The Refinement of Ipsilateral Eye Retinotopic Maps Is Increased by Removing the Dominant Contralateral Eye in Adult Mice

Background: Shortly after eye opening, initially disorganized visual cortex circuitry is rapidly refined to form smooth retinotopic maps. This process asymptotes long before adulthood, but it is unknown whether further refinement is possible. Prior work from our lab has shown that the retinotopic map of the non-dominant ipsilateral eye develops faster when the dominant contralateral eye is removed. We examined whether input from the contralateral eye might also limit the ultimate refinement of the ipsilateral eye retinotopic map in adults. In addition, we examined whether the increased refinement involved the recruitment of adjacent cortical area. Methodology/Principal Findings: By surgically implanting a chronic optical window over visual cortex in mice, we repeatedly measured the degree of retinotopic map refinement using quantitative intrinsic signal optical imaging over four weeks. We removed the contralateral eye and observed that the retinotopic map for the ipsilateral eye was further refined and the maximum magnitude of response increased. However, these changes were not accompanied by an increase in the area of responsive cortex. Conclusions/Significance: Since the retinotopic map was functionally refined to a greater degree without taking over adjacent cortical area, we conclude that input from the contralateral eye limits the normal refinement of visual cortica

Localised enamel hypoplasia of human deciduous canines: genotype or environment?

The document attached has been archived with permission from the Australian Dental Association (9th Jan 2008). An external link to the publisher’s copy is included.A discrete area of defective enamel formation that appears on the labial surface of the crowns of deciduous canine teeth has been described in both recent and prehistoric human population, with reported frequencies varying from 1 to 45 per cent. Suggestions about the aetiology of this localized hypoplasia range from genotypic factors to environmental conditions and systemic effects. The major aims of this study were to describe the frequency of occurrence and pattern of expression of the lesion in Australian Aboriginal and Caucasian ethnic groups, and to clarify the role of genetic factors by examining a sample of twins. The study sample consisted of dental casts of 181 pairs of Australian Caucasian twins, 215 Aborigines and 122 Caucasian singletons, together with 253 extracted deciduous canines. Examination of dental casts and extracted teeth was undertaken under 2X magnification with emphasis being placed upon location and expression of the lesion. The defect was observed in 49 per cent of twins and 44 per cent of Aborigines, but only 36 per cent of singletons. The percentages of affected teeth in each group were: 18 per cent in twins, 17 per cent in Aborigines and 13 per cent in Caucasians. A significant proportion of the defects occurred on the mesial aspect of the labial surface, in the middle area incisocervically, with the majority in the lower jaw. Anumber of significant differences in frequency were observed between groups, sexes, arches and sides. The results confirm some of the findings of previous studies, but also suggest that none of environmental, genetic or systemic factors can be ruled out as being involved in aetiology of the defect. The higher incidence of the lesion occurring on the mesial aspect of the labial surface is suggestive of physical trauma. Also, the vulnerability of the prominent developing mandibular canine, with its thin or missing labial covering of bone, would be expected to lead to higher prevalence of the lesion in the lower jaw. Although not definitive, the results of concordance analyses in twins were suggestive of a possible genetic predisposition in the formation of the lesion. Further research with a greater clinical orientation and emphasis on determing specific aetiological factors within any given environment in different ethnic groups may provide better insight into the ambiguous aetiology of the hypoplastic enamel defect.Sue Taji, Toby Hughes, Jim Rogers, Grant Townsen

BIOHYBRID – Biohybrid templates for peripheral nerve regeneration

[Excerpt] Peripheral nerve injuries represent a major cause for morbidity and disability in affected patients and cause substantial costs for society in a global perspective. It has been estimated that peripheral nerve injuries affect 2.8% of trauma patients,many of whom acquire life-long disability (Noble et al., 1998). With respect to an incidence of nerve injuries of 13.9/100,000 inhabitants per year (Asplund et al., 2009) and the number of inhabitants in the EU (495,000,000 inhabitants in 2007), the number of peripheral nerve injuries requiring repair and reconstruction, excluding nerve injuries by amputations, may be 70,000 annually only in EU countries. Related to peripheral nerve injuries, the costs for society are substantial and consist of direct (costs for surgery, outpatient visits and rehabilitation) and indirect (lost production) costs. Individual median and ulnar nerve injuries in the forearm have total costs of EUR 51,000 and 31,000, respectively, where around 85% of the costs consist of loss of production (Rosberg et al., 2005), still excluding costs for adjusted quality of life ( Eriksson et al., 2011) . Thus, one may estimate that the annual costs only in the EU may be as high as EUR 2.2 billion, indicating that improved treatment strategies for peripheral nerve injuries may not only improve the situation for patients, but may also significantly reduce costs for society. [...](undefined

Tuning of Ranvier node and internode properties in myelinated axons to adjust action potential timing

Action potential timing is fundamental to information processing;however, its determinants are not fully understood. Here we report unexpected structural specializations in the Ranvier nodes and internodes of auditory brainstem axons involved in sound localization. Myelination properties deviated significantly from the traditionally assumed structure. Axons responding best to low-frequency sounds had a larger diameter than high-frequency axons but, surprisingly, shorter internodes. Simulations predicted that this geometry helps to adjust the conduction velocity and timing of action potentials within the circuit. Electrophysiological recordings in vitro and in vivo confirmed higher conduction velocities in low-frequency axons. Moreover, internode length decreased and Ranvier node diameter increased progressively along the distal axon segments, which simulations show was essential to ensure precisely timed depolarization of the giant calyx of Held presynaptic terminal. Thus, individual anatomical parameters of myelinated axons can be tuned to optimize pathways involved in temporal processing

The Presampler for the Forward and Rear Calorimeter in the ZEUS Detector

The ZEUS detector at HERA has been supplemented with a presampler detector in front of the forward and rear calorimeters. It consists of a segmented scintillator array read out with wavelength-shifting fibers. We discuss its desi gn, construction and performance. Test beam data obtained with a prototype presampler and the ZEUS prototype calorimeter demonstrate the main function of this detector, i.e. the correction for the energy lost by an electron interacting in inactive material in front of the calorimeter.Comment: 20 pages including 16 figure

Linking micro‐ and macroevolutionary perspectives to evaluate the role of Quaternary sea‐level oscillations in island diversification

With shifts in island area, isolation, and cycles of island fusion–fission, the role of Quaternary sea‐level oscillations as drivers of diversification is complex and not well understood. Here, we conduct parallel comparisons of population and species divergence between two island areas of equivalent size that have been affected differently by sea‐level oscillations, with the aim to understand the micro‐ and macroevolutionary dynamics associated with sea‐level change. Using genome‐wide datasets for a clade of seven Amphiacusta ground cricket species endemic to the Puerto Rico Bank (PRB), we found consistently deeper interspecific divergences and higher population differentiation across the unfragmented Western PRB, in comparison to the currently fragmented Eastern PRB that has experienced extreme changes in island area and connectivity during the Quaternary. We evaluate alternative hypotheses related to the microevolutionary processes (population splitting, extinction, and merging) that regulate the frequency of completed speciation across the PRB. Our results suggest that under certain combinations of archipelago characteristics and taxon traits, the repeated changes in island area and connectivity may create an opposite effect to the hypothesized “species pump” action of oscillating sea levels. Our study highlights how a microevolutionary perspective can complement current macroecological work on the Quaternary dynamics of island biodiversity.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141544/1/evo13384.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141544/2/evo13384_am.pd

Building sustainable smallholder cooperatives in emerging market economies: findings from a five-year project in Kenya

A comparative study of two smallholder dairy cooperatives in Kenya examines the question: what factors are conducive to producing sustainable smallholder cooperatives that can gain entry into the vertical value chain in liberalized post-colonial economies? The relative weight of income advantage; selective individual incentives and, social capital on maintaining member patronage are assessed within variable environmental constraints and opportunities facing different cooperatives. The methodology includes case study observation of the cooperatives during a five-year period, as well as sample surveys of members and non-members that include indicators of dairy income; reasons why farmers elect to join or not join the cooperative; and assessments of the importance of different services provided by the cooperative. The findings show how the relative weight of specific incentives for cooperative membership can vary from one environment to another within the same nation. The most important finding is that maintaining sustainable smallholder cooperatives within an increasingly competitive environment depends on the ability of managers to create business strategies that are compatible with the cooperative’s environmental constraints but, at the same time, incentivize members’ patronage