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Biomedical subjects

R Epstein

Publications and source records attributed to R Epstein.

At least 127 records · Page 7Linked to original sources
PubMed1980

Resurgence of responding after the cessation of response-independent reinforcement.

In an autoshaping experiment, food-deprived pigeons pecked rapidly at a moving dot that preceded the delivery of food. When the moving dot and food were no longer correlated, the rate of pecking dropped nearly to zero. When, subsequently, no food was given, pecking reappeared at a high rate (nearly 200 pecks per min for each subject), the rate dropping again in subsequent sessions. In two other experiments, designed to clarify relevant variables, the effect was replicated. The data suggest that although response-independent reinforcement produces a decrement in responding, it does not reduce a tendency to respond under other conditions.

Animals↗
PubMed1978

Construction and properties of recombinant plasmids containing the rII genes of bacteriophage T4.

The EcoRI digestion products of phage T4 DNA have been examined using a phage DNA transformation assay. A 2.6 X 10(6) Dalton fragment was found to contain the rII genes. This fragment was purified and then treated with HindIII endonuclease. The cleavage products were ligated to the vector plasmid pBR313 and viable recombinant plasmids recovered. A genetic assay was employed to demonstrate that the recombinants contained T4 DNA and to localize on the phage genetic map the EcoRI and HindIII sites cleaved during the construction of the plasmids. Preliminary characterization suggests that a fragment covering the beginning of the rIIA gene possibly contains a promotor which is active in uninfected cells.

Cell Transformation, Viral↗
PubMed1977

Genetic identification of cloned fragments of bacteriophage T4 DNA and complementation by some clones containing early T4 genes.

Bacteriophage T4 DNA containing cytosine has been obtained from cells infected with phage mutant in genes 42, 56, denA and denB. This DNA can be cut by a number of restriction endonucleases. Fragments obtained by digestion of this DNA with EcoRI have been cloned using the vector plasmid pCR1. Clones containing T4 DNA were identified by hybridization with radioactive early and late T4 RNA. A simple marker rescue technique is described for the genetic identification of the cloned T4 fragments. Some of the T4-hybrid plasmids which contain entire T4 genes can complement temperature sensitive and amber mutants of T4.

Centrifugation, Density Gradient↗
PubMed1977

Characterization of an inhibitory allogeneic effect on humoral responsiveness in vitro.

Evidence is presented that the induction of a humoral response is inhibitable by a thymus-derived cell (TI) that acts on the antigen-sensitive precursors of both the thymus-derived cooperating and the bone marrow-derived antibody-secreting cell-that is, the tC and B cell respectively. The inhibition of induction of the tC and B cell by the TI cell is shown to be reversed by increasing the effective level of cooperation. This competitive interaction between the inhibitory (TI) and cooperating (TC) systems is postulated to be part of the mechanism for regulating the class of the response, cell-mediated or humoral. The following properties of the inhibitory system were demonstrated: [1] The tI cell--the antigen-sensitive precursor of the TI cell--is both paralyzable and inducible. [2] The TI cell appears during the induction of a cell-mediated response and, if not identical to the effector cytotoxic ('killer') TK cell, the TI cell is induced in parallel with it. [3] The effector function of the TI cell, like that of the TK cell, is H-2-restricted.

Animals↗
PubMed1974

The effect of 2-mercaptoethanol on murine mixed lymphocyte cultures.

Mouse spleen cells which have been depleted of adherent cells do not respond to allogeneic lymphocytes in vitro. Their cytotoxic response can be restored by inclusion of mercaptoethanol in the medium. Mercaptoethanol is shown to have a stimulatory effect also on the response of normal (unseparated) spleen cells to alloantigens. The enhancement of the DNA-synthetic and cytotoxic response is similar, varying from 3.5-15-fold. Cytotoxic cells also appear in unmixed lymphocyte cultures in the presence of mercaptoethanol and fetal calf serum. The specificity of these background cytotoxic cells is not known.

Animals↗