Showing papers by "University of California, Irvine published in 1970"

Economics of Information and Job Search

Abstract: I. Introduction, 113. — II. A simple model of job search, 115. — III. A more general model of job search, 123. — IV. An adaptive search model, 125.

The ultrastructure of the developing leg ofDrosophila melanogaster.

Abstract: The ultrastructure of the imaginal discs ofDrosophila melanogaster was compared with that of other chitogenous tissues with different developmental capacities, namely, embryonic, larval, pupal and adult epidermis. Attention was paid to features which might be correlated with specific morphogenetic activities. Previous morphological studies of imaginal discs of Diptera were analyzed in detail and a somewhat revised view of imaginal disc structure emerged. The results reveal that the imaginal discs ofD. melanogaster consist of three types of cells: cells of the single layered disc epithelium, adepithelial cells and nerves. Four types of specialized junctions connect the cells of the disc epithelium: zonulae adhaerens, septate desmosomes, gap junctions and cytoplasmic bridges. The junctions are discussed in relation to their possible roles in adhesion and intercellular communication. It was concluded that gap junctions may be a more likely site for the intercellular communication involved in pattern formation than septate desmosomes. Evidence is presented that adepithelial cells are the precursors of imaginal muscles and that some cell lines (atelotypic) are in fact lines of adepithelial cells which can differentiate into muscle.Specific imaginal discs can be easily recognized by their overall morphology, i.e. patterns of folds. However, no ultrastructural features were found which we could correlate with the state of determination of the cells. Most differences in the ultrastructure of different discs at several developmental stages were attributable to different phases of cuticle secretion. The cells of the imaginal disc epithelium are packed with ribosomes but very little rough ER. The amount of rough ER increases rapidly at puparium formation. Cuticulin is recognizable 4-6 hours after puparium formation. Six hours after puparium formation, the cells of the disc epithelium are secreting the epicuticle of the pupa. As the imaginal disc of a leg everts from a folded sac to the tubular pupal leg, the cells of the disc epithelium change from tall columnar to cuboidal. A loss of microtubules in the long axis of the columnar cells accompanies this change. Prepupal morphogenesis of the leg appears to be caused by the change in cell shape. Evidence is presented which is incompatible with previous explanations of the mechanism of eversion of imaginal discs.There is some turnover of the cells of the disc epithelium as evidenced by autophagy and the occasional heterophagy of a dead neighbor. However this does not appear to be an important factor in the morphogenesis of discs. Plant peroxidase which was used as a tracer of proteins in the blood was taken up from the hemolymph by the disc epithelium. Imaginal disc cells contain many lipid droplets which coalesce and are replaced by glycogen during the prepupal period.

Mass culture of hydra: an improved method and its application to other aquatic invertebrates

Abstract: Virtually unlimited numbers of hydra can be grown under precise conditions in the laboratory with relative ease. Artemia cysts must be treated to remove gross contamination before hatching the nauplii to be used as the food of hydra. Large volumes of a variety of chemically defined culture solutions should be prepared. A particular regimen of animal care especially devised for aquatic invertebrates must be adhered to. General requirements for, and the advantages of, laboratory cultivation of aquatic invertebrates are discussed.

An Improved Single-disk Method for Testing the Antibiotic Susceptibility of Rapidly-growing Pathogens

Abstract: The Kirby-Bauer method of disk antibiotic-susceptibility tests is well standardized and accurate, but the method for standardizing the inoculum is rather time-consuming and is often impractical for routine use. This report describes a somewhat more practical, efficient method for inoculating the test plates. A calibrated inoculum obtained from a small volume of broth culture is spread over the agar surface with a seeded agar overlay. Comparison of this new method with the standardized Kirby-Bauer method shows that the zones of inhibition are nearly identical in size, and thus the same zone standards for interpretation can be applied to both methods. Because the inhibitory zone edges were better defined on plates inoculated with the agar-overlay method, there was a slightly better correlation between zone diameters and minimal inhibitory concentrations, especially with bacteriostatic drugs. Tests with swarming Proteus mirabilis were much more satisfactory with the agar-overlay method. The new technic is recommended as a routine method for testing the common Enterobacteriaceae, P. aeruginosa and S. aureus .

Identification of ten genes that control ribosome formation in yeast.

Abstract: Twenty-three temperature-sensitive mutants of Saccharomyces cerevisiae, all of which undergo a rapid cessation of net RNA accumulation following a shift from the permissive (23°) to the restrictive temperature (36°), have been characterized. Genetic studies demonstrate that these mutants belong to ten different complementation groups and that, in most cases, their properties are the result of a single, recessive mutation in a nuclear gene. Although the mutants were isolated for heat sensitivity, mutants from 2 of the complementation groups are cold sensitive (at 13°) as well. The mutants continue to synthesize protein, including an enzyme, alkaline phosphatase, for two to four hours following a shift from 23° to 36°, suggesting that they are capable of messenger RNA synthesis and the translation of messenger RNA with fidelity at the restrictive temperature. The small amount of RNA that is synthesized in these mutants at the restrictive temperature has been examined on sucrose gradients and by acrylmide gel electrophoresis; in addition, the RNA components in polyribosomes have been fractionated by a new technique that separates messenger RNA from ribosomal RNA. As a result of these analyses we conclude that these mutants are strongly inhibited in the accumulation of 5S, 7S, 17S, and 25S RNA components but are only slight if at all inhibited in the synthesis of messenger RNA and 4S RNA. The results reported here define ten genes, designated rna 2 through rna 11, that play an essential role in the formation or maturation of ribosomes in yeast.

Number Coding in Association Cortex of the Cat

Abstract: In electrophysiological investigations of single neurons in cortical association response areas of the cat, cells have been encountered that appear to code the property of number. In a sequence of stimulus presentations, these cells characteristically discharge to a particular numbered stimulus in the series. This effect is independent of stimulus modality, intensity, and interstimulus interval; thus, the cells seem to be responding to the number of stimulus presentations.

Role of radiotherapy in cancer of the larynx as related to the TNM system of staging. A review

Abstract: An account of the results of treatment of cancer of the larynx is given employing the clinical staging presented by a committee member of the International Union Against Cancer. This system of staging may be valuable and may permit a better comparison of results and selection of treatment methods. It is only by constant comparison and review of the various modes of treatment that we can hope to achieve better results. Surgery and radiotherapy are complementary. External radiotherapy is the recommended choice of primary therapy in the early (T1T2N0M0) lesions. In patients with moderately advanced tumors (T3N0M0), 3 different plans of therapy may be offered: a. planned preoperative radiation therapy followed by total laryngectomy and radical neck dissection; b. initial radiotherapy followed by total laryngectomy and elective neck dissection in selective cases only, i.e., in patients where there is evidence of residual tumor in the larynx; c. initial total laryngectomy and elective radical neck dissection with or without postoperative radiation therapy. Some authors claim good results with plan a; others prefer plan b because a greater number of surviving patients retain their voice. Plan c is losing in popularity but is still recommended by some authors in supraglottic cancer. As the tumor extends to other regions with fixation or outside the larynx (T4N0M0), or metastasizes to cervical nodes (N1-3), total laryngectomy or laryngopharyngectomy with radical neck dissection may give the best chance for long time survival. Radiotherapy is an important adjuvant and is probably most effective when given preoperatively.

Excitation and axonal flow: autoradiographic study on motoneurons intracellularly injected with a 3H-amino acid.

Abstract: Tritiated glycine has been injected intracellularly into cat motoneurons by means of cross barrel iontophoresis through microelectrodes. The amino acid is incorporated into proteins in the cell body and the synthesized radioactive proteins have been localized by autoradiography. The single-cell-injection technique has several advantages over the usual intraperitoneal, intravenous or intrathecal injection, e.g. distribution of the radiochemical is strictly confined to the injected neuron; the amount of injected substance can be estimated; it is easy to investigate simultaneously electrophysiological and morphological characteristics of a defined neuron. Since the injected cell body releases radioactive proteins into the axon, the transport of these substances can be studied under various conditions. In this study the influence of antidromic stimulation has been studied. Stimulated motoneurons demonstrate higher radioactivity in their cell bodies than unstimulated ones, reflecting an increased protein synthesis. The differences are even more pronounced in the axons of stimulated cells when compared with unstimulated ones. A significant, higher amount of radioactive material — up to 100% increase as demonstrated by silver grain counting — can be seen in the axons of stimulated neurons. Although considerable differences seem to exist for the quantity of the exported proteins no significant differences have been detected for the velocity of transportation. In axons of stimulated and unstimulated neurons proteins advance toward the periphery at the same rate.

The population biology of annual grassland hemiparasites. i. the host environment

Abstract: Two traits are common to all hemiparasitic plants: the ability to form root grafts with other plants via haustoria, and the presence of functional chlorophyll. Beyond this, further generalizations are not easily made. Hemiparasites grow as annuals, biennials, perennials, woody shrubs, vines and trees in a variety of habitats ranging from equatorial to polar latitudes. The functional nature of each kind of host-parasite relationship will be related to many parameters, among which life form, physical habitat, breeding system, and host characteristics are important. In this continuing series, annual grassland hemiparasites have been singled out for study because of the interesting characteristics of the grassland environment. In California, annual grasslands range from coastal bluffs to hot inland valleys and montane foothills. Most of the species making up this community are alien; it is a new flora not more than 200 years old (Wells, 1964). Species diversity is usually high within and between hemiparasite sites (Thurman, 1966), however, dominance diversity is usually low within a site during any one year (McNaughton, 1968; Heady, 1958) and there can be great variability in the dominant species from year to year. Members of the genus Orthocarpus (Scrophulariaceae) are the most common hemiparasites in California grasslands. These herbaceous flowering plants gain water, minerals, and organic compounds from host plants via haustorial root connections. Haustoria are small, hemispherical, lateral swellings on the parasite roots which penetrate the host root cortex and connect the two vascular systems. Under laboratory conditions of ample water and nutrients, a majority of individuals in most population samples can complete their life cycles without depending upon a host, though they may remain quite small in some species. In nature seedlings may be free-living for up to several weeks in a continually moist soil. Eventually, most population members indiscriminately form haustoria with one or more adjacent plants, and the increased supply of water, minerals, and organic compounds produces the rapid growth phase characteristic of annual hemiparasites. Orthocarpus species and most of their hosts are annuals; consequently, the members of each Orthocarpus population must annually reestablish a successful relationship with one or more individuals from among many potential hosts. Dispersal is normally independent of host plants and their seeds, but exceptions have been noted (Atsatt, 1965). Germination as well is not dependent upon the presence of host plants as has been shown for the genus Striga (Saunders, 1933). Consequently, the annual reassociation of Orthocarpus individuals and their hosts is a random process. The purpose of this continuing investigation is to describe the functional nature of this facultative heterotrophism. We wish to reveal the selective pressures operating upon annual hemiparasite populations and the specific responses to these pressures.

Quantification of the rem sleep cycle as a rhythm

Abstract: The goal of this study was to develop an objective quantitative method for representing the temporal organization of sleep in terms of the period and rhythmicity of REM sleep occurrences. Data on normative human sleep, already scored for stage REM and not stage REM, were subjected to a “binary autocorrelation.” The mean period over 92 nights of sleep for 10 Ss was 101.5 min and quite stable. Data is also presented on variability of the rhythm in terms of an “index of rhythmicity.” Measures of temporal organization may prove to be as significant for sleep research as amount of the various sleep stages.

P-Chlorophenylalanine Methyl Ester: An Aphrodisiac?

Abstract: P-Chlorophenylalanine methyl ester and the ester plus pargyline have been reported to facilitate sexual mounting behavior in animals, but these studies have shown only a facilitation of homosexual mounting. The present study indicates that these agents do not enhance the probability or frequency of heterosexual interactions in rats.

The effect of cycloheximide upon polyribosome stability in two yeast mutants defective respectively in the initiation of polypeptide chains and in messenger RNA synthesis

Abstract: The effect of cycloheximide upon protein synthesis, RNA metabolism, and polyribosome stability was investigated in the parent and in two temperature-sensitive mutant yeast strains defective respectively in the initiation of polypeptide chains and in messenger RNA synthesis. Cycloheximide at high concentrations (100 μg/ml) severely inhibits but does not completely stop protein synthesis (Fig. 1); the incorporation of 14C-amino acids into polyribosome-associated nascent polypeptide chains continues at a slow but measurable rate (Figs. 2 and 3). Polyribosome structures are stable in the parent strain at 36° whether or not cycloheximide is present (Fig. 5). However, in Mutant ts- 136, a mutant defective in messenger as well as in stable RNA production, polyribosomes decay at the restrictive temperature (36° C) at the same rate whether or not cycloheximide is present (Fig. 5). Thus the maintenance of polyribosome structures is dependent upon the continued synthesis of messenger RNA even under conditions of extremely slow polypeptide chain elongation. In mutant ts- 187, a mutant defective in the initiation of polypeptide chains, all of the polyribosomes decay to monoribosomes within 2 minutes after a shift to the restrictive temperature; cycloheximide completely prevents this decay demonstrating that this mutant is capable of continued messenger RNA synthesis at 36° C. Consistent with these observations is the fact that a newly synthesized heterogeneously sedimenting RNA fraction continues to enter polyribosomes in the presence of cycloheximide whereas the entrance of newly synthesized ribosomal RNA is severely inhibited (Figs. 7, 8, 9). The decay or lack of decay of polyribosomes at the restrictive temperature is, therefore, a rapid and discriminating test for the analysis of mutants defective in macromolecule synthesis. Mutants which exhibit a decay of polyribosomes in the presence of cycloheximide are likely to be defective directly or indirectly in the synthesis of messenger RNA whereas mutants in which decay is prevented or slowed by cycloheximide are likely to be defective in some factor required for the association of ribosomes and messenger RNA.

Early use of xenografts as a biologic dressing in burn trauma.

Abstract: Summary Frozen-irradiated xenografts and fresh refrigerated xenografts in antibiotic solution placed on burn defects in dogs showed no significant histologic difference in the granulating beds. Vascularization of the pigskin was not observed. Heterografts were applied to 150 patients with second and third degree burns as an immediate dressing. The grafts were covered with a layer of Sulfamylon-acetate gauze. Xenografts have been an effective temporary dressing. They have provided a marked reduction in pain, particularly over second degree burns. Clinically, early xenograft application reduced sepsis and hastened eschar separation. Eschar treated with pigskin remained pliable and allowed the patient a greater degree of joint mobility. Less difficulty in maintaining core temperature was noted. We believe that the early use of xenografts may decrease morbidity and that continued investigation is warranted.

The coelomic elements of sea urchins (Strongylocentrotus)

Abstract: The four coelomocyte classes of the red sea urchin,Strongylocentrotus franciscanus, described by light-microscope studies, are confirmed and the fine structure described. Material examined included fresh, non-aggregated cells; partially aggregated ones that had been heldin vitro up to four days; and aggregated cells heldin vitro for 40 days. Leukocytes from youngin-vitro preparations differed from most fresh leukocytes by having enlarged dense nucleoli and enlarged rough endoplasmic reticulum, which was often filled with secretion, and sometimes connected to the perinuclear cisterna. Leukocytes held 40 daysin vitro were mainly plasmodial. Unlike cells held a limited timein vitro, the 40-day leukocytes had nuclei much like those in fresh preparations.

Hypnotic Susceptibility increased by EEG Alpha Training

Abstract: MORE than a decade of research on hypnotic susceptibility and its correlates has demonstrated repeatedly the stability of the phenomenon, its independence from standard tests of suggestibility and of personality, and its relative imperviousness to most efforts to manipulate it, in particular to increase it1,2. Several recent studies have shown, however, that hypnotic susceptibility is significantly correlated with brain wave activity, including the duration of electroencephalogram (EEG) alpha rhythms3–5. Other studies have shown that the production of alpha rhythms can be systematically increased by teaching subjects to accommodate their subjective mental states to sustained auditory feedback signals which indicate the continuous manifestation of this rhythm6,7.