Presynaptic partner selection during retinal circuit reassembly varies with timing of neuronal regeneration in vivo

Whether neurons can restore their original connectivity patterns during circuit repair is unclear. Taking advantage of the regenerative capacity of zebrafish retina, we show here the remarkable specificity by which surviving neurons reassemble their connectivity upon regeneration of their major input. H3 horizontal cells (HCs) normally avoid red and green cones, and prefer ultraviolet over blue cones. Upon ablation of the major (ultraviolet) input, H3 HCs do not immediately increase connectivity with other cone types. Instead, H3 dendrites retract and re-extend to contact new ultraviolet cones. But, if regeneration is delayed or absent, blue-cone synaptogenesis increases and ectopic synapses are made with red and green cones. Thus, cues directing synapse specificity can be maintained following input loss, but only within a limited time period. Further, we postulate that signals from the major input that shape the H3 HC's wiring pattern during development persist to restrict miswiring after damage

The association of hydrogen with nanometre bubbles of helium implanted into zirconium

Electron energy-loss spectroscopy (EELS) is used to investigate the association of hydrogen with helium bubbles in zirconium. Conventional EELS data yield a signal at 13.5 eV (similar to the hydrogen K-edge, 13 eV), which is spatially distributed around the peripheries of bubbles and may correlate with the concentration of hydrogen/deuterium in the material. Ultra-high energy resolution EELS yields a signal at 148.6 meV (comparable to a range of ZrH bonds, 130–156 meV) from a region containing bubbles and no visible hydrides. These signals are interpreted in the context of either bubble surface chemisorption or bubble stress field trapping mechanisms

Retinal tissue engineering using mouse retinal progenitor cells and a novel biodegradable, thin-film poly(e-caprolactone) nanowire scaffold

Retinal progenitor cells (RPCs) can be combined with nanostructured polymer scaffolds to generate composite grafts in culture. One strategy for repair of diseased retinal tissue involves implantation of composite grafts of this type in the subretinal space. In the present study, mouse retinal progenitor cells (RPCs) were cultured on laminin-coated novel nanowire poly(e-caprolactone)(PCL) scaffolds, and the survival, differentiation, and migration of these cells into the retina of C57bl/6 and rhodospsin −/− mouse retinal explants and transplant recipients were analyzed. RPCs were cultured on smooth PCL and both short (2.5 μm) and long (27 μm) nanowire PCL scaffolds. Scaffolds with adherent mRPCs were then either co-cultured with, or transplanted to, wild-type and rhodopsin −/− mouse retina. Robust RPC proliferation on each type of PCL scaffold was observed. Immunohistochemistry revealed that RPCs cultured on nanowire scaffolds increased expression of mature bipolar and photoreceptor markers. Reverse transcription polymerase chain reaction revealed down-regulation of several early progenitor markers. PCL-delivered RPCs migrated into the retina of both wild-type and rhodopsin knockout mice. The results provide evidence that RPCs proliferate and express mature retinal proteins in response to interactions with nanowire scaffolds. These composite grafts allow for the migration and differentiation of new cells into normal and degenerated retina

Biochemical Effects of Carbohydrate Supplementation in a Simulated Competition of Short Terrestrial Duathlon

The purpose of the present study was to investigate the biochemical effects of carbohydrate supplementation in a simulated competition of short terrestrial duathlon. Ten duathletes participated in a simulated competition of short terrestrial duathlon 30 minutes after the ingestion of a 6% (30 g/500 ml) maltodextrin solution (MALT) or a placebo (PLA). This solution was also ingested every 15 minutes during the competition (12 g/200 ml); and immediately after the competition (18 g/300 ml). Samples of blood were collected at 3 time points: 1) at rest 1 hour before the beginning of the competition; 2) during the competition (approximately 1 hour and 45 minutes after the 1st collection); 3) immediately after the competition. Blood was analyzed for blood glucose, lactate, insulin and cortisol. Significant differences were observed in relation to blood glucose levels between MALT and PLA in the post-competition phase. There was also a significant difference in the lactate levels observed between MALT and PLA during the competition phase. Similarly, a significant difference in the cortisol concentrations during and after the competition phases (MALT and PLA) were observed. We conclude that maltodextrin supplementation appears to be beneficial during short terrestrial duathlon competition as evidenced by biochemical markers

Efficiency of primary saliva secretion: an analysis of parameter dependence in dynamic single-cell and acinus models, with application to aquaporin knockout studies

Secretion from the salivary glands is driven by osmosis following the establishment of osmotic gradients between the lumen, the cell and the interstitium by active ion transport. We consider a dynamic model of osmotically driven primary saliva secretion and use singular perturbation approaches and scaling assumptions to reduce the model. Our analysis shows that isosmotic secretion is the most efficient secretion regime and that this holds for single isolated cells and for multiple cells assembled into an acinus. For typical parameter variations, we rule out any significant synergistic effect on total water secretion of an acinar arrangement of cells about a single shared lumen. Conditions for the attainment of isosmotic secretion are considered, and we derive an expression for how the concentration gradient between the interstitium and the lumen scales with water- and chloride-transport parameters. Aquaporin knockout studies are interpreted in the context of our analysis and further investigated using simulations of transport efficiency with different membrane water permeabilities. We conclude that recent claims that aquaporin knockout studies can be interpreted as evidence against a simple osmotic mechanism are not supported by our work. Many of the results that we obtain are independent of specific transporter details, and our analysis can be easily extended to apply to models that use other proposed ionic mechanisms of saliva secretion

Evaluation of Two Internalizing Carcinoembryonic Antigen Reporter Genes for Molecular Imaging

PurposeThe objective of this article is to develop internalizing positron emission tomography (PET) reporter genes for tracking genetically modified T cells in vivo.ProceduresThe transmembrane and cytoplasmic domains of the human transferrin receptor (TfR) and CD5 were each fused to the carcinoembryonic (CEA) minigene N-A3 and expressed in Jurkat T cells. Internalization was evaluated by confocal microscopy or by intracellular uptake of ¹²⁵I-labeled anti-CEA scFv-Fc. Reporter gene-transfected Jurkat xenografts in mice were analyzed by immunohistochemistry (IHC) and imaged by PET using ¹²⁴I- or ⁶⁴Cu-scFv-Fc as tracers.ResultsSurface expression of TR(1-99)-NA3 was lower than that of NA3-CD5. Both reporter genes were internalized following binding of the anti-CEA antibody fragment. IHC of tumors showed strong staining of NA3-CD5, whereas TR(1-99)-NA3 stained weakly. Specific targeting of TR(1-99)-NA3 or NA3-CD5 was shown by PET in xenografted mice.ConclusionsThe in vivo imaging studies suggest a potential application of the internalizing form of CEA (N-A3) as a PET reporter gene

The Reproducibility of Blood Acid Base Responses in Male Collegiate Athletes Following Individualised Doses of Sodium Bicarbonate: A Randomised Controlled Crossover Study

Background: Current evidence suggests sodium bicarbonate (NaHCO3) should be ingested based upon the individualised alkalotic peak of either blood pH or bicarbonate (HCO3−) because of large inter-individual variations (10–180 min). If such a strategy is to be practical, the blood analyte response needs to be reproducible. Objective: This study aimed to evaluate the degree of reproducibility of both time to peak (TTP) and absolute change in blood pH, HCO3− and sodium (Na+) following acute NaHCO3 ingestion. Methods: Male participants (n = 15) with backgrounds in rugby, football or sprinting completed six randomised treatments entailing ingestion of two doses of 0.2 g·kg−1 body mass (BM) NaHCO3 (SBC2a and b), two doses of 0.3 g·kg−1 BM NaHCO3 (SBC3a and b) or two control treatments (CON1a and b) on separate days. Blood analysis included pH, HCO3− and Na+ prior to and at regular time points following NaHCO3 ingestion over a 3-h period. Results: HCO3− displayed greater reproducibility than pH in intraclass correlation coefficient (ICC) analysis for both TTP (HCO3− SBC2 r = 0.77, P = 0.003; SBC3 r = 0.94, P < 0.001; pH SBC2 r = 0.62, P = 0.044; SBC3 r = 0.71, P = 0.016) and absolute change (HCO3− SBC2 r = 0.89, P < 0.001; SBC3 r = 0.76, P = 0.008; pH SBC2 r = 0.84, P = 0.001; SBC3 r = 0.62, P = 0.041). Conclusion: Our results indicate that both TTP and absolute change in HCO3− is more reliable than pH. As such, these data provide support for an individualised NaHCO3 ingestion strategy to consistently elicit peak alkalosis before exercise. Future work should utilise an individualised NaHCO3 ingestion strategy based on HCO3− responses and evaluate effects on exercise performance

Optimised Motion Tracking for Positron Emission Tomography Studies of Brain Function in Awake Rats

Positron emission tomography (PET) is a non-invasive molecular imaging technique using positron-emitting radioisotopes to study functional processes within the body. High resolution PET scanners designed for imaging rodents and non-human primates are now commonplace in preclinical research. Brain imaging in this context, with motion compensation, can potentially enhance the usefulness of PET by avoiding confounds due to anaesthetic drugs and enabling freely moving animals to be imaged during normal and evoked behaviours. Due to the frequent and rapid motion exhibited by alert, awake animals, optimal motion correction requires frequently sampled pose information and precise synchronisation of these data with events in the PET coincidence data stream. Motion measurements should also be as accurate as possible to avoid degrading the excellent spatial resolution provided by state-of-the-art scanners. Here we describe and validate methods for optimised motion tracking suited to the correction of motion in awake rats. A hardware based synchronisation approach is used to achieve temporal alignment of tracker and scanner data to within 10 ms. We explored the impact of motion tracker synchronisation error, pose sampling rate, rate of motion, and marker size on motion correction accuracy. With accurate synchronisation (<100 ms error), a sampling rate of >20 Hz, and a small head marker suitable for awake animal studies, excellent motion correction results were obtained in phantom studies with a variety of continuous motion patterns, including realistic rat motion (<5% bias in mean concentration). Feasibility of the approach was also demonstrated in an awake rat study. We conclude that motion tracking parameters needed for effective motion correction in preclinical brain imaging of awake rats are achievable in the laboratory setting. This could broaden the scope of animal experiments currently possible with PET

Retinal repair by transplantation of photoreceptor precursors

Photoreceptor loss causes irreversible blindness in many retinal diseases. Repair of such damage by cell transplantation is one of the most feasible types of central nervous system repair; photoreceptor degeneration initially leaves the inner retinal circuitry intact and new photoreceptors need only make single, short synaptic connections to contribute to the retinotopic map. So far, brain- and retina-derived stem cells transplanted into adult retina have shown little evidence of being able to integrate into the outer nuclear layer and differentiate into new photoreceptors(1-4). Furthermore, there has been no demonstration that transplanted cells form functional synaptic connections with other neurons in the recipient retina or restore visual function. This might be because the mature mammalian retina lacks the ability to accept and incorporate stem cells or to promote photoreceptor differentiation. We hypothesized that committed progenitor or precursor cells at later ontogenetic stages might have a higher probability of success upon transplantation. Here we show that donor cells can integrate into the adult or degenerating retina if they are taken from the developing retina at a time coincident with the peak of rod genesis(5). These transplanted cells integrate, differentiate into rod photoreceptors, form synaptic connections and improve visual function. Furthermore, we use genetically tagged postmitotic rod precursors expressing the transcription factor Nrl (ref. 6) ( neural retina leucine zipper) to show that successfully integrated rod photoreceptors are derived only from immature post-mitotic rod precursors and not from proliferating progenitor or stem cells. These findings define the ontogenetic stage of donor cells for successful rod photoreceptor transplantation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62596/1/nature05161.pd