Glial Cell Line-derived Neurotrophic Factor Injection Research Articles

The role of Sertoli cells-secreted factors in different stages of germ cells development in mice exposed to BDE-209

Decabromodiphenyl ether (BDE-209), a frequently used brominated flame retardant, readily enters the environment and is difficult to degrade with bioaccumulation. BDE-209 could cause male reproductive toxicity, but the regulatory functions of Sertoli cells-secreted factors remain uncertain. In present study, male mice were treated with 75 mg/kg BDE-209 and then stopped exposure for 50 days. Exogenous Glial cell line-derived neurotrophic factor (GDNF), a Sertoli cell-secreted factor, was injected into testes of mice treated with BDE-209 for 50 days to explore the role of GDNF in BDE-209-induced reproductive toxicity. The mouse spermatogonia cell line GC-1 spg was used in vitro to further verify regulatory effects of Sertoli cells-secreted factors on meiotic initiation. The results showed that BDE-209 inhibited expressions of the self-renewal pathway GFRα-1/RAS/ERK1/2 in spermatogonial stem cells (SSCs), and reduced expressions of spermatogonia proliferation-related pathway NRG3/ERBB4 and meiosis initiation factor Stra8. Furthermore, BDE-209 decreased the levels of both GDNF and retinoic acid (RA) secreted by Sertoli cells in testes. Importantly, the alterations of above indicators induced by BDE-209 did not recover after 50-day recovery period. After exogenous GDNF injection, the decreased expression of GFRα-1/RAS/ERK in SSCs was reversed. However, the level of RA and expressions of NRG3/ERBB4/Stra8 were not restored. The in vitro experimental results showed that exogenous RA reversed the reductions in NRG3/ERBB4/Stra8 and ameliorated inhibition of GC-1 spg cells proliferation induced by BDE-209. These results suggested that Sertoli cells-secreted factors play roles in regulating various stages of germ cell development. Specifically, BDE-209 affected the self-renewal of SSCs by decreasing GDNF secretion resulting in the inhibition of GFRα-1/RAS/ERK pathway; BDE-209 hindered the proliferation of spermatogonia and initiation of meiosis by inhibiting the secretion of RA and preventing RA from binding to RARα, resulting in the suppression of NRG3/ERBB4/Stra8 pathway. As a consequence, spermatogenesis was compromised, leading to persistent male reproductive toxicity.

The central glial cell line-derived neurotrophic factor (GDNF) regulates pulmonary function in asthmatic rats.

Asthma is a common chronic inflammatory disease of the airway, but the mechanism is still not fully understood. This study aimed to investigate the effect of glial cell line-derived neurotrophic factor (GDNF) on asthma attacks. An asthmatic rat model was established. GDNF expression in the airway and brain was observed by immunohistochemistry (IHC), and the concentration of GDNF in bronchoalveolar lavage fluid (BALF) was detected by enzyme-linked immunosorbent assay (ELISA). After injection of GDNF and its antibody into the lateral ventricle of asthmatic rats, the pulmonary function was recorded, and the levels of interferon-γ (IFN-γ) and interleukin-4 (IL-4) in BALF were tested. GDNF expressions were increased significantly in the lung tissues of asthmatic rats. In the central nervous system (CNS), GDNF-positive immunoreactive substances were observed in multiple brain regions, including the medial amygdala (MeA), paraventricular nucleus (PVN), cortex, and nucleus of solitary tract (NTS). After injection of GDNF into the lateral ventricles of asthmatic rats, the symptoms of asthma and airway inflammation were significantly aggravated, which could be improved by injection of GDNF antibody into the lateral ventricles. GDNF expression is increased in the lung and brain in asthmatic rats. During an asthma attack, the increased GDNF expressions in the rat brain remarkably aggravate the asthmatic symptoms.

P002 Glial cell line-Derived Neurotrophic Factor (GDNF) improves intestinal wound healing – A new target for IBD treatment?

Abstract Background Due to the rising incidence and socioeconomic relevance of Inflammatory Bowel Disease (IBD) worldwide, new therapeutic strategies are necessary to improve patient care. Since immunosuppressants are partially insufficient with relevant rates of side effects, novel concepts of treatment need to be developed. Mucosal and/or histological healing represent potential criteria to measure disease activity and are mentioned in current guidelines as favorable prognostic factors regarding disease outcomes. In previous studies, the soluble factor Glial cell line-Derived Neurotrophic Factor (GDNF) has been shown to be significantly reduced in tissue specimens from IBD patients and to be critically involved in intestinal epithelial barrier maturation. Therefore, the goal of this study was to further analyze the potential role of GDNF in IBD. Methods Intestinal wound healing was assessed in endoscopic biopsy-based wound assays as well as dextran sodium sulphate (DSS)-induced colitis in vivo. During the experiments, C57Bl/6 mice were either injected with GDNF or sodium chloride intraperitoneal while tissue samples were used for detailed molecular analyses. Further, scratch wound assays were performed in Caco2 monolayers to identify molecular pathways and cell mechanisms in vitro. Results Intraperitoneal injection of GDNF resulted in significantly enhanced wound closure in vivo. During the DSS-induced colitis model, mice treated with GDNF demonstrated significantly improved recovery from colitis in comparison to mice injected with sodium chloride. Similarly, application of GDNF in a scratch wound assay significantly enhanced wound closure in vitro. Mechanistically, molecular analysis revealed that GDNF application resulted in significantly increased cell proliferation. The effect of GDNF on cell proliferation was based on upregulation of LGR5-positive cells with increased phosphorylation of pSrc. Further studies demonstrated that the effect of GDNF on wound healing and cell proliferation could be inhibited by application of a Src-inhibitor. Conclusion GDNF significantly improves intestinal mucosal healing in vivo and in vitro which results in significantly enhanced recovery from colitis. While this effect is driven by increased cell proliferation due to upregulation of LGR5-positive cells and increased phosphorylation of pSrc, previous studies already demonstrated the critical impact of GDNF on epithelial barrier function. Following that, GDNF might have great potential in IBD treatment and could be a new target for future therapeutic approaches.

GFR-α1 Expression in Substantia Nigra Increases Bilaterally Following Unilateral Striatal GDNF in Aged Rats and Attenuates Nigral Tyrosine Hydroxylase Loss Following 6-OHDA Nigrostriatal Lesion.

Glial cell line-derived neurotrophic factor (GDNF) improved motor function in Parkinson's disease (PD) patients in Phase I clinical trials, and these effects persisted months after GDNF discontinuation. Conversely, phase II clinical trials reported no significant effects on motor improvement vs placebo. The disease duration and the quantity, infusion approach, and duration of GDNF delivery may affect GDNF efficacy in PD treatment. However, identifying mechanisms activated by GDNF that affect nigrostriatal function may reveal additional avenues to partially restore nigrostriatal function. In PD and aging models, GDNF affects tyrosine hydroxylase (TH) expression or phosphorylation in substantia nigra (SN), long after a single GDNF injection in striatum. In aged rats, the GDNF family receptor, GFR-α1, increases TH expression and phosphorylation in SN. To determine if GFR-α1 could be a mechanistic link in long-term GDNF impact, we conducted two studies; first to determine if a single unilateral striatal delivery of GDNF affected GFR-α1 and TH over time (1 day, 1 week, and 4 weeks) in the striatum or SN in aged rats, and second, to determine if soluble GFR-α1 could mitigate TH loss following 6-hydroxydopamine (6-OHDA) lesion. In aged rats, GDNF bilaterally increased ser31 TH phosphorylation and GFR-α1 expression in SN at 1 day and 4 weeks after GDNF, respectively. In striatum, GFR-α1 expression decreased 1 week after GDNF, only on the GDNF-injected side. In 6-OHDA-lesioned rats, recombinant soluble GFR-α1 mitigated nigral, but not striatal, TH protein loss following 6-OHDA. Together, these results show GDNF has immediate and long-term impact on dopamine regulation in the SN, which includes a gradual increase in GFR-α1 expression that may sustain TH expression and dopamine function therein.

Glial cell line-derived neurotrophic factor (GDNF) attenuates the peripheral neuromuscular dysfunction without inhibiting the activation of spinal microglia/monocyte

BackgroundPeripheral neuromuscular dysfunctions were found in elderly individuals, and spinal microglia/monocyte plays an important role on this process. This study aims to test whether the glial cell line-derived neurotrophic factor (GDNF) could attenuate age-related neuromuscular dysfunction by inhibiting the activation of spinal microglia/monocyte.MethodsMale Sprague-Dawley rats were divided into an adult group and an aged group. The aged rats were intrathecally injected with normal saline (NS) and GDNF. All the rats were harvested 5 days after each injection. The muscular function was tested by compound muscle action potential, and the activation of microglia/monocyte was detected by immunofluorescence staining; cytokines were assayed by enzyme-linked immunosorbent assay; the expression level of GDNF and its known receptor GFR-α in the spinal cord, the expression level of neuregulin-1 (NRG-1) in the sciatic nerve, and the expression level of γ- and α7- ε-nicotinic acetylcholine receptors in the tibialis anterior muscle were measured by western blotting.ResultsThe activated microglia/monocyte was found in the aged rats compared to the adult rats. The aged rats showed a significant neuromuscular dysfunction and cytokine release as well as increased expression of γ- and α7-nAChR. The protein expression of GDNF, GFR-α, and NRG-1 in the aged rats were significantly lower than that in the adult rats. However, the exogenous injection of GDNF could alleviate the neuromuscular dysfunction but not inhibit the activation of spinal microglia/monocyte. Furthermore, the levels of GFR-α and NRG-1 also increased after GDNF treatment.ConclusionThe GDNF could attenuate the age-related peripheral neuromuscular dysfunction without inhibiting the activation of microglia/monocyte in the spinal cord.

Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF) Elevates Stimulus-Evoked Release of Dopamine in Freely-Moving Rats

Neurotrophic factors (NTFs) hold potential as disease-modifying therapies for neurodegenerative disorders like Parkinson’s disease. Glial cell line-derived neurotrophic factor (GDNF), cerebral dopamine neurotrophic factor (CDNF), and mesencephalic astrocyte-derived neurotrophic factor (MANF) have shown neuroprotective and restorative effects on nigral dopaminergic neurons in various animal models of Parkinson’s disease. To date, however, their effects on brain neurochemistry have not been compared using in vivo microdialysis. We measured extracellular concentration of dopamine and activity of dopamine neurochemistry-regulating enzymes in the nigrostriatal system of rat brain. NTFs were unilaterally injected into the striatum of intact Wistar rats. Brain microdialysis experiments were performed 1 and 3 weeks later in freely-moving animals. One week after the treatment, we observed enhanced stimulus-evoked release of dopamine in the striatum of MANF-treated rats, but not in rats treated with GDNF or CDNF. MANF also increased dopamine turnover. Although GDNF did not affect the extracellular level of dopamine, we found significantly elevated tyrosine hydroxylase (TH) and catechol-O-methyltransferase (COMT) activity and decreased monoamine oxidase A (MAO-A) activity in striatal tissue samples 1 week after GDNF injection. The results show that GDNF, CDNF, and MANF have divergent effects on dopaminergic neurotransmission, as well as on dopamine synthetizing and metabolizing enzymes. Although the cellular mechanisms remain to be clarified, knowing the biological effects of exogenously administrated NTFs in intact brain is an important step towards developing novel neurotrophic treatments for degenerative brain diseases.

The effects of the glial cell line-derived neurotrophic factor (GDNF) on the levels of mRNA of apoptotic genes Bax and Bcl-xl in the brain of mice genetically predisposed to pathological behavior

Similar to the other neurotrophic factors, the glial cell line-derived neurotrophic factor (GDNF) may inhibit apoptosis in vitro. However, the antiapoptotic GDNF effects in vivo are not known. We studied the effect of GDNF central administration of on the mRNA levels of genes encoding the proapoptotic protein Bax and the antiapoptotic protein Bcl-xl in the brain of ASC mice genetically predisposed to depressivelike behavior and mice of their nondepressive parental CBA strain. We found that the GDNF injection increased the Bcl-xl mRNA content in the hippocampi of mice of both strains (ρ < 0.05) and Bax mRNA (ρ < 0.05) in the hippocampus of ASC mice. Thus, we revealed both the antiand proapoptotic effects of GDNF in vivo. These effects substantially depended on the genotype of the animals. We also observed significant interstrain differences in the Bax and Bcl-xl mRNA levels. In ASC mice, the Bax mRNA levels were significantly higher (ρ < 0.001 and ρ < 0.01) in all investigated structures and the content of Bcl-xl mRNA was elevated in the midbrain. Our data demonstrate the activation of apoptotic processes in ASC mice and the substantial compensatory changes, probably directed to the rise of the threshold for neuronal apoptosis.

Glial cell line-derived neurotrophic factor-mediated enhancement of noradrenergic descending inhibition in the locus coeruleus exerts prolonged analgesia in neuropathic pain.

The locus coeruleus (LC) is the principal nucleus containing the noradrenergic neurons and is a major endogenous source of pain modulation in the brain. Glial cell line-derived neurotrophic factor (GDNF), a well-established neurotrophic factor for noradrenergic neurons, is a major pain modulator in the spinal cord and primary sensory neurons. However, it is unknown whether GDNF is involved in pain modulation in the LC. Rats with chronic constriction injury (CCI) of the left sciatic nerve were used as a model of neuropathic pain. GDNF was injected into the left LC of rats with CCI for 3 consecutive days and changes in mechanical allodynia and thermal hyperalgesia were assessed. The α2 -adrenoceptor antagonist yohimbine was injected intrathecally to assess the involvement of descending inhibition in GDNF-mediated analgesia. The MEK inhibitor U0126 was used to investigate whether the ERK signalling pathway plays a role in the analgesic effects of GDNF. Both mechanical allodynia and thermal hyperalgesia were attenuated 24 h after the first GDNF injection. GDNF increased the noradrenaline content in the dorsal spinal cord. The analgesic effects continued for at least 3 days after the last injection. Yohimbine abolished these effects of GDNF. The analgesic effects of GDNF were partly, but significantly, inhibited by prior injection of U0126 into the LC. GDNF injection into the LC exerts prolonged analgesic effects on neuropathic pain in rats by enhancing descending noradrenergic inhibition.

Inhibition of microglial activation and induction of neurotrophic factors by flavonoids: a potential therapeutic strategy against Parkinson's disease.

Parkinson’s disease(PD)is characterized by the progressive degeneration of dopaminergic(DA)neurons and a decrease in striatal dopamine,which is associated with clinical movement disorders including a tremor at rest,rigidity of the limbs,bradykinesia(slowness and paucity of voluntary movement)and postural instability(a tendency to fall even in the absence of

Amantadine alleviates postoperative cognitive dysfunction possibly by increasing glial cell line-derived neurotrophic factor in rats.

Postoperative cognitive dysfunction is a clinical entity that is associated with poor outcome. We determined the effectiveness of amantadine in reducing surgery-induced cognitive impairment and the role of glial cell line-derived neurotrophic factor (GDNF) in this effect. Four-month old male Fischer 344 rats were subjected to right carotid exposure under intravenous anesthesia. Some rats received intraperitoneal injection of 25 mg/kg/day amantadine for 3 days with the first dose at 15 min before the surgery or intracerebroventricular injection of GDNF or an anti-GDNF antibody at the end of surgery. One week later, rats were started to be tested by Barnes maze and fear conditioning. Hippocampus was harvested at 6 h, 24 h or 10 days after the surgery for biochemical analysis. C8-B4 cells, a microglial cell line, were pretreated with 1 ng/ml GDNF for 30 min before being exposed to 5 ng/ml lipopolysaccharide for 2 h. Surgery increased the time to identify the target box in the Barnes maze when tested 1 day [22 (median) (11-66) (interquartile range) of control group vs. 158 (29-180) of surgery group, n = 15, P = 0.022) or 8 days after the training sessions and reduced context-related freezing behavior in the fear conditioning test. These effects were attenuated by amantadine (25 (14-90), n = 15, P = 0.029 compared with surgery group at 1 day after the training sessions in Barnes maze) and intracerebroventricular GDNF. Amantadine increased GDNF that was co-localized with glial fibrillary acidic protein, an astrocytic marker, in the hippocampus. Intracerebroventricular injection of an anti-GDNF antibody but not the denatured antibody blocked the effects of amantadine on cognition. Surgery induced neuroinflammation that was inhibited by amantadine. Lipopolysaccharide increased interleukin 1β production from C8-B4 cells. This effect was inhibited by GDNF. Our results suggest that amantadine attenuated surgery-induced learning and memory impairment. This effect may be mediated by GDNF via inhibition of neuroinflammation.

Mammalian target of rapamycin complex 1 as an inducer of neurotrophic factors in dopaminergic neurons.

Mammalian target of rapamycin complex 1 as an inducer of neurotrophic factors in dopaminergic neurons.

Glial cell line‐derived neurotrophic factor sensitized the mechanical response of muscular thin‐fibre afferents in rats

The role of glial cell line-derived neurotrophic factor (GDNF) in pain and muscular nociceptor activities is not well understood. We examined pain-related behaviour and mechanical response of muscular thin-fibre afferents after intramuscular injection of GDNF in rats. GDNF and antagonist to transient receptor potential V1 or acid-sensing ion channels were injected into rat gastrocnemius muscle and muscular mechanical hyperalgesia was assessed with a Randall-Selitto analgesiometer. Activities of single C- (conduction velocity < 2.0 m/s) and Aδ-fibres (conduction velocity 2.0-12.0 m/s) were recorded from extensor digitorum longus muscle-nerve preparations in vitro. The changes in the responses to mechanical stimuli before and after GDNF injection were recorded. Mechanical hyperalgesia was observed from 1 h to 1 day after GDNF (0.03 μM, 20 μL) injection. The decreased withdrawal threshold was temporarily reversed after intramuscular injection of amiloride (50 mM, 20 μL), but not capsazepine (50 μM, 20 μL). In single-fibre recordings, both phosphate buffered saline (PBS) and GDNF failed to induce any significant discharges. GDNF significantly enhanced the mechanical response when compared with the PBS group, but only in Aδ-fibre afferents. C-fibres were not affected. Significantly lowered threshold and increased response magnitude to mechanical stimuli were observed 30 or 60-120 min after injection. These times are compatible with the timing of the onset of the hyperalgesic effect of GDNF. These results suggest that GDNF increased the response of muscular Aδ-fibre afferents to mechanical stimuli, resulting in muscular mechanical hyperalgesia.

TRPV1 and TRPV4 Play Pivotal Roles in Delayed Onset Muscle Soreness

Unaccustomed strenuous exercise that includes lengthening contraction (LC) often causes tenderness and movement related pain after some delay (delayed-onset muscle soreness, DOMS). We previously demonstrated that nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF) are up-regulated in exercised muscle through up-regulation of cyclooxygenase (COX)-2, and they sensitized nociceptors resulting in mechanical hyperalgesia. There is also a study showing that transient receptor potential (TRP) ion channels are involved in DOMS. Here we examined whether and how TRPV1 and/or TRPV4 are involved in DOMS. We firstly evaluated a method to measure the mechanical withdrawal threshold of the deep tissues in wild-type (WT) mice with a modified Randall-Selitto apparatus. WT, TRPV1−/− and TRPV4−/− mice were then subjected to LC. Another group of mice received injection of murine NGF-2.5S or GDNF to the lateral gastrocnemius (LGC) muscle. Before and after these treatments the mechanical withdrawal threshold of LGC was evaluated. The change in expression of NGF, GDNF and COX-2 mRNA in the muscle was examined using real-time RT-PCR. In WT mice, mechanical hyperalgesia was observed 6–24 h after LC and 1–24 h after NGF and GDNF injection. LC induced mechanical hyperalgesia neither in TRPV1−/− nor in TRPV4−/− mice. NGF injection induced mechanical hyperalgesia in WT and TRPV4−/− mice but not in TRPV1−/− mice. GDNF injection induced mechanical hyperalgesia in WT but neither in TRPV1−/− nor in TRPV4−/− mice. Expression of NGF and COX-2 mRNA was significantly increased 3 h after LC in all genotypes. However, GDNF mRNA did not increase in TRPV4−/− mice. These results suggest that TRPV1 contributes to DOMS downstream (possibly at nociceptors) of NGF and GDNF, while TRPV4 is located downstream of GDNF and possibly also in the process of GDNF up-regulation.

English

The aim of this study was to investigate the efficiency of intrathecal glial cell line-derived neurotrophic factor (GDNF) on nitric oxide (NO) and nitric oxide synthase (NOS) activity following a spinal nerve ligation (SNL) of male Sprague Dawley rats. The rats were randomly divided into four groups: normal (control), sham-operated, SNL (SNL followed by a physiological saline injection into the subarachnoid space), and GDNF (SNL followed by a GDNF injection into the subarachnoid space). Each group was divided into three subgroups (n = 10). The rats in each subgroup were euthanised 3, 7, and 14&nbsp;days after the operation. Rat behaviour was evaluated before euthanising, and the ipsilateral spinal cords were harvested after euthanising to determine the NO content and NOS activity. Compared with the control and sham-operated groups, the NO content and NOS activity in the SNL group increased significantly 3&nbsp;days after the operation; this increase was maintained until 14&nbsp;days after the operation (P&nbsp;&lt; 0.01 or 0.05). A significant decrease was observed in the NO content and NOS activity in the GDNF group compared with the SNL group. The decrease continued until 14&nbsp;days after the operation (P&nbsp;&lt; 0.01 or 0.05). The results indicated that the NO and NOS activity in the rat spinal cord are associated with SNL-induced neuropathic pain. The decreased neuropathic pain from the intrathecal GDNF is correlated with the decrease in NO content and NOS activity in the spinal cord. &nbsp; Key words:&nbsp;Glial cell line-derived neurotrophic factor, neuralgia, nitric oxide, nitric oxide synthase.

Glial cell-line derived neurotrophic factor (GDNF) replacement attenuates motor impairments and nigrostriatal dopamine deficits in 12-month-old mice with a partial deletion of GDNF

Glial cell-line derived neurotrophic factor (GDNF) has been established as a growth factor for the survival and maintenance of dopamine (DA) neurons. In phase I clinical trials, GDNF treatment in Parkinson's disease patients led to improved motor function and GDNF has been found to be down regulated in Parkinson's disease patients. Studies using GDNF heterozygous (Gdnf+/−) mice have demonstrated that a partial reduction of GDNF leads to an age-related accelerated decline in nigrostriatal DA system- and motor-function and increased neuro-inflammation and oxidative stress in the substantia nigra (SN). Therefore, the purpose of the current studies was to determine if GDNF replacement restores motor function and functional markers within the nigrostriatal DA system in middle-aged Gdnf+/− mice. At 11months of age, male Gdnf+/− and wildtype (WT) mice underwent bilateral intra-striatal injections of GDNF (10μg) or vehicle. Locomotor activity was assessed weekly 1–4weeks after treatment. Four weeks after treatment, their brains were processed for analysis of GDNF levels and various DAergic and oxidative stress markers. An intrastriatal injection of GDNF increased motor activity in Gdnf+/− mice to levels comparable to WT mice (1week after injection) and this effect was maintained through the 4-week time point. This increase in locomotion was accompanied by a 40% increase in striatal GDNF protein levels and SN GDNF expression in Gdnf+/− mice. Additionally, GDNF treatment significantly increased the number of tyrosine hydroxylase (TH)-positive neurons in the SN of middle-aged Gdnf+/− mice, but not WT mice, which was coupled with reduced oxidative stress in the SN. These studies further support that long-term changes related to the dysfunction of the nigrostriatal pathway are influenced by GDNF expression and add that this dysfunction appears to be responsive to GDNF treatment. Additionally, these studies suggest that long-term GDNF depletion alters the biological and behavioral responses to GDNF treatment.

GDNF‐treated acellular nerve graft promotes motoneuron axon regeneration after implantation into cervical root avulsed spinal cord

It is well known that glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor for motoneurons. We have previously shown that it greatly enhanced motoneuron survival and axon regeneration after implantation of peripheral nerve graft following spinal root avulsion. In the current study, we explore whether injection of GDNF promotes axon regeneration in decellularized nerve induced by repeated freeze-thaw cycles. We injected saline or GDNF into the decellularized nerve after root avulsion in adult Sprague-Dawley rats and assessed motoneuron axon regeneration and Schwann cell migration by retrograde labelling and immunohistochemistry. We found that no axons were present in saline-treated acellular nerve whereas Schwann cells migrated into GDNF-treated acellular nerve grafts. We also found that Schwann cells migrated into the nerve grafts as early as 4 days after implantation, coinciding with the first appearance of regenerating axons in the grafts. Application of GDNF outside the graft did not induce Schwann cell infiltration nor axon regeneration into the graft. Application of pleiotrophin, a trophic factor which promotes axon regeneration but not Schwann cell migration, did not promote axon infiltration into acellular nerve graft. We conclude that GDNF induced Schwann cell migration and axon regeneration into the acellular nerve graft. Our findings can be of potential clinical value to develop acellular nerve grafting for use in spinal root avulsion injuries.

Effect of Glial Cell Line-Derived Neurotrophic Factor on Retinal Function after Experimental Branch Retinal Vein Occlusion

The objective of the study was to investigate the effect of glial cell line-derived neurotrophic factor (GDNF) on the multifocal electroretinogram (mfERG) following an induced branch retinal vein occlusion (BRVO) in pigs. Electrophysiological examination of the retina was performed in 20 pigs with standard and four-frame mfERG 4 weeks after induced BRVO and intravitreal injection of GDNF or vehicle. BRVO was induced by intraocular diathermia of the superior retinal vein. Inner retinal function was measured by analysis of the four-frame mfERG (iN1) and outer retinal function with standard mfERG (P1). In GDNF-treated BRVO eyes, P1 and iN1 amplitudes (P = 0.51 and 0.78) or implicit times (P = 0.08 and 0.99) did not differ from those in healthy fellow eyes. After vehicle injection, P1 and iN1 amplitudes of BRVO eyes were significantly lower than in the healthy fellow eye (P = 0.022 and 0.013). The log ratios of mfERG amplitudes between experimental and healthy fellow eyes were calculated (BRVO/healthy). GDNF improved the ratios of the four-frame mfERG (1.29 [0.88-1.88]) compared with vehicle (0.32 [0.21-0.50], P < 0.001). Equally, GDNF improved the ratios of the standard mfERG; GDNF (0.75 [0.51-1.10]) and vehicle (0.42 [0.27-0.63], P = 0.048). GDNF appears neuroprotective on retinal electrophysiological function after BRVO. The efficacy and safety of GDNF remain to be investigated in primate eyes.

IB4(+) nociceptors mediate persistent muscle pain induced by GDNF

Skeletal muscle is a well-known source of glial cell line-derived neurotrophic factor (GDNF), which can produce mechanical hyperalgesia. Since some neuromuscular diseases are associated with both increased release of GDNF and intense muscle pain, we explored the role of GDNF as an endogenous mediator in muscle pain. Intramuscularly injected GDNF induced a dose-dependent (0.1-10 ng/20 μl) persistent (up to 3 wk) mechanical hyperalgesia in the rat. Once hyperalgesia subsided, injection of prostaglandin E(2) at the site induced a prolonged mechanical hyperalgesia (>72 h) compared with naïve rats (<4 h; hyperalgesic priming). Selective neurotoxic destruction of IB4(+) nociceptors attenuated both GDNF hyperalgesia and hyperalgesic priming. Ergonomic muscular injury induced by eccentric exercise or mechanical vibration increased muscle GDNF levels at 24 h, a time point where rats also exhibited marked muscle hyperalgesia. Intrathecal antisense oligodeoxynucleotides to mRNA encoding GFRα1, the canonical binding receptor for GDNF, reversibly inhibited eccentric exercise- and mechanical vibration-induced muscle hyperalgesia. Finally, electrophysiological recordings from nociceptors innervating the gastrocnemius muscle in anesthetized rats, revealed significant increase in response to sustained mechanical stimulation after local GDNF injection. In conclusion, these data indicate that GDNF plays a role as an endogenous mediator in acute and induction of chronic muscle pain, an effect likely to be produced by GDNF action at GFRα1 receptors located in IB4(+) nociceptors.

Pharmacokinetics of intravitreal glial cell line-derived neurotrophic factor: Experimental studies in pigs

The purpose of this study was to establish the intravitreal (ITV) pharmacokinetics of glial cell line-derived neurotrophic factor (GDNF) and observe possible complications after ITV injection. Twenty Danish landrace pigs and 34 eyes were included in the study; 30 were injected with 100 ng of GDNF, two controls were injected without GDNF, and two received no injection. At post-injection time points of 1, 2, 3, 6 hours (h), 1, 2, 4 or 7 days (d) eyes were enucleated and the ITV concentration of GDNF (cGDNF) was determined by enzyme-linked immunosorbent assay, and activity was tested using a retinal ganglion cell line (RGC5) bioassay. Indirect ophthalmoscopy, intraocular pressure assessment, and fundus photography were performed before enucleation. There was initial variability in the cGDNF, but after 24 h GDNF was cleared in a monoexponential fashion with a half-life of 37 h (CL 33–43 h). Therapeutic concentrations were present for 15 d (CL 13–18 d) when an extrapolation was done. GDNF-injected vitreous samples stimulated increased survival of RGC5s at 24 h post-delivery ( p = 0.002) compared with no-GDNF vitreous controls. This effect was independent of intraocular incubation time when cGDNF was normalized to 5 ng/ml. A semi-logarithmic dose–response curve showed linearity between 0.1 and 10 ng/ml. None of the eyes showed any signs of inflammation or other complications. A single ITV GDNF injection of 100 ng leads to therapeutic levels for 15 days in the porcine eye. The GDNF was stable in the intraocular environment and no adverse events were observed. GDNF might therefore play a role in the future treatment of acute retinal damage.

Neurturin Effects on Nigrostriatal Dopamine Release and Content: Comparison with GDNF

Neurturin (NTN) is a member of the glial cell line-derived neurotrophic factor (GDNF) family; and, while GDNF has been shown to increase dopamine (DA) release in normal animals, the ability of NTN to alter DA release has not been previously reported. The purpose of the present study was to determine if NTN could alter striatal DA release, and to compare the effects of NTN to GDNF. Male Fischer-344 rats were given a single injection of vehicle or 5 microg NTN or GDNF into the right substantia nigra. Three weeks later microdialysis experiments were conducted to assess striatal DA release. Basal extracellular levels of striatal DA were not affected by either NTN or GDNF. However, both NTN and GDNF led to increases in amphetamine-evoked overflow of DA from the ipsilateral striatum, and there was a trend for potassium-evoked overflow to be augmented. Postmortem tissue levels of DA were decreased by approximately 20% in the striatum, and increased by approximately 100% in the substantia nigra, on the ipsilateral side of the brain compared to the contralateral side following both NTN and GDNF injection. Thus, NTN, like GDNF, can augment striatal DA release, and the magnitude of the NTN effects are similar to those of GDNF.