Testosterone-induced acceleration of recovery from facial paralysis following crush axotomy of the facial nerve in male hamsters

Distinct neurotoxic effects of select local anesthetics on facial nerve injury and recovery

BACKGROUND

Local anesthetic toxicity has been well-documented to cause neuronal injury, death, and dysfunction, particularly in a susceptible nerve.

OBJECTIVE

To determine whether select local anesthetics affect neuron survival and/or functional recovery of an injured nerve.

METHODS

This report describes 6 separate experiments that test immediate or delayed application of local anesthetics in 3 nerve injury models. Adult C57/black6 male mice underwent a facial nerve sham, transection, or crush injury. Local anesthetic or saline was applied to the facial nerve at the time of injury (immediate) or 1 day after injury (delayed). Average percent facial motoneuron (FMN) survival was evaluated four-weeks after injury. Facial nerve regeneration was estimated by observing functional recovery of eye blink reflex and vibrissae movement after facial nerve crush injury.

RESULTS

FMN survival after: transection + immediate treatment with ropivacaine (54.8%), bupivacaine (63.2%), or tetracaine (66.9%) was lower than saline (85.5%) and liposomal bupivacaine (85.0%); crush + immediate treatment with bupivacaine (92.8%) was lower than saline (100.7%) and liposomal bupivacaine (99.3%); sham + delayed treatment with bupivacaine (89.9%) was lower than saline (96.6%) and lidocaine (99.5%); transection + delayed treatment with bupivacaine (67.3%) was lower than saline (78.4%) and liposomal bupivacaine (77.6%); crush + delayed treatment with bupivacaine (85.3%) was lower than saline (97.9%) and lidocaine (96.0%). The average post-operative time for mice to fully recover after: crush + immediate treatment with bupivacaine (12.83 days) was longer than saline (11.08 days) and lidocaine (10.92 days); crush + delayed treatment with bupivacaine (16.79 days) was longer than saline (12.73 days) and lidocaine (11.14 days).

CONCLUSIONS

Our data demonstrate that some local anesthetics, but not all, exacerbate motoneuron death and delay functional recovery after a peripheral nerve injury. These and future results may lead to clinical strategies that decrease the risk of neural deficit following peripheral nerve blocks with local anesthetics.

Facial nerve repair utilizing intraoperative repair strategies

OBJECTIVES

To determine whether functional and anatomical outcomes following suture neurorrhaphy are improved by the addition of electrical stimulation with or without the addition of polyethylene glycol (PEG).

METHODS

In a rat model of facial nerve injury, complete facial nerve transection and repair was performed via (a) suture neurorrhaphy alone, (b) neurorrhaphy with the addition of brief (30 minutes) intraoperative electrical stimulation, or (c) neurorrhaphy with the addition electrical stimulation and PEG. Functional recovery was assessed weekly for 16 weeks. At 16 weeks postoperatively, motoneuron survival, amount of regrowth, and specificity of regrowth were assessed by branch labeling and tissue analysis.

RESULTS

The addition of brief intraoperative electrical stimulation improved all functional outcomes compared to suturing alone. The addition of PEG to electrical stimulation impaired this benefit. Motoneuron survival, amount of regrowth, and specificity of regrowth were unaltered at 16 weeks postoperative in all treatment groups.

CONCLUSION

The addition of brief intraoperative electrical stimulation to neurorrhaphy in this rodent model shows promising neurological benefit in the surgical repair of facial nerve injury.

LEVEL OF EVIDENCE

Animal study.

miR-216a-targeting theranostic nanoparticles promote proliferation of insulin-secreting cells in type 1 diabetes animal model

Aberrant expression of miRNAs in pancreatic islets is closely related to the development of type 1 diabetes (T1D). The aim of this study was to identify key miRNAs dysregulated in pancreatic islets during T1D progression and to develop a theranostic approach to modify their expression using an MRI-based nanodrug consisting of iron oxide nanoparticles conjugated to miRNA-targeting oligonucleotides in a mouse model of T1D. Isolated pancreatic islets were derived from NOD mice of three distinct age groups (3, 8 and 18-week-old). Total RNA collected from cultured islets was purified and global miRNA profiling was performed with 3D-Gene global miRNA microarray mouse chips encompassing all mouse miRNAs available on the Sanger miRBase V16. Of the miRNAs that were found to be differentially expressed across three age groups, we identified one candidate (miR-216a) implicated in beta cell proliferation for subsequent validation by RT-PCR. Alterations in miR-216a expression within pancreatic beta cells were also examined using in situ hybridization on the frozen pancreatic sections. For in vitro studies, miR-216a mimics/inhibitors were conjugated to iron oxide nanoparticles and incubated with beta cell line, βTC-6. Cell proliferation marker Ki67 was evaluated. Expression of the phosphatase and tensin homolog (PTEN), which is one of the direct targets of miR-216a, was analyzed using western blot. For in vivo study, the miR-216a mimics/inhibitors conjugated to the nanoparticles were injected into 12-week-old female diabetic Balb/c mice via pancreatic duct. The delivery of the nanodrug was monitored by in vivo MRI. Blood glucose of the treated mice was monitored post injection. Ex vivo histological analysis of the pancreatic sections included staining for insulin, PTEN and Ki67. miRNA microarray demonstrated that the expression of miR-216a in the islets from NOD mice significantly changed during T1D progression. In vitro studies showed that treatment with a miR-216a inhibitor nanodrug suppressed proliferation of beta cells and increased the expression of PTEN, a miR-216a target. In contrast, introduction of a mimic nanodrug decreased PTEN expression and increased beta cell proliferation. Animals treated in vivo with a mimic nanodrug had higher insulin-producing functionality compared to controls. These observations were in line with downregulation of PTEN and increase in beta cell proliferation in that group. Our studies demonstrated that miR-216a could serve as a potential therapeutic target for the treatment of diabetes. miR-216a-targeting theranostic nanodrugs served as exploratory tools to define functionality of this miRNA in conjunction with in vivo MR imaging.

Functional and Anatomical Outcomes of Facial Nerve Injury With Application of Polyethylene Glycol in a Rat Model

Importance

Functional and anatomical outcomes after surgical repair of facial nerve injury may be improved with the addition of polyethylene glycol (PEG) to direct suture neurorrhaphy. The application of PEG has shown promise in treating spinal nerve injuries, but its efficacy has not been evaluated in treatment of cranial nerve injuries.

Objective

To determine whether PEG in addition to neurorrhaphy can improve functional outcomes and synkinesis after facial nerve injury.

Design, Setting, and Subjects

In this animal experiment, 36 rats underwent right facial nerve transection and neurorrhaphy with addition of PEG. Weekly behavioral scoring was done for 10 rats for 6 weeks and 14 rats for 16 weeks after the operations. In the 16-week study, the buccal branches were labeled and tissue analysis was performed. In the 6-week study, the mandibular and buccal branches were labeled and tissue analysis was performed. Histologic analysis was performed for 10 rats in a 1-week study to assess the association of PEG with axonal continuity and Wallerian degeneration. Six rats served as the uninjured control group. Data were collected from February 8, 2016, through July 10, 2017.

Intervention

Polyethylene glycol applied to the facial nerve after neurorrhaphy.

Main Outcomes and Measures

Functional recovery was assessed weekly for the 16- and 6-week studies, as well as motoneuron survival, amount of regrowth, specificity of regrowth, and aberrant branching. Short-term effects of PEG were assessed in the 1-week study.

Results

Among the 40 male rats included in the study, PEG addition to neurorrhaphy showed no functional benefit in eye blink reflex (mean [SEM], 3.57 [0.88] weeks; 95% CI, -2.8 to 1.9 weeks; P = .70) or whisking function (mean [SEM], 4.00 [0.72] weeks; 95% CI, -3.6 to 2.4 weeks; P = .69) compared with suturing alone at 16 weeks. Motoneuron survival was not changed by PEG in the 16-week (mean, 132.1 motoneurons per tissue section; 95% CI, -21.0 to 8.4; P = .13) or 6-week (mean, 131.1 motoneurons per tissue section; 95% CI, -11.0 to 10.0; P = .06) studies. Compared with controls, neither surgical group showed differences in buccal branch regrowth at 16 (36.9 motoneurons per tissue section; 95% CI, -14.5 to 22.0; P = .28) or 6 (36.7 motoneurons per tissue section; 95% CI, -7.8 to 18.5; P = .48) weeks or in the mandibular branch at 6 weeks (25.2 motoneurons per tissue section; 95% CI, -14.5 to 15.5; P = .99). Addition of PEG had no advantage in regrowth specificity compared with suturing alone at 16 weeks (15.3% buccal branch motoneurons with misguided projections; 95% CI, -7.2% to 11.0%; P = .84). After 6 weeks, the number of motoneurons with misguided projections to the mandibular branch showed no advantage of PEG treatment compared with suturing alone (12.1% buccal branch motoneurons with misguided projections; 95% CI, -8.2% to 9.2%; P = .98). In the 1-week study, improved axonal continuity and muscular innervation were not observed in PEG-treated rats.

Conclusions and Relevance

Although PEG has shown efficacy in treating other nervous system injuries, PEG in addition to neurorraphy was not beneficial in a rat model of facial nerve injury. The addition of PEG to suturing may not be warranted in the surgical repair of facial nerve injury.

Level of Evidence

NA.

Testosterone propionate can promote effects of acellular nerve allograft-seeded bone marrow mesenchymal stem cells on repairing canine sciatic nerve

Peripheral human nerves fail to regenerate across long tube implants (>2 cm), and tissue-engineered nerve grafts represent a promising treatment alternative. The present study aims to investigate the testosterone propionate (TP) repair effect of acellular nerve allograft (ANA) seeded with allogeneic bone marrow mesenchymal stem cells (BMSCs) on 3-cm canine sciatic nerve defect. ANA cellularized with allogeneic BMSCs was implanted to the defect, and TP was injected into the lateral crus of the defected leg. The normal group, the autograft group, the ANA + BMSCs group, the ANA group, and the nongrafted group were used as control. Five months postoperatively, dogs in the TP + ANA + BMSCs group were capable of load bearing, normal walking, and skipping, the autograft group and the ANA + BMSCs group demonstrated nearly the same despite a slight limp. The compound muscle action potentials (CMAPs) on the injured side to the uninjured site in the TP + ANA + BMSCs group were significantly higher than that in the ANA + BMSCs group [CMAPs ratio at A: F(3, 20) = 191.40; 0.02, CMAPs ratio at B: F(3, 20) = 43.27; 0.01]. Masson trichrome staining revealed that in the TP + ANA + BMSCs group, both the diameter ratio of the myelinated nerve and the thickness ratio of regenerated myelin sheath were significantly larger than that in the other groups [the diameter of myelinated nerve fibers: F(3, 56) = 13.45; P < .01, the thickness ratio of regenerated myelin sheath: F(3, 56) = 51.25; P < .01]. In conclusion, TP could significantly increase the repairing effects of the ANA + BMSCs group, and their combination was able to repair 3-cm canine sciatic nerve defect. It therefore represents a promising therapeutic approach.

The Role of BDNF in Peripheral Nerve Regeneration: Activity-Dependent Treatments and Val66Met

Despite the ability of peripheral nerves to spontaneously regenerate after injury, recovery is generally very poor. The neurotrophins have emerged as an important modulator of axon regeneration, particularly brain derived neurotrophic factor (BDNF). BDNF regulation and signaling, as well as its role in activity-dependent treatments including electrical stimulation, exercise, and optogenetic stimulation are discussed here. The importance of a single nucleotide polymorphism in the BDNF gene, Val66Met, which is present in 30% of the human population and may hinder the efficacy of these treatments in enhancing regeneration after injury is considered. Preliminary data are presented on the effectiveness of one such activity-dependent treatment, electrical stimulation, in enhancing axon regeneration in mice expressing the met allele of the Val66Met polymorphism.

Neuroprotective Effects on the Morphology of Somatic Motoneurons Following the Death of Neighboring Motoneurons: A Role for Microglia?

Partial depletion of spinal motoneuron populations induces dendritic atrophy in neighboring motoneurons, and treatment with testosterone protects motoneurons from induced dendritic atrophy. We explored a potential mechanism for this induced atrophy and protection by testosterone, examining the microglial response to partial depletion of motoneurons. Motoneurons innervating the vastus medialis muscles of adult male rats were killed by intramuscular injection of cholera toxin-conjugated saporin; some saporin-injected rats were treated with testosterone. Microglia were later visualized via immunohistochemical staining, classified as monitoring or activated, and counted stereologically. Partial motoneuron depletion increased the number of activated microglia in the quadriceps motor pool, and this increase was attenuated with testosterone treatment. The attenuation in microglial response could reflect an effect of testosterone on suppressing microglia activation, potentially sparing motoneuron dendrites. Alternatively, testosterone could be neuroprotective, sparing motoneuron dendrites, secondarily resulting in reduced microglial activation. To discriminate between these hypotheses, following partial motoneuron depletion, rats were treated with minocycline to inhibit microglial activation. Motoneurons innervating the ipsilateral vastus lateralis muscle were later labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed. Reduction of microglial activation by minocycline did not prevent induced dendritic atrophy following partial motoneuron depletion. Further, reduction of microglial activation by minocycline treatment resulted in dendritic atrophy in intact animals. Together, these findings indicate that the neuroprotective effect of testosterone on dendrites following motoneuron death is not due to inhibiting microglial activation, and that microglial activity contributes to the normal maintenance of dendritic arbors.

OXIDATIVE STRESS IS MARKEDLY REDUCED BY COMBINED VOLUNTARY EXERCISE AND TESTOSTERONE IN THE HEART OF DIABETIC RATS

Objective

Cardiovascular disorders in diabetes condition arise from increased oxidative stress. Both regular mild exercise and testosterone influence on body's antioxidant system in diabetes. In this study, we evaluated treatment of testosterone and voluntary exercise, alone or together on oxidative stress in the heart and blood of diabetic rats.

Methods

Type 1 diabetes was induced by intraperitoneal injection of 50 mg/kg of streptozotocin in rats. Sixty three rats have been divided into eight groups as follows: Diabetes, diabetes+ testosterone, diabetes+ exercise, diabetes+ testosterone+ exercise, diabetes+ castration, diabetes+ castration+ testosterone, Diabetes+ castration+ exercise, Diabetes+ castration+ exercise+ testosterone. Type 1 diabetes was induced by intraperitoneal injection of 50 mg/kg of streptozotocin in the male Wistar rats and after a week, castration was performed. After 42 days of treatment with testosterone (2 mg/kg/day) or voluntary exercise alone or in combination, SOD, GPX and CAT activities and MDA levels were measured in the blood and heart tissue samples in the groups of study. In the end of study, SOD, GPX and CAT activities and MDA levels were measured in blood and heart tissue samples in the groups of study.

Results

SOD, GPX and CAT activities significantly (p<0.05) increased in groups that treated either testosterone or exercise and MDA level significantly (p<0.01) decreased in the blood and heart tissue of diabetic and castrated diabetic rats. Simultaneously, treatment with testosterone and exercise had a synergistic effect on antioxidant enzymes level in diabetic and diabetic castrated rats. In the castrated animals with diabetes, SOD, GPX and CAT activities significantly decreased (p<0.05) and MDA levels significantly increased (p<0.05) in blood and heart tissue.

Conclusion

Voluntary exercise and testosterone alone or together heightened body's antioxidant system and were able to reduce the MDA levels in blood and heart of diabetic and castrated diabetic rats.

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.

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.

Electrical stimulation and testosterone enhance recovery from recurrent laryngeal nerve crush

OBJECTIVE

This study investigated the effects of a combinatorial treatment, consisting of a brief period of nerve electrical stimulation (ES) and systemic supraphysiologic testosterone, on functional recovery following a crush of the recurrent laryngeal nerve (RLN).

STUDY DESIGN

Prospective, controlled animal study.

METHODS

After a crush of the left RLN, adult male Sprague-Dawley rats were divided into four treatment groups: 1) no treatment, 2) ES, 3) testosterone propionate (TP), and 4) ES + TP. Each group was subdivided into 1, 2, 3, or 4 weeks post-operative survival time points. Groups had an n of 4- 9. Recovery of vocal fold mobility (VFM) was assessed.

RESULTS

Brief ES of the proximal nerve alone or in combination with TP accelerated the initiation of functional recovery. TP administration by itself also produced increased VFM scores compared to controls, but there were no statistical differences between the ES-treated and TP-treated animals. Treatment with brief ES alone was sufficient to decrease the time required to recover complete VFM. Animals with complete VFM were seen in treatment groups as early as 1 week following injury; in the untreated group, this was not observed until at least 3 weeks post-injury, translating into a 66% decrease in time to complete recovery.

CONCLUSIONS

Brief ES, alone or in combination with TP, promise to be effective therapeutic interventions for promoting regeneration following RLN injury.

Improving peripheral nerve regeneration: from molecular mechanisms to potential therapeutic targets

Peripheral nerve injury is common especially among young individuals. Although injured neurons have the ability to regenerate, the rate is slow and functional outcomes are often poor. Several potential therapeutic agents have shown considerable promise for improving the survival and regenerative capacity of injured neurons. These agents are reviewed within the context of their molecular mechanisms. The PI3K/Akt and Ras/ERK signaling cascades play a key role in neuronal survival. A number of agents that target these pathways, including erythropoietin, tacrolimus, acetyl-l-carnitine, n-acetylcysteine and geldanamycin have been shown to be effective. Trk receptor signaling events that up-regulate cAMP play an important role in enhancing the rate of axonal outgrowth. Agents that target this pathway including rolipram, testosterone, fasudil, ibuprofen and chondroitinase ABC hold considerable promise for human application. A tantalizing prospect is to combine different molecular targeting strategies in complementary pathways to optimize their therapeutic effects. Although further study is needed prior to human trials, these modalities could open a new horizon in the clinical arena that has so far been elusive.

The effects of exercise on synaptic stripping require androgen receptor signaling

Following peripheral nerve injury, synapses are withdrawn from axotomized motoneurons. Moderate daily treadmill exercise, which promotes axon regeneration of cut peripheral nerves, also influences this synaptic stripping. Different exercise protocols are required to promote axon regeneration in male and female animals, but the sex requirements for an effect of exercise on synaptic stripping are unknown. In male and female C57BL/6 mice, the sciatic nerve was transected in the mid-thigh. Mice were then exercised five days per week for two weeks, beginning on the third post-transection day. Half of the exercised mice were trained by walking slowly (10 M/min) on a level treadmill for one hour per day (continuous training). Other mice were interval trained; four short (two min) sprints at 20 M/min separated by five minute rest periods. A third group was untrained. The extent of synaptic contacts made by structures immunoreactive to vesicular glutamate transporter 1 and glutamic acid decarboxylase 67 onto axotomized motoneurons was studied in confocal images of retrogradely labeled cells. Both types of presumed synaptic contacts were reduced markedly in unexercised mice following nerve transection, relative to intact mice. No significant reduction was found in continuous trained males or interval trained females. Reductions in these contacts in interval trained males and continuous trained females were identical to that observed in untrained mice. Treatments with the anti-androgen, flutamide, blocked the effect of sex-appropriate exercise on synaptic contacts in both males and females. Moderate daily exercise has a potent effect on synaptic inputs to axotomized motoneurons. Successful effects of exercise have different requirements in males and females, but require androgen receptor signaling in both sexes.

Effects of nandrolone on recovery after neurotization of chronically denervated muscle in a rat model

OBJECT

Suboptimal recovery following repair of major peripheral nerves has been partially attributed to denervation atrophy. Administration of anabolic steroids in conjunction with neurotization may improve functional recovery of chronically denervated muscle. The purpose of this study was to evaluate the effect of the administration of nandrolone on muscle recovery following prolonged denervation in a rat model.

METHODS

Eight groups of female Sprague-Dawley rats (15 rats per group, 120 in all) were divided into 3- or 6-month denervated hind limb and sham surgery groups and, then, nandrolone treatment groups and sham treatment groups. Evaluation of treatment effects included nerve conduction, force of contraction, comparative morphology, histology (of muscle fibers), protein electrophoresis (for muscle fiber grouping), and immunohistochemical evaluation.

RESULTS

Although a positive trend was noted, neither reinnervated nor normal muscle showed a statistically significant increase in peak muscle force following nandrolone treatment. Indirect measures, including muscle mass (weight and diameter), muscle cell size, muscle fiber type, and satellite cell counts, all failed to support significant anabolic effect.

CONCLUSIONS

There does not seem to be a functional benefit from nandrolone treatment following reinnervation of either mild or moderately atrophic muscle (related to prolonged denervation) in a rodent model.

Brain-derived neurotrophic factor and androgen interactions in spinal neuromuscular systems

Neurotrophic factors and steroid hormones interact to regulate a variety of neuronal processes such as neurite outgrowth, differentiation, and neuroprotection. The coexpression of steroid hormone and neurotrophin receptor mRNAs and proteins, as well as their reciprocal regulation provides the necessary substrates for such interactions to occur. This review will focus on androgen brain-derived neurotrophic factor (BDNF) interactions in the spinal cord, describing androgen regulation of BDNF in neuromuscular systems following castration, androgen manipulation, and injury. Androgens interact with BDNF during development to regulate normally-occurring motoneuron death, and in adulthood, androgen-BDNF interactions are involved in the maintenance of several features of neuromuscular systems. Androgens regulate BDNF and trkB expression in spinal motoneurons. Androgens also regulate BDNF levels in the target musculature, and androgenic action at the muscle regulates BDNF levels in motoneurons. These interactions have important implications for the maintenance of motoneuron morphology. Finally, androgens interact with BDNF after injury, influencing soma size, dendritic morphology, and axon regeneration. Together, these findings provide further insight into the development and maintenance of neuromuscular systems and have implications for the neurotherapeutic/neuroprotective roles of androgens and trophic factors in the treatment of motoneuron disease and recovery from injury.

Neuroprotective effects of testosterone on motoneuron and muscle morphology following spinal cord injury

Treatment with testosterone is neuroprotective/neurotherapeutic after a variety of motoneuron injuries. Here we assessed whether testosterone might have similar beneficial effects after spinal cord injury (SCI). Young adult female rats received either sham or T9 spinal cord contusion injuries and were implanted with blank or testosterone-filled Silastic capsules. Four weeks later, motoneurons innervating the vastus lateralis muscle of the quadriceps were labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed in three dimensions. Soma volume, motoneuron number, lesion volume, and tissue sparing were also assessed, as were muscle weight, fiber cross-sectional area, and motor endplate size and density. Contusion injury resulted in large lesions, with no significant differences in lesion volume, percent total volume of lesion, or spared white or gray matter between SCI groups. SCI with or without testosterone treatment also had no effect on the number or soma volume of quadriceps motoneurons. However, SCI resulted in a decrease in dendritic length of quadriceps motoneurons in untreated animals, and this decrease was completely prevented by treatment with testosterone. Similarly, the vastus lateralis muscle weights and fiber cross-sectional areas of untreated SCI animals were smaller than those of sham-surgery controls, and these reductions were both prevented by testosterone treatment. No effects on motor endplate area or density were observed across treatment groups. These findings suggest that regressive changes in motoneuron and muscle morphology seen after SCI can be prevented by testosterone treatment, further supporting a role for testosterone as a neurotherapeutic agent in the injured nervous system.

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.

The use of anabolic steroids as a strategy in reversing denervation atrophy after delayed nerve repair

BACKGROUND

Denervation atrophy is one factor contributing to suboptimal motor recovery following major nerve repair. The hypertrophic effects of anabolic steroids may have a potential role in improving reinnervated muscle strength after delayed repair.

METHODS

Forty-five immature female Sprague-Dawley rats underwent three surgeries and final testing. The tibial nerve was transected in the hind limb of the experimental (n = 13) and control (n = 14) animals and exposed, but not transected in the sham (n = 15) group animals. Three months later, once denervation atrophy was established, all transected nerves underwent repair using an autograft from the contralateral limb. After waiting an additional month to allow axonal regeneration to the gastrocnemius muscles, the rodents were implanted with a subcutaneous infusion pump. For the experimental group, nandrolone was administered over the next 30 days via this pump, while the control and sham group pumps were filled with carrier only.

RESULTS

Final testing, 6 weeks later, showed improved muscle contraction strength in the steroid-treated animals (72% of sham group strength) compared to control animals (57% of sham group strength, p < 0.5). A trend towards increased weight and muscle belly diameter in the steroid-treated group was not statistically significant.

CONCLUSIONS

These findings support the potential role of anabolic steroids in improving recovery of atrophic muscle after delayed reinnervation.

Effects of co-administration of clenbuterol and testosterone propionate on skeletal muscle in paraplegic mice

Spinal cord injury (SCI) is generally associated with a rapid and significant decrease in muscle mass and corresponding changes in skeletal muscle properties. Although beta(2)-adrenergic and androgen receptor agonists are anabolic substances clearly shown to prevent or reverse muscle wasting in some pathological conditions, their effects in SCI patients remain largely unknown. Here we studied the effects of clenbuterol and testosterone propionate administered separately or in combination on skeletal muscle properties and adipose tissue in adult CD1 mice spinal-cord-transected (Tx) at the low-thoracic level (i.e., induced complete paraplegia). Administered shortly post-Tx, these substances were found to differentially reduce loss in body weight, muscle mass, and muscle fiber cross-sectional area (CSA) values. Although all three treatments induced significant effects, testosterone-treated animals were generally less protected against Tx-related changes. However, none of the treatments prevented fat tissue loss or muscle fiber type conversion and functional loss generally found in Tx animals. These results provide evidence suggesting that clenbuterol alone or combined with testosterone may constitute better clinically-relevant treatments than testosterone alone to decrease muscle atrophy (mass and fiber CSA) in SCI subjects.

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.

Neuroprotective effect of testosterone treatment on motoneuron recruitment following the death of nearby motoneurons

Motoneuron loss is a significant medical problem, capable of causing severe movement disorders or even death. We have previously shown that motoneuron death induces marked dendritic atrophy in surviving nearby motoneurons. Additionally, in quadriceps motoneurons, this atrophy is accompanied by decreases in motor nerve activity. However, treatment with testosterone partially attenuates changes in both the morphology and activation of quadriceps motoneurons. Testosterone has an even larger neuroprotective effect on the morphology of motoneurons of the spinal nucleus of the bulbocavernosus (SNB), in which testosterone treatment can completely prevent dendritic atrophy. The present experiment was performed to determine whether the greater neuroprotective effect of testosterone on SNB motoneuron morphology was accompanied by a greater neuroprotective effect on motor activation. Right side SNB motoneurons were killed by intramuscular injection of cholera toxin-conjugated saporin in adult male Sprague-Dawley rats. Animals were either given Silastic testosterone implants or left untreated. Four weeks later, left side SNB motor activation was assessed with peripheral nerve recording. The death of right side SNB motoneurons resulted in several changes in the electrophysiological response properties of surviving left side SNB motoneurons, including decreased background activity, increased response latency, increased activity duration, and decreased motoneuron recruitment. Treatment with exogenous testosterone attenuated the increase in activity duration and completely prevented the decrease in motoneuron recruitment. These data provide a functional correlate to the known protective effects of testosterone treatment on the morphology of these motoneurons, and further support a role for testosterone as a therapeutic agent in the injured nervous system.

Functional recovery and facial motoneuron survival are influenced by immunodeficiency in crush-axotomized mice

Facial nerve axotomy is a well-described injury paradigm for peripheral nerve regeneration and facial motoneuron (FMN) survival. We have previously shown that CD4(+) T helper (Th) 1 and 2 effector subsets develop in the draining cervical lymph node, and that the IL-4/STAT-6 pathway of Th2 development is critical for FMN survival after transection axotomy. In addition, delayed behavioral recovery time in immunodeficient mice may be due to the absence of T and B cells. This study utilized a crush axotomy paradigm to evaluate FMN survival and functional recovery in WT, STAT-6 KO (impaired Th2 response), T-Bet KO (impaired Th1 response), and RAG-2 KO (lacking mature T and B cells) mice to elucidate the contributions of specific CD4(+) T cell subsets in motoneuron survival and recovery mechanisms. STAT-6 KO and RAG-2 KO mice exhibited decreased FMN survival after crush axotomy compared to WT, supporting a critical role for the Th2 effector cell in motoneuron survival before target reconnection. Long term FMN survival was sustained through 10 wpo after crush axotomy in both WT and RAG-2 KO mice, indicating that target derived neurotrophic support maintains FMN survival after target reconnection. In addition, RAG-2 KO mice exhibited delayed functional recovery compared to WT mice. Both STAT-6 and T-Bet KO mice exhibited partially delayed functional recovery compared to WT, though not to the extent of RAG-2 KO mice. Collectively, our findings indicate that both pro- and anti-inflammatory CD4(+) T cell responses contribute to optimal functional recovery from axotomy-induced facial paralysis, while FMN survival is supported by the anti-inflammatory Th2 response alone.

Neuroprotective effects of testosterone on dendritic morphology following partial motoneuron depletion: efficacy in female rats

Motoneuron loss is a significant medical problem, capable of causing severe movement disorders and even death. We have previously demonstrated that partial depletion of motoneurons induces dendritic atrophy in remaining motoneurons, with a concomitant reduction in motor activation. Treatment of male rats with testosterone attenuates the regressive changes following partial motoneuron depletion. To test whether testosterone has similar effects in females, we examined potential neuroprotective effects in motoneurons innervating muscles of the quadriceps of female rats. Motoneurons 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, surviving motoneurons were labeled with cholera toxin-conjugated HRP, and dendritic arbors were reconstructed in three dimensions. Compared to normal females, partial motoneuron depletion resulted in decreased dendritic length in remaining quadriceps motoneurons, and this atrophy was greatly attenuated by testosterone treatment. These findings suggest that testosterone has neuroprotective effects on morphology in both males and females, further supporting a role for testosterone as a neurotherapeutic agent in the injured nervous system.

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.

Accelerating functional recovery after rat facial nerve injury: Effects of gonadal steroids and electrical stimulation

Objective

We investigated the combined effects of electrical stimulation and testosterone propionate on overall recovery time in rats with extracranial crush injuries to the facial nerve.

Study Design

Male rats underwent castration 3 to 5 days prior to right facial nerve crush injury and electrode implantation. Rats were randomly assigned to two groups: crush injury + testosterone or crush injury with electrical stimulation + testosterone. Recovery was assessed by daily subjective examination documenting vibrissae orientation/movement, semi-eye blink, and full eye blink.

Results

Milestones of early recovery were noted to be significantly earlier in the groups with electrical stimulation, with/without testosterone. The addition of testosterone to electrical stimulation showed significant earlier return of late recovery parameters and complete overall recovery.

Conclusion

Electrical stimulation may decrease cell death or promote sprouting to accelerate early recovery. Testosterone may affect the actual rate of axonal regeneration and produce acceleration in functional recovery. By targeting different stages of neural regeneration, the synergy of electrical stimulation and testosterone appears to have promise as a neurotherapeutic strategy for facial nerve injury.

Electrical stimulation facilitates rat facial nerve recovery from a crush injury

Objective

To study the effect of electrical stimulation on accelerating facial nerve functional recovery from a crush injury in the rat model.

Study Design

Experimental.

Method

The main trunk of the right facial nerve was crushed just distal to the stylomastoid foramen, causing right-sided facial paralysis in 17 Sprague-Dawley rats. An electrode apparatus was implanted in all rats. Nine rats underwent electrical stimulation and eight were sham stimulated until complete facial nerve recovery. Facial nerve function was assessed daily by grading eyeblink reflex, vibrissae orientation, and vibrissae movement.

Results

An electrical stimulation model of the rat facial nerve following axotomy was established. The semi-eyeblink returned significantly earlier (3.71 + 0.97 vs 9.57 + 1.86 days post axotomy) in stimulated rats ( P = 0.008). Stimulated rats also recovered all functions earlier, and showed less variability in recovery time.

Conclusion

Electrical stimulation initiates and accelerates facial nerve recovery in the rat model as it significantly reduces recovery time for the semi-eyeblink reflex, a marker of early recovery. It also hastens recovery of other functions.

Androgen regulates neuritin mRNA levels in an in vivo model of steroid-enhanced peripheral nerve regeneration

Following crush injury to the facial nerve in Syrian hamsters, treatment with androgens enhances axonal regeneration rates and decreases time to recovery. It has been demonstrated in vitro that the ability of androgen to enhance neurite outgrowth in motoneurons is dependent on neuritin-a protein that is involved in the re-establisment of neuronal connectivity following traumatic damage to the central nervous system and that is under the control of several neurotrophic and neuroregenerative factors--and we have hypothesized that neuritin is a mediator of the ability of androgen to increase peripheral nerve regeneration rates in vivo. Testosterone treatment of facial nerve-axotomized hamsters resulted in an approximately 300% increase in neuritin mRNA levels 2 days post-injury. Simultaneous treatment with flutamide, an androgen receptor blocker that is known to prevent androgen enhancement of nerve regeneration, abolished the ability of testosterone to upregulate neuritin mRNA levels. In a corroborative in vitro experiment, the androgen dihydrotestosterone induced an approximately 100% increase in neuritin mRNA levels in motoneuron-neuroblastoma cells transfected with androgen receptors, but not in cells without androgen receptors. These data confirm that neuritin is under the control of androgens, and suggest that neuritin is an important effector of androgen in enhancing peripheral nerve regeneration following injury. Given that neuritin has now been shown to be involved in responses to both central and peripheral injuries, and appears to be a common effector molecule for several neurotrophic and neurotherapeutic agents, understanding the neuritin pathway is an important goal for the clinical management of traumatic nervous system injuries.

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.

The spinal nucleus of the bulbocavernosus: firsts in androgen-dependent neural sex differences

Cell number in the spinal nucleus of the bulbocavernosus (SNB) of rats was the first neural sex difference shown to differentiate under the control of androgens, acting via classical intracellular androgen receptors. SNB motoneurons reside in the lumbar spinal cord and innervate striated muscles involved in copulation, including the bulbocavernosus (BC) and levator ani (LA). SNB cells are much larger and more numerous in males than in females, and the BC/LA target muscles are reduced or absent in females. The relative simplicity of this neuromuscular system has allowed for considerable progress in pinpointing sites of hormone action, and identifying the cellular bases for androgenic effects. It is now clear that androgens act at virtually every level of the SNB system, in development and throughout adult life. In this review we focus on effects of androgens on developmental cell death of SNB motoneurons and BC/LA muscles; the establishment and maintenance of SNB motoneuron soma size and dendritic length; BC/LA muscle morphology and physiology; and behaviors controlled by the SNB system. We also describe new data on neurotherapeutic effects of androgens on SNB motoneurons after injury in adulthood.

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.

Androgenic, but not estrogenic, protection of motoneurons from somal and dendritic atrophy induced by the death of neighboring motoneurons

Motoneuron loss is a significant medical problem, capable of causing severe movement disorders or even death. We have been investigating the effects of motoneuron loss on surviving motoneurons in a lumbar motor nucleus, the spinal nucleus of the bulbocavernosus (SNB). SNB motoneurons undergo marked dendritic and somal atrophy following the experimentally induced death of other nearby SNB motoneurons. However, treatment with testosterone at the time of lesioning attenuates this atrophy. Because testosterone can be metabolized into the estrogen estradiol (as well as other physiologically active steroid hormones), it was unknown whether the protective effect of testosterone was an androgen effect, an estrogen effect, or both. In the present experiment, we used a retrogradely transported neurotoxin to kill the majority of SNB motoneurons on one side of the spinal cord only in adult male rats. Some animals were also treated with either testosterone, the androgen dihydrotestosterone (which cannot be converted into estradiol), or the estrogen estradiol. As seen previously, partial motoneuron loss led to reductions in soma area and in dendritic length and extent in surviving motoneurons. Testosterone and dihydrotestosterone attenuated these reductions, but estradiol had no protective effect. These results indicate that the neuroprotective effect of testosterone on the morphology of SNB motoneurons following partial motoneuron depletion is an androgen effect rather than an estrogen effect.

Androgen regulation of beta-amyloid protein and the risk of Alzheimer's disease

Advancing age is the most significant risk factor for the development of Alzheimer's disease (AD), however the age-related changes that underlie this effect remain unclear. In men, one normal consequence of aging is a robust decline in circulating and brain levels of the sex steroid hormone testosterone. Testosterone depletion leads to functional impairments and increased risk of disease in androgen-responsive tissues throughout the body, including brain. In this review we discuss the relationship between age-related testosterone depletion and the development of AD. Specifically, we focus on androgen regulation of beta-amyloid protein (Abeta), the accumulation of which is a key initiating factor in AD pathogenesis. Emerging data suggest that the regulatory actions of androgens on both Abeta and the development of AD support consideration of androgen therapy for the prevention and treatment of AD.

Exogenous androgen treatment delays the stress response following hamster facial nerve injury

Following injury or stress of any type, cells undergo a stress response, involving the cessation of general protein synthesis and the up-regulation of heat shock proteins (HSP), which have been implicated in promoting cell survival and repair. In a variety of neuronal injury models, including the hamster facial motoneurone (FMN) model, steroid hormones augment regeneration and are neuroprotective. We have previously shown that facial nerve axotomy induces expression of HSP70 (HSP70) and/or up-regulates constitutively expressed HSP70 (HSC70) mRNA in axotomised hamster FMN and that testosterone propionate (TP) treatment reduces this response. These previous studies were unable to differentiate between HSC70 mRNA and HSP70 mRNA. Therefore, an objective of the present study was to determine which HSP (HSC70 or HSP70) was being up-regulated by axotomy and reduced by TP. Axotomy increased HSC70 protein in axotomised and non-axotomised FMN, relative to untreated baseline hamsters. Interestingly, TP transiently delayed the stress-induced up-regulation of HSC70 protein in axotomised FMN compared to axotomised FMN from non-TP treated controls. A potential explanation for this delay may involve the TP-induced liberation of HSP from the androgen receptor, which would provide the injured cell with an immediately available pool of protective HSP. An hypothesis is presented suggesting that this TP-induced delay of stress-induced HSC70 up-regulation might allow for the diversion of cellular energy away from HSP synthesis and towards the synthesis of proteins required for regeneration and survival.

Effect of testosterone on oxidative stress and cell damage induced by 3-nitropropionic acid in striatum of ovariectomized rats

This paper evaluates the effects of testosterone (0.5 mg/kg subcutaneously (s.c.) for 8 days) on oxidative stress and cell damage induced by 3-nitropropionic acid (20 mg/kg intraperitoneally (i.p.) for 4 days) in ovariectomized rats. Gonadectomy triggered oxidative damage and cell loss, evaluated by the detection of caspase-3, whereas 3-nitropropionic acid increased the levels of oxidative stress induced by ovariectomy and prompted cell damage characterized by enhanced levels of lactate dehydrogenase. These changes were blocked by testosterone administration. Our results support the following conclusions: i) ovariectomy triggers oxidative and cell damage via caspase-3 in the striatum; ii) 3-nitropropionic acid exacerbates oxidative stress induced by ovariectomy and leads to cell damage characterized by increased levels of lactate dehydrogenase; iii) testosterone administration decreases oxidative stress and cell damage. Additionally, these data support the hypothesis that testosterone might play an important role in the onset and development of neurodegenerative diseases.

The Effect of Androgen Status on the Structural and Functional Success of Cavernous Nerve Grafting in an Experimental Rat Model

PURPOSE

Iatrogenic erectile dysfunction following radical prostatectomy is primarily neurogenic in origin. Attempts to improve postoperative potency aim to preserve or regenerate the autonomic cavernous nerves. Testosterone is integral for erectile function and it has profound positive effects on nerve regeneration. Androgen ablation impairs nerve regeneration. In this animal study we evaluated whether testosterone deprivation effects axonal regeneration in cavernous nerve grafts or the erectile response to cavernous nerve graft stimulation.

MATERIALS AND METHODS

A total of 45 male Sprague-Dawley rats underwent bilateral cavernous nerve neurotomy, followed by unilateral nerve graft using the genitofemoral nerve. Rats were then randomized to castrate, intact and testosterone treated arms. At 3 months grafts were explored and electrostimulation was performed with intracavernous pressure responses recorded. Grafted nerves were then harvested for immunohistochemical analysis.

RESULTS

Univariate analysis demonstrated a significant difference in the maximal intracavernous pressure response between groups. Mean +/- SEM maximal intracavernous pressure was 47 +/- 7.9, 23.7 +/- 4.9 and 59 +/- 7.4 mm Hg in the intact, castrate and testosterone treated groups, respectively (p = 0.003). Total axon counts did not differ between treatment groups with a mean total axon count of 789 +/- 97, 706 +/- 134 and 726 +/- 111, respectively. Castrate animals had lower neuronal nitric oxide synthase axon counts compared to intact animals (p = 0.089). The mean axon count was 480 +/- 78, 285 +/- 53 and 435 +/- 71 in the intact, castrate and testosterone treated groups respectively.

CONCLUSIONS

Castration resulted in a decreased erectile response to electrostimulation following nerve grafting. This may be due to decreased graft neuronal nitric oxide synthase positive axonal regeneration. This has important implications in patients in whom cavernous nerve grafting could be considered.

Motoneuron injury and repair: New perspectives on gonadal steroids as neurotherapeutics

In this review, we will summarize recent work from our laboratory on the role of gonadal steroids as neuroprotective agents in motoneuron viability following cell stress. Three motoneuron models will be discussed: developing axotomized hamster facial motoneurons (FMNs); adult axotomized mouse FMNs; and immortalized, cultured mouse spinal motoneurons subjected to heat shock. New work on two relevant motoneuron proteins, the survival of motor neuron protein, and neuritin or candidate plasticity-related gene 15, indicates differential steroid regulation of these two proteins after axotomy. The concept of gonadal steroids as cellular stress correction factors and the implications of this for acute neurological injury situations will be presented as well.

Effect of testosterone on functional recovery in a castrate male rat stroke model

Both increased and decreased testosterone levels have been reported to correlate with poor outcome after acute ischemic stroke. The present study focused on the role of testosterone during recovery from neurological deficits in a rat focal ischemia model. Castrate male rats were subjected to behavioral tests after 90 min of middle cerebral artery occlusion (MCAO). On day 7 post-MCAO, neurological deficit-matched rats were assigned to a treatment group implanted with subcutaneous testosterone pellets or a control group implanted with sham cholesterol pellets. After 4 weeks post-MCAO, the average infarct volume was not significantly different between the two groups. Rats in the testosterone group demonstrated significantly earlier improvement in neurological deficits and shortened latency of adhesive tape removal compared with the control group as analyzed by Wilcoxon signed ranks test. Walking on parallel bars improved in both groups with a trend towards early recovery observed in the testosterone group. Biased left body swings persisted during the test period in both groups post-MCAO. Serum testosterone was within physiological levels in the treatment group but was not detectable in the control group by radioimmunoassay. GAP-43 and synaptophysin expression did not differ between groups. Less GFAP expression and reactive astrocyte hypertrophy were found around the infarct area in testosterone-treated rats compared with control rats. In conclusion, testosterone replacement post-MCAO accelerated functional recovery in castrate rats, suggesting a potential therapeutic role for testosterone replacement in stroke recovery.

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

In the hamster facial nerve injury paradigm, we have established that androgens enhance both functional recovery from facial nerve paralysis and the rate of regeneration in the adult, through intrinsic effects on the nerve cell body response to injury and via an androgen receptor (AR)-mediated mechanism. Whether these therapeutic effects of gonadal steroids encompass neuroprotection from axotomy-induced cell death is the focus of the present study. Virtually 100% of adult hamster facial motoneurons (FMNs) survive axotomy at the stylomastoid foramen (SMF), whereas, before postnatal day 15 (P15), developing FMNs undergo substantial axotomy-induced cell death. The first part of the present study focuses on determining when ARs are first expressed in developing hamster FMNs. Using AR immunocytochemistry, it was found that males express ARs by P2 and females by P4, which is the earliest demonstration of AR expression in mammalian motoneurons reported thus far in the literature. The second half examines the neuroprotective effects of testosterone propionate, 17-beta estradiol, and dihydrotestosterone on FMNs of P7 hamsters after facial nerve transection at the SMF. The results demonstrate that androgens and estrogens are equally able to rescue approximately 20% of FMNs from axotomy-induced cell death, with the effects permanent. This study is the first to investigate the effects of both androgens and estrogens on axotomy-induced cell death in one system and, with our previously published work, to validate the hamster FMN injury paradigm as a model of choice in the investigation of both neurotherapeutic and neuroprotective actions of gonadal steroids.

Exogenous testosterone prevents motoneuron atrophy induced by contralateral motoneuron depletion

Gonadal steroids exhibit neuroprotective and neurotherapeutic effects. The lumbar spinal cord of male rats contains a highly androgen-sensitive population of motoneurons, the spinal nucleus of the bulbocavernosus (SNB), whose morphology and function are dependent on testosterone in adulthood. Unilateral SNB motoneuron depletion induces dendritic atrophy in contralateral SNB motoneurons, but this atrophy is reversed in previously castrated males treated with testosterone. In the present experiment we test the hypothesis that the morphology of SNB motoneurons is protected from atrophy after contralateral motoneuron depletion by exogenous testosterone alone (i.e., with no delay between castration and testosterone replacement). We unilaterally depleted SNB motoneurons by intramuscular injection of cholera toxin conjugated saporin. Simultaneously, some saporin-injected rats were castrated and immediately given replacement testosterone. Four weeks later, contralateral SNB motoneurons were labeled with cholera toxin conjugated HRP, soma sizes were measured, and dendritic arbors were reconstructed. Contralateral SNB motoneuron depletion induced somal atrophy and dendritic retraction, but testosterone treatment prevented both of these effects. Thus, the presence of high-normal levels of testosterone prevents motoneuron atrophy induced by contralateral motoneuron depletion. These data support a therapeutic role for testosterone in preventing atrophy induced by motoneuron injury.

Sex-related differences in the regeneration of sensory axons and recovery of nociception after peripheral nerve crush in the rat

Sex-related differences regarding the regeneration of nociceptive axons and the recovery of nociception after sural nerve crush injury were examined in rats. The elongation rate of the fastest regenerating sensory axons in females started to increase after the first 6 days. This resulted in about 15% greater axon elongation distance at 8 days after crush in female than in male rats as determined by the nerve pinch test. The number of regenerating sensory axons in female and male rats, however, was not different. The recovery of nociception in the instep started earlier and was more extensive in females than in males during the entire 24-week recovery period, so that the pain sensitive area was finally about 20% larger in females than in males. Although ovariectomy significantly reduced plasma estradiol concentration in female rats, it did not change the elongation distance of regenerating nociceptive axons, which remained significantly greater than in male rats. Elimination of the cells in the distal nerve segment by freezing revealed that a more effective cell support in the distal nerve segment is probably responsible for faster regeneration of nociceptive axons in females than in males, rather than the circulating female sex hormones.

The facial nerve axotomy model

Experimental models such as the facial nerve axotomy paradigm in rodents allow the systematic and detailed study of the response of neurones and their microenvironment to various types of challenges. Well-studied experimental examples include peripheral nerve trauma, the retrograde axonal transport of neurotoxins and locally enhanced inflammation following the induction of experimental autoimmune encephalomyelitis in combination with axotomy. These studies have led to novel insights into the regeneration programme of the motoneurone, the role of microglia and astrocytes in synaptic plasticity and the biology of glial cells. Importantly, many of the findings obtained have proven to be valid in other functional systems and even across species barriers. In particular, microglial expression of major histocompatibility complex molecules has been found to occur in response to various types of neuronal damage and is now regarded as a characteristic component of "glial inflammation". It is found in the context of numerous neurodegenerative disorders including Parkinson's and Alzheimer's disease. The detachment of afferent axonal endings from the surface membrane of regenerating motoneurones and their subsequent displacement by microglia ("synaptic stripping") and long-lasting insulation by astrocytes have also been confirmed in humans. The medical implications of these findings are significant. Also, the facial nerve system of rats and mice has become the best studied and most widely used test system for the evaluation of neurotrophic factors.

Neurotherapeutic action of testosterone on hamster facial nerve regeneration: temporal window of effects

Neurotherapeutic or neuroprotective effects of gonadal steroids on the injured nervous system have been demonstrated in our laboratory and others. We have previously demonstrated that testosterone propionate (TP) administered systemically at supraphysiological levels accelerates both recovery from facial paralysis and regeneration rates following facial nerve injury in the hamster. Initial temporal studies of steroidal enhancement of functional recovery from facial paralysis established that steroid exposure is necessary during the first postoperative week. Furthermore, accumulated evidence suggests that TP manifests its effects on neuronal regeneration in the immediate postoperative or preregenerative phase by altering the cellular stress response. The purpose of this study was to identify the effective temporal window of TP exposure sufficient to enhance regenerative properties of injured facial motoneurons and functional recovery from facial paralysis induced by facial nerve injury. Adult castrated male hamsters received a right facial nerve crush axotomy at the stylomastoid foramen and were divided into (1) short term, (2) delayed, (3) continuous, and (4) no TP treatment groups. Short term and continuous groups were implanted with 1 subcutaneous (sc) TP capsule each immediately after axotomy, with the capsule removed at 30 min, 2, 4, or 6 h in short-term groups and allowed to remain for the duration of the experiment in the continuous group. In the delayed TP group, 1 sc TP capsule was implanted 6 h after axotomy and allowed to remain for the duration of the experiment. For regeneration rate studies, postoperative times ranged from 4 to 7 days. For the behavioral studies, observations were made for 26 days postaxotomy. The results point to a critical 6-h interval immediately after injury when TP enhances nerve outgrowth distances and augments behavioral recovery.