Effect of 17 beta-estradiol on gene expression in lumbar spinal cord following sciatic nerve crush injury in ovariectomized mice

Sex hormone supplementation improves breathing and restores respiratory neuroplasticity following C2 hemisection in rats

In addition to loss of sensory and motor function below the level of the lesion, traumatic spinal cord injury (SCI) may reduce circulating steroid hormones that are necessary for maintaining normal physiological function for extended time periods. For men, who comprise nearly 80% of new SCI cases each year, testosterone is the most abundant circulating sex steroid. SCI often results in significantly reduced testosterone production and may result in chronic low testosterone levels. Testosterone plays a role in respiratory function and the expression of respiratory neuroplasticity. When testosterone levels are low, young adult male rats are unable to express phrenic long-term facilitation (pLTF), an inducible form of respiratory neuroplasticity invoked by acute, intermittent hypoxia (AIH). However, testosterone replacement can restore this respiratory neuroplasticity. Complicating the interpretation of this finding is that testosterone may exert its influence in three possible ways: 1) directly through androgen receptor (AR) activation, 2) through conversion to dihydrotestosterone (DHT) by way of the enzyme 5α-reductase, or 3) through conversion to 17β-estradiol (E2) by way of the enzyme aromatase. DHT signals via AR activation similar to testosterone, but with higher affinity, while E2 activates local estrogen receptors. Evidence to date supports the idea that exogenous testosterone supplementation exerts its influence through estrogen receptor signaling under conditions of low circulating testosterone. Here we explored both recovery of breathing function (measured with whole body barometric plethysmography) and the expression of AIH-induced pLTF in male rats following C2-hemisection SCI. One week post injury, rats were supplemented with either E2 or DHT for 7 days. We hypothesized that E2 would enhance ventilation and reveal pLTF following AIH in SCI rats. To our surprise, though E2 did beneficially impact overall breathing recovery following C2-hemisection, both E2 supplementation and DHT restored the expression of AIH-induced pLTF 2 weeks post-SCI.

Skeletal muscle wasting: the estrogen side of sexual dimorphism

The importance of defining sex differences across various biological and physiological mechanisms is more pervasive now than it has been over the past 15-20 years. As the muscle biology field pushes to identify small molecules and interventions to prevent, attenuate, or even reverse muscle wasting, we must consider the effect of sex as a biological variable. It should not be assumed that a therapeutic will affect males and females with equal efficacy or equivalent target affinities under conditions where muscle wasting is observed. With that said, it is not surprising to find that we have an unclear or even a poor understanding of the effects of sex or sex hormones on muscle wasting conditions. Although recent investigations are beginning to establish experimental approaches that will allow investigators to assess the impact of sex-specific hormones on muscle wasting, the field still needs rigorous scientific tools that will allow the community to address critical hypotheses centered around sex hormones. The focus of this review is on female sex hormones, specifically estrogens, and the roles that these hormones and their receptors play in skeletal muscle wasting conditions. With the overall review goal of assembling the current knowledge in the area of sexual dimorphism driven by estrogens with an effort to provide insights to interested physiologists on necessary considerations when trying to assess models for potential sex differences in cellular and molecular mechanisms of muscle wasting.

Neuronal androgen receptor is required for activity dependent enhancement of peripheral nerve regeneration

Neuronal activity after nerve injury can enhance axon regeneration and the restoration of function. The mechanism for this enhancement relies in part on hormone receptors, and we previously demonstrated that systemic androgen receptor antagonism blocked the effect of exercise or electrical stimulation on enhancing axon regeneration after nerve injury in both sexes. Here, we tested the hypothesis that the site of this androgen receptor signaling is both neuronal and involves the classical, genomic signaling pathway. In vivo, dorsal root ganglion neurons successfully regenerate in response to activity-dependent neuronal activation, and conditional deletion of the DNA-binding domain of the androgen receptor in adults blocks this effect in males and females. Motoneurons in males and females also respond in this manner, but we also observed a sex difference. In vitro, cultured sensory dorsal root ganglion neurons respond to androgens via traditional androgen receptor signaling mechanisms leading to enhanced neurite growth and did not respond to a testosterone conjugate that is unable to cross the cell membrane. Given our previous observation of a requirement for activity-dependent androgen receptor signaling to promote regeneration in both sexes, we interpret our results to indicate that genomic neuronal androgen receptor signaling is required for activity-dependent axon regeneration in both sexes.

Second to fourth digit ratio (2D:4D) in women with carpal tunnel syndrome

BACKGROUND

Carpal tunnel syndrome (CTS), a median nerve compressive neuropathy at the wrist, is the most common entrapment nerve disorder. Sex is an important risk factor of CTS as this condition is to five times more common in women than in men (sex-hormone dependent). There are no studies concerning 2D:4D (biomarker of prenatal sex steroids exposure) in patients with CTS.

AIM

Here we consider the relationship between 2D:4D and CTS in women.

STUDY DESIGN AND METHODS

The study involved 90 female participants (40 with a severe CTS (the mean age - 52.78 yrs., SD 11.44) and 50 control women (the mean age - 47.2 yrs., SD 8.23)). Anthropometric measurements were performed and the following indices were calculated: BMI, WHR and right and left 2D:4D.

RESULTS

A stepwise logistic regression model showed that higher WHR and lower right 2D:4D increase the risk of CTS in women (AUC = 0.8865).

CONCLUSIONS

These associations may suggest a role for prenatal and post-natal sex-hormones in CTS development, i.e. in the context of oestrogen receptor activation (number and/or sensitivity) and the pattern of fat distribution. Further studies examining the role of hormonal influence in this disorder may help to plan prophylaxis of CTS (e.g. early HRT).

Comparison of the effects of progesterone and 17 β-estradiol on Schwann cell markers expression in rat adipose-derived stem cells

Steroids promote the myelination and regeneration in the peripheral nervous system. Whereas, little is known about the inducing effects by which the hormones exert their effects on Schwann cells differentiation. This could be revealed by the expression of Schwann cell markers in adipose-derived stem cells (ADSCs). The purpose of this study was to present the effects of progesterone and 17 β-estradiol on the Schwann cell markers in rat ADSCs. The mesenchymal stem cell markers (CD73, and CD90) were assayed by flow cytometry. Rat ADSCs were sequentially treated with β-mercaptoethanol, and all-trans-retinoic acid, followed by a mixture of basic fibrobroblast growth factor, platelet-derived growth factor, forskolin and heregulin. In experimental groups, forskolin and heregulin were substituted by progesterone and 17 β-estradiol. After induction, the expression of Schwann cell markers P0, and S-100 and the cellular immunocytochemical staining positive rate of anti-S100 and anti-glial fibrillary acidic protein (GFAP) antibodies were compared in the experimental and control groups. Progesterone and 17 β-estradiol triggered P0 and S-100 genes expression and induced a cellular immunocytochemical staining positive rate of S-100 and GFAP in rats ADSCs. Progesterone induced these changes stronger than 17 β-estradiol. Thus, progesterone may induce rat ADSCs toward Schwann-like cells by expression of Schwann cell markers and is more potent than 17 β-estradiol in the expression of these markers.

17β-Estradiol Enhances Schwann Cell Differentiation via the ERβ-ERK1/2 Signaling Pathway and Promotes Remyelination in Injured Sciatic Nerves

Remyelination is critical for nerve regeneration. However, the molecular mechanism involved in remyelination is poorly understood. To explore the roles of 17β-estradiol (E2) for myelination in the peripheral nervous system, we used a co-culture model of rat dorsal root ganglion (DRG) explants and Schwann cells (SCs) and a regeneration model of the crushed sciatic nerves in ovariectomized (OVX) and non-ovariectomized (non-OVX) rats for in vitro and in vivo analysis. E2 promoted myelination by facilitating the differentiation of SCs in vitro, which could be inhibited by the estrogen receptors (ER) antagonist ICI182780, ERβ antagonist PHTPP, or ERK1/2 antagonist PD98059. This suggests that E2 accelerates SC differentiation via the ERβ-ERK1/2 signaling. Furthermore, E2 promotes remyelination in crushed sciatic nerves of both OVX and non-OVX rats. Interestingly, E2 also significantly increased the expression of the lysosome membrane proteins LAMP1 and myelin protein P0 in the regenerating nerves. Moreover, P0 has higher degree of colocalization with LAMP1 in the regenerating nerves. Taking together, our results suggest that E2 enhances Schwann cell differentiation and further myelination via the ERβ-ERK1/2 signaling and that E2 increases the expression of myelin proteins and lysosomes in SCs to promotes remyelination in regenerating sciatic nerves.

Synchrotron Radiation Imaging Reveals the Role of Estrogen in Promoting Angiogenesis After Acute Spinal Cord Injury in Rats

STUDY DESIGN

The efficacy of estrogen on vessel angiogenesis in acute spinal cord injury (SCI) in a rat model was evaluated by synchrotron radiation.

OBJECTIVE

Here, we investigate the change in injured spinal cord vessels and used the synchrotron radiation to investigate the effect of estrogen on vessel angiogenesis and functional recovery in a rat model of SCI.

SUMMARY OF BACKGROUND DATA

The promotion of angiogenesis after SCI may be a therapeutic target in the treatment of SCI. Estrogen has been reported to improve locomotor recovery after SCI. However, how estrogen regulates angiogenesis in acute SCI and enhances neurological functional recovery has not been fully characterized.

METHODS

Synchrotron radiation imaging combined with histological methods was used to image angiogenesis in acute spinal cord treatment with estrogen in rats.

RESULTS

Synchrotron radiation imaging vividly demonstrated three-dimensional vessel changes in the spinal cord after injury. The imaging showed that vessel number, vessel volume fraction, and vessel connectivity value in the groups treated with estrogen after SCI were significantly increased compared to control groups (P < 0.05). Vessel angiogenesis increased in groups treated with estrogen compared with control rats, which was confirmed with histological staining. Estrogen treatment also attenuated the injury-induced lesion area compared with control groups and improved locomotor functional recovery after SCI.

CONCLUSION

The results indicated that synchrotron radiation is a powerful imaging tool for visualizing angiogenesis after acute SCI. Estrogen treatment exerted a neuroprotective effect on acute SCI treatment by promoting angiogenesis and reducing the injury-induced lesion area could be recommended as a potential preclinical treatment approach for acute SCI.

LEVEL OF EVIDENCE

N/A.

Protective effects of gonadal hormones on spinal motoneurons following spinal cord injury

Spinal cord injury (SCI) results in lesions that destroy tissue and disrupt spinal tracts, producing deficits in locomotor and autonomic function. The majority of treatment strategies after SCI have concentrated on the damaged spinal cord, for example working to reduce lesion size or spread, or encouraging regrowth of severed descending axonal projections through the lesion, hoping to re-establish synaptic connectivity with caudal targets. In our work, we have focused on a novel target for treatment after SCI, surviving spinal motoneurons and their target musculature, with the hope of developing effective treatments to preserve or restore lost function following SCI. We previously demonstrated that motoneurons, and the muscles they innervate, show pronounced atrophy after SCI. Importantly, SCI-induced atrophy of motoneuron dendrites can be attenuated by treatment with gonadal hormones, testosterone and its active metabolites, estradiol and dihydrotestosterone. Similarly, SCI-induced reductions in muscle fiber cross-sectional areas can be prevented by treatment with androgens. Together, these findings suggest that regressive changes in motoneuron and muscle morphology seen after SCI can be ameliorated by treatment with gonadal hormones, further supporting a role for steroid hormones as neurotherapeutic agents in the injured nervous system.

Protective Effects of Estradiol and Dihydrotestosterone following Spinal Cord Injury

Spinal cord injury (SCI) results in lesions that destroy tissue and disrupt spinal tracts, producing deficits in locomotor and autonomic function. We previously demonstrated that motoneurons and the muscles they innervate show pronounced atrophy after SCI, and these changes are prevented by treatment with testosterone. Here, we assessed whether the testosterone active metabolites estradiol and dihydrotestosterone have similar protective effects after SCI. Young adult female rats received either sham or T9 spinal cord contusion injuries and were treated with estradiol, dihydrotestosterone, both, or nothing via Silastic capsules. Basso-Beattie-Bresnahan locomotor testing was performed weekly and voiding behavior was assessed at 3 weeks post-injury. Four weeks after SCI, lesion volume and tissue sparing, quadriceps muscle fiber cross-sectional area, and motoneuron dendritic morphology were assessed. Spontaneous locomotor behavior improved after SCI, but hormone treatments had no effect. Voiding behavior was disrupted after SCI, but was significantly improved by treatment with either estradiol or dihydrotestosterone; combined treatment was maximally effective. Treatment with estradiol reduced lesion volume, but dihydrotestosterone alone and estradiol combined with dihydrotestosterone were ineffective. SCI-induced decreases in motoneuron dendritic length were attenuated by all hormone treatments. SCI-induced reductions in muscle fiber cross-sectional areas were prevented by treatment with either dihydrotestosterone or estradiol combined with dihydrotestosterone, but estradiol treatment was ineffective. These findings suggest that deficits in micturition and regressive changes in motoneuron and muscle morphology seen after SCI are ameliorated by treatment with estradiol or dihydrotestosterone, further supporting a role for steroid hormones as neurotherapeutic agents in the injured nervous system.

Integrated molecular landscape of amyotrophic lateral sclerosis provides insights into disease etiology

Amyotrophic lateral sclerosis (ALS) is a severe, progressive and ultimately fatal motor neuron disease caused by a combination of genetic and environmental factors, but its underlying mechanisms are largely unknown. To gain insight into the etiology of ALS, we here conducted genetic network and literature analyses of the top-ranked findings from six genome-wide association studies of sporadic ALS (involving 3589 cases and 8577 controls) as well as genes implicated in ALS etiology through other evidence, including familial ALS candidate gene association studies. We integrated these findings into a molecular landscape of ALS that allowed the identification of three main processes that interact with each other and are crucial to maintain axonal functionality, especially of the long axons of motor neurons, i.e. (1) Rho-GTPase signaling; (2) signaling involving the three regulatory molecules estradiol, folate, and methionine; and (3) ribonucleoprotein granule functioning and axonal transport. Interestingly, estradiol signaling is functionally involved in all three cascades and as such an important mediator of the molecular ALS landscape. Furthermore, epidemiological findings together with an analysis of possible gender effects in our own cohort of sporadic ALS patients indicated that estradiol may be a protective factor, especially for bulbar-onset ALS. Taken together, our molecular landscape of ALS suggests that abnormalities within three interconnected molecular processes involved in the functioning and maintenance of motor neuron axons are important in the etiology of ALS. Moreover, estradiol appears to be an important modulator of the ALS landscape, providing important clues for the development of novel disease-modifying treatments.

Spinal Cord Molecular and Cellular Changes Induced by Adenoviral Vector- and Cell-Mediated Triple Gene Therapy after Severe Contusion

The gene therapy has been successful in treatment of spinal cord injury (SCI) in several animal models, although it still remains unavailable for clinical practice. Surprisingly, regardless the fact that multiple reports showed motor recovery with gene therapy, little is known about molecular and cellular changes in the post-traumatic spinal cord following viral vector- or cell-mediated gene therapy. In this study we evaluated the therapeutic efficacy and changes in spinal cord after treatment with the genes encoding vascular endothelial growth factor (VEGF), glial cell-derived neurotrophic factor (GDNF), angiogenin (ANG), and neuronal cell adhesion molecule (NCAM) applied using both approaches. Therapeutic genes were used for viral vector- and cell-mediated gene therapy in two combinations: (1) VEGF+GDNF+NCAM and (2) VEGF+ANG+NCAM. For direct gene therapy adenoviral vectors based on serotype 5 (Ad5) were injected intrathecally and for cell-mediated gene delivery human umbilical cord blood mononuclear cells (UCB-MC) were simultaneously transduced with three Ad5 vectors and injected intrathecally 4 h after the SCI. The efficacy of both treatments was confirmed by improvement in behavioral (BBB) test. Molecular and cellular changes following post-traumatic recovery were evaluated with immunofluorescent staining using antibodies against the functional markers of motorneurons (Hsp27, synaptophysin, PSD95), astrocytes (GFAP, vimentin), oligodendrocytes (Olig2, NG2, Cx47) and microglial cells (Iba1). Our results suggest that both approaches with intrathecal delivery of therapeutic genes may support functional recovery of post-traumatic spinal cord via lowering the stress (down regulation of Hsp25) and enhancing the synaptic plasticity (up regulation of PSD95 and synaptophysin), supporting oligodendrocyte proliferation (up regulation of NG2) and myelination (up regulation of Olig2 and Cx47), modulating astrogliosis by reducing number of astrocytes (down regulation of GFAP and vimetin) and microglial cells (down regulation of Iba1).

Neuroprotective effects of estrogen in CNS injuries: insights from animal models

Among the estrogens that are biosynthesized in the human body, 17β-estradiol (estradiol or E2) is the most common and the best estrogen for neuroprotection in animal models of the central nervous system (CNS) injuries such as spinal cord injury (SCI), traumatic brain injury (TBI), and ischemic brain injury (IBI). These CNS injuries are not only serious health problems, but also enormous economic burden on the patients, their families, and the society at large. Studies from animal models of these CNS injuries provide insights into the multiple neuroprotective mechanisms of E2 and also suggest the possibility of translating the therapeutic efficacy of E2 in the treatment SCI, TBI, and IBI in humans in the near future. The pathophysiology of these injuries includes loss of motor function in the limbs, arms and their extremities, cognitive deficit, and many other serious consequences including life-threatening paralysis, infection, and even death. The potential application of E2 therapy to treat the CNS injuries may become a trend as the results are showing significant therapeutic benefits of E2 for neuroprotection when administered into the animal models of SCI, TBI, and IBI. This article describes the plausible mechanisms how E2 works with or without the involvement of estrogen receptors and provides an overview of the known neuroprotective effects of E2 in these three CNS injuries in different animal models. Because activation of estrogen receptors has profound implications in maintaining and also affecting normal physiology, there are notable impediments in translating E2 therapy to the clinics for neuroprotection in CNS injuries in humans. While E2 may not yet be the sole molecule for the treatment of CNS injuries due to the controversies surrounding it, the neuroprotective effects of its metabolite and derivative or combination of E2 with another therapeutic agent are showing significant impacts in animal models that can potentially shape the new treatment strategies for these CNS injuries in humans.

Expression of aromatase and estrogen receptors in lumbar motoneurons of mice

Estrogen exerts protective roles in amyotrophic lateral sclerosis (ALS). However, the expression of aromatase (ARO) and estrogen receptors (ERs) in the motoneurons of spinal cord, has not yet been elucidated. By immunohistochemistry, we found that ARO and ERs were present in the ventral horn of adult mice lumbar spinal cord, and colocalized with SMI-32, a motoneuron specific marker. Within motoneurons, we observed that ARO is detected primarily in the cytoplasm, with fewer ARO in the nucleus; ERα and ERβ mainly localized in the nucleus with less in the cytoplasm; while GPR30 is located in soma and processes. In conclusion, we found that ERs and ARO are expressed in the motoneurons of lumbar spinal cord in adult mice. These findings suggest that estrogen may be useful as a promising therapeutic agent for prevention of damage and improvement of locomotor function in ALS.

Estrogen signaling is necessary for exercise-mediated enhancement of motoneuron participation in axon regeneration after peripheral nerve injury in mice

Thousands of people each year suffer from peripheral nerve injury. Treatment options are limited, and recovery is often incomplete. Treadmill exercise can enhance nerve regeneration; however, this appears to occur in a sex-dependent manner. Females respond best to short duration, high speed interval training; whereas, males respond best to slower, continuous training. Previous studies have shown a role for testosterone in this process, but the role of estrogen is unknown. To evaluate the role of estrogen signaling in treadmill exercise, we blocked estrogen receptor (ER) signaling during treadmill exercise in males and female wild type mice. The right common fibular (CF) branch of the sciatic nerve was cut and repaired with fibrin glue that contained the ER antagonist ICI 182,780. Estradiol-filled or blank Silastic capsules were implanted subcutaneously at the time of nerve transection. Starting three days post-transection, exercised mice received treadmill training using the paradigm appropriate to their sex 5 days a week for 2 weeks. Fourteen days after the initial nerve transection, motoneurons whose axons had regenerated at least 1.5 mm distal to the original cut sites were labeled with a retrograde tracer. Regeneration was quantified by counting the number of fluorescent labeled motoneurons in the lumbar region of the spinal cord. Both treadmill training and estradiol administration increased the number of motoneurons participating in axon regeneration, but these effects were blocked by ER antagonist treatment. Estrogen signaling is important for the enhancing effects of treadmill exercise on motoneuron participation after peripheral nerve cut. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1133-1143, 2017.

Exercise, neurotrophins, and axon regeneration in the PNS

Electrical stimulation and exercise are treatments to enhance recovery from peripheral nerve injuries. Brain-derived neurotrophic factor and androgen receptor signaling are requirements for the effectiveness of these treatments. Increased neuronal activity is adequate to promote regeneration in injured nerves, but the dosing of activity and its relationship to neurotrophins and sex steroid hormones is less clear. Translation of these therapies will require principles associated with their cellular mechanisms.

Suppressive effects of 17β-estradiol on tributyltin-induced neuronal injury via Akt activation and subsequent attenuation of oxidative stress

AIMS

Neuroactive steroids are reported to protect neurons from various harmful compounds; however, the protective mechanisms remain largely unclear. In this study, we examined the suppressive effects of 17β-estradiol (E2) on tributyltin (TBT)-induced neurotoxicity.

MAIN METHODS

Organotypic hippocampal slices were prepared from neonatal rats and then cultured. Cell death was assayed by propidium iodide uptake. Levels of reactive oxygen species (ROS) were determined by dihydroethidium staining. Protein phosphorylation was evaluated by immunoblotting.

KEY FINDINGS

Pretreatment of the slices with E2 dose-dependently attenuated the neuronal injury induced by TBT. An estrogen receptor antagonist, ICI182,780 abrogated these neuroprotective effects. The de novo protein synthesis inhibitors actinomycin D and cycloheximide showed no effects on the neuroprotective mechanism, indicating that a nongenomic pathway acting via the estrogen receptor may be involved in the neuroprotection conferred by E2. E2 suppressed the ROS production and lipid peroxidation induced by TBT, and these effects were almost completely canceled by ICI182,780. TBT decreased Akt phosphorylation, and this reduction was suppressed by E2. An Akt inhibitor, triciribine, attenuated the decreases in both the ROS production and neuronal injury mediated by E2.

SIGNIFICANCE

E2 enhances the phosphorylation of Akt, thereby attenuating the oxidative stress and subsequent neuronal injury induced by TBT.

Postinjury administration of 17β-estradiol induces protection in the gray and white matter with associated functional recovery after cervical spinal cord injury in male rats

The majority of spinal cord injuries (SCIs) in the clinic occur at the lower cervical levels, resulting in both white and gray matter disruption. In contrast, most experimental models of SCI in rodents induce damage in the thoracic cord, resulting primarily in white matter disruption. To address this disparity, experimental cervical SCI models have been developed. Thus, we used a recently characterized model of cervical hemicontusion SCI in adult male rats to assess the potential therapeutic effect of post-SCI administration of 17β-estradiol. Rats received a hemicontusion at the level of the fifth cervical vertebra (C5) followed by administration of 17β-estradiol via a slow release pellet (0.5 or 5.0 mg/pellet) beginning at 30 minutes post-SCI. Behavioral evaluation of skilled and unskilled forelimb function and locomotor function were conducted for 7 weeks after SCI. Upon conclusion of the behavioral assessments, spinal cords were collected and histochemistry and stereology were conducted to evaluate the effect of treatment on the lesion characteristics. We found that post-SCI administration of 17β-estradiol decreased neuronal loss in the ventral horn, decreased reactive astrogliosis, decreased the immune response, and increased white mater sparing at the lesion epicenter. Additionally, post-SCI administration of 17β-estradiol improved skilled forelimb function and locomotor function. Taken together, these data suggest that post-SCI administration of 17β-estradiol protected both the gray and white matter in cervical SCI. Moreover, this treatment improved function on skilled motor tasks that involve both gray and white matter components, suggesting that this is likely a highly clinically relevant protective strategy.

Estradiol triggers sonic-hedgehog-induced angiogenesis during peripheral nerve regeneration by downregulating hedgehog-interacting protein

Both estradiol (E2) and Sonic Hedgehog (Shh) contribute to angiogenesis and nerve regeneration. Here, we investigated whether E2 improves the recovery of injured nerves by downregulating the Shh inhibitor hedgehog-interacting protein (HIP) and increasing Shh-induced angiogenesis. Mice were treated with local injections of E2 or placebo one week before nerve-crush injury; 28 days after injury, nerve conduction velocity, exercise duration, and vascularity were significantly greater in E2-treated mice than in placebo-treated mice. E2 treatment was also associated with higher mRNA levels of Shh, the Shh receptor Patched-1, and the Shh transcriptional target Gli1, but with lower levels of HIP. The E2-induced enhancement of nerve vascularity was abolished by the Shh inhibitor cyclopamine, and the effect of E2 treatment on Shh, Gli1, and HIP mRNA expression was abolished by the E2 inhibitor ICI. Gli-luciferase activity in human umbilical-vein endothelial cells (HUVECs) increased more after treatment with E2 and Shh than after treatment with E2 alone, and E2 treatment reduced HIP expression in HUVECs and Schwann cells without altering Shh expression. Collectively, these findings suggest that E2 improves nerve recovery, at least in part, by reducing HIP expression, which subsequently leads to an increase in Shh signaling and Shh-induced angiogenesis.

Effects of estrogen on the neuromuscular system in the embryonic zebrafish (Danio rerio)

Estrogen (E₂) has been shown to play an important role in maintaining central nervous system (CNS) axonal growth, synapse formation, and neurotransmitter release; however, there is less direct evidence for a similar role in the peripheral nervous system (PNS). In a previous study we have shown that when E₂ was removed from embryonic zebrafish (Danio rerio) system using the aromatase inhibiter (AI) 4-hydroxyandrostenedione (4-OH-A) fish did not developmentally express normal sensory-motor (S-M) functions such as tactile, vestibular, and swimming behaviors, creating a condition called 'listless.' These findings led to speculation that E₂ deprivation, under these conditions, caused a neuromuscular-like "denervation" resulting in the 'listless' condition. Morphometric data analysis reported in this study indicated that there was an absence of vesicular acetylcholine transporter (VAChT) staining in the primary motor neurons as a result of AI treatment compared to controls. In contrast, E₂ co-treatment with AI (E₂+AI) rescued a significant number of VAChT stained nerve endings and treatment of fish with E₂ alone exhibited a significantly higher number of VAChT profiles than in control fish. In addition, in the AI treated group znp-1 antibody staining of the primary motor neurons demonstrated: 1) diminished axon branching; 2) shorter primary axons; and 3) an absence in the posterior trunk regions of fish. In turn, trunk muscles were significantly diminished in size and less organized when treated with AI when compared to controls and E₂+AI treatment restored myotome width and height accompanied by some dramatic changes in the α-bungarotoxin-labeled ACh post-synaptic receptor elements of the trunk skeletal muscles. Data from this study suggest that treatment with the AI 4-OH-A essentially denervates the zebrafish trunk skeletal muscles, most likely by compromising the development of the vesicular transport system for ACh preventing it from acting at the synaptic terminals. These findings begin to demonstrate the prominent role that E₂ plays in the developing zebrafish PNS, particularly at the neuromuscular level.

Neuroprotective efficacy of estrogen in experimental spinal cord injury in rats

Spinal cord injury (SCI) leads to neurological deficits and motor dysfunction. Methylprednisolone, the only drug used for treating SCI, renders limited neuroprotection and remains controversial. Estrogen is one of the most potent multiactive neuroprotective agents and it is currently under investigation in our laboratory for its efficacy in SCI. The present review briefly summarizes our earlier findings on the therapeutic potential of pharmacological/supraphysiological levels of estrogen in SCI and outlines our ongoing research, highlighting the efficacy of physiological levels of estrogen against neuronal injury, axonal degeneration, and gliosis and also the molecular mechanisms of such neuroprotection in experimental SCI. Furthermore, our ongoing studies designed to explore the different translational potential of estrogen therapy suggest that this multiactive steroid may act as an adjunct therapy to promote angiogenesis, thus enhancing the functional recovery following chronic SCI. Taken together, these studies confirm that estrogen is a potential therapeutic agent for treating SCI.

Diabetes alters aromatase enzyme levels in sciatic nerve and hippocampus tissues of rats

Diabetes mellitus (DM) is associated with increased risk of impaired cognitive function. Diabetic neuropathy is one of the most common and important complications of DM. Estrogens prevent neuronal loss in experimental models of neurodegeneration and accelerate nerve regeneration. Aromatase catalyzes the conversion of androgens to estrogens and expressed in a variety of tissues including neurons. Although insulin is known to regulate the activity of aromatase there is no study about the effects of diabetes on this enzyme. Present study was designed to investigate the effects of experimental diabetes on aromatase expression in nervous system. Gender-based differences were also investigated. Rats were injected with streptozotocin to induce diabetes. At the end of 4 and 12 weeks sciatic nerve and hippocampus homogenates were prepared and evaluated for aromatase proteins. Aromatase expressions in sciatic nerves of both genders were decreased in 4 weeks of diabetes, but in 12 weeks the enzyme levels were increased in females and reached to control levels in male animals. Aromatase levels were not altered in hippocampus at 4 weeks but increased at 12 weeks in female diabetic rats. No significant differences were observed at enzyme levels of hippocampus in male diabetic rats. Insulin therapy prevented all diabetes-induced changes. In conclusion, these results indicated for the first time that, DM altered the expression of aromatase both in central and peripheral nervous systems. Peripheral nervous system is more vulnerable to damage than central nervous system in diabetes. These effects of diabetes differ with gender and compensatory neuroprotective mechanisms are more efficient in female rats.

Carpal tunnel syndrome in postmenopausal women

OBJECTIVE

Hormonal changes that accompany menopause have a significant impact on the nervous and other physiological systems. Our objective was to evaluate the relationship between carpal tunnel syndrome (CTS) and the clinical features of menopause in postmenopausal women, in comparison to age-matched healthy controls.

METHODS

Overall, 6230 women were seen during the study period. Of these, 5587 were not eligible because they were premenopausal or perimenopausal. 537 women did not meet the criteria used in the study for a diagnosis of idiopathic CTS and were excluded. Finally, one hundred and six patients with CTS and 115 controls were examined. The presence of CTS was confirmed both clinically and electrophysiologically. Socio-demographic variables and reproductive histories were evaluated via a structured interview.

RESULTS

In comparison to healthy controls, patients with CTS showed a significantly greater number of pregnancies and an earlier age at menopause. Regarding the type of menopause, patients and controls showed similar frequencies for natural versus surgical menopause. The frequency of natural menopause was significantly higher than that of surgical menopause in both groups.

CONCLUSION

Our results suggest that age at menopause may be a significant factor in the development of CTS. Pregnancy-related hormonal changes may have long-term effects that increase the incidence of CTS in postmenopausal women.

Sex differences in lumbar spinal cord gene expression following experimental lumbar radiculopathy

Considerable evidence indicates that there are sex-related differences in clinical and experimental pain sensitivity. In the present study, we sought to determine what genes were expressed in the spinal cord in a sexually dimorphic manner. We first analyzed global gene expression in the lumbar spinal cord of uninjured male and female rats using the Affymetrix RAE230A GeneChip platform in order to identify genes that are selectively expressed in male and female rats at a basal level. We subsequently analyzed global gene expression in the lumbar spinal cord of male and female rats at two time points (7 days and 14 d) following a rodent model of lumbar radiculopathy (L5 nerve root ligation) in order to determine what genes were regulated in a sexually dimorphic manner following nerve root injury. We utilized a linear regression analysis method to identify genes that were significantly different from the corresponding sham surgical controls. The expression patterns of several genes of interest were subsequently confirmed using RT-PCR. Our findings demonstrate significant differences in lumbar spinal cord gene expression in both uninjured and injured (L5 nerve root ligation) male and female rats. Further confirmation of a subset of the genes identified Neuregulin 1 and its high affinity receptor, ErbB4, Tachykinin 1, and Metabotropic glutamate receptor 6 as female specific genes upregulated following L5 nerve root injury. These findings provide several target genes for further study that may elucidate the neurochemical mechanisms underlying sex differences in pain sensitivity and lead to improved treatments for chronic pain syndromes.

Neuroactive steroids and peripheral neuropathy

Peripheral neuropathy, either inherited or acquired, represents a very common disorder for which effective clinical treatments are not available yet. Observations here summarized indicate that neuroactive steroids, such as progesterone, testosterone and their reduced metabolites, might represent a promising therapeutic option. Peripheral nerves are able to synthesize and metabolize neuroactive steroids and are a target for these molecules, since they express classical and non-classical steroid receptors. Neuroactive steroids modulate the expression of key transcription factors for Schwann cell function, regulate Schwann cell proliferation and promote the expression of myelin proteins involved in the maintenance of myelin multilamellar structure, such as myelin protein zero and peripheral myelin protein 22. These actions may result in the protection and regeneration of peripheral nerves affected by different forms of pathological alterations. Indeed, neuroactive steroids are able to counteract biochemical, morphological and functional alterations of peripheral nerves in different experimental models of neuropathy, including the alterations caused by aging, diabetic neuropathy and physical injury. Therefore, neuroactive steroids, pharmacological agents able to increase their local synthesis and synthetic ligands for their receptors have a promising potential for the treatment of different forms of peripheral neuropathy.

The hair follicle as an estrogen target and source

For many decades, androgens have dominated endocrine research in hair growth control. Androgen metabolism and the androgen receptor currently are the key targets for systemic, pharmacological hair growth control in clinical medicine. However, it has long been known that estrogens also profoundly alter hair follicle growth and cycling by binding to locally expressed high-affinity estrogen receptors (ERs). Besides altering the transcription of genes with estrogen-responsive elements, 17beta-estradiol (E2) also modifies androgen metabolism within distinct subunits of the pilosebaceous unit (i.e., hair follicle and sebaceous gland). The latter displays prominent aromatase activity, the key enzyme for androgen conversion to E2, and is both an estrogen source and target. Here, we chart the recent renaissance of estrogen research in hair research; explain why the hair follicle offers an ideal, clinically relevant test system for studying the role of sex steroids, their receptors, and interactions in neuroectodermal-mesodermal interaction systems in general; and illustrate how it can be exploited to identify novel functions and signaling cross talks of ER-mediated signaling. Emphasizing the long-underestimated complexity and species-, gender-, and site-dependence of E2-induced biological effects on the hair follicle, we explore targets for pharmacological intervention in clinically relevant hair cycle manipulation, ranging from androgenetic alopecia and hirsutism via telogen effluvium to chemotherapy-induced alopecia. While defining major open questions, unsolved clinical challenges, and particularly promising research avenues in this area, we argue that the time has come to pay estrogen-mediated signaling the full attention it deserves in future endocrinological therapy of common hair growth disorders.

Effect of estrogen on urethral function and nerve regeneration following pudendal nerve crush in the female rat

PURPOSE

We tested the hypothesis that estrogen promotes improvement in urethral function and nerve regeneration following bilateral pudendal nerve crush in ovariectomized female rats.

MATERIALS AND METHODS

A total of 52 female rats underwent ovariectomy 6 days before bilateral pudendal nerve crush. Estrogen and sham capsules were subcutaneously implanted at the time of nerve crush in 16 and 14 of these rats, respectively, while 22 served as unoperated controls. Seven days following nerve crush urethral LPP testing was performed using urethane anesthesia. Spinal cord sections containing motoneurons of Onufrowicz's nucleus were subjected to in situ hybridization to detect the expression of beta(II) tubulin mRNA, a marker of the neuroregenerative response.

RESULTS

Mean LPP +/- SEM was significantly decreased after pudendal nerve crush in sham treated animals compared to unoperated controls (32.1 +/- 6.8 vs 54.4 +/- 11.6 cm H2O). Rats with an estrogen implant had an LPP of 42.5 +/- 16.8 cm H2O, which was significantly greater than rats given sham implants and significantly less than unoperated controls. Rats that received an estrogen implant had increased beta(II) tubulin mRNA expression compared to those that received a sham implant.

CONCLUSIONS

The results of this research suggest that estrogen given at the time of pudendal nerve crush promotes and facilitates the recovery of urethral function and an increase in the nerve regenerative response. Future studies will include the investigation of molecular pathways activated by estrogen in response to peripheral nerve injury.

Microarray analysis of gene expression patterns in adult spinal motoneurons after different types of axonal injuries

Three experimental models of axonal injuries in adult rat spinal motoneurons were established to investigate changes of gene expression in response to such injuries. We took advantage of cDNA microarray analysis to determine the differential expression of genes in injured motoneurons following distal axotomy or root avulsion in the absence or presence of BDNF. The major finding was that, in response to proximal axonal injury (avulsion), expression of genes that are known to facilitate neuronal survival and axonal regeneration (e.g., IGFRII, PI3K, IGFBP-6, GSTs, GalR2) were down-regulated; but following treatment with BDNF they were up-regulated. In addition, the expression of genes known to be involved in apoptosis and DNA damage (e.g., ANX5, TS, ALR) were down-regulated in BDNF-treated animals with avulsion. Furthermore, many functional families of genes previously shown to play roles in the pathophysiology of axonal injury, including SNAP-25A, SV2B, Ras-related ras3a/4b, ERK1/2, 14-3-3 proteins, proteasome proteins, oncogenes, GAP-43, and NMDAR1, were altered after either distal axotomy or avulsion injury. Some of the changes in gene expression, including Lim-2, FRAG1, GlaR2, GSTs, ALR, TS, ANX3/5, and nhe1/2, are first reported here in injured motoneurons. The differential expression of genes identified by the expression arrays was confirmed by gene-specific RT-PCR for eight genes (GAP-43, IGFR II, Lim-2, MIF, NDAP1, TS, PCC3, and FRAG1) and by in situ hybridization for Lim-2. These results suggest that abnormal regulation of particular biochemical pathways may induce motoneuron death after ventral root avulsion in adult animals. This study presents an approach for selecting specific genes and their products that may be involved in motoneuron degeneration following axonal injuries.

Estradiol regulates different genes in human breast tumor xenografts compared with the identical cells in culture

In breast cancers, estrogen receptor (ER) levels are highly correlated with response to endocrine therapies. We sought to define mechanisms of estrogen (E) signaling in a solid breast tumor model using gene expression profiling. ER(+) T47D-Y human breast cancer cells were grown as xenografts in ovariectomized nude mice under four conditions: 1) 17beta-estradiol for 8 wk (E); 2) without E for 8 wk (control); 3) E for 7 wk followed by 1 wk of E withdrawal (Ewd); or 4) E for 8 wk plus tamoxifen for the last week. E-regulated genes were defined as those that differed significantly between control and E and/or between E and Ewd or control and Ewd. These protocols generated 188 in vivo E-regulated genes that showed two major patterns of regulation. Approximately 46% returned to basal states after Ewd (class I genes); 53% did not (class II genes). In addition, more than 70% of class II-regulated genes also failed to reverse in response to tamoxifen. These genes may be interesting for the study of hormone-resistance issues. A subset of in vivo E-regulated genes appears on lists of clinical ER discriminator genes. These may be useful therapeutic targets or markers of E activity. Comparison of in vivo E-regulated genes with those regulated in identical cells in vitro after 6 and 24 h of E treatment demonstrate only 11% overlap. This indicates the extent to which gene expression profiles are uniquely dependent on hormone-treatment times and the cellular microenvironment.

Peripheral nerves: a target for the action of neuroactive steroids

Peripheral nervous system possesses both classical and non-classical steroid receptors and consequently may represent a target for the action of neuroactive steroids. The present review summarizes the state of art of this intriguing field of research reporting data which indicate that neuroactive steroids, like for instance progesterone, dihydroprogesterone, tetrahydroprogesterone, dihydrotestosterone and 3alpha-diol, stimulate the expression of two important proteins of the myelin of peripheral nerves, the glycoprotein P0 (P0) and the peripheral myelin protein 22 (PMP22). Interestingly, the mechanisms by which neuroactive steroids exert their effects involve classical steroid receptors, like for instance progesterone and androgen receptors, in case of P0 and non-classical steroid receptors, like GABA(A) receptor, in case of PMP22. Moreover, neuroactive steroids not only control the expression of these specific myelin proteins, but also influence the morphology of myelin sheaths and axons suggesting that these molecules may represent an interesting new therapeutic approach to maintain peripheral nerve integrity during neurodegenerative events.

Effects of male and female sex steroids on the development of normal and the transient Froriep's dorsal root ganglia of the chick embryo

Sex steroids can influence developmental processes and support the survival of neurons in the embryonic central nervous system. Recent studies have shown that estrogen receptors are also expressed in the peripheral nervous system, in the dorsal root ganglia (DRG) of chick embryos. However, no studies have examined the effects of sex steroids on development of embryonic DRG. In the present study, 0.2 microg, 1.0 microg, 5.0 microg 10 microg, 20 microg, 25 microg, and 40 microg doses of testosterone or estradiol were delivered to chick embryos at Hamburger and Hamilton stage 18 (E3). The actions of these doses of sex steroids on the development of the C5DRG (fifth cervical ganglion, a "normal" DRG) and C2DRG (a transient ganglion known as a "Froriep's DRG") were then evaluated by quantifying ganglionic volumes, cell number, proliferation, and apoptosis after 1 day of growth to stage 23. We found that both testosterone and estradiol promoted proliferation of cells in both normal DRG and the Froriep's ganglia. By contrast, estradiol significantly increased the number of apoptotic cells, while testosterone strongly inhibited apoptosis. These actions of sex steroids on DRG development were dose-dependent, and C5DRG and C2DRG showed different sensitivities to the applied sex steroids. In addition, the present results demonstrated that specific ER and AR inhibitors (tamoxifen and flutamide) did not influence the effects of 5 microg E2 and 5 microg T on C2 and C5DRG significantly. These results demonstrate that male and female sex steroids can modulate DRG development through an epigenetic mechanism, as had been shown for the central nervous system.

Striated urethral sphincter activity does not alter urethral pressure during filling cystometry

OBJECTIVE

The purpose of this study was to determine the relationship between urethral pressure and the neuromuscular activity of the urethral sphincter with the use of quantitative electromyography during bladder filling.

STUDY DESIGN

Women who underwent multichannel urodynamic testing with concentric needle electromyography of the striated urethral sphincter between December 2000 and February 2002 were studied. Raw electromyography signals were processed by a electromyography instrument that was equipped with automated motor unit analysis software programs. Quantitative electromyography software was used to analyze the electrical activity of the urethral sphincter during filling cystometry.

RESULTS

One hundred women (mean age, 60 years [range, 22-82 years]; median parity, 3 children [range, 0-8 children]) were studied. Most women (79%) were postmenopausal, and 68% of those women were receiving hormone replacement therapy. Quantitative electromyography values increased significantly at 300 mL and maximum cystometric capacity; however, there was no significant increase in urethral pressure. The median change in urethral pressure at 300 mL and maximum cystometric capacity were 4 cm water (interquartile range, 0-8 cm) and 0 cm water (interquartile range, -4-8 cm), respectively (P = .229). The median change in quantitative electromyography at 300 mL and maximum cystometric capacity were 9 microV (range, 5-14 microV) and 10 microV (range, 7-19 microV), respectively (P < .0005). There was no correlation between change in urethral pressure and motor unit activation on quantitative electromyography at 300 mL or maximum cystometric capacity. Fifty-six women had no change or a decreased urethral pressure at maximum cystometric capacity, yet all but 1 of these women had increased motor unit activation on quantitative electromyography.

CONCLUSION

Urethral pressure does not increase during filling cystometry, despite increased activity of the striated urethral sphincter, which suggests that urethral pressure change does not reflect the integrity of the striated urethral sphincter.

Long-term effects of melatonin or 17 beta-estradiol on improving spatial memory performance in cognitively impaired, ovariectomized adult rats

Melatonin is an endogenously generated potent antioxidant. Our previous studies indicate that melatonin improved learning and memory deficits in APP695 transgenic mouse of Alzheimer's disease. An ovariectomized (OVX) rat model which is characterized by progressive memory deficits, central cholinergic nerve system degeneration and differentiation/apoptosis imbalance is the ideal in vivo model in which to test the neuroprotective effects of melatonin. OVX Sprague-Dawley rats received daily injections of melatonin (5, 10 and 20 mg/kg) or 17 beta-estradiol (E2, 80 microg/kg) or sesame oil for 16 wk. Morris water maze results showed that ovarian steroid deprivation resulted in spatial memory impairment, while melatonin and E2 significantly ameliorated spatial memory deficits in OVX rats. The latency to find the hidden platform and the distance to reach the platform become shorter in both melatonin and E2-treated rats compared with those that were only OVX. Four months after OVX, the choline acetyltransferase activity in the frontal cortex and hippocampus were greatly decreased in comparison with the controls. Melatonin and E2 antagonized the effects induced by OVX. Interestingly, the activity of the acetylcholinesterase was not altered in any group of rats. DNA fragmentation was presented in the front cortex of the OVX rats. Melatonin and E2 reduced the number of apoptotic neurons. These findings demonstrate the important effects of melatonin and E2 on cholinergic neurons and support the potential application of melatonin in the treatment of dementia in postmenopausal women. Our results indicate that neuroprotection by melatonin partly correlated to modulation of apoptosis and protection of the cholinergic system. Early long-term melatonin application is a promising strategy which could potentially be applied in a clinic setting.

Estrogen increases retrograde labeling of motoneurons: evidence of a nongenomic mechanism

Estrogen has a variety of neurotrophic effects mediated via different signaling cascades, including ERK and phosphatidylinositol 3-kinase (PI3K) pathways. In this study, we investigated effects of estrogen and inhibitors for ERK and PI3K applied directly onto the cut sciatic nerve on retrograde labeling of lumbar motoneurons. A mix of retrograde tracer (Fluorogold) and 17beta-estradiol, in combination with an antagonist for estrogen receptors ICI 182,780, an inhibitor of ERK1/2 pathway (U0126), an inhibitor of PI3K (LY-294002), or a protein synthesis inhibitor (cycloheximide), was applied to the proximal stump of the transected sciatic nerve for 24 h. Coapplication of Fluorogold with 17beta-estradiol produced a significant increase in the number of retrograde-labeled lumbar motoneurons, compared with Fluorogold alone. Estrogen potentiation of retrograde labeling was inhibited by application of ICI 182,780, U0126, LY-294002, and cycloheximide. Immunohistochemical analysis of the sciatic nerve, 24 h following crush injury, revealed accumulation of phospho-ERK in regenerating nerve fibers. The data suggest a role for estrogen, ERK, PI3K, and protein synthesis in the uptake and retrograde transport of Fluorogold. We propose that estrogen action in peripheral nerve fibers is mediated via the ERK and PI3K signaling pathways and is reliant on local protein synthesis.

Effects of injury and progesterone treatment on progesterone receptor and progesterone binding protein 25-Dx expression in the rat spinal cord

Progesterone provides neuroprotection after spinal cord injury, but the molecular mechanisms involved in this effect are not completely understood. In this work, expression of two binding proteins for progesterone was studied in intact and injured rat spinal cord: the classical intracellular progesterone receptor (PR) and 25-Dx, a recently discovered progesterone membrane binding site. RT-PCR was employed to determine their relative mRNA levels, whereas cellular localization and relative protein levels were investigated by immunocytochemistry. We observed that spinal cord PR mRNA was not up-regulated by estrogen in contrast to what is observed in many brain areas and in the uterus, but was abundant as it amounted to a third of that measured in the estradiol-stimulated uterus. In male rats with complete spinal cord transection, levels of PR mRNA were significantly decreased, while those of 25-Dx mRNA remained unchanged with respect to control animals. When spinal cord-injured animals received progesterone treatment during 72 h, PR mRNA levels were not affected and remained low, whereas 25-Dx mRNA levels were significantly increased. Immunostaining of PR showed its intracellular localization in both neurons and glial cells, whereas 25-Dx immunoreactivity was localized to cell membranes of dorsal horn and central canal neurons. As the two binding proteins for progesterone differ with respect to their response to lesion, their regulation by progesterone, their cellular and subcellular localizations, their functions may differ under normal and pathological conditions. These observations point to a novel and potentially important role of the progesterone binding protein 25-Dx after injury of the nervous system and suggest that the neuroprotective effects of progesterone may not necessarily be mediated by the classical progesterone receptor but may involve distinct membrane binding sites.

Differential expression of endothelin receptors in regenerating spinal motor neurons in mice

On day 4 after sciatic nerve crush injury, expression and localization of endothelin receptors ET(A) and ET(B) in the lumbar spinal cord were examined. Immunohistochemical staining with antibodies to ET(A) and ET(B) receptors showed cytoplasmic distribution of ET(A) receptors in motor neurons, whereas ET(B) receptors were localized in the perinuclear region. On the injured side of the lumbar spinal cord, when compared to contralateral, results demonstrated an up-regulation of ET(B) and a down-regulation of ET(A) receptors expression at the level of both mRNA and protein. These results suggest that ET(B) receptors may play a role in the regeneration of axotomized motor neurons.

Raloxifene analog LY117018 enhances the regeneration of sciatic nerve in ovariectomized female mice

The aim of this study was to examine the effects of LY117018, a selective estrogen receptor modulator, on peripheral nerve regeneration, using a model of sciatic nerve crush injury in mice. Sciatic functional index, an index of functional recovery, was significantly higher in LY117018 treated mice throughout regeneration. Analysis of semi-thin sections revealed a significant increase in both the total number of regenerating nerve fibers at day 7, and the mean axonal area of myelinated fibers at 7, 14, and 21 days after injury, in LY117018 treated mice. Analysis of axonal transport through retrograde labeling of motor neurons showed that LY117018 increased transport, and ICI 182,780 blocked the effects of LY117018, delineating estrogen receptors as its target. Our study suggests that LY117018 may markedly accelerate peripheral nerve regeneration and functional recovery through activation of estrogen receptors.