Neurotrophin-3 is a target-derived neurotrophic factor for penile erection-inducing neurons

Neurite outgrowth in cultured mouse pelvic ganglia - Effects of neurotrophins and bladder tissue

Neurotrophic factors regulate survival and growth of neurons. The urinary bladder is innervated via both sympathetic and parasympathetic neurons located in the major pelvic ganglion. The aim of the present study was to characterize the effects of the neurotrophins nerve growth factor (NGF), brain derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3) on the sprouting rate of sympathetic and parasympathetic neurites from the female mouse ganglion. The pelvic ganglion was dissected out and attached to a petri dish and cultured in vitro. All three factors (BDNF, NT-3 and NGF) stimulated neurite outgrowth of both sympathetic and parasympathetic neurites although BDNF and NT-3 had a higher stimulatory effect on parasympathetic ganglion cells. The neurotrophin receptors TrkA, TrkB and TrkC were all expressed in neurons of the ganglia. Co-culture of ganglia with urinary bladder tissue, but not diaphragm tissue, increased the sprouting rate of neurites. Active forms of BDNF and NT-3 were detected in urinary bladder tissue using western blotting whereas tissue from the diaphragm expressed NGF. Neurite outgrowth from the pelvic ganglion was inhibited by a TrkB receptor antagonist. We therefore suggest that the urinary bladder releases trophic factors, including BDNF and NT-3, which regulate neurite outgrowth via activation of neuronal Trk-receptors. These findings could influence future strategies for developing pharmaceuticals to improve re-innervation due to bladder pathologies.

Low-Intensity Extracorporeal Shock Wave Therapy Enhances Brain-Derived Neurotrophic Factor Expression through PERK/ATF4 Signaling Pathway

Low-intensity extracorporeal shock wave therapy (Li-ESWT) is used in the treatment of erectile dysfunction, but its mechanisms are not well understood. Previously, we found that Li-ESWT increased the expression of brain-derived neurotrophic factor (BDNF). Here we assessed the underlying signaling pathways in Schwann cells in vitro and in penis tissue in vivo after nerve injury. The result indicated that BDNF were significantly increased by the Li-ESWT after nerve injury, as well as the expression of BDNF in Schwann cells (SCs, RT4-D6P2T) in vitro. Li-ESWT activated the protein kinase RNA-like endoplasmic reticulum (ER) kinase (PERK) pathway by increasing the phosphorylation levels of PERK and eukaryotic initiation factor 2a (eIF2α), and enhanced activating transcription factor 4 (ATF4) in an energy-dependent manner. In addition, GSK2656157—an inhibitor of PERK—effectively inhibited the effect of Li-ESWT on the phosphorylation of PERK, eIF2α, and the expression of ATF4. Furthermore, silencing ATF4 dramatically attenuated the effect of Li-ESWT on the expression of BDNF, but had no effect on hypoxia-inducible factor (HIF)1α or glial cell-derived neurotrophic factor (GDNF) in Schwann cells. In conclusion, our findings shed new light on the underlying mechanisms by which Li-ESWT may stimulate the expression of BDNF through activation of PERK/ATF4 signaling pathway. This information may help to refine the use of Li-ESWT to further improve its clinical efficacy.

Secreted herpes simplex virus-2 glycoprotein G alters thermal pain sensitivity by modifying NGF effects on TRPV1

Genital herpes is a painful disease frequently caused by the neurotropic pathogen herpes simplex virus type 2 (HSV-2). We have recently shown that HSV-2-secreted glycoprotein G (SgG2) interacts with and modulates the activity of the neurotrophin nerve growth factor (NGF). This interaction modifies the response of the NGF receptor TrkA, increasing NGF-dependent axonal growth. NGF is not only an axonal growth modulator but also an important mediator of pain and inflammation regulating the amount, localization, and activation of the thermal pain receptor transient receptor potential vanilloid 1 (TRPV1). In this work, we addressed whether SgG2 could contribute to HSV-2-induced pain. Injection of SgG2 in the mouse hindpaw produced a rapid and transient increase in thermal pain sensitivity. At the molecular level, this acute increase in thermal pain induced by SgG2 injection was dependent on differential NGF-induced phosphorylation and in changes in the amount of TrkA and TRPV1 in the dermis. These results suggest that SgG2 alters thermal pain sensitivity by modulating TRPV1 receptor.

Developing a functional urinary bladder: a neuronal context

The development of organs occurs in parallel with the formation of their nerve supply. The innervation of pelvic organs (lower urinary tract, hindgut, and sexual organs) is complex and we know remarkably little about the mechanisms that form these neural pathways. The goal of this short review is to use the urinary bladder as an example to stimulate interest in this question. The bladder requires a healthy mature nervous system to store urine and release it at behaviorally appropriate times. Understanding the mechanisms underlying the construction of these neural circuits is not only relevant to defining the basis of developmental problems but may also suggest strategies to restore connectivity and function following injury or disease in adults. The bladder nerve supply comprises multiple classes of sensory, and parasympathetic or sympathetic autonomic effector (motor) neurons. First, we define the developmental endpoint by describing this circuitry in adult rodents. Next we discuss the innervation of the developing bladder, identifying challenges posed by this area of research. Last we provide examples of genetically modified mice with bladder dysfunction and suggest potential neural contributors to this state.

Secreted herpes simplex virus-2 glycoprotein G modifies NGF-TrkA signaling to attract free nerve endings to the site of infection

Herpes simplex virus type 1 (HSV-1) and HSV-2 are highly prevalent viruses that cause a variety of diseases, from cold sores to encephalitis. Both viruses establish latency in peripheral neurons but the molecular mechanisms facilitating the infection of neurons are not fully understood. Using surface plasmon resonance and crosslinking assays, we show that glycoprotein G (gG) from HSV-2, known to modulate immune mediators (chemokines), also interacts with neurotrophic factors, with high affinity. In our experimental model, HSV-2 secreted gG (SgG2) increases nerve growth factor (NGF)-dependent axonal growth of sympathetic neurons ex vivo, and modifies tropomyosin related kinase (Trk)A-mediated signaling. SgG2 alters TrkA recruitment to lipid rafts and decreases TrkA internalization. We could show, with microfluidic devices, that SgG2 reduced NGF-induced TrkA retrograde transport. In vivo, both HSV-2 infection and SgG2 expression in mouse hindpaw epidermis enhance axonal growth modifying the termination zone of the NGF-dependent peptidergic free nerve endings. This constitutes, to our knowledge, the discovery of the first viral protein that modulates neurotrophins, an activity that may facilitate HSV-2 infection of neurons. This dual function of the chemokine-binding protein SgG2 uncovers a novel strategy developed by HSV-2 to modulate factors from both the immune and nervous systems.

Injections of adipose tissue-derived stem cells and stem cell lysate improve recovery of erectile function in a rat model of cavernous nerve injury

INTRODUCTION

Erectile dysfunction (ED) remains a major complication after radical prostatectomy. The use of adipose tissue-derived stem cells (ADSCs) has shown promising results for the treatment of ED. However, the mechanisms of action for stem cell therapy remain controversial, with increasing evidence pointing to paracrine pathways.

AIM

To determine the effects and to identify the mechanism of action of ADSC and ADSC-derived lysate in a rat model of cavernous nerve (CN) crush injury.

METHODS

Thirty-two male Sprague-Dawley rats were randomly divided into four equal groups: one group underwent sham operation, while three groups underwent bilateral CN crush. Crush-injury groups were treated at the time of injury with intracavernous injection of ADSC, lysate, or vehicle only (injured controls). Erectile function was assessed by CN electrostimulation at 4 weeks. Penile tissue was collected for histology.

MAIN OUTCOME MEASURES

  Intracavernous pressure increase upon CN stimulation; neuronal nitric oxide synthase (nNOS) content in the dorsal penile nerve; smooth muscle content, collagen content, and number of apoptotic cells in the corpus cavernosum.

RESULTS

Both ADSC and lysate treatments resulted in significant recovery of erectile function, as compared with vehicle treatment. nNOS content was preserved in both the ADSC and lysate group, with significantly higher expression compared with vehicle-treated animals. There was significantly less fibrosis and a significant preservation of smooth muscle content in the ADSC and lysate groups compared with injured controls. The observed functional improvement after lysate injection supports the hypothesis that ADSCs act through release of intracellular preformed substances or by active secretion of certain biomolecules. The underlying mechanism of recovery appears to involve neuron preservation and cytoprotection by inhibition of apoptosis.

CONCLUSIONS

Penile injection of both ADSC and ADSC-derived lysate can improve recovery of erectile function in a rat model of neurogenic ED.

Nerve growth factor modulation of the cavernous nerve response to injury

INTRODUCTION

Surgical therapies for prostate cancer and other pelvic malignancies often result in neuronal damage and debilitating loss of sexual function due to cavernous nerve (CN) trauma. Advances in the neurobiology of growth factors have heightened clinical interest in the development of protective and regenerative neuromodulatory strategies targeting CN recovery following injury.

AIM

The aim of this review was to offer an examination of current and future nerve growth factor (NGF) modulation of the CN response to injury with a focus on brain-derived nerve growth factor (BDNF), growth differentiation factor-5 (GDF-5), and neurturin (NTN).

METHODS

Information for this presentation was derived from a current literature search using the National Library of Medicine PubMed Services producing publications relevant to this topic. Search terms included neuroprotection, nerve regeneration, NGFs, neurotrophic factors, BDNF, GDF-5, NTN, and CNs.

MAIN OUTCOME MEASURES

Basic science studies satisfying the search inclusion criteria were reviewed.

RESULTS

In this session, BDNF, atypical growth factors GDF-5 and NTN, and their potential influence upon CN recovery after injury are reviewed, as are the molecular pathways by which their influence is exerted.

CONCLUSIONS

Compromised CN function is a significant cause of erectile dysfunction development following prostatectomy and serves as the primary target for potential neuroprotective or regenerative strategies utilizing NGFs such as BDNF, GDF-5, and NTN, and/or targeted novel therapeutics modulating signaling pathways.

Cardiovascular actions of neurotrophins

Neurotrophins were christened in consideration of their actions on the nervous system and, for a long time, they were the exclusive interest of neuroscientists. However, more recently, this family of proteins has been shown to possess essential cardiovascular functions. During cardiovascular development, neurotrophins and their receptors are essential factors in the formation of the heart and critical regulator of vascular development. Postnatally, neurotrophins control the survival of endothelial cells, vascular smooth muscle cells, and cardiomyocytes and regulate angiogenesis and vasculogenesis, by autocrine and paracrine mechanisms. Recent studies suggest the capacity of neurotrophins, via their tropomyosin-kinase receptors, to promote therapeutic neovascularization in animal models of hindlimb ischemia. Conversely, the neurotrophin low-affinity p75(NTR) receptor induces apoptosis of endothelial cells and vascular smooth muscle cells and impairs angiogenesis. Finally, nerve growth factor looks particularly promising in treating microvascular complications of diabetes or reducing cardiomyocyte apoptosis in the infarcted heart. These seminal discoveries have fuelled basic and translational research and thus opened a new field of investigation in cardiovascular medicine and therapeutics. Here, we review recent progress on the molecular signaling and roles played by neurotrophins in cardiovascular development, function, and pathology, and we discuss therapeutic potential of strategies based on neurotrophin manipulation.

Effects of NGF, NT-3 and GDNF family members on neurite outgrowth and migration from pelvic ganglia from embryonic and newborn mice

Background

Pelvic ganglia are derived from the sacral neural crest and contain both sympathetic and parasympathetic neurons. Various members of the neurotrophin and GDNF families of neurotrophic factors have been shown to play important roles in the development of a variety of peripheral sympathetic and parasympathetic neurons; however, to date, the role of these factors in the development of pelvic ganglia has been limited to postnatal and older ages. We examined the effects of NGF, NT-3, GDNF, neurturin and artemin on cell migration and neurite outgrowth from explants of the pelvic ganglia from embryonic and newborn mice grown on collagen gels, and correlated the responses with the immunohistochemical localization of the relevant receptors in fixed tissue.

Results

Cell migration assays showed that GDNF strongly stimulated migration of tyrosine hydroxylase (TH) cells of pelvic ganglia from E11.5, E14.5 and P0 mice. Other factors also promoted TH cell migration, although to a lesser extent and only at discrete developmental stages. The cells and neurites of the pelvic ganglia were responsive to each of the GDNF family ligands – GDNF, neurturin and artemin – from E11.5 onwards. In contrast, NGF and NT-3 did not elicit a significant neurite outgrowth effect until E14.5 onwards. Artemin and NGF promoted significant outgrowth of sympathetic (TH+) neurites only, whereas neurturin affected primarily parasympathetic (TH-negative) neurite outgrowth, and GDNF and NT-3 enhanced both sympathetic and parasympathetic neurite outgrowth. In comparison, collagen gel assays using gut explants from E11.5 and E14.5 mice showed neurite outgrowth only in response to GDNF at E11.5 and to neurturin only in E14.5 mice.

Conclusion

Our data show that there are both age-dependent and neuron type-dependent differences in the responsiveness of embryonic and neo-natal pelvic ganglion neurons to growth factors.

Intracavernous growth differentiation factor-5 therapy enhances the recovery of erectile function in a rat model of cavernous nerve injury

INTRODUCTION

Neurogenic erectile dysfunction remains a serious complication in the postprostatectomy population. Effective protective and regenerative neuromodulatory strategies are needed.

AIM

To determine the effect of growth differentiation factor-5 (GDF-5) on erectile function and its mechanism in a rat model of cavernous nerve (CN) injury.

MAIN OUTCOME MEASURES

Erectile function was assessed by CN electrostimulation at 4 weeks. Penile tissues were examined by real-time polymerase chain reaction (PCR) and immunohistochemical analyses.

METHODS

Forty-eight male Sprague-Dawley rats were randomly divided into six equal groups: one group underwent sham operation (uninjured controls), while five groups underwent bilateral CN crush. Crush-injury groups were treated at the time of injury with intracavernous injection of a slow-release suspension of liquid microparticles containing no GDF-5 (vehicle), 0.4 microg (low concentration), 2 microg (intermediate concentration), or 10 microg GDF-5 (high concentration). One untreated group served as injured controls.

RESULTS

GDF-5 enhanced erectile recovery and significantly increased intracavernous pressure in the low and intermediate-concentration groups vs. injured controls. Low-concentration GDF-5 demonstrated the best functional preservation, as the intracavernous pressure increase in this group did not differ significantly from uninjured controls. A dose-response relationship was confirmed for the effects of GDF-5 in penile tissue. Low-concentration GDF-5 showed better preservation of the penile dorsal nerves and antiapoptotic effects in the corpus cavernosum (P < 0.05 vs. injured controls). Although high concentration GDF-5 did not confer meaningful erectile recovery, this dose was more effective at decreasing transforming growth factor-beta than low-concentration GDF-5.

CONCLUSIONS

Intracavernous injection of low (0.4 microg) or intermediate-concentration GDF-5 (2 microg) was effective in preserving erectile function in a rat model of neurogenic erectile dysfunction. The underlying mechanism appears to involve neuron preservation and antiapoptosis.

Alteration of glial cell line-derived neurotrophic factor family receptor alpha-2 mRNA expression and its co-expression with neuronal nitric oxide synthase in pelvic ganglia following unilateral cavernous nerve injury

OBJECTIVES

The goal of this study was to determine the alterations of glial cell line-derived neurotrophic factor family receptor alpha-2 (GFRalpha2) mRNA expression in the major pelvic ganglia (MPG) and their relationship to the marker for the neural plasticity (growth-associated protein 43: GAP-43) and neuronal nitric oxide synthase (nNOS)-positive neurons following cavernous nerve injury.

METHODS

Cavernous nerves were transected unilaterally in 24 Sprague-Dawley rats aged 8 weeks. We used nine sham operated same animals as controls. Bilateral MPGs were harvested at 1, 3, and 6 months following nerve injury. The GFRalpha2 and GAP-43 mRNA expressions of the sham group and the injury group (3 months after surgery) were investigated by reverse transcription-polymerase chain reaction. We also investigated the expression profile of GFRalpha2 mRNA by in situ hybridization combined with nNOS immunostaining.

RESULTS

It was revealed semi-quantitatively that the GAP43 mRNA expression moderately increased in the intact MPG, and GFRalpha2 mRNA was maintained in the intact MPG but not in the injured one. A histological double-labeling study showed that the number of GFRalpha2 mRNA- and nNOS-positive neurons increased in the intact MPG and most GFRalpha2 mRNA expressions were colocalized with nNOS immunostaining.

CONCLUSIONS

The current study suggested that the GFRalpha2 mRNA alteration closely related to the nNOS expression following the cavernous nerve injury, which would be involved in the maintenance and recovery of erectile function.

Emerging neuromodulatory molecules for the treatment of neurogenic erectile dysfunction caused by cavernous nerve injury

Advances in the neurobiology of growth factors, neural development, and prevention of cell death have resulted in a heightened clinical interest for the development of protective and regenerative neuromodulatory strategies for the cavernous nerves (CNs), as therapies for prostate cancer and other pelvic malignancies often result in neuronal damage and debilitating loss of sexual function. Nitric oxide released from the axonal end plates of these nerves within the corpora cavernosa causes relaxation of smooth muscle, initiating the haemodynamic changes of penile erection as well as contributing to maintained tumescence; the loss of CN function is primarily responsible for the development of erectile dysfunction (ED) after pelvic surgery and serves as the primary target for potential neuroprotective or regenerative strategies. Evidence from pre-clinical studies for select neuromodulatory approaches is reviewed, including neurotrophins, glial cell line-derived neurotrophic factors (GDNF), bone morphogenic proteins, immunophilin ligands, erythropoetin (EPO), and stem cells.

Neurturin regulates postnatal differentiation of parasympathetic pelvic ganglion neurons, initial axonal projections, and maintenance of terminal fields in male urogenital organs

We have investigated the development of autonomic nerves in the urogenital tract of male mice and the effect of neurturin gene deletion on this process. At birth, autonomic innervation of the reproductive organs was sparse, but urinary bladder smooth muscle was well innervated. Further innervation of reproductive tissues occurred until P21, but noradrenergic axons established their complete terminal field later than nitrergic cholinergic axons: in adults the former are more prevalent, yet this became apparent only at P7 (vas deferens, seminal vesicles), P14 (prostate) or after P14 (penis). Neurturin was essential for initial projection of axons (mucosa of vas deferens), maintenance of terminal fields (prostate and seminal vesicles), or both functions (cavernosum of penis). In contrast, some targets (e.g., bladder muscle and suburothelium, vas deferens smooth muscle) were unaffected by neurturin gene deletion. Pelvic ganglion neurons more than doubled between birth and adulthood, probably as aresult of continued maturation of p75-positive undifferentiated neuronal precursors rather than cell division. The adult number of neurons was achieved by P7 (sympathetic) or P21 (parasympathetic). In adult neurturin knockout mice, there were approximately 25% fewer parasympathetic neurons compared with wild types, because of failure of differentiation after P14. This study revealed the complexity of postnatal maturation of urogenital innervation, with each organ showing a distinct chronology of innervation and different requirement for neurturin. Our results also indicate that in adults there will be distinct differences in neurturin dependence between organs, such that proregenerative therapies may have to be tailored specifically for the nerve pathway of interest.

Neurturin enhances the recovery of erectile function following bilateral cavernous nerve crush injury in the rat

Background

The molecular mechanisms responsible for the survival and preservation of function for adult parasympathetic ganglion neurons following injury remain incompletely understood. However, advances in the neurobiology of growth factors, neural development, and prevention of cell death have led to a surge of clinical interest for protective and regenerative neuromodulatory strategies, as surgical therapies for prostate, bladder, and colorectal cancers often result in neuronal axotomy and debilitating loss of sexual function or continence. In vitro studies have identified neurturin, a glial cell line-derived neurotrophic factor, as a neuromodulator for pelvic cholinergic neurons. We present the first in vivo report of the effects of neurturin upon the recovery of erectile function following bilateral cavernous nerve crush injury in the rat.

Methods

In these experiments, groups (n = 8 each) consisted of uninjured controls and animals treated with injection of albumin (blinded crush control group), extended release neurotrophin-4 or neurturin to the site of cavernous nerve crush injury (100 μg per animal). After 5 weeks, recovery of erectile function (treatment effect) was assessed by cavernous nerve electrostimulation and peak aortic pressures were measured. Investigators were unblinded to specific treatments after statistical analyses were completed.

Results

Erectile dysfunction was not observed in the sham group (mean maximal intracavernous pressure [ICP] increase of 117.5 ± 7.3 cmH₂O), whereas nerve injury and albumin treatment (control) produced a significant reduction in ICP elevation of 40.0 ± 6.3 cmH₂O. Neurturin facilitated the preservation of erectile function, with an ICP increase of 55% at 62.0 ± 9.2 cmH₂O (p < 0.05 vs control). Extended release neurotrophin-4 did not significantly enhance recovery of erectile function with an ICP change of 46.9 ± 9.6. Peak aortic blood pressures did not differ between groups. No significant pre- and post-treatment weight differences were observed between control, neurotrophin-4 and neurturin cohorts. All animals tolerated the five-week treatment course.

Conclusion

Treatment with neurturin at the site of cavernous nerve crush injury facilitates recovery of erectile function. Results support further investigation of neurturin as a neuroprotective and/or neuroregenerative agent facilitating functional recovery after cavernous or other pelvic autonomic nerve injuries.

Upregulation of penile brain-derived neurotrophic factor (BDNF) and activation of the JAK/STAT signalling pathway in the major pelvic ganglion of the rat after cavernous nerve transection

OBJECTIVES

Increasing attention is being focused on identifying novel approaches to recover cavernous nerve (CN) function after injury or secondary to disease states such as diabetes mellitus. We examined penile brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) expression, and activation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) molecular pathway in the major pelvic ganglion (MPG) after CN injury in the rat.

METHODS

Five groups of eight male Sprague-Dawley rats (4 mo, 250-300 g) were used in this study. The penis and MPG with attached CN segment were harvested at 0 h (controls), 12, and 24 h, as well as at 5 and 12 d after CN axotomy, for protein, messenger RNA (mRNA), and immunohistochemical analysis.

RESULTS

mRNA and protein expression of BDNF was upregulated in the penis after injury (p<0.05). Levels of NT-3 were unchanged. The JAK/STAT pathway was activated in the MPG after transection, as evidenced by increased STAT1 (peak: 24 h) and STAT3 (peak: 5 d) phosphorylation (p<0.01 vs. controls).

CONCLUSIONS

This study demonstrates increased expression of penile BDNF and upregulation of phosphorylated STAT1 and STAT3 in the MPG in response to CN transection. Activation of the JAK/STAT pathway after injury represents a promising new molecular target for modulating CN survival and regeneration.

Brain‐Derived Neurotrophic Factor (BDNF) Acts Primarily via the JAK/STAT Pathway to Promote Neurite Growth in the Major Pelvic Ganglion of the Rat: Part 2

INTRODUCTION

Surgical and radiation therapies of bladder and prostate cancers may damage cavernous nerves and cause erectile dysfunction (ED). We previously showed that brain-derived neurotrophic factor (BDNF) could restore erectile function in a neurogenic ED rat model. We now investigated the signaling mechanism of BDNF in major pelvic ganglia (MPG) explants.

AIM

To identify the signaling mechanism that mediates the neurotrophic effect of BDNF in cultured MPG.

METHODS

Major pelvic ganglia was isolated from male rats for immunohistochemistry and immunofluorescence staining to locate BDNF receptors, pan-neurotrophin 75 (p75), tropomyosin-related kinase B (TrkB), and tropomyosin-related kinase C (TrkC). The dorso-caudal region of MPG was treated with BDNF to determine the optimal dosage for promoting neurite growth. Specific kinase inhibitors AG490, KT5720, LY294002, and U0126 were then used to treat MPG either alone or prior to BDNF treatment. The treated MPG was examined for neurite growth and for expression and phosphorylation of JAK2, STAT1, and STAT3 by Western blot analysis.

MAIN OUTCOME MEASURES

Lengths of neurite growth from MPG were measured to quantify the effects of BDNF and to identify specific signaling pathways. Ratios of phosphorylated vs. unphosphoryated proteins of JAK2, STAT1, and STAT2 in control and treated MPG were determined to confirm JAK/STAT as the principal signaling pathway.

RESULTS

Tropomyosin-related kinase B and TrkC were localized to neurons whereas p75 to perineuronal satellite glial cells (SGC). The optimal dosage of BDNF for promoting MPG neurite growth was between 25 and 50 ng/mL. Among the four specific kinase inhibitors, AG490 was the strongest in suppressing MPG neurite growth as well as BDNF-induced phosphorylation of JAK2, STAT1, and STAT3.

CONCLUSIONS

In rat MPG, TrkB and TrkC were expressed in neurons, whereas p75 in SGC. Optimal BDNF dosage for promoting MPG neurite growth was between 25 and 50 ng/mL. BDNF promotes MPG neurite growth primarily by activating the JAK/STAT pathway.

Structural effects and potential changes in growth factor signalling in penis-projecting autonomic neurons after axotomy

Background

The responses of adult parasympathetic ganglion neurons to injury and the neurotrophic mechanisms underlying their axonal regeneration are poorly understood. This is especially relevant to penis-projecting parasympathetic neurons, which are vulnerable to injury during pelvic surgery such as prostatectomy. We investigated the changes in pelvic ganglia of adult male rats in the first week after unilateral cavernous (penile) nerve axotomy (cut or crush lesions). In some experiments FluoroGold was injected into the penis seven days prior to injury to allow later identification of penis-projecting neurons. Neurturin and glial cell line-derived neurotrophic factor (GDNF) are neurotrophic factors for penile parasympathetic neurons, so we also examined expression of relevant receptors, GFRα1 and GFRα2, in injured pelvic ganglion neurons.

Results

Axotomy caused prolific growth of axon collaterals (sprouting) in pelvic ganglia ipsilateral to the injury. These collaterals were most prevalent in the region near the exit of the penile nerve. This region contained the majority of FluoroGold-labelled neurons. Many sprouting fibres formed close associations with sympathetic and parasympathetic pelvic neurons, including many FluoroGold neurons. However immunoreactivity for synaptic proteins could not be demonstrated in these collaterals. Preganglionic terminals showed a marked loss of synaptic proteins, suggesting a retrograde effect of the injury beyond the injured neurons. GFRα2 immunofluorescence intensity was decreased in the cytoplasm of parasympathetic neurons, but GFRα1 immunofluorescence was unaffected in these neurons.

Conclusion

These studies show that there are profound changes within the pelvic ganglion after penile nerve injury. Sprouting of injured postganglionic axons occurs concurrently with structural or chemical changes in preganglionic terminals. New growth of postganglionic axon collaterals within the ganglion raises the possibility of the formation of aberrant synaptic connections between injured and un-injured ganglion neurons. Together these changes demonstrate a broader effect on the pelvic autonomic circuitry than simply loss of neuroeffector connections. These structural changes are accompanied by potential changes in neurotrophic factor signalling due to altered expression of receptors for members of the GDNF family. Together our results advance understanding of the responses of pelvic autonomic nerve circuits to injury and may assist in designing strategies for promoting regeneration.

Loss of nitrergic neurotransmission to mouse corpus cavernosum in the absence of neurturin is accompanied by increased response to acetylcholine

The neurotrophic factor, neurturin (NTN), plays an important role in parasympathetic neural development. In the penis, parasympathetic nitrergic/cholinergic nerves mediate the erectile response. However, despite reduced parasympathetic penile innervation in mice lacking the NTN receptor, glial cell line-derived neurotrophic factor family receptor alpha (GFRalpha)2, they are capable of erection and reproduction. Our aim was to assess neural regulation of erectile tissues from mice lacking NTN. Responses of cavernosal smooth muscle were studied in vitro, monitoring agonist- and nerve-evoked changes in tension. Frequency-dependent nerve-evoked relaxations in the presence of guanethidine were markedly reduced in the mutant mice compared to wild types (19 vs 72% of phenylephrine pre-contraction). Atropine reduced the amplitude in wild-type mice to 61%, but abolished relaxations in knockout mice. In wild-type and knockout animals, nitric oxide synthase inhibition abolished neurogenic relaxations. In NTN knockout animals, EC(50) values for nitric oxide-dependent relaxations to acetylcholine and muscarine were increased approximately 0.5 log units. In contrast, contractions to electrical stimulation or phenylephrine, and relaxations to bradykinin or the nitric oxide donor, sodium nitroprusside, were unaltered. Immunohistochemistry confirmed that nerves immunoreactive for nitric oxide synthase, vesicular acetylcholine transporter and vasoactive intestinal polypeptide were substantially reduced in cavernosum of NTN knockout mice. Parallel immunohistochemical and pharmacological studies in GFRalpha2 knockout animals showed the same changes from their wild types as the NTN knockout animals. The data demonstrate that NTN is essential for normal development of penile erection-inducing nerves and that its absence leads to increased responsiveness to muscarinic agonists, possibly as a compensatory mechanism.

Plasticity of pelvic autonomic ganglia and urogenital innervation

Pelvic ganglia contain a mixture of sympathetic and parasympathetic neurons and provide most of the motor innervation of the urogenital organs. They show a remarkable sensitivity to androgens and estrogens, which impacts on their development into sexually dimorphic structures and provide an array of mechanisms by which plasticity of these neurons can occur during puberty and adulthood. The structure of pelvic ganglia varies widely among species, ranging from rodents, which have a pair of large ganglia, to humans, in whom pelvic ganglion neurons are distributed in a large, complex plexus. This plexus is frequently injured during pelvic surgical procedures, yet strategies for its repair have yet to be developed. Advances in this area will come from a better understanding of the effects of injury on the cellular signaling process in pelvic neurons and also the role of neurotrophic factors during development, maintenance, and repair of these axons.