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Biomedical subjects

R Levin

Publications and source records attributed to R Levin.

At least 73 records · Page 4Linked to original sources
PubMed1977

Alterations in the maternal behavior of rats rearing malnourished offspring.

Investigations of maternal behavior of mothers fed a low-protein diet indicated deficits in retrieval and in the rate of nest-building. In addition, they indicated a concomitant increase in time spent with young when assessed during periods not associated with the retrieval/nest-building test session. The adrenalectomized mother, another case that produces growth-stunted progeny, was compared with both low-protein and control mothers for maternal behavior. Unlike the low-protein mother, the adrenalectomized mother did not exhibit retrieval or nest-building deficits; however, the adrenalectomized mother did display an increase in time spent with young. These data suggest that although deficits in retrieval and nest-building can be attributed to the nutritional condition of the mother, the stimulus characteristics of the malnourished pup are important in eliciting the increased time spent with the litter.

Adrenalectomy↗
PubMed1977

Influence of experiential factors and gonadal hormones on pituitary-adrenal response of the mouse to novelty and electric shock.

Plasma corticosterone elevations have been shown to occur in response to exposure to a novel environment and to the delivery of painful stimulation, such as footshock. The present experiment investigated the effects of experience with these types of stimuli upon the responsivity of the pituitary-adrenal system. When mice were subjected to repeated footshock, the adrenocortical response was increased. When animals were repeatedly shocked in a specific environment, the adrenocortical-stimulating properties of the situational stimuli were also elevated. On the other hand, plasma corticosterone elevations in response to merely being placed in an experimental chamber were not affected by 10 exposures to the situation. Previous data showed that animals that had been shocked in one environment were generally more responsive to many types of stimulus changes. Such a pattern of results suggests that the pituitary-adrenal system is subject to sensitization processes and that the central nervous system substrate which controls its function is one that is normally involved with the production of states of arousal. This configuration of results was quite pronounced in the female mouse regardless of hormonal state, and it was absent in the intact male. The results of studies with gonadectomized males suggested that testosterone inhibits sensitization.

Animals↗
PubMed1976

Expression of feline type-C virus in normal and tumor tissues of the domestic cat.

Tumor and normal tissues from domestic cats were examined for FeLV and RD-114 specific nucleic acids and proteins. Virus-positive tissues showed a 100- to 200-fold higher level of FeLV and a 200- to 400-fold higher level of FeLV p30 than virus-negative tumors and normal cat tissues. In contrast, the levels of RD-114 viral RNA and p30 antigen were comparable in the majority of tumorous and normal tissues examined. When the DNA of these tissues was examined for FeLV-related sequences, the virus-positive tumors were found to contain extra copies of FeLV DNA. Virus-negative tumors contained DNA sequences homologous with FeLV but the copy number of these sequences could not be distinguished from normal tissues. The results indicate that in certain FeLV-induced type-C lymphoproliferative diseases, extra type-C sequences not present in normal tissues can be identified.

Animals↗
PubMed1976

Food availability as a determinant of the rats' circadian rhythm in maternal behavior.

Thre present study was designed to determine whether environmental factors other than light would alter the dialy periodicity in the rat's maternal behavior and whether such a change in the dam's behavior pattern would in turn alter the pattern of her sucklings' milk intake. Experiment 1 determined the daily pattern of litter weight gain (which presumably reflects milk intake) displayed by young reared by dams fed and watered either ad lib (Group C), only during the day (Group D), or only at night (Group N). Experiment 2 compared nocturnal and diurnal frequency of maternal behavior in Groups C, D, and N. The pattern of both litter weight gain and maternal behavior was observed to be diurnal in Groups C and N and nocturnal in Group D.

Animals↗
PubMed1976

RP4 promotion of transfer of a large Agrobacterium plasmid which confers virulence.

Introduction of RP4 plasmid into Agrobacterium tumefaciens promotes the transfer on solid medium of large virulence-associated plasmids from virulent donor strains to a plasmidless avirulent recipient. Exconjugants were selected for the ability to utilize octopine or nopaline as the sole source of arginine, traits which are coded for by virulence-associated plasmids in the strains employed here. All exconjugants retained the arginine auxotrophy of the recipient strain, and were resistant to ampicillin and kanamycin, drugs to which RP4 confers resistance. Five exconjugant clones from one cross were shown by alkaline sucrose gradient analysis to contain both RP4 plasmid and the large virulence-associated plasmid of the donor strain. All five exconjugants exhibited virulence on carrot, sunflower and kalanchoe plants. These results indicate that virulence and the ability to degrade octopine are plasmid-borne traits in A. tumefaciens strains 15955 and A6, and extend the evidence that large plasmids in A. tumefaciens are vectors of virulence genes.

Arginine↗
PubMed1976

Studies on phage internal proteins: formation of internal protein - T2 DNA complexes in vivo.

Internal proteins, synthesized in T2-infected Escherichia coli B cells were recovered from bacterial membranes during the early stages of infection. Approx. 15 min after the onset of infection, T2 and T4 internal proteins were released from the bacterial membranes and sedimented along with newly synthesized phage DNA. Internal protein-DNA complexes were also obtained by chromatography on hydroxylapatite columns. Internal proteins were not released from bacterial membranes after infection with amber mutants defective in genes 21, 22 and 23. It has been suggested that these complexes are intermediates in T-even phage morphogenesis.

Cell Membrane↗
PubMed1975

Maternal influences on ontogeny of suckling and feeding rhythms in the rat.

To assess the effects of both maternal and endogenous factors on the ontogeny of nocturnal feeding in the rat, day and night weight gain was determined in the sighted or blind litters of sighted or blind litters of sighted or blind dams and in young weaned at 15 days of age. Sighted dams impose a diurnal milk-intake pattern on their young. The nocturnal pattern of solid-food intake begins at 19 days of age. Blind litters also display nocturnal feeding when kept with sighted dams, but only until 35 days of age.

Age Factors↗
PubMed1975

Quantitative analysis of the rescue of RNA sequences by mammalian type C viruses.

The specificity and quantitation of the rescue of RNA sequences by mammalian type C viruses has been investigated. Type C virus can package with specificity only type C viral RNA. Type C viruses do not encapsidate with comparable efficiency either type B viral or cellular globin mRNA. Conversely, a non-type C mammalian retravirus, MP-MV, cannot encapsidate type C RNA. A revertant of Kirsten sarcoma virus (Ki-SV)-transformed nonproducer cells which fails to rescue biologically active Ki-SV after superinfection with helper virus had no detectable intracellular Ki-SV-specific RNA. The results suggest specific mechanisms by which type C viral proteins can package type C viral RNA and provide an approach to classifying RNA of potentially defective endogenous retraviruses as type C in origin.

Base Sequence↗
PubMed1975

Development of circadian periodicity in base and stress levels of corticosterone.

Base and stress levels of corticosterone were assessed at 4-h intervals over a 24-h period in male and female rats at age 18, 22, and 26 days. A significant periodicity in base levels of corticosterone is present at 22 days of age; however, a rhythm in stress values does not appear until age 26 days. At age 26 days the pattern of the circadian periodicity in both base and stress concentrations of corticosterone resembles that of the mature rhythm.

Animals↗
PubMed1975

Primary adenoid cystic carcinoma of the esophagus. Report of a case and review of the literature.

A case of primary adenoid cystic carcinoma of the esophagus is reported and a total of 15 cases was reviewed. There were 9 men, although earlier reports indicated the disease was more common in women. The lesion was located in the middle third of the esophagus in 10 cases. The possibility of tumor development from embryonal rests of the tracheobronchial tree in the esophagus is discussed. The prognosis of adenoid cystic carcinomas is not well known, but the treatment and prognosis appear similar to those of epidermoid carcinomas of the esophagus.

Aged↗
PubMed1969

Prolactin in the postpartum rat: synthesis and release in the absence of suckling stimulation.

Postpartum female rats deprived of suckling stimulation while being kept continuously with pups nonetheless suspended ovarian cyclicity for an average of 16 days and responded to uterine trauma by forming deciduomata. These results show that the extramammary stimulation afforded by young is alone capable of sustaining prolactin output from the adenohypophysis of the postpartum rat.

Animals↗