Neuroendocrine Mechanisms (neuroendocrine + mechanism)

Distribution by Scientific Domains


Selected Abstracts


Neuroendocrine mechanism of seasonal reproduction in birds and mammals

ANIMAL SCIENCE JOURNAL, Issue 4 2010
Takashi YOSHIMURA
ABSTRACT In temperate zones, animals use changes in day length as a calendar to time their breeding season. However, the photoreceptive and neuroendocrine mechanisms of seasonal reproduction are considered to differ markedly between birds and mammals. This can be understood from the fact that the eye is the only photoreceptive organ, and melatonin mediates the photoperiodic information in mammals, whereas in birds, photoperiodic information is directly received by the deep brain photoreceptors and melatonin is not involved in seasonal reproduction. Recent molecular and functional genomics analysis uncovered the gene cascade regulating seasonal reproduction in birds and mammals. Long day-induced thyroid stimulating hormone in the pars tuberalis of the pituitary gland regulates thyroid hormone catabolism within the mediobasal hypothalamus. Further, this local thyroid hormone catabolism appears to regulate seasonal gonadotropin-releasing hormone secretion. These findings suggest that although the light input pathway is different between birds and mammals (i.e. light or melatonin), the core mechanisms are conserved in these vertebrates. [source]


Neuroendocrine mechanisms controlling female puberty: new approaches, new concepts

INTERNATIONAL JOURNAL OF ANDROLOGY, Issue 1 2006
Sergio R. Ojeda
Summary Sexual development and mature reproductive function are controlled by a handful of neurones that, located in the basal forebrain, produce the decapeptide luteinizing hormone releasing hormone (LHRH). LHRH is released into the portal system that connects the hypothalamus to the pituitary gland and act on the latter to stimulate the synthesis and release of gonadotrophin hormones. The pubertal activation of LHRH release requires coordinated changes in excitatory and inhibitory inputs to LHRH-secreting neurones. These inputs are provided by both transsynaptic and glia-to-neurone communication pathways. Using cellular and molecular approaches, in combination with transgenic animal models and high-throughput procedures for gene discovery, we are gaining new insight into the basic mechanisms underlying this dual control of LHRH secretion and, hence, the initiation of mammalian puberty. Our results suggest that the initiation of puberty requires reciprocal neurone-glia communication involving excitatory amino acids and growth factors, and the coordinated actions of a group of transcriptional regulators that appear to represent a higher level of control governing the pubertal process. [source]


Are cortisol profiles a stable trait during child development?

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 6 2009
Mark V. Flinn
Exposure to stressful experiences can increase vulnerability to adverse health outcomes. A potential neuroendocrine mechanism mediating the link between stress and health is the hypothalamic-pituitary-adrenal (HPA) system, with a key role attributed to the glucocorticoid hormone cortisol. Retrospective and cross sectional clinical studies of humans and experimental studies with nonhuman primates and rodents suggest that traumatic experiences during critical periods in development may have permanent effects on HPA regulation, which in turn can have deleterious effects on health. Here I report results from a continuous 20-year study (1988,2009) of children in a rural community on Dominica. Sequential data on cortisol levels, social stressors, and health in naturalistic, everyday conditions are examined to assess developmental trajectories of HPA functioning. Saliva aliquots were assayed for cortisol in concert with monitoring of growth, morbidity, and social environment. Analyses here include data from 1989 to 1999 for 147 children aged 3,16 years with >100 saliva samples each. Cortisol values were standardized by elapsed time since wake-up. Results do not support the hypothesis that traumatic stress during childhood causes permanent general elevation of cortisol levels. Am. J. Hum. Biol., 2009. 2009 Wiley-Liss, Inc. [source]


Noradrenergic Innervation of the Ventromedial Hypothalamus is Involved in Mating-Induced Pseudopregnancy in the Female Rat

JOURNAL OF NEUROENDOCRINOLOGY, Issue 8 2006
L. E. Northrop
The ventromedial hypothalamus (VMH) is an oestrogen-responsive area known to facilitate female sexual behaviour in the rat. The VMH is innervated by noradrenergic neurones projecting from the brain stem, and it has been demonstrated that noradrenaline receptor activation in the VMH plays a role in the expression of the lordosis reflex. Noradrenaline has been shown to be released within the VMH after a female receives vaginocervical stimulation (VCS) from the male during mating. VCS also is required to induce twice-daily surges of prolactin (PRL) characteristic of early pregnancy or pseudopregnancy (PSP). To determine whether noradrenaline within the ventrolateral ventromedial hypothalamus (VMHvl) plays a facilitatory role in initiation of PSP, we administered the ,1 -noradrenergic receptor agonist, phenylephrine, and the ,2 -autoreceptor antagonist, yohimbine, unilaterally into the VMHvl. Phenylephrine stimulated PSP in 85.7% of females given an amount of VCS known to be subthreshold for the induction of PSP, whereas saline infusion (0%) or cannula misplacement (7.7%) were ineffective. Yohimbine had a similar effect, inducing PSP in 85.7% of females, whereas 7.6% of both control groups together showed PSP. Finally, bilateral blockade of ,1 -receptors using prazosin blocked PSP in 100% of females given sufficient VCS to induce PSP, whereas saline infusion or misplaced intracerebral cannulae failed to prevent PSP in any animal. In all experiments, vaginal dioestrous was indicative of PSP, in that animals showed a mean number of days between oestrus of 12.8 0.9. The results of the study demonstrate an important role for the VMHvl in initiation of PSP and suggest that the release of noradrenaline in the VMHvl at the time of mating contributes to neuroendocrine mechanisms responsible for establishing PSP in the female rat. [source]


Glucocorticoids and the Development of Agonistic Behaviour during Puberty in Male Golden Hamsters

JOURNAL OF NEUROENDOCRINOLOGY, Issue 12 2005
J. C. Wommack
Abstract During puberty, the agonistic behaviour of male golden hamsters undergoes a transition from play fighting to adult aggression. Repeated exposure to social stress early in puberty accelerates this transition. The present study investigated the possible role of glucocorticoids on the maturation of agonistic behaviour. First, we compared serum cortisol levels following a 20-min restraint stress during early puberty, mid-puberty or adulthood. Across puberty, animals exhibited a two-fold increase in post-restraint cortisol levels. We also compared corticotrophin-releasing hormone (CRH) immunoreactive fibres projecting to the median eminence between animals in early puberty and adulthood. The CRH fibre density was two-fold greater in adults compared to juveniles. Furthermore, we investigated the effects of stress hormones on the maturation of agonistic behaviour. Male hamsters were injected daily with dexamethasone, a corticosteroid receptor type II agonist (0, 10 or 40 g/100 g), early in puberty from postnatal day 31 (P-31) to P-36. When paired with a smaller and younger intruder on P-37, attack frequency did not differ between groups. However, dexamethasone-treated animals showed a dose-dependent decrease in the percentage of play-fighting attacks and an increase in the percentage of adult attacks. In summary, puberty can be described as a period of increasing hypothalamic-pituitary-adrenal activity in male golden hamsters. Moreover, increasing glucocorticoid levels influence the maturation of agonistic behaviour. These data shed new light on the neuroendocrine mechanisms that regulate the maturation of social behaviours during puberty. [source]


Temperature and Photoperiod Interact to Affect Reproduction and GnRH Synthesis in Male Prairie Voles

JOURNAL OF NEUROENDOCRINOLOGY, Issue 6 2000
L. J. Kriegsfeld
Prairie voles (Microtus ochrogaster), like most rodent species, exhibit a phenotypic polymorphism in reproductive response to winter conditions or to short day lengths in the laboratory. Laboratory studies on seasonally breeding species have traditionally focused on the role of photoperiod in modulating reproduction and other seasonal adaptions. However, because animals use proximate environmental factors in addition to photoperiod to phase seasonal adaptions with the appropriate time of year, the present study investigated the interaction of photoperiod and temperature on reproductive function and the gonadotropin-releasing hormone (GnRH) neuronal system. Male prairie voles were housed in either long (LD 16:8) or short (LD 8:16) photoperiods. Voles in each photoperiodic condition were also exposed to either mild (20 C) or low (8 C) temperatures. After 10 weeks, voles were killed and their brains were processed using in situ hybridization for mRNA for proGnRH. The results suggest that GnRH synthesis is not affected by exposure to a single inhibitory proximate factor (i.e. short days or low temperatures alone), even when reproduction is inhibited, whereas a combination of inhibitory proximate factors leads to a decrease in GnRH synthesis (i.e. fewer neurones staining for mRNA for proGnRH). These data suggest that the neuroendocrine mechanisms regulating seasonal alterations in reproductive function are likely to differ between harsh and mild winters. [source]


Neuroendocrine mechanism of seasonal reproduction in birds and mammals

ANIMAL SCIENCE JOURNAL, Issue 4 2010
Takashi YOSHIMURA
ABSTRACT In temperate zones, animals use changes in day length as a calendar to time their breeding season. However, the photoreceptive and neuroendocrine mechanisms of seasonal reproduction are considered to differ markedly between birds and mammals. This can be understood from the fact that the eye is the only photoreceptive organ, and melatonin mediates the photoperiodic information in mammals, whereas in birds, photoperiodic information is directly received by the deep brain photoreceptors and melatonin is not involved in seasonal reproduction. Recent molecular and functional genomics analysis uncovered the gene cascade regulating seasonal reproduction in birds and mammals. Long day-induced thyroid stimulating hormone in the pars tuberalis of the pituitary gland regulates thyroid hormone catabolism within the mediobasal hypothalamus. Further, this local thyroid hormone catabolism appears to regulate seasonal gonadotropin-releasing hormone secretion. These findings suggest that although the light input pathway is different between birds and mammals (i.e. light or melatonin), the core mechanisms are conserved in these vertebrates. [source]


Modulation of aggressive behaviour by fighting experience: mechanisms and contest outcomes

BIOLOGICAL REVIEWS, Issue 1 2006
Yuying Hsu
ABSTRACT Experience in aggressive contests often affects behaviour during, and the outcome of, later contests. This review discusses evidence for, variations in, and consequences of such effects. Generally, prior winning experiences increase, and prior losing experiences decrease, the probability of winning in later contests, reflecting modifications of expected fighting ability. We examine differences in the methodologies used to study experience effects, and the relative importance and persistence of winning and losing experiences within and across taxa. We review the voluminous, but somewhat disconnected, literature on the neuroendocrine mechanisms that mediate experience effects. Most studies focus on only one of a number of possible mechanisms without providing a comprehensive view of how these mechanisms are integrated into overt behaviour. More carefully controlled work on the mechanisms underlying experience effects is needed before firm conclusions can be drawn. Behavioural changes during contests that relate to prior experience fall into two general categories. Losing experiences decrease willingness to engage in a contest while winning experiences increase willingness to escalate a contest. As expected from the sequential assessment model of contest behaviour, experiences become less important to outcomes of contests that escalate to physical fighting. A limited number of studies indicate that integration of multiple experiences can influence current contest behaviour. Details of multiple experience integration for any species are virtually unknown. We propose a simple additive model for this integration of multiple experiences into an individual's expected fighting ability. The model accounts for different magnitudes of experience effects and the possible decline in experience effects over time. Predicting contest outcomes based on prior experiences requires an algorithm that translates experience differences into contest outcomes. We propose two general types of model, one based solely on individual differences in integrated multiple experiences and the other based on the probability contests reach the escalated phase. The difference models include four algorithms reflecting possible decision rules that convert the perceived fighting abilities of two rivals into their probabilities of winning. The second type of algorithm focuses on how experience influences the probability that a subsequent contest will escalate and the fact that escalated contests may not be influenced by prior experience. Neither type of algorithm has been systematically investigated. Finally, we review models for the formation of dominance hierarchies that assume that prior experience influences contest outcome. Numerous models have reached varied conclusions depending on which factors examined in this review are included. We know relatively little about the importance of and variation in experience effects in nature and how they influence the dynamics of aggressive interactions in social groups and random assemblages of individuals. Researchers should be very active in this area in the next decade. The role of experience must be integrated with other influences on contest outcome, such as prior residency, to arrive at a more complete picture of variations in contest outcomes. We expect that this integrated view will be important in understanding other types of interactions between individuals, such as mating and predator-prey interactions, that also are affected significantly by prior experiences. [source]