The role of brain-derived neurotrophic factor in the regulation of cell growth and gene expression in melanotrope cells of Xenopus laevis.

Brain-derived neurotrophic factor (BDNF) is, despite its name, also found outside the central nervous system (CNS), but the functional significance of this observation is largely unknown. This review concerns the expression of BDNF in the pituitary gland. While the presence of the neurotrophin in the mammalian pituitary gland is well documented its functional significance remains obscure. Studies on the pars intermedia of the pituitary of the amphibian Xenopus laevis have shown that BDNF is produced by the neuroendocrine melanotrope cells, its expression is physiologically regulated, and the melanotrope cells themselves express receptors for the neurotrophin. The neurotrophin has been shown to act as an autocrine factor on the melanotrope to promote cell growth and regulate gene expression. In doing so BDNF supports the physiological function of the cell to produce and release α-melanophore-stimulating hormone for the purpose of adjusting the animal's skin color to that of its background.

Developmental axon pruning mediated by BDNF-p75NTR-dependent axon degeneration.

The mechanisms that regulate the pruning of mammalian axons are just now being elucidated. Here, we describe a mechanism by which, during developmental sympathetic axon competition, winning axons secrete brain-derived neurotrophic factor (BDNF) in an activity-dependent fashion, which binds to the p75 neurotrophin receptor (p75NTR) on losing axons to cause their degeneration and, ultimately, axon pruning. Specifically, we found that pruning of rat and mouse sympathetic axons that project to the eye requires both activity-dependent BDNF and p75NTR. p75NTR and BDNF are also essential for activity-dependent axon pruning in culture, where they mediate pruning by directly causing axon degeneration. p75NTR, which is enriched in losing axons, causes axonal degeneration by suppressing TrkA-mediated signaling that is essential for axonal maintenance. These data provide a mechanism that explains how active axons can eliminate less-active, competing axons during developmental pruning by directly promoting p75NTR-mediated axonal degeneration.

Comparing the coverage, recall, and precision of searches for 120 systematic reviews in Embase, MEDLINE, and Google Scholar: a prospective study.

BACKGROUND: Previously, we reported on the low recall of Google Scholar (GS) for systematic review (SR) searching. Here, we test our conclusions further in a prospective study by comparing the coverage, recall, and precision of SR search strategies previously performed in Embase, MEDLINE, and GS. METHODS: The original search results from Embase and MEDLINE and the first 1000 results of GS for librarian-mediated SR searches were recorded. Once the inclusion-exclusion process for the resulting SR was complete, search results from all three databases were screened for the SR's included references. All three databases were then searched post hoc for included references not found in the original search results. RESULTS: We checked 4795 included references from 120 SRs against the original search results. Coverage of GS was high (97.2 %) but marginally lower than Embase and MEDLINE combined (97.5 %). MEDLINE on its own achieved 92.3 % coverage. Total recall of Embase/MEDLINE combined was 81.6 % for all included references, compared to GS at 72.8 % and MEDLINE alone at 72.6 %. However, only 46.4 % of the included references were among the downloadable first 1000 references in GS. When examining data for each SR, the traditional databases' recall was better than GS, even when taking into account included references listed beyond the first 1000 search results. Finally, precision of the first 1000 references of GS is comparable to searches in Embase and MEDLINE combined. CONCLUSIONS: Although overall coverage and recall of GS are high for many searches, the database does not achieve full coverage as some researchers found in previous research. Further, being able to view only the first 1000 records in GS severely reduces its recall percentages. If GS would enable the browsing of records beyond the first 1000, its recall would increase but not sufficiently to be used alone in SR searching. Time needed to screen results would also increase considerably. These results support our assertion that neither GS nor one of the other databases investigated, is on its own, an acceptable database to support systematic review searching.

Evidence that brain-derived neurotrophic factor acts as an autocrine factor on pituitary melanotrope cells of Xenopus laevis.

We have investigated the physiological regulation and functional significance of brain-derived neurotrophic factor (BDNF) in the endocrine melanotrope cells of the pituitary pars intermedia of the amphibian Xenopus laevis, which can adapt its skin color to the light intensity of its environment. In black-adapted animals, melanotrope cells produce and release alpha-melanophore-stimulating hormone (alpha-MSH). In white-adapted animals, the activity of melanotrope cells is inhibited by neuronal input. Using Western blotting and immunocytochemistry at the light and electron microscopical level, we have detected both the BDNF precursor and the mature BDNF protein in Xenopus melanotrope cells. In situ hybridization and RT-PCR revealed the presence of BDNF mRNA in the pituitary pars intermedia, indicating that BDNF is synthesized in the melanotropes. Real-time quantitative RT-PCR showed that levels of BDNF mRNA in melanotrope cells are about 25 times higher in black- than in white-adapted animals. Although there is no difference in the amount of stored mature BDNF, the amount of BDNF precursor protein is 3.5 times higher in melanotropes of black-adapted animals than in those of white-adapted animals. These data indicate that BDNF mRNA expression and BDNF biosynthesis are up-regulated in active melanotrope cells. Because immunoelectron microscopy showed that BDNF is located in melanotrope secretory granules, BDNF is probably coreleased with alpha-MSH via the regulated secretory pathway. Superfusion and (3)H-amino acid incorporation studies demonstrated that BDNF stimulates the release of alpha-MSH and the biosynthesis of its precursor protein, POMC. Our results provide evidence that BDNF regulates the activity of Xenopus melanotrope cells in an autocrine fashion.

Alpha-melanophore-stimulating hormone in the brain, cranial placode derivatives, and retina of Xenopus laevis during development in relation to background adaptation.

The amphibian Xenopus laevis can adapt the color of its skin to the light intensity of the background. A key peptide in this adaptation process is alpha-melanophore-stimulating hormone (alpha-MSH), which is derived from proopiomelanocortin (POMC) and released by the endocrine melanotrope cells in the pituitary pars intermedia. In this study, the presence of alpha-MSH in the brain, cranial placode derivatives, and retina of developing Xenopus laevis was investigated using immunocytochemistry, to test the hypothesis that POMC peptide-producing neurons and endocrine cells have a common embryonic origin and a common function, i.e., controlling each other's activities and/or being involved in the process of physiological adaptation. The presence of alpha-MSH-positive cells in the suprachiasmatic nucleus, ventral hypothalamic nucleus, epiphysis, and endocrine melanotrope and corticotrope cells, which are all involved in regulation of adaptation processes, has been detected from stage 37/38 onward. This is consistent with the presumed common origin of these cells, the anterior neural ridge (ANR) of the neural-plate-stage embryo. The olfactory epithelium and the otic and epibranchial ganglia also contain alpha-MSH, indicating that these placodal derivatives originate from a common placodal domain continuous with the ANR. Furthermore, we demonstrate the presence of alpha-MSH in a subpopulation of retinal ganglion cells (RGCs), which is possibly also derived from the ANR. Immunoreactivity for alpha-MSH in RGCs that are located in the dorsal part of the retina is dependent on the background light intensity, suggesting that these cells are involved in the regulation of background adaptation. Taken together, the results support the hypothesis that POMC peptide-producing cells have a common embryonic origin and are involved in adaptation processes.

Regulation of neurons in the suprachiasmatic nucleus of Xenopus laevis.

In the amphibian Xenopus laevis, suprachiasmatic melanotrope-inhibiting neurons (SMINs) play an important role in the regulation of the background adaptation process. In this study, we investigated the innervation of the SMINs at the light- and electron- microscopical level. Immunocytochemistry in combination with confocal laser scanning microscopy revealed co-existence of neuropeptide Y (NPY) and synaptobrevin in spots in the direct vicinity of the SMINs, suggesting the existence of NPY-containing synapses on these cells. At the ultrastructural level, the SMINs showed a high degree of plasticity, containing more electron-dense vesicles and a larger extent of RER in white- than in black-adapted animals. In black-adapted animals, symmetric synapses (Gray type II) were observed on the soma of the SMINs, suggesting an inhibitory input to these cells. The synaptic profiles contained electron-lucent and electron-dense vesicles, indicating the involvement of both a classical neurotransmitter and a neuropeptide (possibly NPY) in this input. In white-adapted animals, synapses were only found at some distance from the SMIN somata. Our findings indicate a striking plasticity of the innervation of the SMINs in relation to background adaptation and support the hypothesis that the SMINs are innervated by NPY-containing interneurons that inhibit SMIN activity in black-adapted animals.

Characterizing physicians' information needs at the point of care.

Physicians have many information needs that arise at the point of care yet go unmet for a variety of reasons, including uncertainty about which information resources to select. In this study, we aimed to identify the various types of physician information needs and how these needs relate to physicians' use of the database PubMed and the evidence summary tool UpToDate. We conducted semi-structured interviews with physicians (Stanford University, United States; n = 13; and University Medical Center Utrecht, the Netherlands; n = 9), eliciting participants' descriptions of their information needs and related use of PubMed and/or UpToDate. Using thematic analysis, we identified six information needs: refreshing, confirming, logistics, teaching, idea generating and personal learning. Participants from both institutions similarly described their information needs and selection of resources. The identification of these six information needs and their relation to PubMed and UpToDate expands upon previously identified physician information needs and may be useful to medical educators designing evidence-based practice training for physicians.

The localization, trafficking and retrograde transport of BDNF bound to p75NTR in sympathetic neurons.

BDNF, through p75NTR, promotes apoptosis and inhibits axonal growth of sympathetic neurons, antagonizing the pro-survival and axon growth-promoting actions of NGF through TrkA. While the trafficking of the TrkA:NGF complex is well characterized, little is known about p75NTR:BDNF trafficking in these neurons. Here we show that BDNF binds to and appears inside sympathetic neurons relatively slowly, although the temperature-sensitive internalization step itself is rapid. P75NTR internalization is partially sensitive to disruption of clathrin- or raft-mediated internalization, while that of TrkA is entirely clathrin-mediated. P75NTR, but not Trk, associates with neurotrophins in lipid rafts and coimmunoprecipitates with the truncated beta-caveolin-1 isoform. Finally, we directly visualize the retrograde transport of p75NTR ligands to cell bodies, which is insensitive to inhibitors of Trk retrograde transport, suggesting mechanistic differences. We postulate that beta-caveolin-1-containing lipid rafts and possibly intracellular endosomes might be compartments to which p75NTR:BDNF complexes are trafficked separately from Trk.