Showing papers by "University of California, Irvine published in 1972"

Regeneration of Hydra from Reaggregated Cells

Abstract: Separated cells of hydra reaggregate and develop into normal animals. The regeneration of serially grafted aggregates derived from different parts of hydra tissue demonstrates that the polarity of morphogenesis in hydra is the result of the cellular composition of the tissue, not cellular orientation.

Cell cycle kinetics and development of Hydra attenuata. I. Epithelial cells.

Abstract: The cell cycle parameters of epithelial cells of Hydra attenuata are described. Specifically the rate of proliferation and the fraction of proliferating cells have been determined under conditions of defined growth rate. Techniques involved standard methods of cell cycle analysis using histological and tissue maceration preparations; pulse-chase and continuous labelling with [ 3 H]thymidine followed by autoradiographic analysis, and microspectrophotometric determination of nuclear DNA content in single cells. The results indicate that more than 90% of hydra epithelial cells are actively proliferating with a cell cycle duration about equal to the tissue doubling time. In well fed hydra the average cell cycle is about 3 days long. S period is 12-15 h, G 1 0-1 h, and mitosis 1.5 h. Most of the cell cycle consists of a long G 2 period of variable duration (24-72 h). The results provide no evidence for a subpopulation of rapidly proliferating cells as predicted by ‘growth zone’ models of hydra morphogenesis. The results also indicate that the population of epithelial cells is self-sustaining requiring no input by differentiation from other cell types. The long and variable G 2 period means that DNA synthesis and the following cell division are effectively uncoupled such that inhibitors of DNA synthesis may not stop epithelial cell division. The variable nature of the G 2 period suggests it as a possible point of control of hydra growth.

Isolation and structural studies on synaptic complexes from rat brain.

Abstract: A fraction enriched in synaptic complexes has been isolated from rat brain. The major structural elements of synaptic complexes after isolation are a sector of pre- and postsynaptic plasma membranes joined together by a synaptic cleft and a postsynaptic density (PSD) located on the inner surface of the postsynaptic membrane. On its outer surface, the postsynaptic membrane has a series of projections which extend about halfway into the cleft and which occur along the entire length of the PSD. Proteolytic enzymes at high concentrations remove the PSD and open the synaptic cleft; at low concentrations the PSD is selectively destroyed. By contrast, the structural integrity of the PSD is resistant to treatment with NaCl, EGTA, and low concentrations of urea. Pre- and postsynaptic membranes also remain joined by the synaptic cleft after NaCl, EGTA, or mild urea treatment. High concentrations of urea cause the partial dissociation of the PSD. We conclude that polypeptides are probably one of the major components of the PSD and that the structural integrity of the PSD depends on polypeptides because disruption of the covalent or hydrophobic bonding of these polypeptides leads to a progressive loss of PSD structure.

The complementarity problem

Abstract: For a given mapF from then-dimensional Euclidean spaceE n into itself, we consider the problem of finding a nonnegative vectorx inE n whose imageF(x) is also nonnegative and such that the two vectors are orthogonal This problem is refered to in the literature as thecomplemcntarity problcm The importance of the complementarity problem lies in the fact that it is the unifying mathematical form for a wide range of problems arising in different fields such as mathematical programming, game theory, economics, mechanics, etc ⋯ This paper is concerned mainly with the question of the existence of a solution Several existence theorems are given under various conditions on the mapF These theorems cover the cases whenF is nonlinear nondifferentiable, nonlinear but differentiable, and affine

Theory of Surface Magnetoplasmons in Semiconductors

Abstract: A theory of surface magnetoplasmons in semiconductors is developed with the inclusion of retardation for the geometry in which the magnetic field is parallel to the surface and the direction of propagation is perpendicular to the magnetic field. If the background dielectric constant ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}$ lies in a suitable range for a given value of the magnetic field, gaps appear in the dispersion relation for the surface magnetoplasmons. The possible experimental observation of these gaps is discussed.

Theory of Inelastic Scattering of Slow Electrons by Long-Wavelength Surface Optical Phonons

Abstract: The purpose of this paper is to present a quantum-mechanical theory of the inelastic scattering of slow electrons by long-wavelength surface optical phonons for simple models of an ionic crystal and for a nonionic crystal such as silicon. It is argued that a quantum-mechanical approach is necessary for this problem. However, the expression we obtain for the one-phonon cross section is found to be identical to the one that follows from the earlier classical theory of Lucas and co-workers, provided one replaces their parameter ${P}_{0}$ by the quantum-mechanical reflection coefficient for specular reflection. The angular distribution of the scattered electrons and the energy dependence of the one-phonon cross section are discussed for the case of ZnO and silicon, where the surface optical modes have a very different character. For the surface mode in silicon, we define a dipole-moment effective charge, which is nonzero by virtue of the absence of inversion symmetry in the surface region. A quantitative estimate of the magnitude of this parameter is extracted from the data of Ibach.

Theta Rhythm: A Temporal Correlate of Memory Storage Processes in the Rat

Abstract: We examined the amount of theta rhythm (4 to 9 hertz) in cortical electroencephalograms of rats for 30 minutes after training in one-trial tasks. Some animals received electroconvulsive shock after training. The amount of theta in the electroencephalogram after training was positively correlated with the degree of subsequent retention of a footshock, whether animals had received electroconvulsive shock or not.

Minimum-Perimeter Polygons of Digitized Silhouettes

Abstract: The minimum-perimeter polygon of a silhouette has been shown to be a means for recognizing convex silhouettes and for smoothing the effects of digitization in silhouettes. We describe a new method of computing the minimum-perimeter polygon (MPP) of any digitized silhouette satisfying certain constraints of connectedness and smoothness, and establish the underlying theory. Such a digitized silhouette is called a ``regular complex,'' in accordance with the usage in piecewise linear topology. The method makes use of the concept of a stretched string constrained to lie in the cellular boundary of the digitized silhouette. We show that, by properly marking the virtual as well as the real vertices of an MPP, the MPP can serve as a precise representation of any regular complex, and that this representation is often an economical one.

Vibrational Edge Modes in Finite Crystals

Abstract: In addition to surfaces, real crystals have edges, corners, and steps. In this paper we present a theory of long-wavelength acoustic phonons localized at an edge of a cubic elastic medium bounded by two (100) faces. The stress-free boundary conditions on the faces of the semi-infinite medium meeting at the edge are incorporated into the equations of motion of the medium by the device of assuming position-dependent elastic constants. The equations of motion of the medium are solved by expanding each displacement component in a double series of Laguerre functions, which are orthonormal and complete in the region ${x}_{1}\ensuremath{\ge}0$, ${x}_{2}\ensuremath{\ge}0$. The edge modes obtained are wavelike parallel to the edge and decay rapidly with increasing distance into the medium from the edge. For the particular case of an elastically isotropic medium for which the Lam\'e constants $\ensuremath{\lambda}$ and $\ensuremath{\mu}$ are equal, the speed of propagation of the lowest-frequency edge mode is $0.9013{c}_{t}$, where ${c}_{t}$ is the speed of sound of bulk transverse modes and is lower than that of Rayleigh waves, which is $0.9194{c}_{t}$. A variational principle for the speeds of edge modes is also presented.

Distribution of creatine, guanidinoacetate and the enzymes for their biosynthesis in the animal kingdom. Implications for phylogeny

Abstract: 1. The distribution of creatine and the creatine-synthesizing enzymes in the animal kingdom has been investigated. Creatine was found in tissues of all vertebrates examined, and in various invertebrates from phyla Annelida, Echinodermata, Hemichordata and Chordata, subphylum Cephalochordata. The activities of the creatine-synthesizing enzymes, arginine–glycine transamidinase and guanidinoacetate methylpherase, were not detected in the hagfish or in any of the invertebrates, including those in which creatine was found, with the exception that transamidinase activities were detected in the amphioxus and salt water clam; however, these activities are considered to be artifacts for reasons mentioned in the text. Additional evidence that the hagfish and various creatine-containing invertebrates could not synthesize creatine was the observation that these animals did not convert one or the other of the likely precursors of creatine (arginine and glycine) into creatine, in vivo. Further, the inability of these animals to synthesize creatine is correlated with the observations that all animals tested were able to abstract creatine from their aqueous environment. 2. The activities of the creatine-synthesizing enzymes were detected in the sea lamprey and in all but a few of the other vertebrates examined. Neither activity could be detected in the sharks and rays (cartilaginous fish), buffalo fish (bony fish) or the snapping turtle. Transamidinase or guanidinoacetate methylpherase activity could not be found in the salamander or garter snake, respectively. 3. The results obtained with the lamprey are in direct contrast with those obtained with the hagfish (both subphylum Agnatha, class Cyclostomata). The lamprey had the ability to synthesize creatine and did not abstract creatine from lake water. The hagfish did not have any apparent ability to synthesize creatine and did abstract creatine from sea water. The present report thus supports the theory that the myxinoid (hagfish) and petromyzoid (lamprey) agnathans are only distantly related. 4. The lack of creatine-synthesizing enzyme activities in the cartilaginous fishes may have phylogenetic significance, but may also be explained by the availability of creatine in the diet of these animals. The lack of one or both enzyme activities in vertebrates other than the hagfish and the cartilaginous fish is suggested to be the result of creatine in the diet.

Isolation and Measurement of Pancreatic Amylase in Human Serum and Urine

Abstract: We describe a sensitive quantitative procedure for separating isoamylases in human serum, urine, and tissue homogenates. Two components have been discerned with chromatographic characteristics resembling those of pancreatic and salivary amylases, respectively. Several lines of evidence—derived from studies in normal subjects, pancreatectomized patients, and patients with acute pancreatitis—indicate that the pancreas is probably the source of the component in serum and urine that exhibits characteristics of pancreatic amylase. The source of the component resembling salivary amylase has not yet been fully defined. Isoamylase analysis of extracts of fallopian tube and liver revealed two amylase components with chromatographic properties similar to pancreatic and salivary amylases, respectively.

Mercury Concentrations in Museum Specimens of Tuna and Swordfish

Abstract: The mercury levels of museum specimens of seven tuna caught 62 to 93 years ago and a swordfish caught 25 years ago have been determined by instrumental neutron activation analysis. These levels are in the same range as those found in specimens caught recently.

Electrostatic Edge Modes in a Dielectric Wedge

Abstract: The dispersion relations are obtained for electrostatic modes localized in the vicinity of the edge of a dielectric wedge formed by the intersection of two semi-infinite planes making an interior angle of $2\ensuremath{\alpha}$. The dielectric constant of the medium is assumed to be isotropic. The resulting modes can be classifed as even or odd under reflection in the plane bisecting the wedge. Their frequencies are functions of one continuously varying quantum number. The general results obtained are specialized to yield the dispersion relations for edge optical modes and edge plasmons. Properties of dielectric edge modes are compared and contrasted with corresponding properties of surface modes.

Energy metabolism and evaporative water loss in the California ground squirrel

Abstract: Rates of metabolism and evaporative water loss were investigated inSpermophilus beecheyi. Special attention was paid to the influence of the micro-climate of the animal's burrow on these parameters. Metabolic rate as measured by oxygen consumption is 25 per cent below that predicted from body weight. A new hypothesis is advanced to account for this commonly observed phenomenon in fossorial rodents. In summer, there is an overlap of the region of thermal neutrality and temperature in the animal's burrow but winter burrow temperatures are below thermal neutrality. Evaporative cooling accounts for approximately 20 per cent of the total heat loss in thermal neutrality and at low humidity. Minimization of this heat loss avenue by high humidities did not result in an increase of body temperature or metabolic rate, therefore the dimension of the thermal neutral zone is independent of ambient humidity. By indirect means, evaporative water loss was partitioned into 37 per cent from cutaneous sources and 63 per cent from pulmonary sources. A direct relationship was found between ambient water vapor pressure and evaporative water loss. The relationship between body and ambient temperature was investigated by telemetry. At lower temperatures, the former is maintained at constant levels, but hyperthermia develops above 30 ° C.

Sexual behavior in continuously cycling rats

Abstract: The succession of vaginal and behavioral changes was followed throughout the estrous cycle of ten continuously cycling female rats Interruption of cycles by pregnancy or pseudopregnancy was prevented by the use of the vaginal mask The behavioral indices were Lordosis Quotient, a measure of sexual responsiveness, and Rejection Quotient, a measure of tolerance by the female of mounting by the male Before the onset of lordosis, which took place during proestrus, females rejected males on many attempted mounts, although rejection decreased rapidly with rise in frequency of lordosis Full receptivity was displayed for 6 to 9 hours, but females began to reject the males while still displaying high levels of lordosis The total period of 19 hours over which lordosis is shown was divided into pre-heat, heat, and post-heat periods

Proline metabolism in Leishmania donovani promastigotes.

Abstract: SYNOPSIS Oxygen uptake of Leishmania donovani culture promastigotes was stimulated by L-proline and to a lesser extent by L-glutamate and L-arginine. L-proline reversed partially KCN-induced inhibition of respiration and completely, inhibition caused by malonate. Labeled proline, glutamate, alanine, and arginine were detected by thin layer chromatography in the free amino acid pool from cells incubated with L-proline-14C. Labeled tricarboxylic acid cycle intermediates, α-ketoglutarate, succinate, fumarate, malate, and oxaloacetate, also were found by this method in extracts from organisms incubated with L-proline-14C which contained also pyruvate. Cells incubated with malic acid-14C contained labeled alanine, glutamate, and arginine. Labeled L-proline was not found in promastigotes incubated with D-glucose-14C, although arginine, glutamate, and alanine were detected in extracts from these organisms. Indirect evidence for the presence of a NADP-dependent malic enzyme was obtained by Ochoa's method. All results suggest the presence of a proline-glutamate interconversion pathway in L. donovani promastigote culture forms.

Photoexcitation of Quasiparticles in Nonequilibrium Superconductors

Abstract: We report measurements on superconducting tunnel junctions illuminated with optical radiation, which confirm the model of nonequilibrium superconductors proposed by Owen and Scalapino. Measurements of the chemical potential ${\ensuremath{\mu}}^{*}$ for quasiparticle excitations and of the temperature dependence of the quasiparticle recombination time are presented.

Temporal Changes in Populations and Species Diversity in a California Rodent Community

Abstract: Population trends and their proximate effects on the species diversity of a rodent community were examined on a stand of coastal sage scrub in southern California, from the summer of 1968 to the autumn of 1969. The rodents comprising the fauna were Dipodomys agilis agilis, Perognathus fallax fallax, P. longimembris pacificus, Peromyscus eremicus fraterculus, P. maniculatus gambellii, P. californicns insignis, Reithrodontomys megalotis longicaudus, Neotoma lepida intermedia , and Neotoma fuscipes macrotis . Live-trapping was done at monthly intervals for a period of 15 months. Individuals collected were examined for reproductive condition, marked and released. Periods of population increase, decrease, or stability were accompanied by variable patterns of survivorship and addition of residents and transients. During periods of population decrease the rodents exhibited reduced survival with the exception of P. maniculatus , which showed increased survival. For the increase phase of the rodent populations, survival was equal to, or greater than, mean survival for the entire period of study; however, the addition of new residents and transients was often high ( P. maniculatus and N. lepida ). The temporal changes in these population components led to asynchronous fluctuations in population densities of the rodents, which yielded the major changes in species diversity. This is further emphasized by examining the correlation of population numbers between the six commonest species. Only six of the 15 pair-wise correlations were significant. Rodent species diversity was measured by employing Brillouin's information formula. Of the three components of diversity—relative abundance, species number, and sample size—a significant relationship was found between species richness and diversity ( r = +0.910), and sample size and diversity ( r = +0.566). Although uncorrelated with diversity, evenness was important, as some of the diversity changes between months were due to shifts in evenness and not changes in species numbers. The fluctuations in the relative abundance of species and the variable presence of the rarer species led to the temporal fluctuations in species diversity.