Relationships among negative life events, physiological reactivity, and health symptomatology

College undergraduates classified as high (n = 25) and low (n = 25) on recent life stress participated in an experiment involving a novel laboratory stressor. Heart rate and pulse arrival time (PAT) were measured during baseline, anticipation, testing, and recovery periods of the experiment. The results did not replicate those obtained by Pardine and Napoli in that high and low life stress subjects did not show differential physiological reactions. In addition, regression analyses failed to demonstrate that physiological reactivity moderated the relationship between life stress and subsequent self-reported psychiatric or physical health symptomatology. The present findings demonstrated neither the stress-buffering effects of physiological reactivity nor a relationship between life stress and reactivity when the latter was conceptualized as an outcome.     

Monoclonal antibodies to rabbit liver cathepsin B

Three stable hybridoma cell lines (AF8, BC11, CE2) have been produced that secrete antibodies specific for cathepsin B. These have been characterized by ELISA, SDS-PAGE immunostaining, immunoprecipitation and immunofluorescent staining. CE2 immunoprecipitated native cathepsin B with retention of enzymic activity, but failed to cross-react with the alkali-denatured enzyme. BC11 bound only to the denatured form of cathepsin B and AF8 cross-reacted with both native and denatured cathepsin B. However, unlike CE2-immunoprecipitated enzyme, activity could be detected only after dissociation of the antigen-AF8 antibody complex. No cross reaction was found with any lysosomal protein includihg the cysteine proteinases, catbepsins H and L.Abbreviations ELISA Enzyme-linked immunoadsorbent assay - EIP Enzyme immunoprecipitation - PAGE polyacrylamide gel electrophoresis - Ep-475 L-trans-epoxysuccinyl-leucylamido (-methyl) butane - Z benzyloxycarbonyl - NMec N-methylcoumarin - PEB phosphate-EDTA-Brij 35 - IAA iodoacetic acid - PBS phosphate-buffered saline - DMEM Dulbecco's Minimal Essential Medium - FITC fluorescein isothiocyanate     

Saccharomyces cerevisiae nuclear fusion requires prior activation by alpha factor.

We have developed a protocol for efficient fusion of spheroplasts of the same mating type. Nuclear fusion in this whole-cell system is also efficient and closely parallels nuclear fusion in heterosexual mating of intact cells. In the spheroplast fusion system, nuclear fusion is dependent on both the KAR1 gene and prior exposure to alpha factor. The major products of nuclear fusion in the spheroplast fusion assay were true diploids that were homozygous at the mating-type locus. An additional 10% of the products were cells of ploidy greater than diploid. The dependence of nuclear fusion on alpha factor treatment could not be replaced by synchronization in G1 by mutations in CDC28 and CDC35 or by prior arrest in stationary phase. These data suggest that nuclear fusion is not a constitutive function of the nucleus, but rather is specifically induced by mating hormone.     

Perception of solid shape from shading

Observers judged the slants and tilts of numerous regions within shaded images of ellipsoid surfaces that varied in shape, orientation, surface reflectance, and direction of illumination. The perceived three-dimensional structure of each surface was calculated from these judgments. Much of the error in observers' responses resulted from a tendency to perceive surfaces whose axes were aligned with the display screen. The presence of specular highlights or cast shadows, in contrast, had no effect on performance. The results of the experiment indicate that several assumption of certain formal models for perception of shape from shading are not psychologically valid. The most notable of these assumptions are that the visual system initially assumes that all surfaces have Lambertian reflectance and that illuminant direction must be known before shape detection can proceed. These assumptions are often accompanied by a third assumption that surface orientation is detected locally, and global shape determined by smoothing over local surface orientation estimates. The present experiment indicates that an alternative approach offered by Koenderink and van Doorn may be more psychologically accurate, as it avoids all three assumptions.Supported in part by the Air Force Office of Scientific Research (AFOSR 82-0148). The research reported in this paper was performed while the first author was a graduate student at the University of Connecticut at Storrs     

Neural coding of difference frequencies in the midbrain of the electric fishEigenmannia: Reading the sense of rotation in an amplitude-phase plane

Eigenmannia is able to discriminate the sign of the difference, Df, between the frequency of a neighbor's electric organ discharge (EOD) and that of its own EOD. This discrimination can be demonstrated at the level of individual neurons of the midbrain. Intracellular and extracellular recordings of such sign-selective cells revealed the following: Units preferring positive Dfs and units preferring negative Dfs were found with equal frequency. The degree of selectivity was also similar for these two classes of neurons. All sign-selective units were sensitive to the magnitude of the frequency difference, i.e. the beat rate. Most units responded best to beat rates in the 4-8 Hz range. Sign-selectivity was observed only when the jamming signal (S2) was presented through electrodes other than those used to deliver the mimic (S1) of the fish's EOD, i.e. only when amplitude modulations were accompanied by modulations of differential phase. Intracellular studies suggest that most sign-selective neurons of the tectum are large, multipolar cells in the stratum album centrale. These cells send projections to the reticular formation, to lamina 9 of the torus semicircularis and to the N. electrosensorius.     

Passive Avoidance Training Increases Fucokinase Activity in Right Forebrain Base of Day-Old Chicks

Fucokinase (EC 2.7.1.52) activity was estimated in supernatants of homogenate from day-old chick forebrain. Enzyme kinetic studies gave a Km of 4.5 X 10(-6) M and Vmax of 3.72 nmol fucose converted into fucose-1-phosphate/mg prot/h. The pH optimum was 7.5. The enzyme is thus considerably more active than was reported for other species and tissues. There were no differences in enzyme activity between the four forebrain regions studied. One hour after chicks were trained on a one-trial passive avoidance learning paradigm, enzyme activity in the right forebrain base increased 14% over control values (p less than 0.02). The 11.3% increase in activity in the left forebrain base and 10.3% increase in the left roof were not statistically significant. The relationship of this change to the increased fucose incorporation into glycoproteins known to occur over a similar time period and the significance of the lateralization of the increase are discussed.     

Plastid number and plastid structural changes associated with tobacco mesophyll protoplast culture and plant regeneration

Mesophyll protoplasts were isolated from Nicotiana tabacum L. cv. Xanthi, and cell-colony formation induced in liquid culture. The plastid changes associated with the morphogenetic sequence from mesophyll protoplast to whole plant were examined. Minor ultrastructural changes in the plastids were evident after 1 d of culture, but by 8 d (four-to-eight-cell stage) the plastids were small, there was much less thylakoid membrane appression, and many prominent plastoglobuli were also present. Plastid-division figures were evident at this point of time and it was common to find plastids clustered around the nucleus. A typical proplastid was the dominant plastid type in the cultured cells from about 11 d until about five weeks when large amyloplasts and pregranal plastids were observed. Normally structured chloroplasts were present in the regenerated plant. There was no plastid division until the four-cell stage, with plastid numbers per cell approximately halving at each cell division, then stabilising around 12 per cell during cell-colony development, a number typical of meristematic cells. Though nucleoids were always present, their numbers in the plastids were reduced by the eight-cell stage.     

Uptake and polar transport of indoleacetic acid in moss rhizoids

In the cucumber ( Cucumis sativus L. cv. Straight Eight) cotyledon expansion assay, cytokinin-stimulated ethylene production was separated from cytokinin-stimulated growth through the use of potassium and calcium salts. Low concentrations of KC1, which dramatically promoted growth induced by cytokinin, inhibited ethylene evolution, while CaCl₂ at a concentration that had no effect on growth, strongly promoted the cytokinin-induced ethylene evolution. In contrast to the growth response, stimulation of ethylene production was not directly related to the presence of potassium or calcium but to their relative concentrations. Concentrations of KCl and CaCl₂ which promoted ethylene evolution singly, strongly inhibited it when mixed together. Low rates of exogenous ethylene had no effect on the growth response. Both the growth and ethylene responses were found to be general cytokinin phenomena. Cotyledon respiration was promoted by KC1, CaCl₂ and cytokinin, but its stimulation was not correlated with either growth or ethylene production. In the presence of KClm cytokinin-induced respiration sharply lowered the content of certain sugars during the large growth response and followed KCl uptake. Analysis of KCl uptake showed that its growth promoting synergism with cytokinin was not due to osmotic effects.     

Characterization and taxonomic status of tick spiroplasmas: a review

Three serologically distinct groups of spiroplasmas have been recovered from ticks. Spiroplasma mirum strains (from rabbit ticks, Haemaphysalis leporispalustris) and Y32 group (VI) spiroplasmas (from Ixodes pacificus) are the only spiroplasmas to have a clear association with these arthropods. Group (VI) spiroplasmas are distinguished by an unusual nonhelical morphology and their capacity to hemadsorb guinea pig erythrocytes. S. mirum strains are unique in their ability to induce cataracts or lethal brain infections in a number of young vertebrates and in their virulence for the chick embryo. The 277F spiroplasma, while initially recovered from a pool of rabbit ticks (H. leporispalustris), is related by certain serological and genetic properties to spiroplasmas in the S. citri complex (serogroup I). These relationships suggest that the 277F spiroplasma may not be a natural inhabitant of the rabbit tick.