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Biomedical subjects

L C Stevens

Publications and source records attributed to L C Stevens.

At least 19 recordsLinked to original sources
PubMed2001

Exercise duration and mood state: how much is enough to feel better?

The effects of exercise duration on mood state were examined. In a repeated-measures design, the Profile of Mood States inventory (D. M. McNair, M. Lorr, & L. F. Droppleman, 1971) was administered before and after 1 quiet resting trial and 3 exercise trials of 10, 20, and 30 min on a bicycle ergometer. Heart rate levels were controlled at 60% of the participant's estimated VO2max level. An overall analysis of variance found improved levels of vigor with reduced levels of confusion, fatigue, and total negative mood. Planned analyses revealed that the improvements in vigor, fatigue, and total mood occurred after 10 min of exercise, with progressive improvements in confusion over 20 min and with no additional improvement over longer periods. These results complement current recommendations, which suggest that to experience positive fitness and health benefits, healthy adults should participate in a total of 30 min of moderate physical exercise daily, accumulated in short bouts throughout the day.

Adult↗
PubMed1993

Experimental testicular germ cell tumorigenesis in mouse strains with and without spontaneous tumours differs from development of germ cell tumours of the adult human testis.

The aim of this study was to undertake a morphological analysis of the earliest stages of experimentally induced (by genital ridge grafting) germ cell tumours in mouse strains with (129/Sv-ter) and without (MA) spontaneous tumorigenesis. Genital ridges from fetuses aged 12 or 13 days from 129/Sv-ter and MA were transplanted into the testes of adult 129/Sv-ter. The results show clearly that experimentally induced carcinoma-in-situ in mouse testes differs considerably from its human counterpart, found in patients with and without testicular germ cell tumours, and considered to be the precursor for all kinds of germ cell tumours of the adult testis apart from spermatocytic seminoma. The results indicate that development of testicular germ cell tumours is different in man and the mouse.

Adult↗
PubMed1990

Innervation and maturation of muscular tissue in testicular teratomas in strain 129/Sv-ter mice.

In strain 129/Sv-ter mice, teratomas develop spontaneously during the 13th day of gestation. These testicular germ cell tumors exhibit characteristics of different germ layers closely resembling normal embryonic tissue. We investigated the interrelationship between nervous and muscular tissues (often found side by side) in teratomas of 4-week-old 129/Sv-ter mice. In well-differentiated mouse teratomas, histochemically and immunohistochemically distinct muscle fiber types could be distinguished, but not with all reactions. According to its aerobic oxidative capacity, teratoma muscle tissue was comparable with normal muscles. However, with respect to myosin-related properties, fiber type differentiation was incomplete. The muscle fibers - generally arranged in bundles - contained one centrally located endplate which was contacted mostly by a single nerve terminal. From this, proper endplate zones within the fiber bundles were formed. Occasionally "type grouping" was encountered, suggesting collateral axonal branching paralleled by synapse elimination. Together with the earlier in vivo observation of muscular contractions, we assume that teratoma muscle fibers are innervated by nerve cells (within the nervous tissue compartments) corresponding to spinal motoneurons. Thus, myogenesis, maturation and innervation of skeletal muscular tissue in mouse teratomas are largely comparable to normal development.

Animals↗
PubMed1983

Mouse genital ridges in organ culture: the effects of temperature on maturation and experimental induction of teratocarcinogenesis.

Testicular teratomas can be induced experimentally by grafting genital ridges from male mouse fetuses to the testes of adults. A high incidence of teratomas occurs in genital ridges grafted to scrotal testes, but not in genital ridges grafted to testes maintained at body temperature. Genital ridges were cultured at 32 degrees C or 37 degrees C prior to grafting to the testes to determine the effect of temperature on the incidence of teratomas. Genital ridges cultured at 32 degrees C for two or three days produced a high incidence of teratomas when grafted to the testes, in contrast to genital ridges cultured at 37 degrees C for two or three days which produced a low incidence. Histologically, genital ridges cultured at 32 degrees C contained disorganized testicular tubules and were retarded in development. Genital ridges continued to develop in vitro at 37 degrees C, but were histologically different from genital ridges maturing in the fetus. Genital ridges cultured at 32 degrees C for 10 to 12 days did not develop teratomas in vitro or after grafting to the testes. Further characterization of temperature effects in vitro may lead to a better understanding of teratocarcinogenesis in vivo.

Animals↗
PubMed1983

Enzyme activity profiles in mouse teratocarcinomas. A quantitative ultramicroscale analysis.

Nine tumour lines with different developmental capacities were derived from spontaneous as well as from one induced teratocarcinoma: three teratocarcinoma-derived rhabdomyosarcomas TDR 602, TDR 694, and TDR 114; two teratocarcinoma-derived neuroblastomas TDN 2151 and TDN 2283; two teratocarcinoma-derived endodermal tumours TDE 274 and TDE 113; one multipotential teratocarcinoma OTT 2289, and one undifferentiated teratocarcinoma OTT 2158. Quantitative analyses of ten catabolic enzymes, i.e. alkaline and acid phosphatase, alpha- and beta-galactosidase, alpha- and beta-glucosidase, alpha-mannosidase, alpha-fucosidase, beta-glucuronidase, and hexosaminidase were carried out at the 20-cell level, and specific enzyme activity profiles were established for each of the tumour lines studied. These profiles may be used for the biochemical identification of a tumour type at the single cell level in addition to morphological and biological criteria.

Acid Phosphatase↗
PubMed1982

Primordial germ cell proliferation in fetal testes in mouse strains with high and low incidences of congenital testicular teratomas.

The development of genital ridges in mouse strains were compared with high and low susceptibility to teratocarcinogenesis. The number of dividing primordial germ cells (PGC) was low at 12 days of gestation. The number increased sharply at 13 days and decreased precipitously by 15 days of gestation. The period of high mitotic activity closely paralleled the period of susceptibility to experimentally induced teratocarcinogenesis. Testes that had a long proliferative period had a higher incidence of teratomas than those that had a short proliferative period. A group of fetuses was identified that had markedly fewer than normal PGC. The incidence of teratomas in this group was very high, and nearly all growths were bilateral.

Animals↗
PubMed1982

Experimental induction of testicular teratomas in dissociated-reaggregated chimaeric gonads.

Testicular teratomas can be experimentally induced in some strains of mice by grafting 12.5-day male genital ridges to the testes of adults. The grafts develop into testes and most of them have teratomas. The cells of 12.5-day foetal gonads were dissociated and the germ cells and somatic cells were separated. When germ cells were reaggregated with somatic cells and implanted in adult testes, they formed seminiferous tubules with teratomas. The somatic cell populations were contaminated with about 1% germ cells, and when they were implanted in adult testes, they formed testes with a comparatively low incidence of teratomas. When germ cells of a highly susceptible strain were combined with somatic cells from a resistant strain, they formed chimaeric testes with a high incidence of teratomas. When germ cells from a resistant strain were combined with somatic cells from a susceptible strain they formed chimaeric gonads and the incidence of teratomas was low. This indicates that at 12.5 days the genotype of the germ cells is responsible for susceptibility. When germ cells from older foetal gonads were combined with somatic cells of 12.5-day gonads, the incidence of teratomas was low. This showed that 12.5-day somatic cells cannot 'rejuvenate' older germ cells in a way to regain their susceptibility. When 12.5-day germ cells of highly susceptible strains were combined with older somatic cells the incidence of tumours was low indicating that the age of the somatic cells influences susceptibility to teratocarcinogenesis.

Animals↗
PubMed1980

Teratocarcinogenesis and spontaneous parthenogenesis in mice.

Teratomas are rare in most strains of mice. Testicular teratomas are common in some sublines of inbred strain 129. Ovarian teratomas are common in inbred strain LT. Testicular teratomas are derived from primordial germ cells and can be experimentally produced by grafting 121/2-day genital ridges to the testes of adults. They develop into testes and for some strains most have teratomas. Ovarian teratomas are derived from parthenogenetically activated ovarian oocytes that have completed the first meiotic division. Teratomas of either sex can be experimentally produced by grafting early embryos to various sites in adults. Embryo-derived teratomas originate directly from undifferentiated embryonal cells. Occasionally teratomas are malignant (teratocarcinomas) and can be maintained as transplantable tumors. Some form embryoid bodies that resemble normal early embryos. When the stem cells of some transplantable teratocarcinomas are injected into blastocysts and transferred to the uteri of pseudopregnant females, they participate in normal development and contribute to the formation of all major tissues including functional sperm and eggs. Spontaneous parthenogenesis is common in strain LT oocytes after ovulation. The eggs cleave, form blastocysts which implant in the uterus, but after the egg cylinder stage they become disorganized and are aborted. Eight-cell embryos from the pigmented LT strain were aggregated with embryos of albino strain 129 and transferred to the uteri of pseudopregnant females. They participated in development and contributed to the formation of normal chimeric tissues. Offspring from eggs derived from parthenogenetic embryonal cells were produced, demonstrating that parthenogenetic embryonic cells are totipotent. It is still a mystery why parthenogenetic embryos will not survive in utero.

Animals↗
PubMed1980

Development of Dickie's small eye: an early lethal mutation in the house mouse.

Mice heterozygous for Dickie's small eye (Dey) are small and have malformed eyes (Theiler et al. 1978). The development of homozygous Dey/Dey was more difficult to analyze than heterozygous Dey/+. This investigation to identify the homozygotes and to distinguish them from Dey/+ and +/+ resorptions. Such a distinction was possible only when enough specimens were available. The mutants are poor breeders and the collection of the necessary material has taken several years.

Animals↗
PubMed1979

Development of velvet coat (Ve/Ve), another early lethal mutation in the house mouse.

A new semidominant mutation in the house mouse, velvet coat (Ve), is described. Ve homozygotes, recognizable on day 5 of gestation by their deficiency of ectodermal cells, never produce mesoderm and are resorbed by days 9-10. Primary Ve action may occur during the formation of the blastocyst or during determination and differentiation of the inner cell mass, or both. Accordingly, Ve/Ve embryos may provide a useful model for investigating primary gene action during blastocyst formation and subsequent differentiation.

Animals↗
PubMed1978

Development of Dickie's small eye, a mutation in the house mouse.

A new semidominant mutation in the laboratory mouse, Dickie's small eye (Dey), is described. It is localized on chromosome 2. Heterozygotes show reduced body size, small eyes with coloboma, small or lacking lens with cataract, abnormal folding of the retina and reduction of the pigment layer. The anterior chamber is usually missing. Homozygotes apparently die early in pregnancy.

Animals↗