Browsing by Subject "Puberty"
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Item Action of manganese on puberty(Texas A&M University, 2007-09-17) Lee, Bo YeonManganese (Mn) is considered important for normal growth and reproduction. Because Mn can cross the blood brain barrier and accumulate in the hypothalamus, and because it has been suggested that infants and children are potentially more sensitive to Mn than adults, we wanted to determine the effects of Mn exposure on puberty-related hormones and the onset of puberty, and discern the site and mechanism of Mn action. We demonstrated that the central administration of manganese chloride (MnCl2) stimulated luteinizing hormone (LH) release in prepubertal rats. Incubation of medial basal hypothalamus (MBH) in vitro showed this effect was due to a Mn-induced stimulation of luteinizing hormone releasing hormone (LHRH). Further demonstration that this is a hypothalamic site of action was shown by in vivo blockade of LHRH receptors and the lack of a direct pituitary action of Mn to stimulate LH release in vitro. Chronic supplementation of low dose of MnCl2 caused elevated serum levels of LH, follicle stimulating hormone (FSH) and estradiol or testosterone. Importantly, Mn supplementation advanced the timing of puberty in both sexes. We investigated the mechanism by which Mn induces LHRH/LH release from the hypothalamus. Blocking the NMDA receptor, IGF1 receptor, or inhibiting nitric oxide synthase in vivo was ineffective in altering Mn-induced LH release. Dose-response, pharmacological blockade and nitrite assessments indicated that the lowest doses of Mn used stimulated LHRH release, but did not induce nitric oxide (NO) production, while only the highest dose of Mn stimulated NO. Conversely, a dose-dependent inhibition of Mn-induced LHRH release was observed in the presence of ODQ, a specific blocker of soluble guanylyl cyclase. Furthermore, Mn stimulated the release of cyclic GMP (cGMP) and LHRH from the same MBH, and a protein kinase G (PKG) inhibitor, KT5823, blocked Mn-induced LHRH release. Collectively, these data demonstrate that Mn can stimulate specific puberty-related hormones both acutely and chronically, and furthermore, suggest that low levels of Mn facilitate the normal onset of puberty. The principal action of Mn within the hypothalamus is to facilitate the activation of guanylyl cyclase, which subsequently stimulates the cGMP/PKG pathway resulting in the stimulation of prepubertal LHRH secretion.Item Effects of experimental fascioliasis on puberty and comparison of mounting activity by radiotelemetry in pubertal and gestating beef heifers(Texas A&M University, 2005-11-01) Paczkowski, Melissa JeanneAngus-sired heifers were allotted by age (mean=4 mo), BW (mean=135 kg), and sire (n=4) to either a control (n=10) or infected group (n=11; 600 metacercariae of Fasciola hepatica, intraruminally) to test our hypothesis that puberty is delayed by experimental fascioliasis. Blood samples were collected biweekly for analysis of steroid hormone concentrations. At 2-wk intervals, BW was recorded, and samples were collected for analysis of liver enzymes and serum proteins and fecal egg counts. A radiotelemetry system (HeatWatch??) was used to detect estrus and ovulation was confirmed by an elevation in serum progesterone (P4) after estrus. Heifers were artificially inseminated (AI) at the second observed estrus. Serum γ-glutamyl transpeptidase (GGT) and aspartate aminotransferase (AST) increased (p<0.0008) between day 0 and 112 in the infected group. Serum estradiol (E2) and P4 concentrations did not differ (p>0.1) between treatment groups. Mean age at puberty was 10 days later (p>0.1) in the infected group. Conception rate did not differ between control and infected heifers. The HeatWatch?? data were used to compare mounting activity during estrus in pubertal and gestating heifers. Mean duration of estrus was longer (p<0.01) for the second than for the pubertal estrus, though total mount duration and number of mounts did not differ. Number of mounts at second estrus was greater (p<0.05) for heifers that conceived (n=9). Mean duration of estrus and total mount duration at second estrus were not associated with pregnancy outcome. Estrus events were detected in all nine heifers during pregnancy (total=73). A majority (75%) of the interestrus intervals during gestation was <17 d. Number of mounts (p=0.035) and total duration of mounts (p=0.022) at second estrus were predictive of number of mounts during gestation. Experimental infection of Fasciola hepatica did not alter serum steroid hormone concentration or delay pubertal development in heifers. Estrus duration was longer for the second estrus compared to the pubertal estrus, and the number of mounts received during the second estrus was greater in heifers that did conceive to AI. Estrus events were detected in each heifer during pregnancy; however, a normal interestrus interval occurred in only 10% of the estrus events.Item Factors influencing age of puberty in confinement reared gilts(Texas Tech University, 1978-05) Savage, Jackie SueA greater number of gilts exposed to a boar in confinement exhibited estrus in confinement (P<.01) and the total number of gilts exhibiting estrus was greater for those gilts exposed to a boar during confinement (P<.05). No significant reduction in age at puberty was found with boar exposure. Boar exposure had no apparent effect on ovulation rate. No significant differences in adjusted urine cortisol concentrations were found between treatments or among trials. Gilts exhibiting estrus during the study were found to have (P<.05) lower urinary cortisol concentrations in confinement than gilts which did not exhibit estrus at any time during the study.Item Influence of Nutrition during the Juvenile Period on Gene Expression Within the Hypothalamic Arcuate Nucleus and on Age at Puberty in Heifers(2011-10-21) Allen, Carolyn C.Developmental changes within the hypothalamus are necessary for maturation of the reproductive neuroendocrine axis. Recent reports have implicated several neuronal networks in this process, but genes involved in their regulation have not been elucidated. Using a well-established model for nutritional induction of precocious puberty, objectives were to 1) use microarray technology to examine changes in gene expression within the arcuate nucleus (ARC) of the hypothalamus in pre-pubertal heifers fed high or low-concentrate diets, and 2) determine if high-concentrate diets are required for nutritional induction of precocious puberty. In Experiment 1, early-weaned, cross-bred heifers were fed either a high-forage/low-gain (HF/LG; 0.45 kg/d) or a highconcentrate/ high-gain (HC/HG; 0.91 kg/d) diet for 91 d. Analysis of microarray data indicated that 346 genes were differentially expressed (P < 0.05) between HC/HG and HF/LG heifers. Expression of three key metabolic genes [neuropeptide Y (NPY), agoutirelated protein (AGRP), and growth hormone receptor (GHR)] observed to be differentially expressed in the microarray analysis was investigated further by quantitative PCR. Real-time RT-PCR indicated that expression of NPY, AGRP and GHR was lower (P < 0.05) in HC/HG compared to HF/LG heifers. In contrast, concentrations of insulin (P < 0.05), IGF-1 (P < 0.002) and leptin (P = 0.1) were greater in HC/HG compared to HF/LG. For Experiment 2, 48 heifers were used in 2 replicates (24 heifers/replicate) in a 2 x 2 factorial design to examine the roles of diet type (HF vs HC) and rate of gain (LG, 0.45 kg/d vs HG, 0.91 kg/d) on age at puberty. Heifers were fed HC/HG, HC/LG, HF/HG or HF/LG (n = 12/group) for 14 wk, and then switched to a common growth diet (0.68 kg/d) until puberty. Heifers in both HG groups reached puberty at a younger age (54.5 ? 1.8 wk) than heifers in both LG groups (60.2 ? 1.9 wk; P < 0.04). A marked increase (P < 0.01) in serum concentrations of leptin occurred in HC/HG heifers between 24 and 30 wk of age. This increase in circulating leptin was not observed in other groups. Overall, results indicate that nutritional regulation of reproductive neuroendocrine development involves the control of NPY, AGRP and GHR expression. The abrupt increase noted for circulating leptin in heifers fed HC/HG diets, if timed and sustained appropriately, could represent an important temporal cue for activation of the neuroendocrine system and the onset of puberty.Item Kiss1 Gene Expression and the Effects of Kisspeptin During Pubertal Development in the Ewe Lamb(2012-02-14) Redmond, Jeremy ScottIncreased pulsatile release of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) is critical for pubertal initiation of ovarian cycles in female mammals. Kisspeptin, a peptide product of the Kiss1 gene, is required for normal puberty. In Experiment 1, ovariectomized ewe lambs bearing subcutaneous estradiol implants were used to investigate Kiss1 gene expression in the preoptic area (POA) and hypothalamus during pubertal maturation of the reproductive neuroendocrine system. Brain tissue was collected from ewes at 25, 30, and 35 wk of age (n=6/group). Patterns of LH release in circulation were determined on the day before euthanasia and cells containing Kiss1-mRNA were identified by in situ hybridization. Mean concentrations of LH and the frequency of LH pulses increased (P < 0.01) as ewe lambs matured. In the POA/Periventricular area (PEV), the number of Kiss1-expressing cells was greater (P < 0.04) in 30- and 35-wk-old than in 25-wk-old ewe lambs. In the arcuate nucleus (ARC), although no significant changes in number Kiss1-expressing cells were observed among age groups, the number of Kiss1 cells increased (P < 0.02) with increased frequency of LH release. This resulted in greater (P < 0.01) number of Kiss1 cells in the ARC of ewes demonstrating elevated frequency (> 6 pulses/12 h) of LH pulses. In Experiment 2, 28-wk-old ewe lambs were used to determine the effects of intermittent injections of kisspeptin on the release of LH and stimulation of gonadal function in peripubertal ewe lambs. Ewe lambs were treated intravenously with saline (Controls; n=6) or kisspeptin (n=6) hourly for 24 h. Blood samples were collected throughout the experiment for hormone analysis. Kisspeptin-treated lambs had greater (P < 0.02) mean circulating concentrations of LH, and frequency and amplitude of LH pulses than controls. Four of six kisspeptin-treated ewe lambs exhibited LH surge and luteal activity in response to treatments. However, onset of regular estrous cycles was not established immediately following kisspeptin-induced ovulation and no difference in age at onset of puberty was observed between groups. In conclusion, activation of the hypothalamic kisspeptin system may support elevated episodic release of LH critical for establishment of normal estrous cycle during pubertal development.Item Nutritional Programming of Neuroendocrine Pathways Controlling the Onset of Puberty in Heifers(2014-05-01) Alves, Bruna R. C.Accelerated body weight gain during the juvenile period leads to early maturation of the reproductive neuroendocrine system and puberty by advancing the onset of high-frequency release of gonadotropin-releasing hormone (GnRH). In a series of studies conducted as part of this dissertation, it was hypothesized that nutritional regimens that accelerate pubertal development alter the function of kisspeptin and neuropeptide Y (NPY) neurons, known modulators of the release of GnRH. In addition, alterations in the pattern of methylation of target genome sequences were investigated in DNA collected from the arcuate nucleus, a hypothalamic region well-characterized for its role in mediating the metabolic control of reproductive function. Early-weaned crossbred heifers were fed diets to promote an average daily gain of 0.5 Kg (Low Gain; n=12) or 1.0 Kg (High Gain; n=12) from approximately 4 to 8 mo of age. This nutritional regimen has been demonstrated to facilitate early onset of puberty in heifers. At eight mo of age, heifers were slaughtered and a block of tissue containing the preoptic area and hypothalamus was collected and processed for examining the expression of NPY and KISS1, investigating the innervation of GnRH and kisspeptin neurons by NPY fibers, and characterizing the methylation profile of target genomic DNA sequences isolated from the arcuate nucleus. Mean body weight and circulating concentrations of leptin were greater in High-gain than in Low-gain heifers. Elevated rate of body weight gain was associated with reduced expression of NPY in the arcuate nucleus, reduced proportion of GnRH neurons in apposition to NPY-containing varicosities, particularly in GnRH neurons located in the mediobasal hypothalamus, and a reduced number of KISS1-expressing cells in the mid portion of the arcuate nucleus. The rate of body weight gain during the juvenile period did not affect NPY innervation of kisspeptin neurons. Differential methylation of target genomic DNA sequences isolated from the arcuate nucleus was observed in association with rate of body weight gain in juvenile heifers, and genes affected included GHR, IGF2, IGF1R, LEPR, PEG3, LIN28B and HMGA2. Overall, results from these studies support the hypothesis that accelerated body weight gain during the juvenile period promotes alterations in cellular functions within the hypothalamus that facilitate early onset of puberty in heifers.Item Nutritional Programming of Puberty in Beef Heifers(2014-06-26) De Carvalho Cardoso, RodolfoNutritional and metabolic statuses during postnatal development control the timing of pubertal maturation in mammals. Studies reported herein had two overall aims. In Aim I, objectives were to characterize functional and morphological modifications that occur in the neuroendocrine system of prepubertal heifers in response to increased body weight (BW) gain during calfhood. We first tested the hypothesis that hypothalamic release of neuropeptide Y (NPY), an important inhibitory peptide involved in the integration of metabolism and reproduction, would be decreased in heifers that gained BW at higher rates. Confirming our hypothesis, heifers that gained 1 kg/day had lower concentrations of NPY in the third ventricle cerebrospinal fluid than heifers that gained 0.5 kg/day. These data corroborate previous results from our group that demonstrated that similar nutritional treatments result in decreased hypothalamic NPY expression and neuronal projections to gonadotropin-releasing hormone (GnRH) cells. We then tested the hypothesis that proopiomelanocortin (POMC) cells, a critical excitatory metabolic-sensing pathway in the hypothalamus, could be involved in the nutritional control of puberty. Heifers that gained BW at higher rates had greater POMC expression in the arcuate nucleus and an increased number of kisspeptin neurons innervated by fibers containing melanocyte-stimulating hormone alpha (?MSH), a product of the POMC gene. Very few GnRH neurons were observed in close apposition to ?MSH fibers and these projections were not dependent on metabolic status. Results suggest that melanocortin signaling through arcuate kisspeptin neurons may be an important mechanism involved in the nutritionally-programed acceleration of puberty in heifers. In Aim II we hypothesized that metabolic programming of processes underlying puberty could be shifted temporally during calfhood through the use of a stair-step, compensatory growth model. Results indicated that nutritional restriction between 6.5 to 9 mo of age did not affect the proportion of heifers pubertal by 12 mo of age when compared to continuous accelerated BW gain. Furthermore, we observed that increasing nutrient availability between 6 and 9 mo of age may potentially time pubertal onset consistently at around 12 mo of age while avoiding precocious puberty. Therefore, similar managerial strategies may allow optimal timing of sexual maturation in replacement beef heifers.Item Parents Talking About the Birds and the Bees With Their Elementary School Aged Children: A Naturalistic Study(2013-07-22) Reichel, LoriThis dissertation presents three separate studies exploring parents? perceptions and recommendations for communicating with their third, fourth, and fifth grade children about human sexuality. First, a systematic literature review is presented summarizing past qualitative studies completed in the United States focusing on parents with children aged 18 years and under. This review summarizes (1) demographic information of parents from past studies, (2) perceived communication barriers experienced by parents regarding sexuality communication, and (3) perceived communication facilitators experienced by parents regarding sexuality communication. Second, noting the lack of research within a specific population of parents in the United States, a naturalistic study of parents with children in the third, fourth, and fifth grade is presented. Utilizing an emergent design, one-on-one interviews were conducted with 20 parents living in a town in central Texas. By coding collected data, a thematic analysis was used to summarize emergent themes. Themes included techniques parents utilized to have parent-child conversations about sexuality and discussed topics. Although different techniques and topics were raised, parents showed overall inconsistency in experiences or past discussions. Third, using data from the same 20 interviews, themes emerged from parents regarding recommendations. These included the recommendations that a booklet with age appropriate information on sexuality topics be developed for parents and parent workshops or classes covering age appropriate sexuality knowledge as well as techniques to use in parent-child communication be offered. Schools were the recommended source for these resources. Parents also shared feedback on the newly released National Sexuality Education Standards. Comparing past parent-child conversations on sexuality topics to the NSES, certain topics were discussed yet inconsistency was shown. In addition, parents disagreed on specific standards including those pertaining to the functions of reproductive parts, reproduction, and same sex orientation. Implications of this study are that parental resources are needed to help parents communicate with their children about sexuality beginning at a young age. And, for those resources already existing, including workshops, books, and on-line sources, parents need to be made aware of their existence. In addition, future research is needed to explore if younger children are learning from parent-child conversations about sexuality.Item Pubertal development and adolescent risk-taking : understanding individual differences(2016-08) Kretsch, Natalie Sara; Harden, Kathryn Paige; Cavanagh, Shannon E; Fromme, Kim; Josephs, Robert A; Yeager, David SThis set of projects focused on individual differences—specifically, how variation in the timing, context, and perception of this universal milestone might contribute to individual differences in risky behavior. Study 1 looked at testosterone as a potential endophenotype for substance use in adolescence. Combining self-report, hormonal, and behavioral measures, this study used a twin design to test the hypothesis that testosterone mediated genetic risk for substance use via its effect on reward seeking. The primary hypothesis was not supported, as there were no phenotypic associations between testosterone, reward seeking, and initiation of substance use. Study 2 focused on girls’ perceived pubertal timing in the context of their peer group, testing whether peer delinquency moderated the association between pubertal timing and delinquency. A twin comparison design was used to control for unmeasured between-family differences (family-level genetic and environmental selection effects) that would affect both peer and individual delinquency. Pubertal timing moderated the quasi-causal association between peer and individual delinquency: girls with earlier perceived pubertal timing were more similar to their nominated friends in delinquency. This interaction was only found for relative pubertal timing (asking girls to compare their development to their peers) and not for age-standardized ratings of body changes or for age at menarche. Study 3 examined whether pubertal timing reported by one’s friends and schoolmates related to perceived pubertal timing. Results showed gender differences: boys appeared similar to their peers in perceived body changes and girls appeared similar to peers in perceived relative pubertal timing. Collectively, these 3 studies highlight complexity inherent in studying sources of individual differences at a stage when numerous changes—biological, psychological, social—are underway. Understanding the extent to which these concurrent changes may or may not interact is an important step toward identifying factors that make some children prone to risk behavior.Item Pubertal timing and peer influence on risky decision-making(2012-12) Kretsch, Natalie Sara; Harden, Kathryn Paige; Fromme, KimAdolescents engage in more risky behavior when they are with peers and show heightened susceptibility to peer influence relative to children and adults. Recent experimental studies suggest that peer influence on adolescent risk-taking may be mediated by activity in reward-related regions of the brain (Gardner & Steinberg, 2005; Chein et al., 2011). Because reward-related regions are modified by the hormonal changes of puberty, it is possible that the heightened influence of peers on adolescent risk-taking is more closely linked to pubertal development than chronological age. The current study examined whether the effect of peers on risk-taking was moderated by pubertal status. Participants (62 youth, ages 11-16) completed a performance-based measure of risky decision-making, once alone and once in the presence of two peers. Pubertal timing was assessed using self-report. Adolescents made riskier decisions in the presence of peers, and more advanced pubertal development predicted greater risky decision-making, controlling for chronological age. However, the relationship between pubertal timing and risk-taking was only apparent when adolescents completed the task alone. The effect of peer presence on risky decision-making was attenuated for adolescents with more advanced pubertal development. These findings suggest that the presence of peers may override biologically-based individual differences in propensity for risk-taking.Item Regulation of ESR1 in Kisspeptin Neurons during Reproductive Maturation in Ewe Lambs(2014-08-28) Bedenbaugh, Michelle NicholeThe pubertal initiation of a high-frequency, pulsatile release of gonadotropin-releasing hormone (GnRH) involves an escape from estradiol negative feedback. Kisspeptin neurons are proposed to mediate the effects of estradiol, and estrogen receptor alpha (ESR1) may play a role in this process. The present study investigated the hypothesis that reduced ESR1 expression in kisspeptin neurons is associated with decreased sensitivity to estradiol negative feedback that underlies reproductive maturation. Ewe lambs were ovariectomized at approximately 24 wk of age and received no implant (OVX; n=7) or received a subcutaneous implant containing estradiol (OVX+E; n=14). At 30 wk of age, blood samples were collected to characterize the pattern of luteinizing hormone (LH) secretion. Lambs were then euthanized and a block of tissue containing the preoptic area (POA) and hypothalamus was collected. Detection of ESR1 mRNA and kisspeptin was performed by dual-label in situ hybridization/immunocytochemistry. The abundance of ESR1 mRNA in the middle arcuate nucleus (mARC) was greater in OVX than in OVX+E ewe lambs but did not differ between groups in any other hypothalamic area investigated. Posthoc analysis of the LH data obtained from OVX+E lambs indicated three distinct patterns of LH release: low (1-2 pulses/12 h; n=3), moderate (6-7 pulses/12 h; n=6) and high (>10 pulses/12 h; n=5) frequency of LH pulses. The proportion of kisspeptin cells containing ESR1 mRNA in the POA/periventricular area did not differ among OVX+E lambs exhibiting low, moderate and high frequency of LH pulses. However, the proportion of kisspeptin cells containing ESR1 mRNA in the mid ARC was greater in OVX+E lambs exhibiting high frequency of LH pulses (0.57) than in lambs exhibiting moderate (0.36) or low (0.27) LH pulsatility, and did not differ from OVX (0.50) lambs. Contrary to our hypothesis, the increase in LH pulsatility in maturing ewe lambs is associated with enhanced ESR1 expression in kisspeptin neurons in the ARC. This indicates that the mechanism of decreased sensitivity to estradiol negative feedback during maturation of the reproductive neuroendocrine axis does not involve limiting ESR1 transcription in kisspeptin neurons.Item Repeated social stress and the maturation of sexual behavior in juvenile male golden hamsters(2011-08) Bastida, Christel Celeste; Delville, Yvon; Duvauchelle, Christine; Dominguez, Juan; Gonzalez-Lima, Francisco; Gore, AndreaIn certain species, puberty is thought to be a period of susceptibility to various stressors, resulting in pathological behavioral and physiological changes subsequent to exposure during this period. However, juvenile male golden hamsters appear to be fairly resilient to pubertal stress, as compared to adult hamsters and many other species. In these experiments, repeatedly stressed juvenile male hamsters were found to be avoidant of aggressive adult male social stimuli, but did not display anxious behavior outside of a social context. In addition, several long-term changes in neural activity were associated with social stress during early puberty. The medial preoptic area and medial preoptic nucleus, and ventral tegmental area showed decreased neural activity in subjugated juveniles than in naïve individuals. Since these brain areas are involved in the expression of motivated behaviors, specifically sexual behavior, and reward pathways, we next investigated sexual behavior in virgin juveniles. When placed in a confined space with receptive females, consummatory behavior in subjugated juveniles was similar to those observed in naive juveniles. Appetitive aspects of sexual behavior were also tested in a Y-maze to allow subjects to choose whether to approach a social stimulus. When given a choice between a sexually receptive and non-receptive female social stimulus, socially stressed individuals showed anxiety related behaviors and did not show a preference. However, naïve hamsters preferred the non-receptive female. Interestingly, this effect was less significant in naïve animals tested during late puberty and early adulthood, and a preference for sexually receptive females was not observed. In addition, stressed hamsters tested with harnessed females at mid-puberty were slower to approach females, indicating altered motivation to approach adult conspecifics. This research is unique in that it is the first to suggest the disconnect between the development of consummatory and appetitive aspects of sexual behavior. Together, these data examine the effects of stress on the development of pubertal social behaviors.