Biomedical subjects

N J MacLusky

Publications and source records attributed to N J MacLusky.

At least 19 recordsLinked to original sources

PubMed1997

Effects of different estrogen and progestin regimens on the mechanical properties of rat femur.

The purpose of this study was to examine the effects of estrogen replacement, in concert with three different progestin regimens, on the mechanical properties of rat femoral cortical bone. Ninety-two 11-month-old female Sprague-Dawley rats were randomly divided into six groups and were treated for a duration of 6 months. Group-1 rats were intact controls, group-2 rats were ovariectomized controls, and groups 3-6 were ovariectomized and given continuous doses of estrogen with 5% estradiol 17B silicone-rubber implants. Groups 4, 5, and 6 were also given different doses of progestin (norethindrone): group 4 received a continuous dose of 3 micrograms per animal per day, group 5 received a cyclic dose of 6 micrograms per animal per day for 14 days of a 28-day cycle, and group 6 received an interrupted dose of 3 micrograms per animal per day for 3 days of a 6-day cycle. Femurs from each group were mechanically tested. Bending stiffness was measured by nondestructive three-point bending tests and maximum torque capacity, by destructive torsion tests. Geometrical properties and apparent density of cortical bone were also measured. The significant differences were: the increases in elastic modulus (measured from the three-point bending stiffness) of group 5 (cyclic norethindrone) compared with those of group 2 (ovariectomized controls) and group 3 (estrogen only); the increases in the size represented by the moment of inertia, the moment of the area, and medial-lateral width of group 2 compared with those of group 5; and the increases in apparent density and decreases in moment of inertia of group 6 (interrupted norethindrone) compared with those of group 2. Cyclic or interrupted treatment of progestin along with continuous treatment of estrogen after ovariectomy likely improves material properties of cortical bone, increases its density, and reduces the size of the bone compared with ovariectomized rats.

Animals↗

PubMed1997

Sex and the developing brain: suppression of neuronal estrogen sensitivity by developmental androgen exposure.

The developmental effects of androgen play a central role in sexual differentiation of the mammalian central nervous system. The cellular mechanisms responsible for mediating these effects remain incompletely understood. A considerable amount of evidence has accumulated indicating that one of the earliest detectable events in the mechanism of sexual differentiation is a selective and permanent reduction in estrogen receptor concentrations in specific regions of the brain. Using quantitative autoradiographic methods, it has been possible to precisely map the regional distribution of estrogen receptors in the brains of male and female rats, as well as to study the development of sexual dimorphisms in receptor distribution. Despite previous data suggesting that the left and right sides of the brain may be differentially responsive to early androgen exposure, there is no significant right-left asymmetry in estrogen receptor distribution, in either sex. Significant sex differences in receptor density are, however, observed in several regions of the preoptic area, the bed nucleus of the stria terminalis and the ventromedial nucleus of the hypothalamus, particularly in its most rostral and caudal aspects. In the periventricular preoptic area of the female, highest estrogen receptor density occurs in the anteroventral periventricular region: binding in this region is reduced by approximately 50% in the male, as compared to the female. These data are consistent with the hypothesis that androgen-induced defeminization of feminine behavioral and neuroendocrine responses to estrogen may involve selective reductions in the estrogen sensitivity of critical components of the neural circuitry regulating these responses, mediated in part through a reduction in estrogen receptor biosynthesis.

Androgens↗

PubMed1996

Sex differences in estrogen receptor and progestin receptor induction in the guinea pig hypothalamus and preoptic area.

Quantitative in vitro autoradiography was used to determine if regional sex differences in estrogen receptor (ER) content and/or estrogen responsiveness, as indicated by an increase in progestin receptor (PR), are present in the adult guinea pig brain. Adult male and female guinea pigs were gonadectomized 1 week before subcutaneous injection of 25 micrograms estradiol benzoate (EB)/kg body wt or the sesame oil vehicle. Animals were killed by decapitation 44 h after injection. Unoccupied PRs, and unoccupied and occupied ERs, were measured in discrete brain regions by quantitative in vitro autoradiography using [3H]R5020 and [3H]estradiol as ligands, respectively. In vehicle-injected controls, a higher level of ER was found in the arcuate nucleus (ARC), dorsal medial nucleus (DMN) and ventrolateral nucleus (VLN) of females as compared to males. At 44 h after EB injection, 32-55% of the ERs were occupied; however, EB treatment caused a marked down-regulation of total receptor (calculated as occupied+ unoccupied receptor) in most of the brain regions examined, including the periventricular preoptic area (PVP), medial preoptic area (MPO), bed nucleus of the stria terminalis, paraventricular nucleus, ARC, ventrolateral hypothalamus (VLH), VLN, and DMN. In EB-treated animals, PR binding was detectable in the PVP, MPO, ARC, VLH, and VLN, with higher levels of binding observed in the PVP, MPO, and VLN of the female as compared to the male. No PR binding was observed in oil-injected control animals. These results demonstrate region-specific sex differences in ER as well as estrogen-induced regulation of progestin and ERs in the guinea pig brain. The discordance between the regional distributions of sex differences in ER and estrogen-induced PR implies that sex differences in ER and estrogen-induced PR implies that sex differences in estrogen response may not be clearly linked to a sex difference in receptor number. Instead, sex differences in response may involve differences in receptor number within specific subpopulations of estrogen target cells or may involve differences in ER dynamics.

Animals↗

PubMed1996

Sex differences in corticosteroid binding in the rat brain: an in vitro autoradiographic study.

Several previous studies have raised the possibility of sex differences in the distribution of corticosteroid receptors in the brain. The direction and magnitude of these differences have, however, remained controversial. In the present study, we have re-examined the concentrations of mineralocorticoid (MR) and glucocorticoid (GR) receptors in the brains of male and female rats at varying times (1 to 6 days) after combined gonadectomy (GDX) and adrenalectomy (ADX). Cytosol binding assays confirmed the presence of higher MR levels in short-term (3-day) GDX-ADX males. This difference disappeared by 6 days after surgery, as receptor levels in females rose to be equivalent to those in males. Using an improved in vitro autoradiographic method, the distribution of MR and GR was studied in males and females 3 days after GDX-ADX. The distribution of MR and GR in the brains of these rats was similar in the two sexes. MR binding in the male, however, was significantly greater than that in the female throughout the principal cell fields of the hippocampus. Measurements of circulating corticosterone levels at the time of GDX-ADX suggest that this sex difference may reflect a more rapid recovery of the MR system in males than in females following the stress-induced rise in corticosterone secretion occurring at the time of surgery.

Adrenal Cortex Hormones↗

PubMed1996

HLA-G expression during preimplantation human embryo development.

HLA-G is a nonclassical class I major histocompatibility complex molecule with a restricted pattern of expression that includes the placental extravillus cytotrophoblast cells in direct contact with maternal tissues. Circumstantial evidence suggests that HLA-G may play a role in protection of the semiallogeneic human fetus. We examined whether HLA-G is expressed during the critical period of preimplantation human development and whether expression of this molecule could be correlated with the cleavage rate of embryos. Using reverse transcription PCR on surplus human embryos and unfertilized oocytes from patients undergoing in vitro fertilization we detected HLA-G heavy chain mRNA in 40% of 148 of blastocysts tested. The presence of HLA-G mRNA was also detected in unfertilized oocytes and in early embryos, but not in control cumulus oophorus cells. beta 2-Microglobulin mRNA was also found in those embryos expressing HLA-G. In concordance with our mRNA data, a similar proportion of embryos stained positive for HLA-G utilizing a specific monoclonal antibody. Interestingly, expression of HLA-G mRNA was associated with an increased cleavage rate, as compared to embryos lacking HLA-G transcript. Thus, HLA-G could be a functional homologue of the mouse Qa-2 antigen, which has been implicated in differences in the rate of preimplantation embryo development. To our knowledge, the presence of HLA-G mRNA and protein in human preimplantation embryos and oocytes has not been reported previously. The correlation of HLA-G mRNA expression with cleavage rate suggests that this molecule may play an important role in human pre-embryo development.

Antibodies, Monoclonal↗

PubMed1996

Regulation of estrogen receptor concentrations in the rat brain: effects of sustained androgen and estrogen exposure.

To determine whether estrogen and androgens either alone or in combination downregulate estrogen receptors in the brain, ovariectomized/adrenalectomized female rats received one of the following four treatments: (1) one subcutaneously placed Silastic capsule containing 10% estradiol in cholesterol, (2) one capsule containing 10% estradiol and two capsules containing 100% 5 alpha-dihydrotestosterone (DHT), (3) two capsules containing DHT, or (4) empty Silastic capsules (control animals). Animals were killed 4 or 8 days after capsule insertion and the occupied, unoccupied and total estrogen receptor content in specific brain nuclei was determined by quantitative in vitro autoradiography. To determine if the effects of the androgen were reversible, DHT capsules were removed after 4 days from half of the estradiol+DHT-treated rats, and the animals were killed 4 days later. Estradiol downregulated estrogen receptor expression in the periventricular preoptic area, medial preoptic area, bed nucleus of the stria terminalis (BNST), arcuate nucleus (ARC), ventromedial nucleus (VMN), and medial and cortical amygdala, decreasing receptor content by 30-41% in animals treated for 4 days, and by 44-60% in animals treated for 8 days with estradiol alone. DHT treatment in combination with estradiol further decreased estrogen receptor content in the BNST, ARC and VMN, relative to the estradiol-only animals. DHT in the absence of estrogen was without effect. In animals in which the DHT capsules were removed after 4 days of exposure, allowing the estradiol to remain for a further 4 days, estrogen receptor levels were indistinguishable from those measured in control animals treated for 8 days with estradiol alone. These results demonstrate that sustained estrogen exposure downregulates levels of estrogen receptor in the brain and confirm that DHT synergizes with estrogen in inducing this response in some, but not all, target neuronal groups.

Animals↗

PubMed1996

Embryonic human leukocyte antigen-G expression: possible implications for human preimplantation development.

OBJECTIVE: To investigate further the association between human leukocyte antigen G (HLA-G) expression in human embryos and other factors known to influence IVF pregnancy outcome. SETTING: A university-based tertiary referral center (The Toronto Hospital). INTERVENTIONS: Nontransferred embryos at the two- to four-cell stage were obtained from patients undergoing IVF and were cultured in Ham's F-10 medium supplemented with 10% human sera or cocultured with ovarian cancer cells in the same medium. Embryos that reached blastocyst stage (n = 148) were analyzed by reverse transcriptase-polymerase chain reaction for HLA-G and beta 2 microglobulin (beta 2m) expression. Statistical analysis was performed to identify possible factors associated with variability of expression. RESULTS: Approximately 40% of studied blastocysts had detectable expression of both HLA-G and beta 2m messenger RNA. In 46% of blastocysts, beta 2m alone was observed. Interestingly, sibling embryos from patients that became pregnant were significantly more likely to express HLA-G than embryos from patients that did not conceive as a result of their IVF cycles. No association was found between HLA-G expression and culture conditions, patients age, or infertility diagnosis. CONCLUSION: The population of embryos obtained through IVF is heterogeneous in expression of HLA-G and beta 2m, which may reflect overall health of the embryos. Blastocysts showing positive HLA-G expression may have increased viability and implantation potential, although the underlying mechanisms remain to be elucidated.

Base Sequence↗

PubMed1995

Sexual differentiation of estrogen receptor concentrations in the rat brain: effects of neonatal testosterone exposure.

This study tests the hypothesis that sex differences in estrogen receptor (ER) expression in the rat hypothalamus and preoptic area may at least partly result from androgen exposure during the immediate postnatal period. Male rats were castrated and female rats were injected with androgen, at either 15-30 min, 24 h or 10 days after birth. ER distribution in the brain was evaluated by in vitro autoradiography at 28 days of age. Males castrated immediately after birth exhibited higher ER levels in the preoptic area and the ventromedial and arcuate nuclei of the hypothalamus than either control males or males castrated on day 10. Females injected at birth with testosterone propionate exhibited reduced ER binding in the same brain regions. These data suggest that postnatal androgen secretion prior to postnatal day 10 permanently alters patterns of ER expression in the brain.

Analysis of Variance↗

PubMed1995

The effect of different hormone replacement therapy regimens on the mechanical properties of rat vertebrae.

The purpose of this study was to examine the effects of estrogen replacement, in concert with three different progestin regimens, on the mechanical properties of rat lumbar vertebrae. Ninety-two Sprague-Dawley rats (11 months old) were divided into six groups for treatment. The first group was an intact control, the second group (OVX) was ovariectomized only, and the third group (estrogen-only) was ovariectomized and received continuous estrogen through a 17 beta-estradiol implant. The remaining groups were ovariectomized and received estrogen and progestin (norethindrone, NET) therapy; 3 micrograms of NET was injected daily (estrogen plus continuous NET), or 6 micrograms of NET was injected for 14 consecutive days of a 28-day cycle (estrogen plus cyclic NET), or for 3 consecutive days of a 6-day cycle (estrogen plus interrupted NET). The animals were sacrificed after 6 months, and the vertebrae were dissected out. The vertebral processes of the fourth lumbar vertebrae were removed, and the density of the vertebral bodies was determined. They were then subjected to compression testing. We found that all three estrogen/progestin regimens maintain bone density and all mechanical properties at a level indistinguishable from the control. However, the cyclic and continuous NET treatment results were, with the exception of density, also indistinguishable from those of the ovariectomized group. The estrogen plus interrupted NET group on the other hand, has a significantly greater compressive modulus and density than the ovariectomized group. In conclusion, with respect to the ovariectomized group, the estrogen plus interrupted NET treatment resulted in a superior density and compressive modulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Lumbar vertebral density and mechanical properties in aged ovariectomized rats treated with estrogen and norethindrone or norgestimate.

OBJECTIVE: This study was designed to investigate the effects of estrogen alone or combined with two different progestins, norethindrone or norgestimate, on bone density and compressive mechanical properties in an aged rat model. STUDY DESIGN: Twenty 11-month-old female Sprague-Dawley rats were sham operated (intact control) and 80 wee ovariectomized. Three groups of 20 ovariectomized rats were implanted with Silastic silicon rubber (Dow Corning, Midland, Mich.) capsules containing 5% estradiol (wt/wt) in cholesterol. All rats in the intact control (group 1) and the ovariectomized (group 2) and the first of the ovariectomized plus estrogen (group 3) groups were injected subcutaneously daily for 6 months with corn oil (vehicle). Two other groups of rats with estrogen capsules received daily injections of norethindrone (3 micrograms/rat/day) or norgestimate (1.5 micrograms/rat/day) in corn oil for 3 days out of every 6 days (interrupted progestin). The effects of these various treatments on bone mineral content and bone mineral density in the vertebrae were measured by dual energy x-ray absorptiometry. The L4 vertebral bodies were also tested to failure in compression. RESULTS: The ovariectomized rats receiving corn oil alone had the lowest bone mineral density compared with intact controls. Estrogen treatment alone resulted in a lower bone mineral density than in the intact controls. In contrast, both interrupted progestin regimens resulted in vertebral bone mass index at the same level as the intact controls. Compression tests revealed that ovariectomized controls also had the lowest modulus of elasticity of all groups. However, unlike bone mineral density, estrogen alone resulted in mechanical properties similar to intact controls, whereas the vertebrae in both interrupted progestin groups had variable mechanical properties compared with the ovariectomized and intact control groups. CONCLUSIONS: We conclude that in this experimental model hormone replacement therapy with estrogen and an androgenic (norethindrone) or nonadrogenic (norgestimate) progestin result in similar bone mineral density and mechanical properties. In addition, both interrupted progestin regimens had a better effect than estrogen alone on vertebral bone density.

Absorptiometry, Photon↗

PubMed1995

Localization and measurement of occupied androgen receptors in thaw-mounted rat and human prostate tissue sections by in vitro autoradiography.

In this paper we present an in vitro exchange binding assay procedure for measurement of androgen receptors in slide-mounted tissue sections. This method allows quantitative autoradiographic determinations with an anatomical resolution approaching the cellular level. Tissue sections are incubated with the synthetic androgen [3H]R1881 in the presence of triamcinolone acetonide to suppress possible binding of the radioligand to the progestin receptor. Adjacent tissue sections are incubated with [3H]R1881 in the presence of excess unlabeled 5 alpha- dihydrotestosterone or R1881 to assess nonspecific binding. Following incubation, the tissue sections are washed to remove unbound radioligand and either scraped for immediate determination of androgen receptor binding or placed against emulsion-coated film for the production of an autoradiographic image. In validation experiments with rat prostate sections from castrated, gonad-intact, and androgen-supplemented animals, maximum levels of androgen binding were observed with incubation at 4 degrees C or 72 h. Markedly less binding was detected with shorter incubations or with incubations at even slightly elevated temperatures. Very little androgen receptor binding was detected in castrated animals whereas receptor levels in intact and androgen-supplemented animals were 79.3 fmol/mg and 143.6 fmol/mg protein, respectively, suggesting that the method is selective for occupied receptors. Saturation binding analysis revealed binding to a single class binding site with high affinity (kd = 1.475 +/- 0.12 nM). Autoradiographic images of androgen binding in the prostate reflected the findings with the scraped sections: essentially no specific binding was present in sections from castrated animals whereas much heavier labeling was present in sections from intact animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

In vitro labeling of gonadal steroid hormone receptors in brain tissue sections.

Autoradiographic methods have been developed for measurement of gonadal steroid receptors in situ in brain tissue sections. Based on principles established previously for estrogen receptors in the rat brain using a 125I-labeled ligand, procedures have been developed for in vitro labeling of estrogen, androgen, and progestin receptors with commercially available tritiated ligands. Addition of protamine sulfate to the incubation buffer precipitates the receptors in situ in the tissue sections, allowing them to be detected autoradiographically after incubation with labeled steroid and subsequent washing to remove unbound and nonspecifically bound ligand. Occupied and unoccupied estrogen receptors can be measured selectively using appropriately modified incubation conditions. In the case of androgen and progestin receptors, unoccupied receptors are readily detected by in vitro labeling of tissue sections, but occupied receptors do not appear to label efficiently. Preliminary data suggest that these methods should be equally applicable to a variety of laboratory animals, including the rat, mouse, guinea pig, and monkey.

Animals↗

PubMed1995

Immunocytochemical detection of androgen receptor in human temporal cortex characterization and application of polyclonal androgen receptor antibodies in frozen and paraffin-embedded tissues.

Immunocytochemical and biochemical studies have demonstrated the presence of androgen receptor protein in various regions of the rodent and non-human primate cortex. Localization of androgen receptor in the human brain has, however, not been studied as extensively, because of difficulties in obtaining suitable tissue samples. In the present study, we have localized androgen receptors in both frozen and paraffin-embedded temporal cortex from epileptic patients undergoing resection. Polyclonal antibodies were raised against fusion proteins containing fragments of the human androgen receptor protein. The antibodies were affinity-purified against the corresponding fusion protein. Immunoprecipitation and Western blotting using extracts from human cell lines demonstrated the specificity of the antibodies for the human androgen receptor and lack of cross-reactivity with other steroid hormone receptors. Immunocytochemistry was performed on frozen and paraffin sections of human temporal cortex and in paraffin-embedded benign hyperplastic prostates (BPH), as well as prostate and breast carcinomas, by the streptavidin-biotin-peroxidase method. Antigen-retrieval was performed in paraffin-embedded sections using microwave irradiation. Specific nuclear and cytoplasmic immunoreactivity for androgen receptor was detected in neurons, astrocytes, oligodendrocytes, and microglia cells of the temporal cortex. In contrast, only nuclear staining was observed in BPH, prostate and breast carcinomas. Immunoprecipitation of human temporal cortex lysate and subsequent Western blot analysis demonstrated the expression of a 98 kDa immunoreactive protein, slightly smaller than the reported molecular weight of the wild-type androgen receptor. These results provide further evidence for the expression of androgen receptor in the human temporal cortex. The use of these immunocytochemical techniques should enable the retrospective determination of possible changes in androgen receptor expression in a variety of archival paraffin-embedded tissues, including samples of the human central nervous system.

Adolescent↗

PubMed1995

Distribution of occupied and unoccupied estrogen receptors in the rat brain: effects of physiological gonadal steroid exposure.

In vitro autoradiographic methods have been developed for selective measurement of occupied and unoccupied estrogen receptors (ERs) in brain tissue sections. Addition of protamine sulfate traps unoccupied ERs in the tissue sections, allowing them to be detected after a short period of incubation with labeled estrogen. Occupied ERs are assessed, after washing in buffer without protamine to eliminate unoccupied receptor, by incubating the sections for 2 h at 37 C to exchange isotopically labeled steroid for the endogenous unlabeled ligand. Total ER binding capacity is estimated by summing the values for occupied and unoccupied ER. In all brain regions of normal females, ER occupation is low at estrus, reflecting the very low levels of circulating estradiol present at this stage of the estrous cycle, rising to approximately 50% of binding capacity at proestrus. By contrast, in intact males ER occupation varies considerably between brain regions, from a high of 55% of binding capacity in the bed nucleus of the stria terminalis to a low of 21% in the hypothalamic arcuate nucleus. Gonadectomy or treatment of intact males with the aromatase inhibitor 4-hydroxy androstenedione greatly reduces or eliminates ER occupation, depending on the brain region. In both sexes, changes in levels of endogenous gonadal steroids have little effect on total (occupied plus unoccupied) ER concentrations, with the exception of the hypothalamic ventromedial nucleus of the female, in which total ER concentration declines at estrus. These results are consistent with the hypothesis that local aromatization may be the primary determinant of regional ER occupation in the brain of the male rat, in contrast to the female, in which high levels of ER occupation are found only during the preovulatory estrogen surge. Although physiological changes in circulating estradiol and aromatizable androgen concentrations induce large changes in ER occupation, they have little effect on total ER content in most regions of the brain, suggesting that previous reports of changes in ER messenger RNA levels under different conditions of gonadal steroid exposure may not be directly reflected in steady state levels of the cognate receptor site.

Animals↗

PubMed1995

Hyaluronidase activity in human semen: correlation with fertilization in vitro.

OBJECTIVES: To characterize the relationship between hyaluronidase activity and the currently used methods of assessing sperm function and to determine whether the measurement of hyaluronidase activity can provide a reliable index of sperm fertilizing capacity in man. DESIGN: Nonrandomized prospective study. SETTING: Tertiary referral IVF and andrology clinics affiliated with the University of Toronto. SUBJECTS: Four hundred eight samples were collected, 248 from men undergoing investigation in andrology and fertility clinics and 160 from men participating in an IVF program. INTERVENTIONS: Semen samples were treated with NP-40 in buffer to extract hyaluronidase and applied to a circular well cut into a petri dish containing a mixture of hyaluronic acid and agar. Enzyme activity was assessed by measuring the area of substrate hydrolysis. RESULTS: Significant positive correlations were found between hyaluronidase activity and sperm concentration, motility, and the percentage of sperm with normal morphology in the studied samples. In the IVF samples, hyaluronidase activity was found to be related significantly to the fertilization rate. Moreover, we were able to establish values of hyaluronidase below which no fertilization occurred and above which fertilization of at least one oocyte was achieved. CONCLUSION: These results suggest that measurement of hyaluronidase activity may provide a useful method for assessing the integrity of the acrosomal enzyme system, providing a simple and reliable predictor of the fertilizing potential of human sperm.

Enzyme Stability↗

PubMed1995

The effect of three hormone replacement regimens on bone density in the aged ovariectomized rat.

OBJECTIVE: To investigate the effects of estrogen (E) alone or with cyclic, continuous, or interrupted P regimens on bone density in an aged rat model. DESIGN: Randomized controlled trial. ANIMALS: Twenty 12-month-old female Sprague-Dawley rats were sham operated (intact control) and 100 were ovariectomized (OVX). INTERVENTION: Four groups of 20 OVX rats were implanted with silastic capsules containing 5% E2 (wt/wt) in cholesterol. All rats in the intact control (group 1), OVX (group 2), and the first of the OVX plus E groups (group 3) were injected subcutaneously daily for 6 months with corn oil (vehicle). Three other groups of rats with E capsules received daily injections of norethindrone in corn oil, according to the following dosage schedules: 6 micrograms norethindrone/rat per day for 2 of every 4 weeks (cyclic; group 4); 3 micrograms norethindrone/rat per day every day (continuous; group 5); or 3 micrograms norethindrone/rat per day for 3 of every 6 days (interrupted; group 6). MAIN OUTCOME MEASURES: Bone mineral content (BMC) and bone mineral density (BMD) in the femur and vertebrae were measured by dual-energy roentgenogram absorptiometry. RESULTS: The OVX rats (group 2) receiving corn oil alone had the lowest BMD. Intact controls (group 1), E plus cyclic P (group 4), and E and interrupted P (group 6) were all similar and had significantly greater bone density in the vertebrae than the OVX controls. In contrast, vertebral BMD with E alone (group 3) and continuous E and P (group 5) was not significantly different from the OVX group. Femur BMD was significantly lower in the OVX group compared with the other five groups, which did not differ significantly from each other. CONCLUSION: In this experimental model, compared with OVX controls, combined hormone replacement therapy with E and cyclic or interrupted P resulted in the best vertebral BMD whereas continuous E and P resulted in the worst BMD. In the femurs, E alone and E plus P had equal effects on BMD.

Adrenal Glands↗

PubMed1994

Ontogenesis of prostaglandin E2 binding sites in the brainstem of the sheep.

Perinatal changes in plasma prostaglandin E2 (PGE2) act at the level of the fetal brainstem to modulate respiratory activity. In-vitro receptor autoradiography was used to determine whether PGE2 binding sites (putative receptors) are located in brainstem regions responsible for respiratory control. Frozen brainstem sections were obtained from fetal sheep at 140 d of gestation, lambs at 5 h and 10 d after birth, and adults (n = 3 at each age). In the perinatal brainstem, high density binding was localized near the following nuclei: hypoglossal, tractus solitarius, parabrachial and spinal trigeminal-oral. Moderate levels of binding were localized near the nuclei of the spinal trigeminal tract, ambiguus, inferior olivary, cuneate, gracilis, facial, medial vestibular, superior vestibular, and abducens. Binding density did not change with age within the perinatal period. However, binding in three high density regions (hypoglossal, spinal trigeminal and parabrachial nuclei) decreased significantly in adulthood, whereas the binding in the nucleus of the solitary tract remained high. We hypothesize that the PGE2 binding sites that we identified near respiratory regions of the brainstem may mediate the central respiratory effects of PGE2.

Animals↗

PubMed1994

Sex differences in the development of estrogen receptors in the rat brain.

The mechanisms involved in sexual differentiation of the brain remain incompletely defined. In mammals, testosterone secretion by the male during early development permanently alters the capacity of the brain to respond to circulating estrogen. In rats, this change in estrogen responsiveness is associated with a reduction in estrogen receptor (ER) levels in the periventricular region of the preoptic area (PVP), the medial preoptic nucleus (MPO), and the hypothalamic ventromedial nucleus (VMN) of the male. To determine whether these differences represent a response to early testosterone exposure or a secondary consequence of gonadal secretions at puberty, ER levels were measured by quantitative in vitro autoradiography in the brains of rats killed at intervals between 1-10 and 28-49 days of age. As early as 24 hr after birth, ER sex differences in the MPO and PVP are already quantitatively similar to those observed in adulthood. A sex difference in the VMN emerges later, between 5 and 10 days of age. Differences between brain regions are also observed in the rate of ER development after the first week of life, ER concentrations in the PVP and MPO being close to adult levels within 1 day of birth, in contrast to the VMN where they increase markedly between Day 10 and adulthood in both sexes. These observations suggest that changes in ER concentrations may be one of the earliest hallmarks of brain sexual differentiation. Sex differences in ER in different brain regions may, however, be expressed asynchronously, providing a possible mechanism for variation in the duration of "critical periods" for testosterone-mediated organization of specific CNS functions.

Animals↗