PubMed Health⌕ Search

Biomedical subjects

J F Nelson

Publications and source records attributed to J F Nelson.

At least 19 recordsLinked to original sources
PubMed1996

Diminished alpha-inhibin messenger ribonucleic acid in in vitro fertilization-embryo transfer poor responders reflects declining follicle reserve.

OBJECTIVES: To quantitate and compare granulosa cell alpha-inhibin messenger RNA (mRNA) levels in IVF-ET poor and good responders and thereby learn how alpha-inhibin mRNA levels change in states of diminished ovarian responsiveness. DESIGN: Ribonucleic acid analysis of stored luteinized granulosa cell samples. SETTING: Academic tertiary care institution. PATIENTS: Fifty-three women undergoing follicle aspiration for IVF-ET were studied. Patients were classified as poor responders (n = 16) or good responders (n = 37) according to their E2 concentration on the day of hCG; the E2 of poor responders was < 1,000 pg/mL (3,671 pmol/L) and that of good responders was > or = 1,000 pg/mL (3,671 pmol/L). MAIN OUTCOME MEASURES: Messenger RNA levels were measured using dot blot RNA analysis. The following parameters were determined or derived: total mRNA levels, total alpha-inhibin mRNA levels, alpha-inhibin mRNA per follicle, and proportional alpha-inhibin mRNA as the ratio of alpha-inhibin mRNA:total mRNA. RESULTS: Proportional alpha-inhibin mRNA and alpha-inhibin mRNA per follicle were not significantly different between poor responders and good responders. Total mRNA and total alpha-inhibin mRNA levels, however, were diminished significantly in poor responders. CONCLUSIONS: The observations that proportional alpha-inhibin mRNA and alpha-inhibin mRNA per follicle do not significantly change in poor responders, whereas total alpha-inhibin mRNA does, indicate that the decrease in total alpha-inhibin mRNA in poor responders reflects a decreased pool of total mRNA, likely because of a reduction in follicle number. These findings are in contrast to other recent reports that describe a change in granulosa cell function accompanying states of decreased ovarian responsiveness.

Adolescent↗
PubMed1995

Hyperadrenocorticism, attenuated inflammation, and the life-prolonging action of food restriction in mice.

Food restriction (FR), which extends life span, is associated with an enhanced diurnal elevation of glucocorticoids. This increase in glucocorticoids may contribute to longevity by chronically enhancing the same protective mechanisms mobilized during acute stress. The objective of this study was to determine if attenuation of inflammation, a presumably protective effect of glucocorticoids, occurs in FR mice. Two-month-old male BALB/c mice were either fed ad lib (AL) or FR (60% AL calories) for 2 months. After one month, the diurnal elevation of plasma corticosterone was threefold higher in FR mice. Two weeks after corticosterone sampling, a hind foot pad of each mouse was injected with 20 microliters of 4% carrageenan. Maximum observed edema did not differ between FR and AL groups, but edema was reduced at onset and fell earlier in FR mice. Results indicate that at least one inflammatory reaction is attenuated by FR and are consistent with the hypothesis that FR enhances a potentially protective glucocorticoid activity.

Adrenal Cortex↗
PubMed1995

Hyperadrenocorticism and food restriction-induced life extension in the rat: evidence for divergent regulation of pituitary proopiomelanocortin RNA and adrenocorticotropic hormone biosynthesis.

The increased diurnal elevation of plasma corticosterone (B) induced by food restriction (FR) may play a role in the life span extension of FR. We investigated whether FR alters adrenocorticotropic hormone (ACTH) and proopiomelanocortin (POMC) mRNA levels in plasma and anterior pituitary (AP), since these molecules both regulate and can be suppressed by B. Measurements were made in 3-month-old male Fischer 344 rats that had been ad libitum (AL) or FR (60% of AL calories) since 6 weeks of age. Plasma B was 2-fold higher in FR rats in the PM samples, but did not differ in AM samples. By contrast, plasma ACTH did not differ in the PM samples of FR and AL rats and was 20% lower in AM samples (p < .05) of FR rats. AP content of ACTH was 50% lower in FR rats in both AM and PM samples (p < .01). In contrast, AP contents of POMC and mRNA, primary transcript, and processing intermediate were not reduced in FR rats, and PM content of POMC primary transcript was elevated in FR rats (p < .05). The reduced pituitary and plasma ACTH of FR rats may be the consequence of their elevated plasma B levels. This study also suggests that factors other than elevated ACTH account for FR-induced hyperadrenocorticism. These results also indicate that POMC mRNA and ACTH biosyntheses are differentially regulated in FR rats.

Adrenocorticotropic Hormone↗
PubMed1995

Proliferating cell nuclear antigen marks the initiation of follicular growth in the rat.

Despite expanding knowledge on the kinetic aspects of folliculogenesis, the question of what initiates follicle growth remains unanswered. Efforts to solve this problem have been thwarted by the absence of sensitive markers to identify the onset of follicular growth. In this study, we determined whether increased proliferating cell nuclear antigen (PCNA) correlates with initiation of follicle growth and might therefore be useful for studying early events in this process. Paraffin sections of ovaries from cycling adult rats, prepubertal eCG+hCG-primed rats, and prepubertal control rats were processed for immunocytochemistry by use of a PCNA primary antibody. In primordial follicles, neither granulosa cells nor oocytes stained for PCNA. PCNA immunoreactivity coincided with the earliest sign of follicle growth, appearing in pregranulosa cells of early primary follicles just beginning to grow. In all primary follicles, some granulosa cells were PCNA-positive. PCNA immunoreactivity in oocytes first appeared in primary follicles, preceding oocyte enlargement. In preantral and antral follicles, granulosa cell PCNA staining was uniform throughout the granulosa cell layers. Oocytes were positive for PCNA in both preantral and antral follicles. PCNA expression diminished in atretic follicles. In CL, granulosa cell PCNA expression was also decreased. Theca cell PCNA expression was first evident in the transitional follicle (1-2-layer granulosa cells) and was present in all stages thereafter. The pattern of PCNA expression did not differ among adult cycling, prepubertal eCG+hCG-stimulated, and control rat ovaries.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Dissociation kinetics of the uterine estrogen receptor-estradiol complex are unaltered in aging C57BL/6 mice.

Several, though not all, estrogen-dependent phenomena show reduced responsiveness to estradiol (E2) during aging. One factor contributing to this reduced sensitivity could be an increase in the dissociation rate of the estrogen receptor-hormone complex. We therefore studied the effect of aging on the dissociation rate of 3HE2 from the uterine cytosolic estrogen receptor (ER) of C57BL/6 mice that had been ovariectomized 48 h earlier. Measurements were made at 28 degrees C at two concentrations of cytosol. In dilute cytosol ([ER] = 0.01 nM) the dissociation of ER-3HE2 displayed a single phase, first order profile which did not differ among young (4-6 month), middle-aged (15-18 month) and old (23-30 month) mice. In more concentrated cytosol ([ER] = 2 or 6 nM) the dissociation of ER-3HE2 displayed a biphasic first order profile that consisted of an initial rapidly dissociating phase followed by a more slowly dissociating phase. There was no effect of age on the dissociation rate constant (K) of either the rapid (K-1) or slow (K-2) phase. Shortening the time allotted for the concentrated cytosol to equilibrate with 3HE2 before measuring the dissociation rate reduced the fraction of the receptor hormone complex that dissociated in the slow phase, but, once again, the dissociation profiles did not differ between age groups. These results indicate that uterine ER dissociation kinetics remain unaltered in middle-aged and old mice and are therefore unlikely to play a role in the attenuated responsiveness to estrogen during aging.

Aging↗
PubMed1992

Accelerated disappearance of ovarian follicles in mid-life: implications for forecasting menopause.

Menopause is triggered by the number of ovarian follicles falling below a threshold number and is irreversible because oogonial stem cells disappear after birth. Since it is the result of programmed disappearance of a limited store of follicles, menopause can be predicted using mathematical models based on total follicle counts at different ages. Our model shows follicle numbers decline bi-exponentially rather than as a simple exponential function of age, as had been assumed, with a first exponential rate parameter of -0.097 and a second of -0.237. The change occurred when numbers had fallen to the critical figure of 25,000 at age 37.5 years. The unexpectedly faster rate of ovarian ageing afterwards lowers the follicle population to 1000 at approximately 51 years, and was adopted as the menopausal threshold because it corresponds to the median age of menopause in the general population. Had the earlier rate persisted menopause would not be expected until 71 years. The impact of step reductions of follicle numbers on the prospective span of menstrual life was predicted by the model. A reduction by 50% before age 30 years resulted in the threshold being reached at 44 years and 0.6 year later for every subsequent year until age 37.5 years after which it is reached at 48 years. A reduction of 90% in childhood before age 14 years could result in menopause as early as 27 years, with increments of 0.6 year per year afterwards until after 37.5 years when it is expected at age 41 years.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Aging impairs estrogenic suppression of hypothalamic proopiomelanocortin messenger ribonucleic acid in the mouse.

Altered neuroendocrine sensitivity to estrogen is a characteristic of reproductive aging in female rodents, but its molecular basis is not well understood. The objective of this study was to determine whether altered modulation of hypothalamic proopiomelanocortin (POMC) mRNA by estradiol (E2) is a component of reduced neuroendocrine sensitivity to estrogen in the aging mouse. Young (4 month-old), middle-aged (13 month-old), and old (25 month-old) C57BL/6J mice were ovariectomized, implanted 2 weeks later with Silastic capsules containing E2 or cholesterol (CHOL), and sacrificed 3 days later. Hypothalamic POMC mRNA was measured by solution hybridization/RNase protection, using a RNA probe complementary to a fragment of mouse POMC mRNA. In the group with CHOL implants, POMC mRNA was 36% lower in middle-aged and old mice compared to young mice. E2 treatment reduced POMC mRNA levels by 44% in young mice but failed to lower POMC mRNA in middle-aged and old animals. These results confirm earlier evidence of reduced levels of POMC mRNA in hypothalami of aging rodents and indicate that the ability of E2 to reduce hypothalamic POMC mRNA is lost by middle age.

Aging↗
PubMed1992

Differential contributions of ovarian and extraovarian factors to age-related reductions in plasma estradiol and progesterone during the estrous cycle of C57BL/6J mice.

The relative contributions of ovarian and extra-ovarian factors to the altered ovarian steroidal profiles of middle-aged mice were assessed by reciprocal, heterochronic ovarian grafting. Ovaries from cycling, young (2 months), and middle-aged (12 months) mice were exchanged by grafting under the renal capsules. Blood samples were obtained daily at midday throughout the estrous cycle for measurement of estradiol (E2) and 3-4 h after lights-out on proestrus to measure the preovulatory elevation of progesterone (P4). Middle-aged intact mice had lower mean concentrations of E2 during the cycle, no detectable midday preovulatory elevation of E2, and an attenuated preovulatory increase of P4 compared to young mice. Ovarian grafts from young donors failed to increase mean E2 levels of middle-aged mice, but did restore the preovulatory elevation of E2 and preovulatory P4 to levels of young controls. Reciprocal grafting confirmed these findings: ovaries from middle-aged donors in young hosts produced mean E2 levels equivalent to those of young mice but were unable to support a preovulatory increase of E2 or a preovulatory P4 level equivalent to that of young controls. These results reveal differential contributions of ovarian and extra-ovarian factors to age changes in E2 and P4. They indicate that ovarian aging plays an important role in attenuating the preovulatory increase of E2 and P4, but extra-ovarian, presumably neuroendocrine, age changes underlie the mean reduction of E2 levels across the estrous cycle.

Aging↗
PubMed1992

Up-regulation of the uterine estrogen receptor and its messenger ribonucleic acid during the mouse estrous cycle: the role of estradiol.

Uterine estrogen receptor (ER) and ER mRNA were measured in cycling and ovariectomized (OVX) estrogen-treated mice to probe the physiological regulation of the intracellular distribution and biosynthesis of ER. On proestrus, when plasma estradiol (E2) levels are highest, the cell nuclear ER concentration was 2.4-fold greater than on metestrus. This increase was primarily attributable to an increase in total cellular ER (cytosolic plus nuclear ER) and only secondarily to an activation of ER, as measured by its redistribution from the cytosolic (i.e. nuclear-extractable) to the nuclear (nonextractable) fraction. Total cellular ER concentration was 1.8-fold higher on proestrus than on metestrus, whereas the fraction of total ER in the nuclear compartment (i.e. the percentage activated) was only 1.3-fold higher. The concentration of cellular ER mRNA was 3-fold greater on proestrus than on the other days of the estrous cycle, suggesting that the increased concentration of ER on proestrus was a consequence of increased ER gene expression. In OVX mice, physiological and, to a lesser extent, supraphysiological levels of E2 increased cell nuclear ER. As in proestrous mice, the increased ER content contributed more than ER activation to the increased cell nuclear ER concentration. Physiological, but not supraphysiological, concentrations of E2 increased ER mRNA in OVX mice. Together, these results suggest that up-regulation by E2 of ER mRNA and ER accounts for most of the increased nuclear binding of ER on proestrus. E2-dependent activation and consequent DNA binding of ER presumably initiate this process, but quantitatively account for only a small fraction of the increased nuclear binding of ER.

Animals↗
PubMed1992

Ingesting an onlay. A case report.

When a patient attempted to speak during a dental procedure, she swallowed an onlay. After four weeks, it was mechanically removed from her colon.

Colon↗
PubMed1992

Genetic influences on oestrous cyclicity in mice: evidence that cycle length and frequency are differentially regulated.

Studies in C57BL/6J, DBA/2J and C3H/HeJ mice and in two F1 hybrid strains (B6D2F1 and B6C3HF1) 2-5 months old revealed marked genotypic differences among inbred strains. C57 mice had three times as many regular (3-6 days) cycles as DBA and C3H mice, due largely to fewer pseudopregnant-like (7-14 day) cycles. C57 had longer regular cycles than DBA and C3H mice. Although the frequencies of regular cycles of DBA and C3H mice were similar, the cycles of C3H mice were shorter than those of DBA mice. The results indicated that the genetic determinants of the frequency of regular cycles differ from those specifying cycle length. Frequency of regular cycles of F1 hybrids was either intermediate between the parent strains (B6D2F1) or similar to the C57 strain (B6C3HF1), suggesting that regular cycle frequency shows additive genetic variation in the former crosses, but mostly dominant variance in the latter background. Regular cycles were either shorter than in both parent strains (B6D2F1) or similar to one of them (B6C3HF1), indicating heterosis and dominance for genes specifying short cycles. Although the lack of reciprocal crosses meant that maternal effects and possible genomic imprinting effects could not be assessed, these results reveal marked genetic influences on cycle length and frequency and suggest that some of the genes specifying these two traits differ.

Animals↗
PubMed1991

Age-related alterations in estrogen receptor dynamics are independent of cycling status in middle-aged C57BL/6J mice.

The objective of this study was to determine whether changes in estrogen receptor (ER) levels and dynamics that were previously observed in old acyclic mice were present in middle-aged mice and whether the cycling status of the mice influenced those changes. Young (3-6 months) regularly cycling and middle-aged (12-14 months) C57BL/6J mice that were either acyclic or still cycling regularly were injected with a dose of E2 (0.05 microgram/10 g body wt) sufficient to achieve maximal levels of nuclear ER (ERn) in all tissues examined: hypothalamus (HYPO), pituitary (PIT), and uterus (UT). The rise and fall of ERn and the replenishment of cytosolic ER (ERc) were measured 0, 1, 2, 4, 8, 12, and 24 h later. Cycling status did not affect ER binding profiles in middle-aged tissues. Therefore, data from cycling and acyclic subgroups were pooled for comparison with young mice. The increase in ERn following E2 injection, measured as the integrated area under the ERn profile, was reduced 33, 23, and 17%, respectively, in HYPO, PIT, and UT of middle-aged mice. In addition, the duration of elevated ERn was selectively reduced in middle-aged HYPO. ERc levels were reduced in middle-aged HYPO and UT, but replenishment rates were not altered. Reductions in total ER (ERn + ERc) were sufficient to account for the decline in ERn in middle-aged HYPO and UT, but factors in addition to ER loss appear to contribute to reduced ERn in middle-aged PIT. These results indicate that alterations in ER levels and dynamics occur prior to the transition to acyclicity, that these alterations are not secondary to hormonal or other changes associated with acyclicity, and that receptor loss appears to account for most of the age-related reduction in nuclear ER binding.

Aging↗
PubMed1991

Absence of estrogenic activity in a diet that promotes estrous cyclicity in C57BL/6J mice.

A breeder diet that shortens estrous cycles in mice has been reported to contain estrogenic substances, based on its ability to increase uterine weight of immature mice. However, the estrogenicity of the diet was inferred from uterine weight gain of immature mice that were intact. The increased uterine weight of mice on the breeder diet could thus have resulted from a precocious pubertal increase of endogenous estrogens induced by the diet rather than estrogenic substances in the diet. We therefore measured the estrogenicity of the breeder diet in ovariectomized animals. C57BL/6J mice were fed the breeder diet or a standard diet for 1 or 4 weeks. The breeder diet failed to increase uterine weights above control values for either treatment interval. Intact mice that were fed the breeder diet had twice the number of cycles of mice fed the standard diet, a confirmation of earlier studies. These results indicate that the breeder diet does not contain biologically significant estrogenic activity, and thus potentiates cyclicity by other means.

Animals↗
PubMed1991

Dental care utilization among dental students.

The purpose of this study was to determine the proportion of needed dental care actually received by dental students during their dental education. This was accomplished by a review of dental records for recent Baylor College of Dentistry graduates. Collected data included restorative, periodontal, endodontic and extraction procedures planned and dental care actually accomplished prior to graduation. Comparisons of these findings were made based on gender, ethnicity and academic standing of the sample subjects. The sample size of 134 included 98 males and 36 females; 111 were Caucasian and 23 Minorities. Fifty-six individuals were in the upper academic third of their class, 37 in the middle third and 41 in the lower third. The treatments required were primarily operative dental restorations (7.28 +/- 7.19 surfaces per student), crowns (0.43 +/- 1.22 units per student) and extractions (0.90 +/- 1.58 per student). Periodontal and endodontic needs were minimal. Students received approximately 60% of the required care during their dental education. Minimal relationships were identified between gender, academic standing and ethnicity and the students' care needs and treatments. The results suggest a relatively low priority for receiving needed dental care among dental students.

Crowns↗
PubMed1990

Reactions of rat odontogenic tissues to heat.

Twenty-four Wistar rats were anesthetized and 200 degrees C heat was applied for 4 minutes to each mandibular left first molar. Eight of these rats were then killed at 2, 8, and 14 weeks. The subject and control teeth were radiographed and compared. They were then prepared for histologic evaluation and scored for levels of inflammation in both the pulpal and periradicular tissues. Furcal, interproximal, and apical radiographic changes were found at all three time intervals. These changes involved progressively larger percentages of teeth at 8 and 14 weeks. Histologically, complete necrosis and/or abscess formation were found in the coronal portions of all experimental pulps. With time, inflammatory changes increased in intensity and progressed through the radicular pulps, resulting in necrosis or calcific changes and, finally, inflammatory changes in the periradicular areas. The pathosis created by the application of heat was devoid of microorganisms as evaluated by the Brown and Brenn stain.

Animals↗
PubMed1990

Genetic influences on the timing of puberty in mice.

Genetic influences on the timing of three pubertal events--vaginal opening, first vaginal cornification, and onset of cyclicity--were studied in C57BL/6J, DBA/2J, and C3H/HeJ mice and in two F1 hybrid strains (B6D2F1 and B6C3HF1). Marked genotypic differences were found. Among inbred strains, differences in the onset of vaginal opening and first vaginal cornification (C3H less than DBA less than C57) did not parallel those for the onset of cyclicity (C3H much greater than DBA = C57). Compared to parental strains, F1 hybrid strains were intermediate for times of vaginal opening and first vaginal cornification, consistent with the model in which the genetic effects on the timing of these events are additive. By contrast, onset of cyclicity occurred significantly earlier in the F1 hybrids than in their parent strains, indicating heterosis for one or more genes specifying this event. Body weights also differed among the genotypes from weaning onward, but these differences were only partially correlated with the differences in the timing of the pubertal events. Thus, genetic influences other than those affecting body weight contribute to the differential timing of pubertal events in these mouse strains. These results reveal marked genetic variation in the timing of puberty, and indicate that the set of genes specifying the timing of vaginal opening and first vaginal cornification differs from those specifying the onset of cyclicity.

Age Factors↗
PubMed1990

Effects of chronic exposure to estradiol on ovarian cyclicity in C57BL/6J mice: potentiation at low doses and only partial suppression at high doses.

Long-term exposure to ovarian hormones contributes to age-related changes in estrous cyclicity in rodents. Estrogens are implicated in this process, but the concentration of estrogen required to exert these effects is not well established. Also, although estrogens are presumed to alter vaginal cyclicity by affecting the hypothalamic-pituitary axis, they may also impair the ability of the vaginal epithelium to cornify. To address these issues, young and middle-aged ovariectomized (ovx) C57BL/6J mice were exposed for 7-10 wk to plasma levels of estradiol (E2) at one of three ranges (30-40, 50-80, or 120-160 pg/ml). Ovaries from young mice were then transplanted under the renal capsule, and vaginal cyclicity was monitored for 4 mo. Mice exposed to the lowest level of E2 not only failed to stop cycling, but had a higher monthly frequency of estrous cycles than did controls (nearly 1 extra cycle/mo). Mice exposed to the intermediate level of E2 showed no impairment in cyclicity. Although mice exposed to the highest concentrations of E2 showed no vaginal cyclicity, they continued to ovulate as evidenced by fresh, albeit reduced, numbers of corpora lutea. These results indicate that, in ovx mice, (1) chronic exposure to relatively low concentrations of E2 potentiates cyclicity, (2) very high levels of E2 are required to induce acyclicity, and (3) this acyclicity reflects vaginal as well as neuroendocrine alterations. The results also indicate that vaginal acylicity may be a poor indicator of ovulatory acyclicity in mice that have been chronically exposed to E2.

Aging↗