A significant challenge to understanding dynamic and heterogeneous brain systems lies in the chemical complexity of secreted intercellular messengers that change rapidly with space and time. Two solid-phase extraction collection strategies are presented that relate time and location of peptide release with mass spectrometric characterization. Here, complex suites of peptide-based cell-to-cell signaling molecules are characterized from the mammalian suprachiasmatic nucleus (SCN), site of the master circadian clock. Observed SCN releasates are peptide rich and demonstrate the corelease of established circadian neuropeptides and peptides with unknown roles in circadian rhythms. Additionally, the content of SCN releasate is stimulation specific. Stimulation paradigms reported to alter clock timing, including electrical stimulation of the retinohypothalamic tract, produce releasate mass spectra that are notably different from the spectra of compounds secreted endogenously over the course of the 24-h cycle. In addition to established SCN peptides, we report the presence of proSAAS peptides in releasates. One of these peptides, little SAAS, exhibits robust retinohypothalamic tract-stimulated release from the SCN, and exogenous application of little SAAS induces a phase delay consistent with light-mediated cues regulating circadian timing. These mass spectrometry-based analyses provide a new perspective on peptidergic signaling within the SCN and demonstrate that the integration of secreted compounds with information relating time and location of release generates new insights into intercellular signaling in the brain.little SAAS ͉ neuropeptides ͉ solid-phase extraction ͉ peptidomics ͉ suprachiasmatic nucleus A fundamental component of cell-to-cell signaling in the brain is the release of endogenously derived neuropeptidebased transmitters and modulators within dynamic neural networks. Neuropeptides include a broad set of structurally diverse molecules that are physiologically active at low concentrations and localize across heterogeneous brain regions, particularly throughout neuroendocrine systems. These properties contribute marked chemical complexity to neurotransmission within heterogeneous and dynamic brain systems. Directly acquiring releasate information about chemical content, release site distribution, and stimulation dependence is a significant challenge to the study of neuronal networks incorporating neuropeptide intercellular signaling.This article describes the use of several unique peptide sampling approaches to characterize chemically complex releasates from the rat suprachiasmatic nucleus (SCN), the site of the master circadian clock (1, 2). The SCN is highly innervated with peptidergic efferents, afferents, and interneurons (3). Moreover, SCN humoral signals are critical elements for the coordination of biological rhythms because SCN transplants can restore aspects of circadian rhythms in SCN-ablated animals (4). In the present work, SCN releasates were collected and concentrated directly from brain sl...

The honey bee genome predicts Ϸ100 peptides from 36 prohormones, but the functions of many of these peptides are unknown. We used differential isotope labeling combined with mass spectrometric analysis to quantify Ϸ50% of known bee brain peptides in the context of foraging, with 8 showing robust and dynamic regulation. Some showed differences in brain abundance as a function of experience; specifically, nectar and pollen collection led to quick changes in abundance. These changes were related to the act of food collection, not ingestion, because foragers bring food back to the hive for storage rather than eating it themselves. Other peptide differences in brain abundance were seen in bees that either flew to a nectar feeder or a pollen feeder, but did not yet collect any food. These differences likely reflect well-known predispositions of some bees to collect either nectar or pollen, but not both. Tachykinin, PBAN, and sNPF were among the peptides with the strongest changes in association with nectar and pollen foraging. These peptides are known to be involved in regulating food intake in solitary insects, suggesting an evolutionary connection between that behavior and social foraging. These results demonstrate that it is now possible to use quantitative peptidomics to help determine which brain peptides are bioactive and to elucidate their function in the regulation of behavior.Apis mellifera ͉ behavioral maturation ͉ foraging ͉ neuropeptides B rain peptides play an important role in orchestrating physiological and behavioral processes in animals by functioning as neurohormones, neuromodulators, and neurotransmitters (1). These cell-cell signaling peptides are produced from their corresponding precursor genes by cleavage at specific sites followed by additional posttranslational modifications, a complex process that can make bioactive peptides difficult to predict (2). The availability of genome sequences has led to a new, high-throughput approach for neuropeptide discovery: algorithms that predict cleavage sites in peptide precursors (3, 4) followed by sequencing from brain samples with mass spectrometry (5-7). Applying this methodology to the honey bee genome, Hummon et al. (6) predicted 36 peptide-encoding genes and confirmed 100 endogenous peptides in the bee brain, numbers similar to what is known for other animals such as the fruit fly (Drosophila melanogaster) and the house mouse (Mus musculus) (7,8).As with other species, however, the physiological and behavioral functions of most (neuro)peptides in the honey bee are unknown (2, 9-11). Until very recently, most brain peptides were discovered one at a time via biochemical techniques, and functional experiments focused on physiological effects (12). Recent advances in peptidomics have greatly accelerated peptide characterization (13-15). However, corresponding high-throughput approaches to discover peptide function have been much less common. A goal of this study was to determine whether combining a recently established quantitative peptidomic method with...

Clearance by the retinal pigment epithelium (RPE) of shed photoreceptor outer segments (OSs), a tissue with one of the highest turnover rates in the body, is critical to the maintenance and normal function of the retina. We hypothesized that there is a potential role for photo-oxidation in OS uptake by RPE via scavenger receptor-mediated recognition of structurally defined lipid peroxidation products. We now demonstrate that specific structurally defined oxidized species derived from arachidonyl, linoleoyl, and docosahexanoyl phosphatidylcholine may serve as endogenous ligands on OSs for uptake by RPE via the scavenger receptor CD36. Mass spectrometry studies of retinal lipids recovered from dark-adapted rats following physiological light exposure demonstrate in vivo formation of specific oxidized phosphatidylcholine molecular species possessing a CD36 recognition motif, an oxidatively truncated sn-2 acyl group with a terminal ␥-hydroxy(or oxo)-␣,␤-unsaturated carbonyl. Cellular studies using RPE isolated from wild-type versus CD36 null mice suggest that CD36 plays a role in engulfment, but not initial binding, of OSs via these oxidized phospholipids. Parallel increases in OS protein-bound nitrotyrosine, a post-translational modification by nitric oxide (NO)-derived oxidants, were also observed, suggesting a possible role for light-induced generation of NO-derived oxidants in the initiation of OS lipid peroxidation. Collectively, these studies suggest that intense light exposure promotes "oxidative tagging" of photoreceptor outer segments with structurally defined choline glycerophospholipids that may serve as a physiological signal for CD36-mediated phagocytosis under oxidant stress conditions.

The mammalian supraoptic nucleus (SON) is a neuroendocrine center in the brain regulating a variety of physiological functions. Within the SON, peptidergic magnocellular neurons that project to the neurohypophysis (posterior pituitary) are involved in controlling osmotic balance, lactation, and parturition, partly through secretion of signaling peptides such as oxytocin and vasopressin into the blood. An improved understanding of SON activity and function requires identification and characterization of the peptides used by the SON. Here, small-volume sample preparation approaches are optimized for neuropeptidomic studies of isolated SON samples ranging from entire nuclei down to single magnocellular neurons. Unlike most previous mammalian peptidome studies, tissues are not immediately heated or microwaved. SON samples are obtained from ex vivo brain slice preparations via tissue punch and the samples processed through sequential steps of peptide extraction. Analyses of the samples via liquid chromatography mass spectrometry and tandem mass spectrometry result in the identification of 85 peptides, including 20 unique peptides from known prohormones. As the sample size is further reduced, the depth of peptide coverage decreases; however, even from individually isolated magnocellular neuroendocrine cells, vasopressin and several other peptides are detected.

The application of mass spectrometry to imaging, or MS imaging (MSI), allows for the direct investigation of tissue sections to identify biological compounds and determine their spatial distribution. We present an approach to MSI that combines secondary ion mass spectrometry (SIMS) and MALDI MS for the imaging and analysis of rat spinal cord sections, thereby enhancing the chemical coverage obtained from an MSI experiment. The spinal cord is organized into discrete, anatomically defined areas that include motor and sensory networks composed of chemically diverse cells. The MSI data presented here reveal the spatial distribution of multiple phospholipids, proteins, and neuropeptides obtained within single, 20-μm sections of rat spinal cord. Analyte identities are initially determined by primary mass match and confirmed in follow-up experiments using LC MS/ MS from extracts of adjacent spinal cord sections. Additionally, a regional analysis of differentially localized signals serves to rapidly screen compounds of varying intensities across multiple spinal regions. These MSI analyses reveal new insights into the chemical architecture of the spinal cord and set the stage for future imaging studies of the chemical changes induced by pain, anesthesia, and drug tolerance.

SUMMARY Background The Drosophila bHLH gene dimmed promotes a neurosecretory/neuroendocrine phenotype in cells but is not associated with specific neuropeptides or neurohormones. Rather, it is expressed by those peptidergic neurons that project long axons and appear to produce large amounts of secretory peptides. Here we genetically transform non-peptidergic neurons in Drosophila to study DIMM’s action mechanisms. Results Non-peptidergic neurons normally fail to accumulate ectopic neuropeptides. We now show they will do so when they are also forced to express ectopic DIMM. Furthermore, mass spectrometry shows that photoreceptors, which are normally non-peptidergic, fail to process an ectopic neuropeptide precursor to make bioactive peptides, but will do so efficiently when DIMM is co-misexpressed. Likewise photoreceptors, which normally package the fast neurotransmitter histamine within small clear synaptic vesicles, now produce numerous large dense-core vesicles (LDCVs) when they misexpress DIMM. These novel LDCVs accumulate ectopic neuropeptide when photoreceptors co-misexpress a neuropeptide transgene. Thus, DIMM-expressing photoreceptors no longer accumulate histamine and lose synaptic organelles critical to their normal physiology. Conclusions These findings indicate that DIMM suppresses conventional fast neurotransmission and promotes peptidergic neurosecretory properties. We conclude that DIMM normally provides a comprehensive transcriptional control to direct the differentiation of dedicated neuroendocrine neurons.

Proteomics, the large-scale study of protein expression in organisms, offers the potential to evaluate global changes in protein expression and their post-translational modifications that take place in response to normal or pathological stimuli. One challenge has been the requirement for substantial amounts of tissue in order to perform comprehensive proteomic characterization. In heterogeneous tissues, such as brain, this has limited the application of proteomic methodologies. Efforts to adapt standard methods of tissue sampling, protein extraction, arraying, and identification are reviewed, with an emphasis on those appropriate to smaller samples ranging in size from several microliters down to single cells. The effects of miniaturization on these analyses are highlighted using neuroscience-related examples, as are statistical issues unique to the high-dimensional datasets generated by proteomic experiments.

BackgroundAmong songbirds, the zebra finch (Taeniopygia guttata) is an excellent model system for investigating the neural mechanisms underlying complex behaviours such as vocal communication, learning and social interactions. Neuropeptides and peptide hormones are cell-to-cell signalling molecules known to mediate similar behaviours in other animals. However, in the zebra finch, this information is limited. With the newly-released zebra finch genome as a foundation, we combined bioinformatics, mass-spectrometry (MS)-enabled peptidomics and molecular techniques to identify the complete suite of neuropeptide prohormones and final peptide products and their distributions.ResultsComplementary bioinformatic resources were integrated to survey the zebra finch genome, identifying 70 putative prohormones. Ninety peptides derived from 24 predicted prohormones were characterized using several MS platforms; tandem MS confirmed a majority of the sequences. Most of the peptides described here were not known in the zebra finch or other avian species, although homologous prohormones exist in the chicken genome. Among the zebra finch peptides discovered were several unique vasoactive intestinal and adenylate cyclase activating polypeptide 1 peptides created by cleavage at sites previously unreported in mammalian prohormones. MS-based profiling of brain areas required for singing detected 13 peptides within one brain nucleus, HVC; in situ hybridization detected 13 of the 15 prohormone genes examined within at least one major song control nucleus. Expression mapping also identified prohormone messenger RNAs in areas associated with spatial learning and social behaviours. Based on the whole-genome analysis, 40 prohormone probes were found on a commonly used zebra finch brain microarray. Analysis of these newly annotated transcripts revealed that six prohormone probes showed altered expression after birds heard song playbacks in a paradigm of song recognition learning; we partially verify this result experimentally.ConclusionsThe zebra finch peptidome and prohormone complement is now characterized. Based on previous microarray results on zebra finch vocal learning and synaptic plasticity, a number of these prohormones show significant changes during learning. Interestingly, most mammalian prohormones have counterparts in the zebra finch, demonstrating that this songbird uses similar biochemical pathways for neurotransmission and hormonal regulation. These findings enhance investigation into neuropeptide-mediated mechanisms of brain function, learning and behaviour in this model.