Photoperiod regulates neuronal bromodeoxyuridine labeling in the brain of a seasonally breeding mammal

Seasonal changes in vertebrate brain function are pervasive, but annual cycles in the rates of neuronal incorporation are established only in songbirds. Although cell division continues in the subependymal and hippocampal subgranular zones of adult rodents, there exists no parallel evidence that seasonal plasticity in mammals extends to changes in neuronal or glial number. We examined the effect of photoperiod on incorporation of new neurons in the brain of the adult golden hamster, a long-day breeder. We administered the cell birth marker 5′-bromode-oxyuridine (BrdU) to males which had either been maintained in long days, transferred to short days for 10 weeks, or moved acutely from long to short or short to long days. The number of cells in specific brain regions immunoreactive (ir) for this thymidine analog was determined 7 weeks later. The number of BrdU-ir cells in the dentate gyrus and subependymal zone increased twofold in short days. Transfer between photoperiods 10 days before the BrdU injections produced intermediate numbers of BrdU-labeled cells in the dentate gyrus, but was as effective as long-term photoperiodic exposure in the subependymal zone. Photoperiod also had similar effects in the hypothalamus and cingulate/retrosplenial cortex, but not in the central gray or preoptic area. Double-label immunocytochemistry indicated that very few of the BrdU-ir cells were glia, but that a majority had neuronal phenotype. In the subependymal zone, short days significantly increased the number of BrdU-labeled neurons. We did not detect significant effects of photoperiod on the volume of either the granule cell layer of the hippocampus or the dentate gyrus as a whole. We conclude that short day lengths increase neuronal birth and/or survival in several brain regions of adult hamsters. © 1998 John Wiley & Sons, Inc. J Neurobiol 36: 410–420, 1998     

SIMS MICROSCOPY: METHODOLOGY,PROBLEMS AND PERSPECTIVES IN MAPPING DRUGS AND NUCLEAR MEDICINE COMPOUNDS

Secondary ion mass spectrometry (SIMS) microscopy, a mass spectrometry method designed in the 1960s, offers new analytical capabilities, high sensitivity (ppm to ppb region), high specificity and improved lateral resolution, thus facilitating insight into many physiological and biomedical questions. Apart from the sample preparation and the physical characteristics of the detection, the biological model must also be considered. SIMS analysis of diffusible ions and molecules requires strict cryogenic procedures which always begin by a flash-freeze fixation. Cellular integrity can be checked by mapping the major element distributions since intra and extracellular ions are redistributed only in damaged cells. Cryofixing may be followed either by a freeze-fracture methodology or by cryoembedding and dry-cutting. Chemical sample preparation is only used for ions or molecules bound to fixed cell structures. The use of scanning procedures ameliorates the lateral resolution and chromosome imaging has been reported with probe size of below 50nm. Absolute quantification can be derived for embedded specimen by using internal references included in tissue equivalent resins. The sensitivity is limited by the ionization yield of the tag element and may be further impaired when working at high mass resolution (≥5000) to eliminate interfering cluster ions. SIMS drug mapping is usually performed after in vitro administration of a molecule to cell culture systems. Drug detection is accomplished indirectly by detecting a tag isotope naturally present or introduced by labelling, mainly with halogens,¹⁵N and¹⁴C. Molecular imaging with TOF-SIMS is an appealing alternative especially for heavier compounds. We stress some biological problems through a critical review of published SIMS drug studies. SIMS proved useful in assessing the targeting specificity of nuclear medicine pharmaceutics, even after in vivo administration. The first microscopic evidence of a thionamide induced follicular blockade of the iodine organification process is presented in a human sample.     

beta-arrestins regulate interleukin-8-induced CXCR1 internalization.

The functional role of neutrophils during acute inflammatory responses is regulated by two high affinity interleukin-8 receptors (CXCR1 and CXCR2) that are rapidly desensitized and internalized upon binding their cognate chemokine ligands. The efficient re-expression of CXCR1 on the surface of neutrophils following agonist-induced internalization suggests that CXCR1 surface receptor turnover may involve regulatory pathways and intracellular factors similar to those regulating beta2-adrenergic receptor internalization and re-expression. To examine the internalization pathway utilized by ligand-activated CXCR1, a CXCR1-GFP construct was transiently expressed in two different cell lines, HEK 293 and RBL-2H3 cells. While interleukin-8 stimulation promoted CXCR1 sequestration in RBL-2H3 cells, receptor internalization in HEK 293 cells required co-expression of G protein-coupled receptor kinase 2 and beta-arrestin proteins. The importance of beta-arrestins in CXCR1 internalization was confirmed by the ability of a dominant negative beta-arrestin 1-V53D mutant to block internalization of CXCR1 in RBL-2H3 cells. A role for dynamin was also demonstrated by the lack of CXCR1 internalization in dynamin I-K44A dominant negative mutant-transfected RBL-2H3 cells. Agonist-promoted co-localization of transferrin and CXCR1-GFP in endosomes of RBL-2H3 cells confirmed that receptor internalization occurs via clathrin-coated vesicles. Our data provides a direct link between agonist-induced internalization of CXCR1 and a requirement for G protein-coupled receptor kinase 2, beta-arrestins, and dynamin during this process.     

Optimal range of prey size for antlions

1. Antlions are opportunistic trap building predators that cannot control prey encounter. Their trap should ideally retain a great diversity of prey. However, building a single trap that captures many prey with varying characteristics can be challenging. 2. A series of five different ant species ranging from thin to large, of sizes ranging from 2.75 to 6.5 mm, and a mean weight ranging from 0.54 to 6.00 mg were offered in a random succession to antlions. The state of satiation of the antlions was controlled, and their mass and the depth of their pit were recorded. The reaction of antlion to the prey, the probability of capture as well as the time to escape were recorded. 3. The probability of an antlion reaction is an increasing function of the pit depth and a decreasing function of antlion mass. The probability of capture is highest for intermediate prey mass and is an increasing function of pit depth. The time to escape is a declining function of prey mass and an increasing function of pit depth. 4. There is an upper limit to prey mass given that large prey escape out of the pit. There is a lower limit to prey mass given the difficulty to apprehend the smallest, thin species. Consequently, there is a range of prey mass, corresponding to a medium‐sized ant of 2 mg, for which the pit functions best. The physics of insect locomotion on sandy slopes was identified as the key to understanding the functioning of antlion pits.     

When species accumulation curves intersect: implications for ranking diversity using small samples

Diversity in biological communities frequently is compared using species accumulation curves, plotting observed species richness versus sample size. When species accumulation curves intersect, the ranking of communities by observed species richness depends on sample size, creating inconsistency in comparisons of diversity. We show that species accumulation curves for two communities are expected to intersect when the community with lower actual species richness has higher Simpson diversity (probability that two random individuals belong to different species). This may often occur when comparing communities that differ in habitat heterogeneity or disturbance, as we illustrate using data from neotropical butterflies. In contrast to observed species richness, estimated Simpson diversity always produces a consistent expected ranking among communities across sample sizes, with the statistical accuracy to confidently rank communities using small samples. Simpson diversity should therefore be particularly useful in rapid assessments to prioritize areas for conservation.     

Poster Sessions BP02: Oligodendrocytes and Schwann Cells

Neurofibromatosis Type 1 tumors are highly vascularized and contain Schwann cells with hyperactivated Ras. In vitro , the NF1-derived neurofibromin deficient Schwann cells have an angiogenic profile, which favors angiogenesis and sustains the growth of the NF1-derived tumors. This study examined the relationship of the activation state of Ras as it related to the expression of angiogenic and antiangiogenic factors in both cultured NF1-derived Schwann cells and normal human Schwann cells. Western blot analysis of normal human Schwann cells revealed low expression of angiogenic vascular endothelial growth factor (VEGF) as well as low expression of the antiangiogenic pigment epithelium derived factor (PEDF). Relative to normal human Schwann cells, NF1-derived Schwann cells have increased RAS activity and a three-fold increase in VEGF expression. Surprisingly, PEDF was also expressed in the NF1-derived Schwann cells at approximately the same level as VEGF expression. Using a retroviral construct, we introduced the GAP-related domain of neurofibromin into the NF1-derived Schwann cells to reduce the level of activated Ras. Relative to the untreated NF1-derived Schwann cells the Schwann cells expressing the GAP-related domain expressed about one-half the VEGF but twice the PEDF. We conclude that decreasing the Ras activity in NF1-drived Schwann cells will not only decrease proliferation, but also slow tumor angiogenesis due to the decreased expression of angiogenic and increased expression of antiangiogenic factors.