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Biomedical subjects

D A Thomas

Publications and source records attributed to D A Thomas.

At least 109 records · Page 6Linked to original sources
PubMed1983

Influence of androgen on the development of sexual behavior in the rat. II. Time and dosage of androgen administration during the neonatal period and masculine and feminine copulatory behavior in females.

The objective of the present study was to delineate the period of sensitivity to a single androgen exposure during the initial neonatal hours on the development of masculine and feminine copulatory behavior in female rats. Female rats were injected once with either 500, 50, or 5 micrograms testosterone propionate (TP) at either 1 or 24 hr after birth. Following castration in adulthood and TP replacement, the females were tested four times at weekly intervals in prolonged sessions for masculine copulatory behavior. One month following the masculine copulatory tests the females were tested for 3 weeks for feminine copulatory behavior with weekly increasing levels of estradiol benzoate (2.5, 10, and 25 micrograms) and progesterone (200 micrograms). The results demonstrate that a single injection of TP administered at either 1 or 24 hr after birth can significantly increase the capacity of female rats to exhibit ejaculation patterns and that the amount of androgen that is administered is critical in determining the levels of ejaculatory responding. Similarly, the females given high doses (50 and 500 micrograms) of TP at either 1 or 24 hr neonatally were almost completely defeminized. In contrast, however, the females treated with 5 micrograms TP at 1 and 24 hr showed different levels of lordotic performance indicating a greater sensitivity to androgen immediately after birth than at 24 hr in female rats as has been shown in male rats.

Age Factors↗
PubMed1983

Analysis of ultrasonic vocalizations emitted by intruders during aggressive encounters among rats (Rattus norvegicus).

This investigation was concerned with the identification of the ultrasonic vocalizations produced by intruders during aggressive interactions and the role of these signals in agonistic behavior of rats. In the first experiment, experienced resident males were paired with both devocalized and intact vocalizing naive intruder males. Devocalization of the intruder males resulted in a drastic decrease in 50-kHz vocalizations and the elimination of all 22-kHz vocalizations. This almost total absence of ultrasonic vocalizations was not accompanied by any change in resident aggressive behavior or intruder defensive and submissive behavior. In a second experiment, naive intruders were tested with either deafened or intact resident males. Similarly, preventing residents from hearing intruder ultrasounds had no detectable effect on any aggressive behavior. These experiments are not consistent with the correlative evidence that intruder-produced 22-kHz vocalizations inhibit the aggressive behavior of the resident. The results also show that most of the ultrasonic vocalizations emitted during aggressive encounters are probably produced by the intruder.

Aggression↗
PubMed1983

Analysis of ultrasonic vocalizations emitted by residents during aggressive encounters among rats (Rattus norvegicus).

This investigation was concerned with the extent to which aggressive resident rats emit 40-70-kHz vocalizations and the effect of these signals on intruders. In Experiment 1, deafened and intact intruder males were given two encounters with resident animals. Deafened intruders engaged in a higher duration of immobile or freezing postures than intact animals. Experiment 2 indicated that the augmentation of freezing found among deafened intruders was not due to an inability to detect ultrasounds made by residents since intruders encountering devocalized resident males showed no reliable differences in specific motor patterns from intruders paired with intact residents. The results further demonstrated that 40-70-kHz vocalizations are produced almost entirely by intruding animals since there were no significant changes in occurrence of these calls when resident males were devocalized. Under the constraints of the testing procedures employed, the role of ultrasonic communication during the initial formation of agonistic relations could not be determined experimentally.

Aggression↗
PubMed1982

Collaborative practice in obstetrics/gynecology: implications for cost, quality, and productivity.

Rising costs, concern over quality of care, and low worker productivity are some of the factors suggesting a need for revision in the organization of the health care delivery system. Reorganization of the nurse-physician working relationship through the establishment of collaborative practice can serve as the mechanism for improving cost, quality, and productivity outcomes. This analysis evaluates collaborative practice within the disciplines of obstetrics and gynecology.

Cost-Benefit Analysis↗
PubMed1982

Collection development using interlibrary loan borrowing and acquisitions statistics.

Libraries, especially those supporting the sciences, continually face the problem of selecting appropriate new books for their users. Traditional collection development techniques include the use of librarian or user subject specialists, user recommendations, and approval plans. These methods of selection, however, are most effective in large libraries and do not systemically correlate new book purchases with the actual demands of users served. This paper describes a statistical method for determining subject strengths and weaknesses in a library book collection in relation to user demand. Using interlibrary loan borrowing and book acquisition statistics gathered for one fiscal year from three health sciences libraries, the authors developed a way to graph the broad and narrow subject fields of strength and potential weakness in a book collection. This method has the advantages of simplicity, speed of implementation, and clarity. It can also be used over a period of time to verify the success or failure of a collection development program. Finally, the method has potential as a tool for use by two or more libraries seeking to improve cooperative collection development in a network or consortium.

Interlibrary Loans↗
PubMed1976

Glycogen phosphorylase in Dictyostelium discoideum. I. Purification and properties of the enzyme.

The glycogen phosphorylase of Dictyostelium discoideum has been purified over 200-fold from cells in the culmination stage of development. Analytical gel electrophoresis of the purified enzyme indicates one major protein band with a molecular weight of approximately 210,000. Gel elution verified the presence of phosphorylase activity associated with the protein band. Electrophoresis of partially purified extracts prepared from amoebae cells revealed the absence of phosphorylase protein. Sodium dodecyl sulfate electrophoresis on 6% gels indicated that the purified phosphorylase is composed of subunits, 95,000 in molecular weight. The purified enzyme exhibited normal Michaelis-Menten kinetics and activity was not stimulated by added nucleotides such as 5'-AMP. Nucleotide sugars (GDP-glucose, UDP-glucose, ADP-glucose) were competitive inhibitors of the phosphorylase reaction.

Dictyostelium↗
PubMed1976

Glycogen phosphorylase in Dictyostelium discoideum. II. Synthesis and degradation during differentiation.

A purified preparation of glycogen phosphorylase from Dictyostelium discoideum was used to elicit specific antisera in rabbits. The antisera were used to quantitate the amount of precipitable phosphorylase protein from cell extracts prepared at various stages of the developmental cycle. Following isotope incorporation studies in differentiating cells, the specific radioactivity of enzyme isolated by antibody precipitation was compared to that of acid-insoluble protein. Prior to 5 hours of development, glycogen phosphorylase could not be detected enzymatically or immunologically. Between aggregation and culmination, the rate of enzyme synthesis increased about 6-fold, then decreased to an insignificant value in young sorocarps. The rate of enzyme degradation was negligible during the period of maximal enzyme accumulation, then increased to a peak value of 40% after culmination, coincident with a rapid drop in phosphorylase activity. The data indicated that the increase in glycogen phosphorylase activity during development results from an increase in the rate of enzyme synthesis.

Dictyostelium↗