Cellular and molecular mechanisms underlying plasticity in uterine sympathetic nerves

Blood vessel assessment using computed tomography : Effects of ephedrine on uterine artery

Background: Ephedrine increased blood pressure due to the contractile properties of resistance vessels. Excessive contraction of the uterine arteries might cause fetal distress. This study was to determine the diameter of the uterine artery of female New Zealand rabbits after the administration of different doses of ephedrine using CT.

Methods: Thirty-two rabbits were randomly divided into a control group (Group C), low dosage group (Group L), medium dosage group (Group M) and high dosage group (Group H). Normal saline and doses corresponding to the human dose of 7.5, 15 and 30 mg of ephedrine were injected respectively. The marginal ear and uterine artery diameters were measured 5, 10, 15, 30, and 45 min after injection using CT, and the hemodynamic changes were recorded.

Results: The increase in mean arterial pressure in group M (p = 0.009), and H (p = 0.013) was higher than that in group C. Compared with group C, substantial contraction of the marginal ear artery was observed at the three doses of ephedrine. There were no differences in the uterine artery diameter among groups L, M and C, However, in Group H, a significant contraction of the uterine artery compared with the other groups (p < 0.001) was observed.

Discussion: CT can be used to evaluate the effects of drugs on organs and blood vessels. Ephedrine can not only constrict the peripheral blood vessels but also do not affect the uterine artery at a dose of 15 mg or less. However, the dose should not exceed 30 mg, which may cause severe uterine artery depression.

Toward the Existence of a Sympathetic Neuroplasticity Adaptive Mechanism Influencing the Immune Response. A Hypothetical View-Part II

In the preceding work, a hypothesis on the existence of a specific neural plasticity program from sympathetic fibers innervating secondary lymphoid organs was introduced. This proposed adaptive mechanism would involve segmental retraction and degeneration of noradrenergic terminals during the immune system (IS) activation followed by regeneration once the IS returns to the steady-state. Starting from such view, this second part presents clinical and experimental evidence allowing to envision that this sympathetic neural plasticity mechanism is also operative on inflamed non-lymphoid peripheral tissues. Importantly, the sympathetic nervous system regulates most of the physiological bodily functions, ranging from cardiovascular, respiratory and gastro-intestinal functions to endocrine and metabolic ones, among others. Thus, it seems sensible to think that compensatory programs should be put into place during inflammation in non-lymphoid tissues as well, to avoid the possible detrimental consequences of a sympathetic blockade. Nevertheless, in many pathological scenarios like severe sepsis, chronic inflammatory diseases, or maladaptive immune responses, such compensatory programs against noradrenergic transmission impairment would fail to develop. This would lead to a manifest sympathetic dysfunction in the above-mentioned settings, partly accounting for their underlying pathophysiological basis; which is also discussed. The physiological/teleological significance for the whole neural plasticity process is postulated, as well.

Toward the Existence of a Sympathetic Neuroplasticity Adaptive Mechanism Influencing the Immune Response. A Hypothetical View-Part I

The nervous system exerts a profound influence on the function of the immune system (IS), mainly through the sympathetic arm of the autonomic nervous system. In fact, the sympathetic nervous system richly innervates secondary lymphoid organs (SLOs) such as the spleen and lymph nodes. For decades, different research groups working in the field have consistently reported changes in the sympathetic innervation of the SLOs during the activation of the IS, which are characterized by a decreased noradrenergic activity and retraction of these fibers. Most of these groups interpreted these changes as a pathological phenomenon, referred to as "damage" or "injury" of the noradrenergic fibers. Some of them postulated that this "injury" was probably due to toxic effects of released endogenous mediators. Others, working on animal models of chronic stimulation of the IS, linked it to the very chronic nature of processes. Unlike these views, this first part of the present work reviews evidence which supports the hypothesis of a specific adaptive mechanism of neural plasticity from sympathetic fibers innervating SLOs, encompassing structural and functional changes of noradrenergic nerves. This plasticity mechanism would involve segmental retraction and degeneration of these fibers during the activation of the IS with subsequent regeneration once the steady state is recovered. The candidate molecules likely to mediate this phenomenon are also here introduced. The second part will extend this view as to the potential changes in sympathetic innervation likely to occur in inflamed non-lymphoid peripheral tissues and its possible immunological implications.

Exercise as a therapeutic intervention to optimize fetal weight

The Developmental Origins of Health and Disease suggest the in utero environment programs offspring obesity and cardiovascular disease. Therefore, there is a need to implement safe therapeutic interventions that do not involve the intake of medications or biological products during pregnancy that can improve maternal and fetal health. Prenatal exercise is established to promote maternal and fetal health. It is generally recommended that women accumulate at least 150 min per week of moderate-intensity exercise. It has been demonstrated that prenatal exercise maintains healthy weight gain and improves maternal glucose control, maternal cardiac autonomic control, placental efficiency (increases angiogenesis, downregulates genes involved in fatty acid transport and insulin transport across the placenta, and upregulates genes involved in amino acid transport across the placenta), and oxidative stress. These adaptations following exercise improve maternal metabolism and provide adequate uteroplacental perfusion. In this review, we will focus on exercise as a therapeutic intervention to optimize fetal weight. It has been established that prenatal exercise does not increase the risk of having a small for gestational age baby. To the contrary, prenatal exercise has been associated with the prevention of excessive fat accumulation in the newborn and the maintenance of fetal muscle mass.

Maternal testosterone and placental function: Effect of electroacupuncture on placental expression of angiogenic markers and fetal growth

Women with polycystic ovary syndrome (PCOS) have elevated circulating androgens during pregnancy and are at an increased risk of adverse pregnancy outcomes. Here we tested the hypotheses that maternal androgen excess decrease placental and fetal growth, and placental expression of markers of steroidogenesis, angiogenesis and sympathetic activity, and that acupuncture with low-frequency electrical stimulation prevents these changes. Pregnant rats were exposed to vehicle or testosterone on gestational day (GD)15-19. Low-frequency electroacupuncture (EA) or handling, as a control for the EA procedure, was given to control or testosterone exposed dams on GD16-20. On GD21, blood pressure was measured and maternal blood, fetuses and placentas collected. Placental steroid receptor expression and proteins involved in angiogenic, neurotrophic and adrenergic signaling were analyzed. EA did not affect any variables in control rats except maternal serum corticosterone, which was reduced. EA in testosterone exposed dams compared with controls increased systolic pressure by 30%, decreased circulating norepinephrine and corticosterone, fetal and placental weight and placental VEGFR1 and proNGF protein expression, and increased the VEGFA/VEGFR1 ratio, mature NGF (mNGF) and the mNGF/proNGF ratio. In conclusion, low-frequency EA in control animals did not have any negative influence on any of the studied variables. In contrast, EA in pregnant dams exposed to testosterone increased blood pressure and impaired placental growth and function, leading to decreased fetal growth.

Estrogen and female reproductive tract innervation: cellular and molecular mechanisms of autonomic neuroplasticity

The female reproductive tract undergoes remarkable functional and structural changes associated with cycling, conception and pregnancy, and it is likely advantageous to both individual and species to alter relationships between reproductive tissues and innervation. For several decades, it has been appreciated that the mammalian uterus undergoes massive sympathetic axon depletion in late pregnancy, possibly representing an adaptation to promote smooth muscle quiescence and sustained blood flow. Innervation to other structures such as cervix and vagina also undergo pregnancy-related changes in innervation that may facilitate parturition. These tissues provide highly tractable models for examining cellular and molecular mechanisms underlying peripheral nervous system plasticity. Studies show that estrogen elicits rapid degeneration of sympathetic terminal axons in myometrium, which regenerate under low-estrogen conditions. Degeneration is mediated by the target tissue: under estrogen's influence, the myometrium produces proteins repulsive to sympathetic axons including BDNF, neurotrimin, semaphorins, and pro-NGF, and extracellular matrix components are remodeled. Interestingly, nerve depletion does not involve diminished levels of classical sympathetic neurotrophins that promote axon growth. Estrogen also affects sympathetic neuron neurotrophin receptor expression in ways that appear to favor pro-degenerative effects of the target tissue. In contrast to the uterus, estrogen depletes vaginal autonomic and nociceptive axons, with the latter driven in part by estrogen-induced suppression of BMP4 synthesis. These findings illustrate that hormonally mediated physiological plasticity is a highly complex phenomenon involving multiple, predominantly repulsive target-derived factors acting in concert to achieve rapid and selective reductions in innervation.

Effects of skin-to-skin contact and breastfeeding at birth on the incidence of PPH: A physiologically based theory

BACKGROUND

The importance of optimising maternal/baby psychophysiology has been integrated into contemporary midwifery theories but not in the detail required to really understand the underpinning biological basis.

METHOD

The functioning of the autonomic nervous system, as it relates to the uterus is reviewed. The physiology of myometrial cell contraction and relaxation is outlined. The main focus is on the factors that affect the availability and uptake of oxytocin and adrenaline/noradrenaline in the myometrial cells. These are the two key neuro-hormones, active in the 3rd and 4th stages of labour, that affect uterine contraction and retraction and therefore determine whether the woman will have an atonic PPH or not.

DISCUSSION

The discussion explains and predicts the physiological functioning of the uterus during the 3rd and 4th stages of labour when skin-to-skin contact and breastfeeding occurs and when it does not.

CONCLUSION

This biologically based theory hypothesises that to achieve and maintain eutony and eulochia, midwives and birthing women should ensure early, prolonged and undisturbed skin-to-skin contact for mother and baby at birth including easy access for spontaneous breastfeeding.

Bone morphogenetic protein 4 mediates estrogen-regulated sensory axon plasticity in the adult female reproductive tract

Peripheral axons are structurally plastic even in the adult, and altered axon density is implicated in many disorders and pain syndromes. However, mechanisms responsible for peripheral axon remodeling are poorly understood. Physiological plasticity is characteristic of the female reproductive tract: vaginal sensory innervation density is low under high estrogen conditions, such as term pregnancy, whereas density is high in low-estrogen conditions, such as menopause. We exploited this system in rats to identify factors responsible for adult peripheral neuroplasticity. Calcitonin gene-related peptide-immunoreactive sensory innervation is distributed primarily within the vaginal submucosa. Submucosal smooth muscle cells express bone morphogenetic protein 4 (BMP4). With low estrogen, BMP4 expression was elevated, indicating negative regulation by this hormone. Vaginal smooth muscle cells induced robust neurite outgrowth by cocultured dorsal root ganglion neurons, which was prevented by neutralizing BMP4 with noggin or anti-BMP4. Estrogen also prevented axon outgrowth, and this was reversed by exogenous BMP4. Nuclear accumulation of phosphorylated Smad1, a primary transcription factor for BMP4 signaling, was high in vagina-projecting sensory neurons after ovariectomy and reduced by estrogen. BMP4 regulation of innervation was confirmed in vivo using lentiviral transduction to overexpress BMP4 in an estrogen-independent manner. Submucosal regions with high virally induced BMP4 expression had high innervation density despite elevated estrogen. These findings show that BMP4, an important factor in early nervous system development and regeneration after injury, is a critical mediator of adult physiological plasticity as well. Altered BMP4 expression may therefore contribute to sensory hyperinnervation, a hallmark of several pain disorders, including vulvodynia.

Baroreflex function in females: changes with the reproductive cycle and pregnancy

This review briefly describes the changes in baroreflex function that occur during female reproductive life, specifically during the reproductive cycle and pregnancy. The sensitivity or gain of baroreflex control of heart rate and sympathetic activity fluctuates during the reproductive cycle, reaching a peak when gonadal hormone levels increase, during the follicular phase in women and proestrus in rats. The increase in baroreflex sensitivity (BRS) is likely mediated by estrogen because ovariectomy in rats eliminates the BRS increase, the cyclic profile of changes in BRS mirror the changes in estrogen, and estrogen acts in the brainstem to increase BRS. In contrast, pregnancy depresses both BRS and the maximal level of sympathetic activity and heart rate evoked by severe hypotension. The decrease in BRS may be mediated by a reduction in the actions of insulin in the arcuate nucleus to support the baroreflex. In addition, increased levels of the neurosteroid progesterone metabolite 3α-OH-DHP act downstream in the rostral ventrolateral medulla to suppress maximal baroreflex increases in sympathetic activity. Consequently, these changes in baroreflex function impair blood pressure regulation in the presence of hypotensive challenges such as orthostasis and hemorrhage, a common event during delivery. As a result, peripartum hemorrhage is a major cause of human maternal death.

Highlights in basic autonomic neuroscience: Semaphorins in the remodeling of autonomic innervation

Chemorepellent signals of the semaphorin family are known to play a crucial role in the development of the nervous system. Some semaphorins continue being expressed in the adult life when they regulate plasticity and regeneration. Increasing evidence indicates that semaphorins are implicated in the development of the autonomic nervous system as well as in the regulation of different forms of plasticity observed in the adulthood. Here we present selected examples illustrating the involvement of semaphorins in the regulation of autonomic plasticity in physiological and pathological conditions.

Fibroid-associated heavy menstrual bleeding: correlation between clinical features, Doppler ultrasound assessment of vasculature, and tissue gene expression profiles

Despite the prevalence of uterine fibroids (Fs), few studies have investigated the links between clinical features and the cellular or molecular mechanisms that drive F growth and development. Such knowledge will ultimately help to differentiate symptomatic from asymptomatic Fs and could result in the development of more effective and individualized treatments. The aim of this study was to investigate the relationship between ultrasound appearance, blood flow, and angiogenic gene expression in F, perifibroid (PM), and distant myometrial (DM) tissues. We hypothesized that angiogenic gene expression would be increased in tissues and participants that showed increased blood flow by Doppler ultrasound. The study was performed using Doppler ultrasound to measure blood flow prior to hysterectomy, with subsequent tissue samples from the F, PM, and DM being investigated for angiogenic gene expression. Overall, PM blood flow (measured as peak systolic velocity [PSV]) was higher than F blood flow, although significant heterogeneity was seen in vascularity and blood flow between different Fs and their surrounding myometrium. We did not find any correlation between PSV and any other clinical or molecular parameter in this study. We identified 19 angiogenesis pathway-related genes with significant differences in expression between F and DM, and 2 genes, matrix metalloproteinase 9 (MMP9) and Neuropilin 2 (NRP2), that were significantly different between F and PM. These results are consistent with subtle differences between PM and DM. Understanding the differences between symptomatic versus asymptomatic Fs may eventually lead to more effective treatments that directly target the source of heavy menstrual bleeding.

Expression of nerve growth factor and its receptors TrkA and p75 in the uterus of wild female ground squirrel (Citellus dauricus Brandt)

In this study, we investigated the presence of nerve growth factor (NGF) and its receptors tyrosine kinase A (TrkA) and p75 in the uterus of the wild ground squirrels during the estrous period, early pregnancy and non-breeding period. In the estrous period and early pregnancy, NGF and TrkA were immunolocalized in stromal cells, luminal epithelial cells, glandular cells and smooth muscle cells whereas in the non-breeding period, both of them were detected only in luminal epithelial cells and glandular cells, but not in stromal cells or smooth muscle cells. Stronger immunostaining of NGF and TrkA was observed in luminal epithelial cells and glandular cells in the estrous period and early pregnancy as compared to the non-breeding period. p75 was immunolocalized only in luminal epithelial and glandular cells during the estrous period, early pregnancy and non-breeding period. The intensity of the immunohistochemical signals for p75 did not vary significantly in the estrous period, early pregnancy and non-breeding period. The mean mRNA levels of NGF and TrkA and p75 were significantly higher in the estrous period and early pregnancy as compared to the non-breeding period. Besides, plasma estradiol-17β and progesterone concentrations were higher in the estrous period and early pregnancy than in the non-breeding period, suggesting that the expression patterns of NGF and TrkA are correlated with changes in plasma estradiol-17β and progesterone concentrations. These results indicate that NGF and its receptor TrkA may be involved in the regulation of seasonal changes in the uterine functions of wild female ground squirrels.

Sympathetic reactivity in late pregnancy is related to labour onset in women

Stress regulation during pregnancy is considered to be connected to the timing of labour initiation. Although increasing knowledge is emerging on the regulation of parturition, there is currently no way to predict the start of spontaneous labour in women. The main aim of this study was to assess pain threshold and the sympathetic nervous system response to cold pain in relation to the onset of labour in healthy pregnant women. Ninety-three pregnant women were recruited and assessed for skin conductance (SC) activity during a cold pressor test in gestational week 38. Pain threshold and cold endurance were also measured and the results were compared with data obtained from hospital records. Seventy-four women had a spontaneous labour onset and a valid SC measurement. SC activity during the cold pressor test decreased significantly with the number of days left to spontaneous parturition. This may indicate a gradual decrease in sympathetic autonomic nervous system reactivity even during the last weeks of pregnancy. Measuring SC activity during mild stress provocation is a rapid and non-invasive means to study variation in sympathetic reactivity during pregnancy, and may be useful in research on stress regulation in pregnancy and its relation to labour initiation.

Paracrine control of vascular innervation in health and disease

Proper vascular regulation is of paramount importance for the control of blood flow to tissues. In particular, the regulation of peripheral resistance arteries is essential for several physiological processes, including control of blood pressure, thermoregulation and increase of blood flow to central nervous system and heart under stress conditions such as hypoxia. Arterial tone is regulated by the periarterial autonomic nervous plexus, as well as by endothelium-dependent, myogenic and humoral mechanisms. Underscoring the importance of proper vascular regulation, defects in these processes can lead to diseases such as hypertension, orthostatic hypotension, Raynaud's phenomenon, defective thermoregulation, hand-foot syndrome, migraine and congestive heart failure. Here, we review the molecular mechanisms controlling the development of the periarterial nerve plexus, retrograde and localized signalling at neuro-effector junctions, the molecular and cellular mechanisms of vascular regulation and adult plasticity and maintenance of periarterial innervation. We particularly highlight a newly discovered role for vascular endothelial growth factor in the structural and functional maintenance of arterial neuro-effector junctions. Finally, we discuss how defects in neuronal vascular regulation can lead to disease.

Estrogen up-regulation of semaphorin 3F correlates with sympathetic denervation of the rat uterus

Current evidence indicates that rises in systemic levels of estrogen create in the uterus an inhibitory environment for sympathetic nerves. However, molecular insights of these changes are far from complete. We evaluated if semaphorin 3F mRNA, a sympathetic nerve repellent, was produced by the rat uterus and if its expression was modulated by estrogen. We also analyzed whether uterine nerves express the semaphorin 3F binding receptor, neuropilin-2. Uterine levels of semaphorin 3F mRNA were measured using real time reverse transcriptase-polymerase chain reaction in prepubertal rat controls and following chronic estrogen treatment. Localization of semaphorin 3F transcripts was determined by in situ hybridization and the expression of neuropilin-2 was assessed by immunohistochemistry. These studies showed that: (1) chronic estrogen treatment led to a 5-fold induction of semaphorin 3F mRNA in the immature uterus; (2) estrogen provoked a tissue-specific induction of semaphorin 3F which was particularly localized in the connective tissue that borders muscle bundles and surrounds intrauterine blood vessels; (3) two major cell-types were recognized in the areas where transcripts were concentrated, fibroblast-like cells and infiltrating eosinophil leukocytes; and (4) some delicate nerve terminal profiles present in the estrogenized uterus were immunoreactive for neuropilin-2. Temporal and spatial expression patterns of semaphorin 3F/neuropilin-2 are consistent with a possible role of this guidance cue in the remodeling of uterine sympathetic innervation by estrogen. Though correlative in its nature, these data support a model whereby semaphorin 3F, in combination with other inhibitory molecules, converts the estrogenized myometrium to an inhospitable environment for sympathetic nerves.

Adaptive plasticity of vaginal innervation in term pregnant rats

Changes in reproductive status place varied functional demands on the vagina. These include receptivity to male intromission and sperm transport in estrus, barrier functions during early pregnancy, and providing a conduit for fetal passage at parturition. Peripheral innervation regulates vaginal function, which in turn may be influenced by circulating reproductive hormones. We assessed vaginal innervation in diestrus and estrus (before and after the estrous cycle surge in estrogen), and in the early (low estrogen) and late (high estrogen) stages in pregnancy. In vaginal sections from cycling rats, axons immunoreactive for the pan-neuronal marker protein gene product 9.5 (PGP 9.5) showed a small reduction at estrus relative to diestrus, but this difference did not persist after correcting for changes in target size. No changes were detected in axons immunoreactive for tyrosine hydroxylase (sympathetic), vesicular acetylcholine transporter (parasympathetic), or calcitonin gene-related peptide and transient receptor potential vanilloid type 1 (TRPV-1; sensory nociceptors). In rats at 10 days of pregnancy, innervation was similar to that observed in cycling rats. However, at 21 days of pregnancy, axons immunoreactive for PGP 9.5 and each of the subpopulation-selective markers were significantly reduced both when expressed as percentage of sectional area or after correcting for changes in target size. Because peripheral nerves regulate vaginal smooth muscle tone, blood flow, and pain sensitivity, reductions in innervation may represent important adaptive mechanisms facilitating parturition.

Age-associated alterations in sympathetic noradrenergic innervation of primary and secondary lymphoid organs in female Fischer 344 rats

Normal aging processes, as well as, psychological stress affect the immune system; each can act alone, or interact with each other, to cause dysregulation of immune function substantially altering physical and mental health. The sympathetic nervous system (SNS), a major mediator of stress effects on immune function, is significantly affected by normal aging process, and stress can affect aging of the SNS. Previously, we have shown age-associated changes in sympathetic noradrenergic (NA) innervation of lymphoid organs in male rodents that affect immune regulation. The purpose of this study was to investigate sympathetic innervation of lymphoid organs and associated alterations in immune responses in young and aging female Fischer 344 (F344) rats. Histofluorescence and immunocytochemistry for NA innervation, and neurochemistry for norepinephrine (NE) levels were performed in the thymus, spleen, and mesenteric lymph nodes (MLN) isolated from 3-month-old young (normal estrous cycle), 8- to 9-month-old (onset of irregular estrous cycling), and 24-25 month, and 30-31 month female F344 rats (acyclic) at diestrus based on vaginal smears. Age-related alterations in natural killer (NK) cell activity, interleukin-2 (IL-2) and interferon-γ (IFN-γ) production, T and B lymphocyte proliferation were examined in splenocytes. Sympathetic NA innervation and NE levels increased with aging in the thymus, declined in spleen and MLN, and was accompanied by significant reductions in NK cell activity, IL-2 and IFN-γ production, and T and B cell proliferation in old female rats. In 8-9 mo rats, NE levels in the hilar region of the spleen and IFN-γ production were unaltered, while NE levels in the end region of the spleen and IL-2 production were reduced. Collectively, these results suggest that aging is characterized by significant alterations in sympathetic NA innervation in the thymus, spleen, and MLN associated with immunosuppression, and that there is a marked shift in NA activity and immune reactivity occurring during middle-aged female rats.

Effects of experimentally induced diabetes mellitus on pharmacologically and electrically elicited myometrial contractility

1. Diabetes is one of the most frequent complications of gestation, affecting approximately 7% of pregnancies. However, little is known about its effects on electrically and pharmacologically stimulated myometrial contractility. The aim of the present study was to investigate the consequences of streptozotocin (STZ)-induced diabetes on: (i) electrical field stimulation (EFS)-evoked contraction of isolated uterine rings as a function of gestational age; and (ii) the uterotonic and tocolytic actions of α- and β-adrenoceptor stimulation, respectively. The effects of oxytocin in late pregnancy were also investigated. 2. During pregnancy, EFS-evoked contractions of isolated uterine rings from intact rats declined, whereas isolated uterine rings from diabetic rats exhibited continuously low sensitivity to EFS. 3. In non-pregnant rats, diabetes resulted in increased noradrenaline-mediated contractility and a decreased relaxation response to terbutaline. At the mRNA level, diabetes enhanced the expression of α1B-adrenoceptors in non-pregnant rats from 14.65 to 18.39 μg/mL (P < 0.05), whereas the expression of α1D-adrenoceptors decreased (from 42.87 to 35.67 μg/mL; P < 0.05). During pregnancy, the responses to these sympathomimetics did not differ between diabetic and intact rats. 4. In late pregnancy (on Days 15 and 21), oxytocin caused greater maximum contractility of uterine rings from diabetic rats without affecting the EC(50). In addition, on Day 15 of pregnancy, the expression of oxytocin receptors in the myometrium of diabetic rats was higher than that in intact rats. 5. The results of the present study indicate that experimental diabetes facilitates gestation-induced denervation and increases myometrial sensitivity to oxytocin in late pregnancy. If similar mechanisms operate in humans, this could contribute to a tendency to premature uterine contractions in diabetes-complicated pregnancies.