Gonadal steroid attenuation of developing hamster facial motoneuron loss by axotomy: equal efficacy of testosterone, dihydrotestosterone, and 17-beta estradiol

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.

Effects of 17-β-estradiol released from shape-memory terpolymer rods on sciatic nerve regeneration after injury and repair with chitosan nerve conduit in female rats

The aim of this study was to assess 17-β-estradiol (E2) influence on sciatic nerve regeneration after injury followed by a repair with chitosan conduit in ovariectomized female rats. The study was performed in 2 groups (n = 16) of rats: OVChit - after excision of a fragment of the sciatic nerve, a chitosan conduit was implanted; OVChitE10 group - additionally to chitosan conduit, shape-memory terpolymer rods based on poly(L-lactide-co-glycolide- co-trimethylene carbonate) releasing 17-β-estradiol for 20 weeks were implanted. The mean number of regenerating axons and mean fiber area were significantly greater in 17-β-estradiol-treated animals. In this group, the infiltrate of leukocytes was diminished. The presence of 17-β-estradiol receptors alpha and beta in motoneurons in the spinal cord were discovered. This may indicate the location where 17-β-estradiol affects the regeneration of the injured nerve. Estradiol released from the terpolymer rods for 20 weeks could enhance, to some extent, sciatic nerve regeneration after injury, and diminish the inflammatory reaction. In the future, 17-β-estradiol entrapped in terpolymer rods could be used in the repair of injured peripheral nerves, but there is a need for further studies.

Testosterone treatment restores vestibular function by enhancing neuronal survival in an experimental closed-head repetitive mild traumatic brain injury model

Repetitive mild traumatic brain injury (rmTBI) results in a myriad of symptoms, including vestibular impairment. The mechanisms underlying vestibular dysfunction in rmTBI patients remain poorly understood. Concomitantly, acute hypogonadism occurs following TBI and can persist chronically in many patients. Using a repetitive mild closed-head animal model of TBI, the role of testosterone on vestibular function was tested. Male Long Evans Hooded rats were randomly divided into sham or rmTBI groups. Significant vestibular deficits were observed both acutely and chronically in the rmTBI groups. Systemic testosterone was administered after the development of chronic vestibular dysfunction. rmTBI animals given testosterone showed improved vestibular function that was sustained for 175 days post-rmTBI. Significant vestibular neuronal cell loss was, however, observed in the rmTBI animals compared to Sham animals at 175 days post-rmTBI and testosterone treatment significantly improved vestibular neuronal survival. Taken together, these data demonstrate a critical restorative role of testosterone in vestibular function following rmTBI. This study has important clinical implications because it identifies testosterone treatment as a viable therapeutic strategy for the long-term recovery of vestibular function following TBI.

Mapping Motor Neuron Vulnerability in the Neuraxis of Male SOD1G93A Mice Reveals Widespread Loss of Androgen Receptor Occurring Early in Spinal Motor Neurons

Sex steroid hormones have been implicated as disease modifiers in the neurodegenerative disorder amyotrophic lateral sclerosis (ALS). Androgens, signalling via the androgen receptor (AR), predominate in males, and have widespread actions in the periphery and the central nervous system (CNS). AR translocates to the cell nucleus when activated upon binding androgens, whereby it regulates transcription of target genes via the classical genomic signalling pathway. We previously reported that AR protein is decreased in the lumbar spinal cord tissue of symptomatic male SOD1^G93A mice. Here, we further explored the changes in AR within motor neurons (MN) of the CNS, assessing their nuclear AR content and propensity to degenerate by endstage disease in male SOD1^G93A mice. We observed that almost all motor neuron populations had undergone significant loss in nuclear AR in SOD1^G93A mice. Interestingly, loss of nuclear AR was evident in lumbar spinal MNs as early as the pre-symptomatic age of 60 days. Several MN populations with high AR content were identified which did not degenerate in SOD1^G93A mice. These included the brainstem ambiguus and vagus nuclei, and the sexually dimorphic spinal MNs: cremaster, dorsolateral nucleus (DLN) and spinal nucleus of bulbocavernosus (SNB). In conclusion, we demonstrate that AR loss directly associates with MN vulnerability and disease progression in the SOD1^G93A mouse model of ALS.

Deficiency in Androgen Receptor Aggravates Traumatic Brain Injury-Induced Pathophysiology and Motor Deficits in Mice

Androgens have been shown to have a beneficial effect on brain injury and lower reactive astrocyte expression after TBI. Androgen receptors (ARs) are known to mediate the neuroprotective effects of androgens. However, whether ARs play a crucial role in TBI remains unknown. In this study, we investigated the role of ARs in TBI pathophysiology, using AR knockout (ARKO) mice. We used the controlled cortical impact model to produce primary and mechanical brain injuries and assessed motor function and brain-lesion volume. In addition, the AR knockout effects on necrosis and autophagy were evaluated after TBI. AR knockout significantly increased TBI-induced expression of the necrosis marker alpha-II-spectrin breakdown product 150 and astrogliosis marker glial fibrillary acidic protein. In addition, the TBI-induced astrogliosis increase in ARKO mice lasted for three weeks after a TBI. The autophagy marker Beclin-1 was also enhanced in ARKO mice compared with wild-type mice after TBI. Our results also indicated that ARKO mice showed a more unsatisfactory performance than wild-type mice in a motor function test following TBI. Further, they were observed to have more severe lesions than wild-type mice after injury. These findings strongly suggest that ARs play a role in TBI.

Androgen deprivation therapy and risk of cognitive dysfunction in men with prostate cancer: is there a possible link?

The expansion of the indication to use androgen deprivation therapy (ADT) to treat patients with advanced or metastatic prostate cancer has dramatically increased over the recent decades, resulting in the progress of patients’ survival. However, chronic health implications can become more apparent as the number of long-term cancer survivors is expected to be increased along with the adverse effect of ADT. In particular, interest in investigating ADT, especially luteinizing hormone-releasing hormone (LHRH) agonist association with cognitive dysfunction has been growing. Previous studies in animals and humans suggest that the level of androgen decreases with age and that cognitive decline occurs with decreases in androgen. Correspondingly, some of the extensive studies using common neurocognitive tests have shown that LHRH agonists may affect specific domains of cognitive function (e.g., visuospatial abilities and executive function). However, the results from these studies have not consistently demonstrated the association because of its intrinsic limitations. Large-scale studies based on electronic databases have also failed to show consistent results to make decisive conclusions because of its heterogeneity, complexity of covariates, and possible risk of biases. Thus, this review article summarizes key findings and discusses the results of several studies investigating the ADT association with cognitive dysfunction and risk of dementia from various perspectives.

Klinefelter syndrome or testicular dysgenesis: Genetics, endocrinology, and neuropsychology

Klinefelter syndrome (47,XXY) is a frequent chromosomal disorder among males, often presenting with hypergonadotropic hypogonadism, small firm testicles, metabolic disorders, neurocognitive challenges, and increased height. Neurologic disorders such as epilepsy, seizures, and tremor as well as psychiatric disorders are also seen more frequently. The neurocognitive deficits seen are present in many areas of cognition, typically affecting general cognitive abilities, language, and executive functioning. Also, social dysfunction is frequent. Dyslexia is present in more than half of all males. Brain imaging studies generally show a typical pattern, with many nuclei and brain areas being smaller than among controls. However, it has not been possible to link the brain alterations found in imaging studies with the neurocognitive profile. The genetics underlying the phenotypic traits found among males with Klinefelter syndrome still remains to be elucidated; however, recent studies have described pervasive changes in the methylome and transcriptome and new and interesting candidate genes have been pinpointed, but their involvement in the phenotype of Klinefelter syndrome has not been proven.

The Role of Estradiol in Traumatic Brain Injury: Mechanism and Treatment Potential

Patients surviving traumatic brain injury (TBI) face numerous neurological and neuropsychological problems significantly affecting their quality of life. Extensive studies over the past decades have investigated pharmacological treatment options in different animal models, targeting various pathological consequences of TBI. Sex and gender are known to influence the outcome of TBI in animal models and in patients, respectively. Apart from its well-known effects on reproduction, 17β-estradiol (E2) has a neuroprotective role in brain injury. Hence, in this review, we focus on the effect of E2 in TBI in humans and animals. First, we discuss the clinical classification and pathomechanism of TBI, the research in animal models, and the neuroprotective role of E2. Based on the results of animal studies and clinical trials, we discuss possible E2 targets from early to late events in the pathomechanism of TBI, including neuroinflammation and possible disturbances of the endocrine system. Finally, the potential relevance of selective estrogenic compounds in the treatment of TBI will be discussed.

Physiopathological Role of Neuroactive Steroids in the Peripheral Nervous System

Peripheral neuropathy (PN) refers to many conditions involving damage to the peripheral nervous system (PNS). Usually, PN causes weakness, numbness and pain and is the result of traumatic injuries, infections, metabolic problems, inherited causes, or exposure to chemicals. Despite the high prevalence of PN, available treatments are still unsatisfactory. Neuroactive steroids (i.e., steroid hormones synthesized by peripheral glands as well as steroids directly synthesized in the nervous system) represent important physiological regulators of PNS functionality. Data obtained so far and here discussed, indeed show that in several experimental models of PN the levels of neuroactive steroids are affected by the pathology and that treatment with these molecules is able to exert protective effects on several PN features, including neuropathic pain. Of note, the observations that neuroactive steroid levels are sexually dimorphic not only in physiological status but also in PN, associated with the finding that PN show sex dimorphic manifestations, may suggest the possibility of a sex specific therapy based on neuroactive steroids.

Deletion of CD38 and supplementation of NAD+ attenuate axon degeneration in a mouse facial nerve axotomy model

Following facial nerve axotomy, nerve function is not fully restored even after reconstruction. This may be attributed to axon degeneration/neuronal death and sustained neuroinflammation. CD38 is an enzyme that catalyses the hydrolysis of nicotinamide adenine dinucleotide (NAD+) and is a candidate molecule for regulating neurodegeneration and neuroinflammation. In this study, we analyzed the effect of CD38 deletion and NAD+ supplementation on neuronal death and glial activation in the facial nucleus in the brain stem, and on axon degeneration and immune cell infiltration in the distal portion of the facial nerve after axotomy in mice. Compared with wild-type mice, CD38 knockout (KO) mice showed reduced microglial activation in the facial nucleus, whereas the levels of neuronal death were not significantly different. In contrast, the axon degeneration and demyelination were delayed, and macrophage accumulation was reduced in the facial nerve of CD38 KO mice after axotomy. Supplementation of NAD+ with nicotinamide riboside slowed the axon degeneration and demyelination, although it did not alter the level of macrophage infiltration after axotomy. These results suggest that CD38 deletion and supplementation of NAD+ may protect transected axon cell-autonomously after facial nerve axotomy.

Deletion of CD38 and supplementation of NAD+ attenuate axon degeneration in a mouse facial nerve axotomy model

Following facial nerve axotomy, nerve function is not fully restored even after reconstruction. This may be attributed to axon degeneration/neuronal death and sustained neuroinflammation. CD38 is an enzyme that catalyses the hydrolysis of nicotinamide adenine dinucleotide (NAD⁺) and is a candidate molecule for regulating neurodegeneration and neuroinflammation. In this study, we analyzed the effect of CD38 deletion and NAD⁺ supplementation on neuronal death and glial activation in the facial nucleus in the brain stem, and on axon degeneration and immune cell infiltration in the distal portion of the facial nerve after axotomy in mice. Compared with wild-type mice, CD38 knockout (KO) mice showed reduced microglial activation in the facial nucleus, whereas the levels of neuronal death were not significantly different. In contrast, the axon degeneration and demyelination were delayed, and macrophage accumulation was reduced in the facial nerve of CD38 KO mice after axotomy. Supplementation of NAD⁺ with nicotinamide riboside slowed the axon degeneration and demyelination, although it did not alter the level of macrophage infiltration after axotomy. These results suggest that CD38 deletion and supplementation of NAD⁺ may protect transected axon cell-autonomously after facial nerve axotomy.

The Role of Sex and Sex Hormones in Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are a wide class of disorders of the central nervous system (CNS) with unknown etiology. Several factors were hypothesized to be involved in the pathogenesis of these diseases, including genetic and environmental factors. Many of these diseases show a sex prevalence and sex steroids were shown to have a role in the progression of specific forms of neurodegeneration. Estrogens were reported to be neuroprotective through their action on cognate nuclear and membrane receptors, while adverse effects of male hormones have been described on neuronal cells, although some data also suggest neuroprotective activities. The response of the CNS to sex steroids is a complex and integrated process that depends on (i) the type and amount of the cognate steroid receptor and (ii) the target cell type-either neurons, glia, or microglia. Moreover, the levels of sex steroids in the CNS fluctuate due to gonadal activities and to local metabolism and synthesis. Importantly, biochemical processes involved in the pathogenesis of NDs are increasingly being recognized as different between the two sexes and as influenced by sex steroids. The aim of this review is to present current state-of-the-art understanding on the potential role of sex steroids and their receptors on the onset and progression of major neurodegenerative disorders, namely, Alzheimer's disease, Parkinson's diseases, amyotrophic lateral sclerosis, and the peculiar motoneuron disease spinal and bulbar muscular atrophy, in which hormonal therapy is potentially useful as disease modifier.

Physiopathological role of the enzymatic complex 5α-reductase and 3α/β-hydroxysteroid oxidoreductase in the generation of progesterone and testosterone neuroactive metabolites

The enzymatic complex 5α-reductase (5α-R) and 3α/3β-hydroxysteroid oxidoreductase (HSOR) is expressed in the nervous system, where it transforms progesterone (PROG) and testosterone (T) into neuroactive metabolites. These metabolites regulate myelination, brain maturation, neurotransmission, reproductive behavior and the stress response. The expression of 5α-R and 3α-HSOR and the levels of PROG and T reduced metabolites show regional and sex differences in the nervous system and are affected by changing physiological conditions as well as by neurodegenerative and psychiatric disorders. A decrease in their nervous tissue levels may negatively impact the course and outcome of some pathological events. However, in other pathological conditions their increased levels may have a negative impact. Thus, the use of synthetic analogues of these steroids or 5α-R modulation have been proposed as therapeutic approaches for several nervous system pathologies. However, further research is needed to fully understand the consequences of these manipulations, in particular with 5α-R inhibitors.

Sex differences in steroid levels and steroidogenesis in the nervous system: Physiopathological role

The nervous system, in addition to be a target for steroid hormones, is the source of a variety of neuroactive steroids, which are synthesized and metabolized by neurons and glial cells. Recent evidence indicates that the expression of neurosteroidogenic proteins and enzymes and the levels of neuroactive steroids are different in the nervous system of males and females. We here summarized the state of the art of neuroactive steroids, particularly taking in consideration sex differences occurring in the synthesis and levels of these molecules. In addition, we discuss the consequences of sex differences in neurosteroidogenesis for the function of the nervous system under healthy and pathological conditions and the implications of neuroactive steroids and neurosteroidogenesis for the development of sex-specific therapeutic interventions.

Neuroactive steroids, neurosteroidogenesis and sex

The nervous system is a target and a source of steroids. Neuroactive steroids are steroids that target neurons and glial cells. They include hormonal steroids originated in the peripheral glands, steroids locally synthesized by the neurons and glial cells (neurosteroids) and synthetic steroids, some of them used in clinical practice. Here we review the mechanisms of synthesis, metabolism and action of neuroactive steroids, including the role of epigenetic modifications and the mitochondria in their sex specific actions. We examine sex differences in neuroactive steroid levels under physiological conditions and their role in the establishment of sex dimorphic structures in the nervous system and sex differences in its function. In addition, particular attention is paid to neuroactive steroids under pathological conditions, analyzing how pathology alters their levels and their role as neuroprotective factors, considering the influence of sex in both cases.

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.

Postmenopausal cognitive changes and androgen levels in the context of apolipoprotein E polymorphism

INTRODUCTION

The focus of this study was to assess cognitive functions in relation to androgens and specifically testosterone and dehydroepiandrosterone in postmenopausal women as well as the correlation between cognitive functions and these two androgens according to polymorphism of the apolipoprotein E gene (APOE).

MATERIAL AND METHODS

A group of 402 women was recruited to the study (minimum 2 years after the last menstruation, follicle-stimulating hormone (FSH) more than 30 U/ml and no dementia signs on Montreal Cognitive Assessment). The computerized battery of the Central Nervous System Vital Signs test was used to diagnose cognitive functions. APOE genotyping was performed by multiplex polymerase chain reaction (PCR). Testosterone (TTE) and dehydroepiandrosterone (DHEA) in the blood serum were assessed for further statistical correlations analysis.

RESULTS

In the group of postmenopausal women, higher testosterone concentration was associated with lower scores for Neurocognition Index (NCI) (p = 0.028), memory (p = 0.008) and psychomotor speed (p < 0.001). Presence of at least one APOE ε4 allele potentiated testosterone's negative influence on cognitive functions (p < 0.05). Woman with a high normal level of DHEA scored significantly better in verbal (p = 0.027) and visual memory (p < 0.001) than other participants. APOE polymorphism did not modify the relationship between DHEA concentration and scores for cognitive functions.

CONCLUSIONS

Hormonal balance variations after menopause may influence brain processes concerned with cognition, especially memory and psychomotor speed. The observed effects may be related to androgens' influence on higher cortical functions in the changed hormonal dynamics of the postmenopausal period.

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.

Neuroprotective effects of testosterone metabolites and dependency on receptor action on the morphology of somatic motoneurons following the death of neighboring motoneurons

Partial depletion of spinal motoneuron populations induces dendritic atrophy in neighboring motoneurons, and treatment with testosterone is neuroprotective, attenuating induced dendritic atrophy. In this study we examined whether the protective effects of testosterone could be mediated via its androgenic or estrogenic metabolites. Furthermore, to assess whether these neuroprotective effects were mediated through steroid hormone receptors, we used receptor antagonists to attempt to prevent the neuroprotective effects of hormones after partial motoneuron depletion. Motoneurons innervating the vastus medialis muscles of adult male rats were selectively killed by intramuscular injection of cholera toxin-conjugated saporin. Simultaneously, some saporin-injected rats were treated with either dihydrotestosterone or estradiol, alone or in combination with their respective receptor antagonists, or left untreated. Four weeks later, motoneurons innervating the ipsilateral vastus lateralis muscle were labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed in three dimensions. Compared with intact normal animals, partial motoneuron depletion resulted in decreased dendritic length in remaining quadriceps motoneurons. Dendritic atrophy was attenuated with both dihydrotestosterone and estradiol treatment to a degree similar to that seen with testosterone, and attenuation of atrophy was prevented by receptor blockade. Together, these findings suggest that neuroprotective effects on motoneurons can be mediated by either androgenic or estrogenic hormones and require action via steroid hormone receptors, further supporting a role for hormones as neurotherapeutic agents in the injured nervous system. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 691-707, 2017.

Neuroprotective Role of Steroidal Sex Hormones: An Overview

Progesterone, estrogens, and testosterone are the well-known steroidal sex hormones, which have been reported to have "nonreproductive "effects in the brain, specifically in the neuroprotection and neurotrophy. In the last one decade, there has been a surge in the research on the role of these hormones in neuroprotection and their positive impact on different brain injuries. The said interest has been sparked by a desire to understand the action and mechanisms of these steroidal sex hormones throughout the body. The aim of this article was to highlight the potential outcome of the steroidal hormones, viz. progesterone, estrogens, and testosterone in terms of their role in neuroprotection and other brain injuries. Their possible mechanism of action at both genomic and nongenomic level will be also discussed. As far as our knowledge goes, we are for the first time reporting neuroprotective effect and possible mechanism of action of these hormones in a single article.

Gonadectomy reduces the density of androgen receptor-immunoreactive neurons in male rat's hippocampus: testosterone replacement compensates it

BACKGROUND

In the present study, the role of gonadectomy on memory impairment and the density of androgen receptor-immunoreactive neurons in rats' hippocampus as well as the ability of testosterone to compensate of memory and the density of androgen receptors in the hippocampus was evaluated.

METHODS

Adult male rats (except intact-no testosterone group) were bilaterally castrated, and behavioral tests performed 2 weeks later. Animals bilaterally cannulated into lateral ventricles and then received testosterone (10, 40 and 120 µg/0.5 µl DMSO) or vehicle (DMSO; 0.5 µl) for gonadectomized-vehicle group, 30 min before training in water maze test. The androgen receptor-immunoreactive neurons were detected by immunohistochemical technique in the hippocampal areas.

RESULTS

In the gonadectomized male rats, a memory deficit was found in Morris water maze test on test day (5th day) after DMSO administration. Gonadectomy decreased density of androgen receptor-immunoreactive neurons in the rats' hippocampus. The treatment with testosterone daily for 5 days attenuated memory deficits induced by gonadectomy. Testosterone also significantly increased the density of androgen receptor-immunoreactive neurons in the hippocampal areas. The intermediate dose of this hormone (40 µg) appeared to have a significant effect on spatial memory and the density of androgen receptor-immunoreactive neurons in gonadectomized rats' hippocampus.

CONCLUSIONS

The present study suggests that testosterone can compensate memory failure in gonadectomized rats. Also testosterone replacement can compensate the reduction of androgen receptor-immunoreactive neurons density in the rats' hippocampus after gonadectomy.

Neuroactive steroids and the peripheral nervous system: An update

In the present review we summarize observations to date supporting the concept that neuroactive steroids are synthesized in the peripheral nervous system, regulate the physiology of peripheral nerves and exert notable neuroprotective actions. Indeed, neuroactive steroids have been recently proposed as therapies for different types of peripheral neuropathy, like for instance those occurring during aging, chemotherapy, physical injury and diabetes. Moreover, pharmacological tools able to increase the synthesis of neuroactive steroids might represent new interesting therapeutic strategy to be applied in case of peripheral neuropathy.

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.

Gender, sex steroid hormones, and Alzheimer's disease

Age-related loss of sex steroid hormones is a established risk factor for the development of Alzheimer's disease (AD) in women and men. While the relationships between the sex steroid hormones and AD are not fully understood, findings from both human and experimental paradigms indicate that depletion of estrogens in women and androgens in men increases vulnerability of the aging brain to AD pathogenesis. We review evidence of a wide range of beneficial neural actions of sex steroid hormones that may contribute to their hypothesized protective roles against AD. Both estrogens and androgens exert general neuroprotective actions relevant to a several neurodegenerative conditions, some in a sex-specific manner, including protection from neuron death and promotion of select aspects of neural plasticity. In addition, estrogens and androgens regulate key processes implicated in AD pathogenesis, in particular the accumulation of β-amyloid protein. We discuss evidence of hormone-specific mechanisms related to the regulation of the production and clearance of β-amyloid as critical protective pathways. Continued elucidation of these pathways promises to yield effective hormone-based strategies to delay development of AD.

Immune cell-mediated neuroprotection is independent of estrogen action through estrogen receptor-alpha

It has been well documented that both estrogen and immune cells (CD4+ T cells) mediate neuroprotection in the mouse facial nerve axotomy model. Estrogen has been shown to play an important role in regulating the immune response. However, it is unclear whether immune cell-mediated neuroprotection is dependent on estrogen signaling. In this study, using FACS staining, we confirmed that the majority of CD4+ T cells express high levels of estrogen receptor-alpha (ERα), suggesting that CD4+ T cell-mediated neuroprotection may be modulated by estrogen signaling. We previously found that immunodeficient Rag-2KO mice showed a significant increase in axotomy-induced facial motoneuron death compared to immunocompetent wild-type mice. Therefore, we investigated axotomy-induced facial motoneuron loss in immunodeficient Rag-2KO mice that received 17β-estradiol treatment or adoptive transfer of immune cells from mice lacking functional ERα. Our results indicate that while estradiol treatment failed to rescue facial motoneurons from axotomy-induced cell death in Rag-2KO mice, immune cells lacking ERα successfully restored facial motoneuron survival in Rag-2 KO mice to a wild-type level. Collectively, we concluded that CD4+ T cell-mediated neuroprotection is independent of estrogen action through ERα.

Developmental facial paralysis: a review

The purpose of this study is to clarify the confusing nomenclature and pathogenesis of Developmental Facial Paralysis, and how it can be differentiated from other causes of facial paralysis present at birth. Differentiating developmental from traumatic facial paralysis noted at birth is important for determining prognosis, but also for medicolegal reasons. Given the dramatic presentation of this condition, accurate and reliable guidelines are necessary in order to facilitate early diagnosis and initiate appropriate therapy, while providing support and counselling to the family. The 30 years experience of our center in the management of developmental facial paralysis is dependent upon a thorough understanding of facial nerve embryology, anatomy, nerve physiology, and an appreciation of well-recognized mishaps during fetal development. It is hoped that a better understanding of this condition will in the future lead to early targeted screening, accurate diagnosis and prompt treatment in this population of facially disfigured patients, which will facilitate their emotional and social rehabilitation, and their reintegration among their peers.

Validação de um radioimunoensaio para a quantificação de metabólitos fecais de testosterona em hamster Sírio (Mesocricetus auratus)

Modelo para o estudo de diversas doenças humanas, o hamster tem sido objeto de numerosos estudos comportamentais e envolvendo estresse e/ou comportamento agonístico que supõem, muitas vezes, o monitoramento das flutuações hormonais nos indivíduos envolvidos. O objetivo do presente trabalho foi confirmar a adequação de um conjunto comercial para dosagem de testosterona em sangue humano para a quantificação de metabólitos fecais de testosterona (MFT) em hamsters Sírios machos e fêmeas. Dez machos foram submetidos a um desafio com um agonista de GnRH para estimular a atividade testicular, elevando os níveis circulantes de testosterona. Cinco fêmeas receberam uma injeção de testosterona enquanto cinco outras receberam uma injeção de solução salina. Amostras de fezes coletadas antes e depois dos procedimentos, assim como amostras fecais de 20 fêmeas gestantes coletadas ao longo da gestação foram analisadas com um conjunto comercial para radioimunoensaio. Um pico de MFT 12h após a injeção seguido de uma queda abaixo do nível basal comprovou que, nos machos, as alterações nos níveis de MFT refletem as alterações da concentração de testosterona no sangue. Nestes observou-se um ciclo circadiano das concentrações de MFT com acrofase no início do período claro correspondendo ao ciclo descrito para as concentrações sanguíneas na literatura. Nas fêmeas a administração de testosterona exógena provocou uma elevação importante dos níveis de MFT, mas as concentrações medidas ao longo da gestação não refletiram o padrão dos níveis sanguíneos do hormônio endógeno. O conjunto para radioimunoensaio para testosterona em sangue humano mostrou-se adequado para o monitoramento da função testicular no hamster macho, mas um ensaio mais específico seria necessário para as fêmeas.

Role of neuroactive steroids in the peripheral nervous system

Several reviews have so far pointed out on the relevant physiological and pharmacological role exerted by neuroactive steroids in the central nervous system. In the present review we summarize observations indicating that synthesis and metabolism of neuroactive steroids also occur in the peripheral nerves. Interestingly, peripheral nervous system is also a target of their action. Indeed, as here reported neuroactive steroids are physiological regulators of peripheral nerve functions and they may also represent interesting therapeutic tools for different types of peripheral neuropathy.

Acute gonadotroph and somatotroph hormonal suppression after traumatic brain injury

Hormonal dysfunction is a known consequence of moderate and severe traumatic brain injury (TBI). In this study we determined the incidence, time course, and clinical correlates of acute post-TBI gonadotroph and somatotroph dysfunction. Patients had daily measurement of serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, estradiol, growth hormone, and insulin-like growth factor-1 (IGF-1) for up to 10 days post-injury. Values below the fifth percentile of a healthy cohort were considered abnormal, as were non-measurable growth hormone (GH) values. Outcome measures were frequency and time course of hormonal suppression, injury characteristics, and Glasgow Outcome Scale (GOS) score. The cohort consisted of 101 patients (82% males; mean age 35 years; Glasgow Coma Scale [GCS] score <or=8 in 87%). In men, 100% had at least one low testosterone value, and 93% of all values were low; in premenopausal women, 43% had at least one low estradiol value, and 39% of all values were low. Non-measurable GH levels occurred in 38% of patients, while low IGF-1 levels were observed in 77% of patients, but tended to normalize within 10 days. Multivariate analysis revealed associations of younger age with low FSH and low IGF-1, acute anemia with low IGF-1, and older age and higher body mass index (BMI) with low GH. Hormonal suppression was not predictive of GOS score. These results indicate that within 10 days of complicated mild, moderate, and severe TBI, testosterone suppression occurs in all men and estrogen suppression occurs in over 40% of women. Transient somatotroph suppression occurs in over 75% of patients. Although this acute neuroendocrine dysfunction may not be TBI-specific, low gonadal steroids, IGF-1, and GH may be important given their putative neuroprotective functions.

Androgens selectively protect against apoptosis in hippocampal neurones

Androgens can protect neurones from injury, although androgen neuroprotection is not well characterised in terms of either specificity or mechanism. In the present study, we compared the ability of androgens to protect neurones against a panel of insults, empirically determined to induce cell death by apoptotic or non-apoptotic mechanisms. Three criteria defining but not inclusive of apoptosis are: protection by caspase inhibition, protection by protein synthesis inhibition and the presence of pyknotic nuclei. According to these criteria, beta-amyloid, staurosporine, and Apoptosis Activator II induced cell death involving apoptosis, whereas hydrogen peroxide (H(2)O(2)), iron, calcium ionophore and 3-nitropropionic acid induced cell death featuring non-apoptotic characteristics. Pretreatment of hippocampal neurones with testosterone or dihydrotestosterone attenuated cell death induced by beta-amyloid, staurosporine and Apoptosis Activator II, but none of the other insults. The anti-oxidant Trolox did not reduce cell death induced by beta-amyloid, staurosporine and Apoptosis Activator II, but did protect against H(2)O(2) and iron. Similarly, a supra-physiological concentration of oestrogen reduced cell death induced by H(2)O(2) and iron, an effect not observed with androgens. We also show that activation of oestrogen pathways was not necessary for androgen neuroprotection. These data suggest that androgens directly activate a neuroprotective mechanism specific to inhibition of cell death involving apoptosis. Determining the specificity of androgen neuroprotection may enable the development of androgen compounds for the treatment of neurodegenerative disorders.

Effect of endogenous androgens on 17beta-estradiol-mediated protection after spinal cord injury in male rats

Several groups have recently shown that 17beta-estradiol is protective in spinal cord injury (SCI). Testosterone can be aromatized to 17beta-estradiol and may increase estrogen-mediated protection. Alternatively, testosterone has been shown to increase excitotoxicity in models of central nervous system (CNS) injury. These experiments test the hypothesis that endogenous testosterone in male rats alters 17beta-estradiol-mediated protection by evaluating a delayed administration over a clinically relevant dose range and manipulating testicular-derived testosterone. Adult male Sprague Dawley rats were either gonadectomized or left gonad-intact prior to SCI. SCI was produced by a midthoracic crush injury. At 30 min post SCI, animals received a subcutaneous pellet of 0.0, 0.05, 0.5, or 5.0 mg of 17beta-estradiol, released over 21 days. Hindlimb locomotion was analyzed weekly in the open field. Spinal cords were collected and analyzed for cell death, expression of Bcl-family proteins, and white-matter sparing. Post-SCI administration of the 0.5- or 5.0-mg pellet improved hindlimb locomotion, reduced urinary bladder size, increased neuronal survival, reduced apoptosis, improved the Bax/Bcl-xL protein ratio, and increased white-matter sparing. In the absence of endogenous testicular-derived androgens, SCI induced greater apoptosis, yet 17beta-estradiol administration reduced apoptosis to the same extent in gonadectomized and gonad-intact male rats. These data suggest that delayed post-SCI administration of a clinically relevant dose of 17beta-estradiol is protective in male rats, and endogenous androgens do not alter estrogen-mediated protection. These data suggest that 17beta-estradiol is an effective therapeutic intervention for reducing secondary damage after SCI in males, which could be readily translated to clinical trials.

Trolox ameliorates 3-nitropropionic acid-induced neurotoxicity in rats

3-nitropropionic acid (3-NPA) is a naturally occurring neurotoxin produced by legumes of the genus Astragalus and Arthrium fungi. Acute exposure to 3-NPA results in striatal astrocytic death and variety of behavior dysfunction in rats. Oxidative stress has been reported to play an important role in 3-NPA-induced neurotoxicity. Trolox is a potent free radical chain breaking antioxidant which has been shown to restore structure and function of the nervous system following oxidative stress. This rapid and efficient antioxidant property of trolox was attributed to its enhanced water solubility as compared with alpha-tocopherol. This investigation was aimed to study the effect of trolox against 3-NPA-induced neurotoxicity in female Wistar rats. The animals received trolox (0, 40 mg, 80 mg and 160 mg/kg, orally) daily for 7 days. 3-NPA (25mg/kg, i.p.) was administered daily 30 min after trolox for the same duration. One additional group of rats served as control (vehicle only). On day 8, the animals were observed for neurobehavioral performance. Immediately after behavioral studies, the animal's brains were dissected out for histological studies. Lesions in the striatal dopaminergic neurons were assessed by immunohistochemical method using tyrosine hydroxylase immunostaining. Administration of 3-NPA alone caused significant depletion of striatal dopamine and glutathione, whereas, the levels of thiobarbituric acid reactive substance (TBARS) and nitric oxide (NO) were significantly increased suggesting an elevated level of oxidative stress. Trolox significantly and dose-dependently protected animals against 3-NPA-induced neurobehavioral, neurochemical and structural abnormalities. These results clearly suggest that protective effect of trolox against 3-NPA-induced neurotoxicity is mediated through its free radical scavenging activity.

Dihydrotestosterone activates CREB signaling in cultured hippocampal neurons

Although androgens induce numerous actions in brain, relatively little is known about which cell signaling pathways androgens activate in neurons. Recent work in our laboratory showed that the androgens testosterone and dihydrotestosterone (DHT) activate androgen receptor (AR)-dependent mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling. Since the transcription factor cyclic AMP response element binding protein (CREB) is a downstream effector of MAPK/ERK and androgens activate CREB in non-neuronal cells, we investigated whether androgens activate CREB signaling in neurons. First, we observed that DHT rapidly activates CREB in cultured hippocampal neurons, as evidenced by CREB phosphorylation. Further, we observed that DHT-induced CREB phosphorylation is AR-dependent, as it occurs in PC12 cells stably transfected with AR but in neither wild-type nor empty vector-transfected cells. Next, we sought to identify the signal transduction pathways upstream of CREB phosphorylation using pharmacological inhibitors. DHT-induced CREB phosphorylation in neurons was found to be dependent upon protein kinase C (PKC) signaling but independent of MAPK/ERK, phosphatidylinositol 3-kinase, protein kinase A, and Ca(2+)/calmodulin-dependent protein kinase IV. These results demonstrate that DHT induces PKC-dependent CREB signaling, which may contribute to androgen-mediated neural functions.

Chronic stress effects on dendritic morphology in medial prefrontal cortex: sex differences and estrogen dependence

A growing body of work has documented sex differences in many behavioral, neurochemical, and morphological responses to stress. Chronic stress alters morphology of dendrites in medial prefrontal cortex in male rats. However, potential sex differences in stress-induced morphological changes in medial prefrontal cortex have not been examined. Thus, in Experiment 1 we assessed dendritic morphology in medial prefrontal cortex in male and female rats after chronic stress. Male and female rats underwent either 3 hours of restraint daily for 1 week or were left unhandled except for weighing. On the final day of restraint, all rats were euthanized and brains were stained using a Golgi-Cox procedure. Pyramidal neurons in layer II-III of medial prefrontal cortex were drawn in three dimensions, and morphology of apical and basilar arbors was quantified. In males, stress decreased apical dendritic branch number and length, whereas in females, stress increased apical dendritic length. In Experiment 2, we assessed whether estradiol mediates this stress-induced dendritic hypertrophy in females by assessing the effects of restraint stress on female rats that had received either ovariectomy with or without 17-beta-estradiol replacement or sham ovariectomy. Brains were processed and neurons reconstructed as described in Experiment 1. Both sham-operated and ovariectomized rats with estradiol implants showed stress-induced increases in apical dendritic material, whereas ovariectomy without estradiol replacement prevented the stress-induced increase. Thus, the stress-induced increase in apical dendritic material in females is estradiol-dependent.

Expression of estrogen receptor GPR30 in the rat spinal cord and in autonomic and sensory ganglia

The G protein-coupled receptor GPR30 has recently been identified as a nonnuclear estrogen receptor. Reverse transcriptase-polymerase chain reaction revealed expression of GPR30 mRNA in varying quantities in the rat spinal cord, dorsal root ganglia, nodose ganglia, trigeminal ganglia, hippocampus, brain stem, and hypothalamus. Immunohistochemical studies that used a rabbit polyclonal antiserum against the human GPR30 C-terminus revealed a fine network of GPR30-immunoreactive (irGPR30) cell processes in the superficial layers of the spinal cord; some of which extended into deeper laminae. A population of neurons in the dorsal horn and ventral horn were irGPR30. Dorsal root, nodose, and trigeminal ganglionic neurons displayed varying intensities of irGPR30. Positively labeled neurons were detected in the major pelvic ganglion, but not in the superior cervical ganglion. A population of chromaffin cells in the adrenal medulla was irGPR30, so were cells of the zona glomerulosa. Double-labeling the adrenal medulla with GPR30 antiserum and tyrosine hydroxylase antibody or phenylethanolamine-N-methyltransferase antiserum revealed that irGPR30 is expressed in the majority of tyrosine hydroxylase-positive chromaffin cells. Last, some of the myenteric ganglion cells were irGPR30. Tissues processed with preimmune serum resulted in no staining. Voltage-sensitive dye imaging studies showed that the selective GPR30 agonist G-1 (1, 10, and 100 nM) depolarized cultured spinal neurons in a concentration-dependent manner. Collectively, our result provides the first evidence that GPR30 is expressed in neurons of the dorsal and ventral horn as well as in sensory and autonomic neurons, and activation of GPR30 by the selective agonist G-1 depolarizes cultured spinal neurons.

Neuroprotective actions of androgens on motoneurons

Androgens have a variety of protective and therapeutic effects in both the central and peripheral nervous systems. Here we review these effects as they related specifically to spinal and cranial motoneurons. Early in development, androgens are critical for the formation of important neuromuscular sex differences, decreasing the magnitude of normally occurring cell death in select motoneuron populations. Throughout the lifespan, androgens also protect against motoneuron death caused by axonal injury. Surviving motoneurons also display regressive changes to their neurites as a result of both direct axonal injury and loss of neighboring motoneurons. Androgen treatment enhances the ability of motoneurons to recover from these regressive changes and regenerate both axons and dendrites, restoring normal neuromuscular function. Androgens exert these protective effects by acting through a variety of molecular pathways. Recent work has begun to examine how androgen treatment can interact with other treatment strategies in promoting recovery from motoneuron injury.

Protective actions of sex steroid hormones in Alzheimer's disease

Risk for Alzheimer's disease (AD) is associated with age-related loss of sex steroid hormones in both women and men. In post-menopausal women, the precipitous depletion of estrogens and progestogens is hypothesized to increase susceptibility to AD pathogenesis, a concept largely supported by epidemiological evidence but refuted by some clinical findings. Experimental evidence suggests that estrogens have numerous neuroprotective actions relevant to prevention of AD, in particular promotion of neuron viability and reduction of beta-amyloid accumulation, a critical factor in the initiation and progression of AD. Recent findings suggest neural responsiveness to estrogen can diminish with age, reducing neuroprotective actions of estrogen and, consequently, potentially limiting the utility of hormone therapies in aged women. In addition, estrogen neuroprotective actions are also modulated by progestogens. Specifically, continuous progestogen exposure is associated with inhibition of estrogen actions whereas cyclic delivery of progestogens may enhance neural benefits of estrogen. In recent years, emerging literature has begun to elucidate a parallel relationship of sex steroid hormones and AD risk in men. Normal age-related testosterone loss in men is associated with increased risk to several diseases including AD. Like estrogen, testosterone has been established as an endogenous neuroprotective factor that not only increases neuronal resilience against AD-related insults, but also reduces beta-amyloid accumulation. Androgen neuroprotective effects are mediated both directly by activation of androgen pathways and indirectly by aromatization to estradiol and initiation of protective estrogen signaling mechanisms. The successful use of hormone therapies in aging men and women to delay, prevent, and or treat AD will require additional research to optimize key parameters of hormone therapy and may benefit from the continuing development of selective estrogen and androgen receptor modulators.

Neuroprotective effects of testosterone on the morphology and function of somatic motoneurons following the death of neighboring motoneurons

Motoneuron loss is a significant medical problem, capable of causing severe movement disorders or even death. We have previously shown that partial depletion of motoneurons from sexually dimorphic, highly androgen-sensitive spinal motor populations induces dendritic atrophy in remaining motoneurons, and this atrophy is attenuated by treatment with testosterone. To test whether testosterone has similar effects in more typical motoneurons, we examined potential neuroprotective effects in motoneurons innervating muscles of the quadriceps. Motoneurons innervating the vastus medialis muscle were selectively killed by intramuscular injection of cholera toxin-conjugated saporin. Simultaneously, some saporin-injected rats were given implants containing testosterone or left untreated. Four weeks later, motoneurons innervating the ipsilateral vastus lateralis muscle were labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed in three dimensions. Compared with intact normal males, partial motoneuron depletion resulted in decreased dendritic length in remaining quadriceps motoneurons, and this atrophy was attenuated by testosterone treatment. To examine the functional consequences of the induced dendritic atrophy, and its attenuation with testosterone treatment, the activation of remaining quadriceps motoneurons was assessed using peripheral nerve recording. Partial motoneuron depletion resulted in decreased amplitudes of motor nerve activity, and these changes were attenuated by treatment with testosterone, providing a functional correlate to the neuroprotective effects of testosterone treatment on quadriceps motoneuron morphology. Together these findings suggest that testosterone has neuroprotective effects on morphology and function in both highly androgen-sensitive as well as more typical motoneuron populations, further supporting a role for testosterone as a neurotherapeutic agent in the injured nervous system.

Androgen receptor function in motor neuron survival and degeneration

Polyglutamine repeat expansion in the androgen receptor is responsible for the motor neuron degeneration in X-linked spinal and bulbar muscular atrophy (SBMA; Kennedy's disease). This mutation, like the other polyglutamine repeat expansions, has proven to be toxic itself by a gain-of-function effect; however, a growing body of evidence indicates that loss of androgen receptor normal function simultaneously contributes to SBMA disease pathology, and, conversely, that normal androgen receptor signaling mediates important trophic effects upon motor neurons. This review considers the trophic requirements of motor neurons, focusing upon the role of known neurotrophic factors in motor neuron disease natural history, and the interactions of androgen receptor signaling pathways with motor neuron disease pathogenesis and progression. A thorough understanding of androgen receptor signaling in motor neurons should provide important inroads toward the development of effective treatments for a variety of devastating motor neuron diseases.

Androgen regulation of axon growth and neurite extension in motoneurons

Androgens act on the CNS to affect motor function through interaction with a widespread distribution of intracellular androgen receptors (AR). This review highlights our work on androgens and process outgrowth in motoneurons, both in vitro and in vivo. The actions of androgens on motoneurons involve the generation of novel neuronal interactions that are mediated by the induction of androgen-dependent neurite or axonal outgrowth. Here, we summarize the experimental evidence for the androgenic regulation of the extension and regeneration of motoneuron neurites in vitro using cultured immortalized motoneurons, and axons in vivo using the hamster facial nerve crush paradigm. We place particular emphasis on the relevance of these effects to SBMA and peripheral nerve injuries.

Oestradiol rapidly enhances spontaneous glycinergic synaptic inhibition of hypoglossal motoneurones

Whereas oestradiol is well-known to facilitate excitatory glutamatergic synaptic transmission, its effects on fast inhibitory neurotransmission are not as well established. Possible acute modulation of the spontaneous glycinergic synaptic activity by oestradiol was investigated in voltage-clamped hypoglossal motoneurones by whole-cell patch-clamp recording in rat brainstem slices. The spontaneous glycinergic synaptic activity was continuously recorded in each neurone under control conditions, during 12-20 min of perfusion with 17beta-oestradiol and during washing. When oestradiol was diluted in ethanol, the control solution contained the same amount of ethanol. At 100 nM, oestradiol markedly increased the frequency of the total spontaneous glycinergic activity. Similar experiments were performed after blockade of action potentials by tetrodotoxin, aiming to isolate miniature glycinergic synaptic currents. Oestradiol increased the frequency of glycinergic miniatures in most slices, in some cases within less than 1 min. In some slices, oestradiol also favoured the occurrence of glycinergic miniatures of large amplitude. These effects were slowly reversible during washing. At 1 nm, oestradiol still increased the frequency of glycinergic miniatures. The results were confirmed in the absence of ethanol by using water-soluble cyclodextrin-encapsulated oestradiol. In these experiments, the control solution contained the same amount of (2-hydroxypropyl)-beta-cyclodextrin as the oestradiol-containing solution. In addition, prolonged control recordings were performed without applying oestradiol to check the stability of the glycinergic synaptic activity during prolonged whole-cell recordings. The results show, for the first time, that, within a few minutes, oestradiol can enhance the spontaneous synaptic release of a major inhibitory transmitter, glycine.

Neuroactive Steroid Levels in a transgenic rat model of CMT1A Neuropathy

Charcot-Marie-Tooth type 1A (CMT1A) represents 80% of all the demyelinating hereditary motor and sensory neuropathies. As recently suggested, neuroactive steroids may have a role in a therapeutic strategy for peripheral neuropathies, including CMT1A. To this aim, an accurate qualitative and quantitative analysis of neuroactive steroid levels in this disease could be extremely important to define effective pharmacological strategies. We here analyzed by liquid chromatography-tandem mass spectrometry the levels of neuroactive steroids present in the sciatic nerve of male and female peripheral myelin protein 22 transgenic rats (PMP22(tg) rats; i.e., an experimental model of CMT1A) and of the corresponding wild-type littermates. We observed that, both in PMP22(tg) rats and in the wild types, the levels of neuroactive steroids, such as progesterone, tetrahydroprogesterone (THP), isopregnanolone (3beta,5alpha-THP), testosterone, dihydrotestosterone, and 5alpha-androstane-3alpha, 17beta-diol (3alpha-diol) are sexually dimorphic. It is interesting to note that the levels of 3beta,5alpha-THP and of 3alpha-diol, which are exclusively detectable in sciatic nerve of female and male rats, respectively, are strongly decreased in PMP22(tg) rats. 3beta,5alpha-THP and 3alpha-diol are modulators of gamma-amino butyric acid A receptor. Thus, the present findings may be considered an interesting background for experiments aimed to evaluate the possible therapeutic effects of modulators of this neurotransmitter receptor in male and female PMP22(tg) rats.

Cellular localization of androgen and estrogen receptors in mouse-derived motoneuron hybrid cells and mouse facial motoneurons

The ability of gonadal steroid hormones to augment axonal regeneration after peripheral nerve injury has been well established in rat and hamster motoneuron systems, and provides a foundation for the use of these agents as neurotherapeutics. With the advent of mouse genetics and the availability of transgenic and knockout mice, the use of mice in studies of neuroprotection is growing. It has recently been demonstrated that both androgens and estrogens rescue motoneurons (MN) from injury in mouse-derived motoneuron hybrid cells in vitro and mouse facial motoneurons (FMN) in vivo (Tetzlaff et al. [2006] J Mol Neurosci 28:53-64). To elucidate the molecular mechanisms of these effects, the present study examined the cellular localization of androgen and estrogen receptors in mouse MN in vitro and in vivo. Immunoblotting and immunocytochemistry studies established the presence of androgen receptor (AR) and estrogen receptor alpha/beta in immortalized mouse motoneuron hybrid cells and AR and estrogen receptor alpha in mouse FMN.

Progesterone: Therapeutic opportunities for neuroprotection and myelin repair

Progesterone and its metabolites promote the viability of neurons in the brain and spinal cord. Their neuroprotective effects have been documented in different lesion models, including traumatic brain injury (TBI), experimentally induced ischemia, spinal cord lesions and a genetic model of motoneuron disease. Progesterone plays an important role in developmental myelination and in myelin repair, and the aging nervous system appears to remain sensitive to some of progesterone's beneficial effects. Thus, the hormone may promote neuroregeneration by several different actions by reducing inflammation, swelling and apoptosis, thereby increasing the survival of neurons, and by promoting the formation of new myelin sheaths. Recognition of the important pleiotropic effects of progesterone opens novel perspectives for the treatment of brain lesions and diseases of the nervous system. Over the last decade, there have been a growing number of studies showing that exogenous administration of progesterone or some of its metabolites can be successfully used to treat traumatic brain and spinal cord injury, as well as ischemic stroke. Progesterone can also be synthesized by neurons and by glial cells within the nervous system. This finding opens the way for a promising therapeutic strategy, the use of pharmacological agents, such as ligands of the translocator protein (18 kDa) (TSPO; the former peripheral benzodiazepine receptor or PBR), to locally increase the synthesis of steroids with neuroprotective and neuroregenerative properties. A concept is emerging that progesterone may exert different actions and use different signaling mechanisms in normal and injured neural tissue.

Effect of progesterone on recovery from nerve injury during leg lengthening in rats

We investigated the effect of progesterone on the nerve during lengthening of the limb in rats. The sciatic nerves of rats were elongated by leg lengthening for ten days at 3 mm per day. On alternate days between the day after the operation and nerve dissection, the progesterone-treated group received subcutaneous injections of 1 mg progesterone in sesame oil and the control group received oil only. On the fifth, tenth and 17th day, the sciatic nerves were excised at the midpoint of the femur and the mRNA expression level of myelin protein P0 was analysed by quantitative real time polymerase chain reaction. On day 52 nodal length was examined by electron microscopy, followed by an examination of the compound muscle action potential (C-MAP) amplitude and the motor conduction velocity (MCV) of the tibial nerve on days 17 and 52. The P0 (a major myelin glycoprotein) mRNA expression level in the progesterone-treated group increased by 46.6% and 38.7% on days five and ten, respectively. On day 52, the nodal length in the progesterone-treated group was smaller than that in the control group, and the MCV of the progesterone-treated group had been restored to normal. Progesterone might accelerate the restoration of demyelination caused by nerve elongation by activating myelin synthesis.