Biomedical subjects

April E Ronca

Publications and source records attributed to April E Ronca.

7 recordsLinked to original sources

PubMed2006

Effects of labor contractions on catecholamine release and breathing frequency in newborn rats.

Plasma catecholamines in newborn rats (0-2 hr old) were analyzed following vaginal birth, cesarean section with simulated labor contractions, or cesarean section without labor contractions. Upon delivery, pups were exposed to key elements of the rat's natural birth process, that is, umbilical cord occlusion, tactile stimulation, and cooling. Only pups exposed to actual or simulated labor showed an immediate rise in norepinephrine and epinephrine. Initial postpartum respiratory frequencies were higher in vaginal than in cesarean delivered pups and, in all groups, inversely correlated with catecholamine titers, suggesting respiratory distress or transient tachypnea at lower catecholamine levels. These findings establish a rat model for analyzing effects of labor on neonatal adaptive response during the transition from prenatal to postnatal life.

Analysis of Variance↗

PubMed2005

Development as adaptation: a paradigm for gravitational and space biology.

Adaptation is a central precept of biology; it provides a framework for identifying functional significance. We equate mammalian development with adaptation, by viewing the developmental sequence as a series of adaptations to a stereotyped sequence of habitats. In this way development is adaptation. The Norway rat is used as a mammalian model, and the sequence of habitats that is used to define its adaptive-developmental sequence is (a) the uterus, (b) the mother's body, (c) the huddle, and (d) the coterie of pups as they gain independence. Then, within this framework and in relation to each of the habitats, we consider problems of organismal responses to altered gravitational forces (micro-g to hyper-g), especially those encountered during space flight and centrifugation. This approach enables a clearer identification of simple "effects" and active "responses" with respect to gravity. It focuses our attention on functional systems and brings to the fore the manner in which experience shapes somatic adaptation. We argue that this basic developmental approach is not only central to basic issues in gravitational biology, but that it provides a natural tool for understanding the underlying processes that are vital to astronaut health and well-being during long duration flights that will involve adaptation to space flight conditions and eventual re-adaptation to Earth's gravity.

Adaptation, Physiological↗

PubMed2004

Effects of 2 G hypergravity exposure on Bobwhite (Colinus virginianus) and Japanese quail (Coturnix coturnix japonica).

We compared reproductive fitness and early postnatal growth of Bobwhite (Colinus virginianus) and Japanese (Coturnix coturnix japonica) quail incubated and hatched during 2 G centrifugation. Fertilized Bobwhite and Japanese quail eggs were placed in portable incubators on the 8-ft International Space Station Test Bed (ISSTB) Centrifuge at NASA Ames Research Center. The quail eggs were incubated throughout hatching and reared until Postnatal day (P)4 at either 1.0, 1.2 or 2.0 G. Two days before hatching, candling revealed significantly greater numbers of viable Bobwhite than Japanese quail eggs at all g-loads. Bobwhite quail exhibited significantly better hatching success at all g-loads than did Japanese quail. Bobwhite hatchlings were sensitive to gravitational loading as evidenced by reduced postnatal body mass and length of 2 G hatchlings relative to 1 G control hatchlings. In contrast, mass and length of Japanese quail hatchlings were unaffected by 1.2 or 2 G exposure. Together, our findings provide evidence for superior viability and hatching success in Bobwhite quail relative to Japanese quail, coupled with greater sensitivity of postnatal body growth and development to 2 G loading. Bobwhite quail may be better suited than Japanese quail for scientific studies on space biology platforms.

Animals↗

PubMed2003

Studies toward birth and early mammalian development in space.

Sustaining life beyond Earth on either space stations or other planets will require a clear understanding of how the space environment affects key phases of mammalian reproduction and development. Pregnancy, parturition (birth) and the early development of offspring are complex processes essential for successful reproduction and the proliferation of mammalian species. While no mammal has yet undergone birth within the space environment, studies spanning the gravity continuum from 0- to 2-g are revealing startling insights into how reproduction and development may proceed under gravitational conditions deviating from those typically experienced on Earth. In this report, I review studies of pregnant Norway rats and their offspring flown in microgravity onboard the NASA Space Shuttle throughout the period corresponding to mid- to late gestation, and analogous studies of pregnant rats exposed to hypergravity (hg) onboard the NASA Ames Research Center 24-ft centrifuge. Studies of postnatal rats flown in space or exposed to centrifugation are reviewed. Although many important questions remain unanswered, the available data suggest that numerous aspects of pregnancy, birth and early mammalian development can proceed under altered gravity conditions.

Animals↗

PubMed2003

Mammalian development in space.

Life on Earth, and thus the reproductive and ontogenetic processes of all extant species and their ancestors, evolved under the constant influence of the Earth's l g gravitational field. These considerations raise important questions about the ability of mammals to reproduce and develop in space. In this chapter, I review the current state of our knowledge of spaceflight effects on developing mammals. Recent studies are revealing the first insights into how the space environment affects critical phases of mammalian reproduction and development, viz., those events surrounding fertilization, embryogenesis, pregnancy, birth, postnatal maturation and parental care. This review emphasizes fetal and early postnatal life, the developmental epochs for which the greatest amounts of mammalian spaceflight data have been amassed. The maternal-offspring system, the coordinated aggregate of mother and young comprising mammalian development, is of primary importance during these early, formative developmental phases. The existing research supports the view that biologically meaningful interactions between mothers and offspring are changed in the weightlessness of space. These changes may, in turn, cloud interpretations of spaceflight effects on developing offspring. Whereas studies of mid-pregnant rats in space have been extraordinarily successful, studies of young rat litters launched at 9 days of postnatal age or earlier, have been encumbered with problems related to the design of in-flight caging and compromised maternal-offspring interactions. Possibilities for mammalian birth in space, an event that has not yet transpired, are considered. In the aggregate, the results indicate a strong need for new studies of mammalian reproduction and development in space. Habitat development and systematic ground-based testing are important prerequisites to future research with young postnatal rodents in space. Together, the findings support the view that the environment within which young mammals develop, comprised of its mother and siblings, is of paramount importance in interpreting spaceflight effects.

Animals↗

PubMed2003

Effects of hypergravity on ovarian-hypophyseal function in antepartum and postpartum rats.

BACKGROUND: Rats exposed to microgravity during the post-implantation phase of pregnancy had minimal alterations in ovarian and hypophyseal parameters during the antepartum and postpartum periods. In the current study, a similar parallel experimental design was employed to ascertain the effects of hypergravity on ovarian and hypophyseal function. HYPOTHESIS: We hypothesized that hypergravity exposure during the post-implantation stage of pregnancy would not alter antepartum and postpartum ovarian and hypophyseal function. METHODS: Pregnant rats were assigned to hypergravity (1.5 G, 1.75 G, or 2.0 G), rotational control, or stationary control groups (n = 10 each group) beginning on gestation day 11 and ending on day 20. Hypophyseal and ovarian analyses were conducted on 5 of the animals from each group at day 20. The remaining animals in each group were allowed to go to term and the same analyses were conducted 3 h postpartum. RESULTS: Hypergravity at all levels decreased the percent body mass gain from gestation day 11 to 20 (p < 0.05); however, the wet weight of the pituitaries and ovaries was not changed. There was no effect of hypergravity on the number of healthy or atretic antral follicles of any size at gestation day 20 or postpartum. The number of corpora lutea of pregnancy was decreased in all hypergravity groups, but the number of live fetuses at gestation day 20 or pups at term was not altered. Plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin, and progesterone were not changed at gestation day 20 or postpartum. Pituitary content of LH, FSH, and prolactin was not altered by hypergravity at gestation day 20, but LH content was significantly increased (p < 0.05) at 1.5 and 1.75 G postpartum. CONCLUSIONS: We conclude that hypergravity, up to and including 2.0 G, is compatible with maintenance of pregnancy and has minimal effects on hypophyseal parameters. Ovarian follicles are not altered by hypergravity, but corpora lutea may regress at a more rapid rate.

Animals↗

PubMed2002

Effects of hypergravity exposure on plasma oxytocin concentration in pregnant and lactating rat dams.

Rat dams and offspring were exposed to 1.5-g, 1.75-g or 2.0-g hypergravity (hg) from gestational day [G] 11 until postnatal day [P] 10. To ascertain the role of maternal factors in reduced postnatal body weights of offspring developed in hg, the dams' lactational hormones were measured. Oxytocin (OT), the major hormone responsible for milk ejection, was reduced in hg dams whereas prolactin (Prl), involved in milk production, was unchanged. Video analyses of nursing behavior revealed that hg dams spent more time nursing relative to 1-g controls. We hypothesized impaired milk transfer from dam to pup, however pup body weight gains following a discrete suckling episode were comparable across conditions. Changes in lactational hormones and nursing behavior by dams exposed to hg do not account for reduced body masses of their offspring.

NASA Center ARC↗