University of Colorado Boulder

About: University of Colorado Boulder is a education organization based out in Boulder, Colorado, United States. It is known for research contribution in the topics: Population & Galaxy. The organization has 48794 authors who have published 115151 publications receiving 5387328 citations. The organization is also known as: CU Boulder & UCB.

The molecular architecture of axonemes revealed by cryoelectron tomography.

Abstract: Eukaryotic flagella and cilia are built on a 9 + 2 array of microtubules plus >250 accessory proteins, forming a biological machine called the axoneme. Here we describe the three-dimensional structure of rapidly frozen axonemes from Chlamydomonas and sea urchin sperm, using cryoelectron tomography and image processing to focus on the motor enzyme dynein. Our images suggest a model for the way dynein generates force to slide microtubules. They also reveal two dynein linkers that may provide "hard-wiring" to coordinate motor enzyme action, both circumferentially and along the axoneme. Periodic densities were also observed inside doublet microtubules; these may contribute to doublet stability.

Dynamic Dopamine Modulation in the Basal Ganglia: A Neurocomputational Account of Cognitive Deficits in Medicated and Nonmedicated Parkinsonism

Abstract: Dopamine (DA) depletion in the basal ganglia (BG) of Parkinson's patients gives rise to both frontal-like and implicit learning impairments. Dopaminergic medication alleviates some cognitive deficits but impairs those that depend on intact areas of the BG, apparently due to DA "overdose." These findings are difficult to accommodate with verbal theories of BG/DA function, owing to complexity of system dynamics: DA dynamically modulates function in the BG, which is itself a modulatory system. This article presents a neural network model that instantiates key biological properties and provides insight into the underlying role of DA in the BG during learning and execution of cognitive tasks. Specifically, the BG modulates the execution of "actions" (e.g., motor responses and working memory updating) being considered in different parts of the frontal cortex. Phasic changes in DA, which occur during error feedback, dynamically modulate the BG threshold for facilitating/suppressing a cortical command in response to particular stimuli. Reduced dynamic range of DA explains Parkinson and DA overdose deficits with a single underlying dysfunction, despite overall differences in raw DA levels. Simulated Parkinsonism and medication effects provide a theoretical basis for behavioral data in probabilistic classification and reversal tasks. The model also provides novel testable predictions for neuropsychological and pharmacological studies, and motivates further investigation of BG/DA interactions with the prefrontal cortex in working memory.

Hydrogel properties influence ECM production by chondrocytes photoencapsulated in poly(ethylene glycol) hydrogels.

Abstract: When using hydrogel scaffolds for cartilage tissue engineering, two gel properties are particularly important: the equilibrium water content (q, equilibrium swelling ratio) and the compressive modulus, K. In this work, chondrocytes were photoencapsulated in degrading and nondegrading poly(ethylene glycol)-based hydrogels to assess extracellular matrix (ECM) formation as a function of these gel properties. In nondegrading gels, the glycosaminoglycan (GAG) content was not significantly different in gels when q was varied from 4.2 to 9.3 after 2 and 4 weeks in vitro. However, gels with a q of 9.3 allowed GAGs to diffuse throughout the gels homogenously, but a q < or = 5.2 resulted in localization of GAGs pericellularly. Interestingly, in the moderately crosslinked gels with a K of 360 kPa, an increase in type II collagen synthesis was observed compared with gels with a higher (960 kPa) and lower (30 kPa) K after 4 weeks. With the incorporation of degradable linkages into the network, gel properties with an initially high K (350 kPa) and final high q (7.9) were obtained, which allowed for increased type II collagen synthesis coupled with a homogenous distribution of GAGs. Thus, a critical balance exists between gel swelling, mechanics, and degradation in forming a functional ECM.

9: Integrating Findings: The Meta-Analysis of Research

Abstract: Maccoby and Jacklin's (1974) review of research on the psychology of sex differences encompassed 1,600 works published before 1973. Considering the literature on that topic since 1973, and the fact that many other studies that are not focused specifically on sex differences may contain data on the question, a population of over 5,000 studies on sex differences can be imagined. There are dozens of educational problems on which the research literature is comprised of several hundred articles: ability grouping, reading instruction, programmed learning, instructional television, integration, and so on. Educational research and evaluation is a large and widely scattered enterprise. On problems of importance, it produces literally hundreds of studies in less than five years. The research techniques used, the measurements taken, the types of person studied—all may vary from one st;udy to the next, even though the topic is the same. The research enterprise in education and the social sciences is a rough-hewn, variegated undertaking of huge proportions. Determining what knowledge this enterprise has produced on some question is itself a genuinely important scholarly endeavor. The evolution of style of research integration has been shaped by the size of the research literature. In the 1940s and 1950s, a reviewer contributing to the Review of Educational Research or Psychological Bulletin might find one or two dozen studies on a topic. A narrative, rhetorical integration of so few studies was probably satisfactory. By the late 1960s, the research

Brain-derived neurotrophic factor regulates energy balance downstream of melanocortin-4 receptor

Abstract: The melanocortin-4 receptor (MC4R) is critically involved in regulating energy balance, and obesity has been observed in mice with mutations in the gene for brain-derived neurotrophic factor (BDNF). Here we report that BDNF is expressed at high levels in the ventromedial hypothalamus (VMH) where its expression is regulated by nutritional state and by MC4R signaling. In addition, similar to MC4R mutants, mouse mutants that expresses the BDNF receptor TrkB at a quarter of the normal amount showed hyperphagia and excessive weight gain on higher-fat diets. Furthermore, BDNF infusion into the brain suppressed the hyperphagia and excessive weight gain observed on higher-fat diets in mice with deficient MC4R signaling. These results show that MC4R signaling controls BDNF expression in the VMH and support the hypothesis that BDNF is an important effector through which MC4R signaling controls energy balance.