in mice. This finding may be of particular importance for the analysis and interpretation of ERG data in mice with reduced visual responses.

A rapid MALDI-TOF mass spectrometry workflow for Drosophila melanogaster differential neuropeptidomics.

BACKGROUND: Neuropeptides are a diverse category of signaling molecules in the nervous system regulating a variety of processes including food intake, social behavior, circadian rhythms, learning, and memory. Both the identification and functional characterization of specific neuropeptides are ongoing fields of research. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis of nervous tissues from a variety of organisms allows direct detection and identification of neuropeptides. Here, we demonstrate an analysis workflow that allows for the detection of differences in specific neuropeptides amongst a variety of neuropeptides being simultaneously measured. For sample preparation, we describe a straight-forward and rapid (minutes) method where individual adult Drosophila melanogaster brains are analyzed. Using a MATLAB-based data analysis workflow, also compatible with MALDI-TOF mass spectra obtained from other sample preparations and instrumentation, we demonstrate how changes in neuropeptides levels can be detected with this method. RESULTS: Over fifty isotopically resolved ion signals in the peptide mass range are reproducibly observed across experiments. MALDI-TOF MS profile spectra were used to statistically identify distinct relative differences in organ-wide endogenous levels of detected neuropeptides between biological conditions. In particular, three distinct levels of a particular neuropeptide, pigment dispersing factor, were detected by comparing groups of preprocessed spectra obtained from individual brains across three different D. melanogaster strains, each of which express different amounts of this neuropeptide. Using the same sample preparation, MALDI-TOF/TOF tandem mass spectrometry confirmed that at least 14 ion signals observed across experiments are indeed neuropeptides. Among the identified neuropeptides were three products of the neuropeptide-like precursor 1 gene previously not identified in the literature. CONCLUSIONS: Using MALDI-TOF MS and preprocessing/statistical analysis, changes in relative levels of a particular neuropeptide in D. melanogaster tissue can be statistically detected amongst a variety of neuropeptides. While the data analysis methods should be compatible with other sample preparations, the presented sample preparation method was sufficient to identify previously unconfirmed D. melanogaster neuropeptides.