Metabolic studies in isolated rat liver cells: I. Lipid synthesis

Rat liver cells, isolated by chelate perfusion and extrusion through a tissue press, incorporated labeled acetate into cellular lipids and into lipids released into the suspending medium. Optimal rates of incorporation required supplementation of tris-KCl medium with Mg⁺⁺, Mn⁺⁺, succinate, citrate, nicotinamide, Coenzyme A, NADP and glucose-6-phosphate. The rate of acetate incorporation was markedly altered by changes in incubation media; tris-KCl was the most effective buffer. All the major classes of cellular lipids were labeled. ATP, BSA, inorganic phosphate, Ca⁺⁺, 2,4-dinitrophenol and sodium clofibrate were potent inhibitors of acetate incorporation. When added to the incubation mixture, several hormones altered the rate of acetate incorporation into lipids.     

Trabecular scaffolds created using micro CT guided fused deposition modeling

Free form fabrication and high resolution imaging techniques enable the creation of biomimetic tissue engineering scaffolds. A 3D CAD model of canine trabecular bone was produced via micro CT and exported to a fused deposition modeler, to produce polybutylene terephthalate (PBT) trabeculated scaffolds and four other scaffold groups of varying pore structures. The five scaffold groups were divided into subgroups (n=6) and compression tested at two load rates (49 N/s and 294 N/s). Two groups were soaked in a 25 °C saline solution for 7 days before compression testing. Micro CT was used to compare porosity, connectivity density, and trabecular separation of each scaffold type to a canine trabecular bone sample. At 49 N/s the dry trabecular scaffolds had a compressive stiffness of 4.94±1.19 MPa, similar to the simple linear small pore scaffolds and significantly more stiff (p<0.05) than either of the complex interconnected pore scaffolds. At 294 N/s, the compressive stiffness values for all five groups roughly doubled. Soaking in saline had an insignificant effect on stiffness. The trabecular scaffolds matched bone samples in porosity; however, achieving physiologic connectivity density and trabecular separation will require further refining of scaffold processing.     

Harnessing the sun

NOW IS THE TIME TO PLAN FOR THE integration of signifi cant quantities of solar energy into the electricity grid. Although solar energy constitutes a very small portion of our energy system today, the size of the resource is enormous: The earth receives more energy from the sun in one hour than the global population uses in an entire year. In addition, the solar photovoltaic (PV) industry is growing very rapidly, sustaining an annual growth rate of more than 40% for the last decade. The combination of this rapid growth, falling costs, and a vast technical potential could make solar energy a serious contender for meeting our future energy needs.     

Stimulation of bile acid synthesis by dibutyryl cyclic AMP in isolated rat hepatocytes

Freshly isolated rat hepatocytes were used to examine the effects of dibutyryl cyclic AMP on the incorporation of¹⁴C-acetate and¹⁴C-cholesterol into bile acids. After an initial lag period, both precursors were incorporated into cholic and chenodeoxycholic acids at a linear rate for the subsequent 60 min. An apparent stimulation of bile acid formation from¹⁴C-acetate by dibutyryl cyclic AMP was complicated by the concomitant inhibition of cholesterol synthesis. In experiments with¹⁴C-cholesterol, dibutyryl cyclic AMP (1 mM) increased the labeled cholic and chenodeoxycholic acids in the medium by 83 and 224%, respectively, but cellular levels of labeled bile acids were unchanged. As a result, the nucleotide stimulated the overall incorporation of¹⁴C-cholesterol into cholic acid by 39% and into chenodeoxycholic acid by 123%. The mean ratio of labeled cholic to chenodeoxycholic acid declined from 55∶45 in control cells to 41∶59 in cells incubated with dibutyryl cyclic AMP. The results demonstrate that label incorporation can be used to study the regulation of bile acid synthesis in isolated hepatocytes. We propose that dibutyryl cyclic AMP enhances bile acid production by phosphorylating, and thus stimulating the activity of, cholesterol 7α-hydroxylase, the rate-limiting enzyme in bile acid synthesis.     

Parent comments and instruction during the first four months of supervised driving: An opportunity missed?

The present study examined the nature of the comments and instruction provided by parents during supervised driving. Unlike previous studies which rely on self-report, the data in this study were obtained through direct observation of parents and teens using in-vehicle cameras with audio recording. The cameras were installed in the vehicles of 50 families for the first four months of the learner license stage. The findings show a great deal of conversation takes place while teens are driving with a supervisor, and that much of this conversation concerns driving. Sixty-one percent (61%) of all recorded clips included driving-related conversation. The most common type of comment by parents was instruction about vehicle handling or operation, observed in 53% of those clips with conversation about driving. This was followed by pointing out something about the driving environment (such as when it was clear to enter traffic; 23%), negative comments about the teen's driving (22%), and helping the driver navigate (18%). Other potentially helpful types of instruction, including explanation or insights regarding higher order skills (e.g., hazard anticipation and detection), were noticeably less frequent. Moreover, higher order instruction remained low during the first four months of the learner stage, even as instruction about vehicle handling/operation decreased. These findings suggest parents are not taking full advantage of the opportunity provided by mandatory periods of supervised driving to help their children develop an understanding of important aspects of driving.     

OMP gene deletion results in an alteration in odorant quality perception.

To test the hypothesis that odorant quality perception is altered in olfactory marker protein (OMP)-null mice, we trained and tested adult OMP-null and control mice, using a 5-odorant identification confusion matrix task (animal odorant confusion matrix [AOCM]). On average, control and null mice performed the task at equivalent levels. The composite 5?×?5 response matrix from 40 testing sessions for each subject (both OMP-null and control) was compared with that of every other subject, yielding a dissimilarity matrix of AOCM responses. A multidimensional scaling (MDS) analysis of the dissimilarity data yielded a 4-dimensional solution, with each mouse occupying a point in MDS animal space. Statistical analysis demonstrated significant effects of genotype in determining the location of a mouse in the MDS space. These data suggest, therefore, that compared with that of controls, odorant quality perception is altered in the OMP-null mouse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What Is Conceptual Glue?

Conceptual structures are commonly likened to scientific theories, yet the content and motivation of the theory analogy are rarely discussed. Gregory Murphy and Douglas Medin's The Role of Theories in Conceptual Coherence is a notable exception and has become an authoritative exposition of the utility of the theory analogy. For Murphy and Medin, the theory analogy solves what they call the problem of conceptual coherence or the problem of conceptual glue. I argue that they conflate a number of issues under these rubrics and that in each case either the problem to be solved isn't subject to a general solution or the theory analogy is of little use. The issues I consider are: (1) what makes a concept efficient, useful, and informative, (2) what makes a concept refer to what it does, (3) what makes a set of objects form a single category, and (4) what makes concepts combine in one way rather than another.     

Methods for measuring the temporal characteristics and filter response of electroacoustic impedance instruments

Methods for determining the temporal response of electroacoustic impedance instruments are presented along with sample measurements from one instrument. The conditions under which reflex artifacts may occur are discussed in light of electrical measurements of filter response characteristics and measurements of the "threshold" of the artifact measured from two subjects with no acoustic reflex.     

Chronic varicella-zoster virus epithelial keratitis in patients with acquired immunodeficiency syndrome

OBJECTIVE: To characterize further a chronic epithelial keratitis caused by varicella-zoster virus infection in patients with acquired immunodeficiency syndrome (AIDS). METHODS: Patients with AIDS and chronic epithelial keratitis associated with varicella-zoster virus from 3 institutions were identified. Patient records were reviewed retrospectively for the following data: medical and demographic characteristics, techniques of diagnosis, physical findings, course, response to treatment, and outcome. RESULTS: Sixteen patients were studied. CD4+ T-lymphocyte cell counts were available in 11 patients, with a median of 0.034 x 10(9)/L (range, 0-0.094 x 10(9)/L). Two patients had no history of a zosteriform rash. In the remaining patients, the interval between rash and keratitis ranged from 0 days to 6 years. In all cases, the keratitis was chronic and characterized by gray, elevated, dendriform epithelial lesions that stained variably with fluorescein and rose bengal. The peripheral and midperipheral cornea was most commonly affected, and, in 13 of the 16 patients, the lesions crossed the limbus. Pain was a prominent feature, occurring in 12 of 16 patients. In 9 of 12 patients tested, varicella-zoster virus was identified by culture, direct fluorescent antibody testing, polymerase chain reaction testing, or a combination of these studies, with direct fluorescent antibody testing (6 of 8 positive results) and polymerase chain reaction testing (3 of 3 positive results) appearing to be the most sensitive. Response to antiviral medication was variable. CONCLUSIONS: In patients with AIDS, varicella-zoster virus may cause a chronic infection of the corneal epithelium. The keratitis is characterized by dendriform lesions, prolonged course, and frequently by extreme pain. It can occur without an associated dermatitis.     

The computer science pipeline in urban high schools: access to what? For whom?

Our research was conceived out of a desire to understand why so few underrepresented students of color are learning computer science at the high school level. High school is a critical time for pre-college preparation and for getting on the right "track" for college and future career opportunities. Yet, by college the number of students of color obtaining bachelors degrees in computer science is remarkably small. In this article, we discuss our research on the high school "computer science pipeline." We define the "computer science pipeline" as the curriculum and opportunities available to students to learn computer science within their schools. Considering the tremendous economic and educational advantages, and the professional opportunities, that are available to students who understand computer science, this is a critical time to understand what factors are influencing African-American and Latino/a students' enrollment decisions.