Fixed interval and fixed time treadle pressing in the pigeon: A comparison with FI and FT keypecking

Experiment I used non-naive pigeons having previously performed on both keypecking and treadlepressing Fixed Interval schedules. In condition IT, treadlepressing was reinforced on successive Fixed Interval 60 seconds, Fixed Time 60 seconds and Fixed Interval 60 seconds schedules. Subsequently (condition IK), the same subjects pecked a key on an identical schedule sequence (FI60, FT60, FI60). In Experiment II, separate groups of naïve subjects were assigned either to treadlepressing (condition IIT) or keypecking (condition IIK) and to the same schedule sequence (FI60, FT60, FI60). Treadle pressing and keypecking decreased greatly in Fixed Time schedules. Curvature indices, pauses and running rates were less sensitive than response rates to the switching from one schedule to the other. Experiments I and II yielded similar results, experimental history accounting only for minor differences. The results were discussed in relation to interspecies differences in the temporal regulation of behavior and operant versus respondent control of the response and schedule-induced behaviour.     

Isolation and characterization of the plasma membrane from the yeast Pichia pastoris

Despite similarities of cellular membranes in all eukaryotes, every compartment displays characteristic and often unique features which are important for the functions of the specific organelles. In the present study, we biochemically characterized the plasma membrane of the methylotrophic yeast Pichia pastoris with emphasis on the lipids which form the matrix of this compartment. Prerequisite for this effort was the design of a standardized and reliable isolation protocol of the plasma membrane at high purity. Analysis of isolated plasma membrane samples from P. pastoris revealed an increase of phosphatidylserine and a decrease of phosphatidylcholine compared to bulk membranes. The amount of saturated fatty acids in the plasma membrane was higher than in total cell extracts. Ergosterol, the final product of the yeast sterol biosynthetic pathway, was found to be enriched in plasma membrane fractions, although markedly lower than in Saccharomyces cerevisiae. A further characteristic feature of the plasma membrane from P. pastoris was the enrichment of inositol phosphorylceramides over neutral sphingolipids, which accumulated in internal membranes. The detailed analysis of the P. pastoris plasma membrane is discussed in the light of cell biological features of this microorganism especially as a microbial cell factory for heterologous protein production.     

Queuine in plants and plant tRNAs: Differences between embryonic tissue and mature leaves

In eubacterial and eukaryotic tRNAs specific for Asn, Asp, His and Tyr the modified deazaguanosinederivative queuosine occurs in position 34, the first position of the anticodon. Analysis of unfractionated tRNAs from wheat and from tobacco leaves shows that these tRNAs contain high amounts of guanosine (G) in place of queuosine (Q). This was measured by the exchange of G34 for [³H]guanine catalysed by the specific tRNA guanine transglycosylase from E. coli. Upon gel electrophoretic separation of the labeled tRNAs, seven Q-deficient tRNA species including isoacceptors are detectable. Two are identified as cytoplasmic tRNAs^Tyr and tRNA^Asp and two represent chloroplast tRNA^Tyr isoacceptors. In contrast to leaf cytoplasm and chloroplasts, wheat germ has low amounts of tRNAs with G34 in place of Q.A new enzymatic assay is described for quantitation of free queuine in cells and tissues. Analysis of queuine in plant tissues shows that wheat germ contains about 200 ng queuine per g wet weight. In wheat and tobacco leaves queuine is present, if at all, in amounts lower than 10 ng/g wet weight. The absence of Q in tRNAs from plant leaves is therefore caused by a deficiency of queuine. Tobacco cells cultivated in a synthetic medium without added queuine do not contain Q in tRNA, indicating that these rapidly growing cells do not synthesize queuine de novo.     

Cell attachment properties of collagen type VI and arg-gly-asp dependent binding to its α2(VI) and α3(VI) chains

Twelve of sixteen different cell types including fibroblasts and tumor cells were able to attach and spread on substrates of pepsin-solubilized or intact collagen VI, and on its triple helical domain. Attachment and spreading were independent of soluble mediator proteins (fibronectin, laminin) and collagen VI was distinct from collagens I, IV and V in the cells with which it interacted. Many of the same cells bound and spread on substrates prepared from unfolded α2(VI) and α3(VI) chains but not on the α1(VI) chain. The interactions with the chains were inhibited by low concentrations (10–100 μM) of synthetic RGDS and RGDT but not RGES peptides while the binding of cells to pepsin-solubilized collagen VI was more than 20-fold less sensitive to these peptides. The data incidate that cells have the ability to bind to collagen VI in a specific manner suggesting a similar function for collagen VI in situ.     

Influence of hormones and drugs on glutathione-S-transferase levels in primary culture of adult rat hepatocytes

GST activities against 1-Chloro-2,4-dinitrobenzene (CDNB) and 1,2-dichloro-4-nitrobenzene (DCNB) were measured in isolated and cultured adult rat hepatocytes. Within 24 h in culture, both GST activities decreased to about 70% and either stabilized at this level (CDNB) or recovered (DCNB) to the initial level. Use of hyaluronidase in addition to collagenase during the isolation of the cells strongly reduced both activities and its stimulation by various drugs for up to 168 h. The hormones insulin, glucagon, triiodothyronine, estradiol, testosterone, and progesterone did not affect GST activity, while dexamethasone showed some interference. In the presence of dexamethasone the activity against CDNB was mainly stimulated by the combination of methylcholanthrene (MC) and phenobarbital (PB) to about 260% within 168 h. The activity against DCNB was stimulated predominantly by MC alone reaching 170% after 168 h. Quantification of the GST subunits Ya, Yb₁ and Yp by an ELISA technique revealed a strong decrease of Ya, a transient increase of Yb₁ after 24 h followed by a moderate decrease, and a stable low level of the transformation marker Yp during cultivation. The level of Ya was markedly induced by PB, particularly in combination with MC. The level of Yb₁ was equally induced by MC or PB with no synergistic effect. Yp was not affected by these drugs. None of the hormones affected the level of these GST subunits. These results indicate that the physiological type of regulation of the GSTs is maintained during primary culture and no signs of dedifferentiation or transformation are observed. Furthermore, they demonstrate that the interaction of drugs and hormones and their inducing potential can be efficiently studied in the cultured hepatocytes.Abbreviations ABTS 2,2-Azino-bis(3-ethylbenzthiazoline-6-sulfonate) - CDNB I-Chloro-2,4-dinitrobenzene - DCNB 1,2-dichloro-4-nitrobenzene; DEX, dexamethasone - DMSO dimethylsulfoxide - GST glutathione Stransferase - MC methylcholanthrene - N, NIC nicotinamide - -NF -naphthoflavone - PB phenobarbital - PBS phosphate buffered saline     

A report from Australia: when a human life has not yet begun--according to the law

Victoria, Australia's Infertility (Medical Procedures) Act 1984, the first legislation to regulate reproductive technologies, permits research on surplus embryos fertilized in vitro but prohibits the creation of embryos for research purposes. The failure to define when an embryo has come into existence or when fertilization has occurred has prevented the continuation of potentially valuable research directed at overcoming infertility. The Standing Review and Advisory Committee on Infertility must now consider the debate over when fertilization occurs, an event that is no longer regarded as a discrete or instantaneous act but as a process revealing no clear point at which a human individual begins to exist. Because the law requires a clear line of demarcation, any legislation in this area will face the problem of defining this point. Interpretation of a 1987 amendment to the 1984 Act may allow the fertilization of ova for purposes other than implantation.