Performance on two fixed-interval schedules in the absence of neocortex in rats.

Rats with complete surgical removal of the neocortex (neodecorticates) were trained, with milk as the reinforcer, on a 40-sec fixed-interval (FI-40) schedule, then on an FI-120, and finally reexposed to the FI-40. Like controls, neodecorticates developed and appropriately adjusted their postreinforcement pauses and response distributions and showed scallop-type responding on the FI-120 and a positive correlation between running rate and the preceding postreinforcement pause on both FI-40 schedules but not on the FI-120. On some variables neodecorticates reached asymptotic levels of performance more slowly than controls. Extended training on the first FI-40 did not differentially affect neodecorticates' performance. The results suggest that neodecorticates retain a functional timing mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Presence of pterin pigments in wings of libytheidae butterflies

A few pterin pigments were discovered in the wings of six of eight libytheid species tested, using thin-layer chromatography with 1 % HC1 in butanol as a solvent. A 10X sample ofLibytheana bachmanii larvata (Strecker) produced xanthopterin, isoxanthopterin, erythropterin, and leucopterin. Leucopterin was absent in the other libytheids tested. Morphology and pterin pigment data from wings suggest a Pieridae ancestry for the Libytheidae from the region of the northern Neotropical realm (including the Greater Antilles).Research Associate in Entomology, Los Angeles County Museum of Natural History.     

A deconvolution technique for improved estimation of rapid changesin ion concentration recorded with ion-selective microelectrodes

In biological preparations, measurements of rapid, stimulus-evoked changes in ion concentration by ion-selective microelectrodes can be distorted by the limited bandwidth of these sensors. Techniques were developed to reconstruct the actual change in ion concentration using deconvolution of the electrode's output signal and the electrode's transfer function. In the vertebrate retina, a knowledge of the actual time course of a light-evoked increase in extracellular K+ concentration was used to provide a rigorous test of a hypothesis regarding the electrical origin of a clinically important component of the electroretinogram.     

Kinetics of trace metal partitioning in model anoxic marine sediments

A model anaerobic sediment consisting of humic acid, clay, ferrous sulfide, sand, and seawater was utilized to study the partitioning of Cu, Cd, Pb, and Zn between different geochemical phases. An extraction scheme was developed that was selective for each geochemical phase. Metals were dosed on one phase separately, and then mixed into the other undosed phrases. The kinetics of partitioning were rapid, regardless of which phase was initially dosed; equilibrium was reached within 2–5 days. The stoichiometry of distribution was also indepencent of the initially dosed phase. The final metal distributions showed that the metal sulfide phase was not necessarily the dominant trace metal sink in anaerobic sediments.     

The morphogenesis of mouse vallate gustatory epithelium and taste buds requires BDNF-dependent taste neurons

Heterotypic coupling, defined as gap-junctional coupling between cells of different classes, may be common among the different types of non-neuronal cells in the central nervous system. Since gap junctions provide a route for the intercellular exchange of signaling molecules, heterotypic coupling may serve to coordinate the activities of many types of "support cells" in the brain. The evidence for heterotypic coupling between astrocytes and oligodendrocytes, astrocytes and retinal Müller glial cells, and astrocytes and ependymal cells is reviewed. The finding that some heterotypic gap junctions are chemically rectifying implies that there is asymmetry between the two sides of these gap junctions, and the connexin composition of heterotypic gap junctions is discussed. Finally, I speculate about the functions of heterotypic gap junctions, including their proposed roles in K+ spatial buffering around axons and in the propagation of intercellular Ca2+ waves between astrocytes and other glial cells.     

Large-Area Direct Hetero-Epitaxial Growth of 1550-nm InGaAsP Multi-Quantum-Well Structures on Patterned Exact-Oriented (001) Silicon Substrates by Metal Organic Chemical Vapor Deposition

We employ a simple two-step growth technique to grow large-area 1550-nm laser structures by direct hetero-epitaxy of III–V compounds on patterned exact-oriented (001) silicon (Si) substrates by metal organic chemical vapor deposition. Densely-packed, highly uniform, flat and millimeter-long indium phosphide (InP) nanowires were grown from Si v-grooves separated by silicon dioxide (SiO₂) stripes with various widths and pitches. Following removal of the SiO₂ patterns, the InP nanowires were coalesced and, subsequently, 1550-nm laser structures were grown in a single overgrowth without performing any polishing for planarization. X-ray diffraction, photoluminescence, atomic force microscopy and transmission electron microscopy analyses were used to characterize the epitaxial material. PIN diodes were fabricated and diode-rectifying behavior was observed.     

Topographic compensation: guidance and directed locomotion of fibroblasts on grooved micromachined substrata in the absence of microtubules

Fibroblasts cultured on grooved substrata align themselves and migrate in the direction of the grooves, a phenomenon called contact guidance. Microtubules have been deemed important for cell polarization, directed locomotion, and contact guidance. Because microtubules were the first cytoskeletal element to align with the grooves when fibroblasts spread on grooved substrata, we investigated the consequences of eliminating the influence of microtubules by seeding fibroblasts onto smooth and grooved micromachined substrata in the presence of colcemid. Fibroblasts were examined by time-lapse cinematography and epifluorescence or confocal microscopy to determine cell shape and orientation and the distribution of cytoskeletal or associated elements including actin filaments, vinculin, intermediate filaments, microtubules, and kinesin. As expected, cells spreading on smooth surfaces in the presence of colcemid did not polarize or locomote. Surprisingly however, by 24 hours, cells spread on grooves in the presence of colcemid were morphologically indistinguishable from controls spread on grooves. Both groups were aligned and polarized with the direction of the grooves and demonstrated directional locomotion along the grooves. In the absence of microtubules, kinesin localized to some of the aligned stress fibers and to leading edges of cells spreading on grooves. The grooved substratum compensated for the microtubule deficiency by organizing and maintaining an aligned actin filament framework. Thus, microtubules are not required to establish or maintain stable, polarized cell shapes or directed locomotion, provided an alternate oriented cytoskeletal component is available.