Localization of glial cell line-derived neurotrophic factor receptor alpha and c-ret mRNA in rat central nervous system

The Influence of Neurotrophins on the Brain-Lung Axis: Conception, Pregnancy, and Neonatal Period

Neurotrophins (NTs) are four small proteins produced by both neuronal and non-neuronal cells; they include nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4). NTs can exert their action through both genomic and non-genomic mechanisms by interacting with specific receptors. Initial studies on NTs have identified them only as functional molecules of the nervous system. However, recent research have shown that some tissues and organs (such as the lungs, skin, and skeletal and smooth muscle) as well as some structural cells can secrete and respond to NTs. In addition, NTs perform several roles in normal and pathological conditions at different anatomical sites, in both fetal and postnatal life. During pregnancy, NTs are produced by the mother, placenta, and fetus. They play a pivotal role in the pre-implantation process and in placental and embryonic development; they are also involved in the development of the brain and respiratory system. In the postnatal period, it appears that NTs are associated with some diseases, such as sudden infant death syndrome (SIDS), asthma, congenital central hypoventilation syndrome (CCHS), and bronchopulmonary dysplasia (BPD).

Exogenous neuritin restores auditory following cochlear spiral ganglion neuron denervation of gerbils

Spiral ganglion neurons (SGNs) transmit sound signals received by hair cells to the auditory center to produce hearing. The quantity and function are important for maintaining normal hearing function. Limited by the regenerative capacity, SGNs are unable to regenerate spontaneously after injury. Various neurotrophic factors play an important role in the regeneration process. Neuritin is a neurite growth factor that plays an important role in neural plasticity and nerve injury repair. In this study, we used bioinformatics analysis to show that neuritin was negatively correlated with cochlear damage. Then, we aimed to establish a cochlear spiral ganglion-specific sensorineural deafness model in gerbils using ouabain and determine the effects of exogenous neuritin protein in protecting damaged cochlear SGNs and repairing damaged auditory nerve function. The provides a new research strategy and scientific basis for the prevention and treatment of sensorineural deafness caused by the loss of SGNs. We were discovered that neuritin is expressed throughout the development of the gerbil cochlea, primarily in the SGNs and Corti regions. The expression of neuritin was negatively correlated with the sensorineural deafness induced by ouabain. In vitro and in vivo revealed that neuritin significantly maintained the number and arrangement of SGNs and nerve fibers in the damaged cochlea and effectively protected the high-frequency listening function of gerbils.

Central Facial Nervous System Biomolecules Involved in Peripheral Facial Nerve Injury Responses and Potential Therapeutic Strategies

Peripheral facial nerve injury leads to changes in the expression of various neuroactive substances that affect nerve cell damage, survival, growth, and regeneration. In the case of peripheral facial nerve damage, the injury directly affects the peripheral nerves and induces changes in the central nervous system (CNS) through various factors, but the substances involved in these changes in the CNS are not well understood. The objective of this review is to investigate the biomolecules involved in peripheral facial nerve damage so as to gain insight into the mechanisms and limitations of targeting the CNS after such damage and identify potential facial nerve treatment strategies. To this end, we searched PubMed using keywords and exclusion criteria and selected 29 eligible experimental studies. Our analysis summarizes basic experimental studies on changes in the CNS following peripheral facial nerve damage, focusing on biomolecules that increase or decrease in the CNS and/or those involved in the damage, and reviews various approaches for treating facial nerve injury. By establishing the biomolecules in the CNS that change after peripheral nerve damage, we can expect to identify factors that play an important role in functional recovery from facial nerve damage. Accordingly, this review could represent a significant step toward developing treatment strategies for peripheral facial palsy.

Growth Factors and Alcohol Use Disorder

Neurotrophic growth factors were originally characterized for their support in neuronal differentiation, outgrowth, and survival during development. However, it has been acknowledged that they also play a vital role in the adult brain. Abnormalities in growth factors have been implicated in a variety of neurological and psychiatric disorders, including alcohol use disorder (AUD). This work focuses on the interaction between alcohol and growth factors. We review literature suggesting that several growth factors play a unique role in the regulation of alcohol consumption, and that breakdown in these growth factor systems is linked to the development of AUD. Specifically, we focus on the brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), fibroblast growth factor 2 (FGF2), and insulin growth factor 1 (IGF-1). We also review the literature on the potential role of midkine (MDK) and pleiotrophin (PTN) and their receptor, anaplastic lymphoma kinase (ALK), in AUD. We show that alcohol alters the expression of these growth factors or their receptors in brain regions previously implicated in addiction, and that manipulations on these growth factors and their downstream signaling can affect alcohol-drinking behaviors in animal models. We conclude that there is a need for translational and clinical research to assess the therapeutic potential of new pharmacotherapies targeting these systems.

GDNF and GFRα1 Are Required for Proper Integration of Adult-Born Hippocampal Neurons

The glial cell line-derived neurotrophic factor (GDNF) is required for the survival and differentiation of diverse neuronal populations during nervous system development. Despite the high expression of GDNF and its receptor GFRα1 in the adult hippocampus, the functional role of this system remains unknown. Here, we show that GDNF, acting through its GFRα1 receptor, controls dendritic structure and spine density of adult-born granule cells, which reveals that GFRα1 is required for their integration into preexisting circuits. Moreover, conditional mutant mice for GFRα1 show deficits in behavioral pattern separation, a task in which adult neurogenesis is known to play a critical role. We also find that running increases GDNF in the dentate gyrus and promotes GFRα1-dependent CREB (cAMP response element-binding protein) activation and dendrite maturation. Together, these findings indicate that GDNF/GFRα1 signaling plays an essential role in the plasticity of adult circuits, controlling the integration of newly generated neurons.

GDNF and alcohol use disorder

Glial cell line-derived neurotrophic factor (GDNF) has been extensively studied for its role in the development and maintenance of the midbrain dopaminergic system, although evidence suggests that GDNF also plays a role in drug and alcohol addiction. This review focuses on the unique actions of GDNF in the mechanisms that prevent the transition from recreational alcohol use to abuse. Specifically, we describe studies in rodents suggesting that alcohol acutely increases GDNF expression in the ventral tegmental area, which enables the activation of the mitogen-activated protein kinase signaling pathway and the gating of alcohol intake. We further provide evidence to suggest that GDNF acts in the ventral tegmental area via both nongenomic and genomic mechanisms to suppress alcohol consumption. In addition, we describe findings indicating that when this endogenous protective pathway becomes dysregulated, alcohol intake levels escalate. Finally, we describe the potential use of GDNF inducers as a novel therapeutic approach to treat alcohol use disorder.

GDNF/GFRα1 Complex Abrogates Self-Renewing Activity of Cortical Neural Precursors Inducing Their Differentiation

The balance between factors leading to proliferation and differentiation of cortical neural precursors (CNPs) determines the correct cortical development. In this work, we show that GDNF and its receptor GFRα1 are expressed in the neocortex during the period of cortical neurogenesis. We show that the GDNF/GFRα1 complex inhibits the self-renewal capacity of mouse CNP cells induced by fibroblast growth factor 2 (FGF2), promoting neuronal differentiation. While GDNF leads to decreased proliferation of cultured cortical precursor cells, ablation of GFRα1 in glutamatergic cortical precursors enhances its proliferation. We show that GDNF treatment of CNPs promoted morphological differentiation even in the presence of the self-renewal-promoting factor, FGF2. Analysis of GFRα1-deficient mice shows an increase in the number of cycling cells during cortical development and a reduction in dendrite development of cortical GFRα1-expressing neurons. Together, these results indicate that GDNF/GFRα1 signaling plays an essential role in regulating the proliferative condition and the differentiation of cortical progenitors.

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GFRα1 receptor is expressed in the neocortex during the period of neurogenesis

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GDNF/GFRα1 complex inhibits self-renewing of cortical neuronal precursors

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GDNF and GFRα1 promote neurogenic differentiation of cortical neural progenitors

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Requirement of GFRα1 for proper dendrite development of cortical neurons

Putative roles of soluble trophic factors in facial nerve regeneration, target reinnervation, and recovery of vibrissal whisking

It is well-known that, after nerve transection and surgical repair, misdirected regrowth of regenerating motor axons may occur in three ways. The first way is that the axons enter into endoneurial tubes that they did not previously occupy, regenerate through incorrect fascicles and reinnervate muscles that they did not formerly supply. Consequently the activation of these muscles results in inappropriate movements. The second way is that, in contrast with the precise target-directed pathfinding by elongating motor nerves during embryonic development, several axons rather than a single axon grow out from each transected nerve fiber. The third way of misdirection occurs by the intramuscular terminal branching (sprouting) of each regenerating axon to culminate in some polyinnervation of neuromuscular junctions, i.e. reinnervation of junctions by more than a single axon. Presently, "fascicular" or "topographic specificity" cannot be achieved and hence target-directed nerve regeneration is, as yet, unattainable. Nonetheless, motor and sensory reinnervation of appropriate endoneurial tubes does occur and can be promoted by brief nerve electrical stimulation. This review considers the expression of neurotrophic factors in the neuromuscular system and how this expression can promote functional recovery, with emphasis on the whisking of vibrissae on the rat face in relationship to the expression of the factors. Evidence is reviewed for a role of neurotrophic factors as short-range diffusible sprouting stimuli in promoting complete functional recovery of vibrissal whisking in blind Sprague Dawley (SD)/RCS rats but not in SD rats with normal vision, after facial nerve transection and surgical repair. Briefly, a complicated time course of growth factor expression in the nerves and denervated muscles include (1) an early increase in FGF2 and IGF2, (2) reduced NGF between 2 and 14days after nerve transection and surgical repair, (3) a late rise in BDNF and (4) reduced IGF1 protein in the denervated muscles at 28days. These findings suggest that recovery of motor function after peripheral nerve injury is due, at least in part, to a complex regulation of nerve injury-associated neurotrophic factors and cytokines at the neuromuscular junctions of denervated muscles. In particular, the increase of FGF2 and concomittant decrease of NGF during the first week after facial nerve-nerve anastomosis in SD/RCS blind rats may prevent intramuscular axon sprouting and, in turn, reduce poly-innervation of the neuromuscular junction.

Simultaneous Detection of Both GDNF and GFRα1 Expression Patterns in the Mouse Central Nervous System

Glial cell line-derived neurotrophic factor (GDNF) is proposed as a therapeutic tool in Parkinson's disease, addiction-related disorders, and neurodegenerative conditions affecting motor neurons (MNs). Despite the high amount of work about GDNF therapeutic application, the neuronal circuits requiring GDNF trophic support in the brain and spinal cord (SC) are poorly characterized. Here, we defined GDNF and GDNF family receptor-α 1 (GFRα1) expression pattern in the brain and SC of newborn and adult mice. We performed systematic and simultaneous detection of EGFP and LacZ expressing alleles in reporter mice and asked whether modifications of this signaling pathway lead to a significant central nervous system (CNS) alteration. GFRα1 was predominantly expressed by neurons but also by an unexpected population of non-neuronal cells. GFRα1 expression pattern was wider in neonatal than in adult CNS and GDNF expression was restricted in comparison with GFRα1 at both developmental time points. The use of confocal microscopy to imaging X-gal deposits and EGFP allowed us to identify regions containing cells that expressed both proteins and to discriminate between auto and non-autotrophic signaling. We also suggested long-range GDNF-GFRα1 circuits taking advantage of the ability of the EGFP genetically encoded reporter to label long distance projecting axons. The complete elimination of either the ligand or the receptor during development did not produce major abnormalities, suggesting a preponderant role for GDNF signaling during adulthood. In the SC, our results pointed to local modulatory interneurons as the main target of GDNF produced by Clarke's column (CC) cells. Our work increases the understanding on how GDNF signals in the CNS and establish a crucial framework for posterior studies addressing either the biological role of GDNF or the optimization of trophic factor-based therapies.

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

BACKGROUND AND PURPOSE

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.

EXPERIMENTAL APPROACH

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.

KEY RESULTS

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.

CONCLUSIONS AND IMPLICATIONS

GDNF injection into the LC exerts prolonged analgesic effects on neuropathic pain in rats by enhancing descending noradrenergic inhibition.

Short-term ethanol exposure causes imbalanced neurotrophic factor allocation in the basal forebrain cholinergic system: a novel insight into understanding the initial processes of alcohol addiction

Alcohol ingestion affects both motor and cognitive functions. One brain system that is influenced by ethanol is the basal forebrain (BF) cholinergic projection system, which projects to diverse neocortical and limbic areas. The BF is associated with memory and cognitive function. Our primary interest is the examination of how regions that receive BF cholinergic projections are influenced by short-term ethanol exposure through alterations in the mRNA levels of neurotrophic factors [nerve growth factor/TrkA, brain-derived neurotrophic factor/TrkB, and glial-derived neurotrophic factor (GDNF)/GDNF family receptor α1]. Male BALB/C mice were fed a liquid diet containing 5 % (v/v) ethanol. Pair-fed control mice were maintained on an identical liquid diet, except that the ethanol was isocalorically substituted with sucrose. Mice exhibiting signs of ethanol intoxication (stages 1-2) were used for real-time reverse transcription-polymerase chain reaction analyses. Among the BF cholinergic projection regions, decreased levels of GDNF mRNA and increased levels of TrkB mRNA were observed in the basal nucleus, and increased levels of TrkB mRNA were observed in the cerebral cortex. There were no significant alterations in the levels of expression of relevant neurotrophic factors in the septal nucleus and hippocampus. Given that neurotrophic factors function in retrograde/anterograde or autocrine/paracrine mechanisms and that BF cholinergic projection regions are neuroanatomically connected, these findings suggested that an imbalanced allocation of neurotrophic factor ligands and receptors is an initial phenomenon in alcohol addiction. The exact mechanisms underlying this phenomenon in the BF cholinergic system are unknown. However, our results provide a novel notion for the understanding of the initial processes in alcohol addiction.

Neuroprotective effects of NGF, BDNF, NT-3 and GDNF on axotomized extraocular motoneurons in neonatal rats

Neurotrophic factors delivered from target muscles are essential for motoneuronal survival, mainly during development and early postnatal maturation. It has been shown that the disconnection between motoneurons and their innervated muscle by means of axotomy produces a vast neuronal death in neonatal animals. In the present work, we have evaluated the effects of different neurotrophic factors on motoneuronal survival after neonatal axotomy, using as a model the motoneurons innervating the extraocular eye muscles. With this purpose, neonatal rats were monocularly enucleated at the day of birth (postnatal day 0) and different neurotrophic treatments (NGF, BDNF, NT-3, GDNF and the mixture of BDNF+GDNF) were applied intraorbitally by means of a Gelfoam implant (a single dose of 5 μg of each factor). We first demonstrated that extraocular eye muscles of neonatal rats expressed these neurotrophic factors and therefore constituted a natural source of retrograde delivery for their innervating motoneurons. By histological and immunocytochemical methods we determined that all treatments significantly rescued extraocular motoneurons from axotomy-induced cell death. For the dose used, NGF and GDNF were the most potent survival factors for these motoneurons, followed by BDNF and lastly by NT-3. The simultaneous administration of BDNF and GDNF did not increase the survival-promoting effects above those obtained by GDNF alone. Interestingly, the rescue effects of all neurotrophic treatments persisted even 30 days after lesion. The administration of these neurotrophic factors, with the exception of NT-3, also prevented the loss of the cholinergic phenotype observed by 10 days after axotomy. At the dosage applied, NGF and GDNF were revealed again as the most effective neuroprotective agents against the axotomy-induced decrease in ChAT. Two remarkable findings highlighted in the present work that contrasted with other motoneuronal types after neonatal axotomy: first, the extremely high efficacy of NGF as a neuroprotective agent and, second, the long-lasting effects of neurotrophic administration on cell survival and ChAT expression in extraocular motoneurons.

Dopamine D2 receptor activation leads to an up-regulation of glial cell line-derived neurotrophic factor via Gβγ-Erk1/2-dependent induction of Zif268

Glial cell line-derived neurotrophic factor (GDNF) is a potent growth factor essential to the development, survival, and function of dopaminergic neurons (Airaksinen and Saarma 2002). The molecular mechanisms underlying GDNF expression remain elusive; thus, we set out to identify a signaling pathway that governs GDNF levels. We found that treatment of both differentiated dopaminergic-like SH-SY5Y cells and rat midbrain slices with the dopamine D2 receptor (D2R) agonist, quinpirole, triggered an increase in the expression of GDNF that was temporally preceded by an increase in the levels of zinc-finger protein 268 (Zif268), a DNA-binding transcription factor encoded by an immediate-early gene. Moreover, the D2R inhibitor raclopride blocked the increase of both GDNF and Zif268 expression following potassium-evoked dopamine release in SH-SY5Y cells. We used adenoviral delivery of small hairpin RNA (shRNA) targeting Zif268 to down-regulate its expression and found that Zif268 is specifically required for the D2R-mediated up-regulation of GDNF. Furthermore, the D2R-mediated induction of GDNF and Zif268 expression was dependent on Gβγ-mediated signaling and activation of extracellular signal-regulated kinase 1/2. Importantly, using chromatin immunoprecipitation assay, we identified a direct association of Zif268 with the GDNF promoter. These results suggest that D2R activation induces a Gβγ- and extracellular signal-regulated kinase 1/2-dependent increase in the level of Zif268, which functions to directly up-regulate the expression of GDNF.

Positive autoregulation of GDNF levels in the ventral tegmental area mediates long-lasting inhibition of excessive alcohol consumption

Glial cell line-derived neurotrophic factor (GDNF) is an essential growth factor for the survival and maintenance of the midbrain dopaminergic (DA-ergic) neurons. Activation of the GDNF pathway in the ventral tegmental area (VTA), where the GDNF receptors are expressed, produces a long-lasting suppression of excessive alcohol consumption in rats. Previous studies conducted in the DA-ergic-like cells, SHSY5Y, revealed that GDNF positively regulates its own expression, leading to a long-lasting activation of the GDNF signaling pathway. Here we determined whether GDNF activates a positive autoregulatory feedback loop in vivo within the VTA, and if so, whether this mechanism underlies the long-lasting suppressive effects of the growth factor on excessive alcohol consumption. We found that a single infusion of recombinant GDNF (rGDNF; 10 μg) into the VTA induces a long-lasting local increase in GDNF mRNA and protein levels, which depends upon de novo transcription and translation of the polypeptide. Importantly, we report that the GDNF-mediated positive autoregulatory feedback loop accounts for the long-lasting inhibitory actions of GDNF in the VTA on excessive alcohol consumption. Specifically, the long-lasting suppressive effects of a single rGDNF infusion into the VTA on excessive alcohol consumption were prevented when protein synthesis was inhibited, as well as when the upregulation of GDNF expression was prevented using short hairpin RNA to focally knock down GDNF mRNA in the VTA. Our results could have implications for the development of long-lasting treatments for disorders in which GDNF has a beneficial role, including drug addiction, chronic stress and Parkinson's disease.

Efficient gene therapy for Parkinson's disease using astrocytes as hosts for localized neurotrophic factor delivery

Current gene therapy approaches for Parkinson's disease (PD) deliver neurotrophic factors like glial cell line-derived neurotrophic factor (GDNF) or neurturin via neuronal transgene expression. Since these potent signaling-inducing neurotrophic factors can be distributed through long-distance neuronal projections to unaffected brain sites, this mode of delivery may eventually cause side effects. To explore a localized and thus potentially safer alternative for gene therapy of PD, we expressed GDNF exclusively in astrocytes and evaluated the efficacy of this approach in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and rat 6-hydroxy-dopamine (6-OHDA) models of PD. In terms of protection of dopaminergic cell bodies and projections, dopamine (DA) synthesis and behaviour, astrocyte-derived GDNF demonstrated the same efficacy as neuron-derived GDNF. In terms of safety, unilateral striatal GDNF expression in astrocytes did not result in delivery of bio-active GDNF to the contralateral hemispheres (potential off-target sites) as happened when GDNF was expressed in neurons. Thus, astrocytic GDNF expression represents a localized but efficient alternative to current gene therapeutic strategies for the treatment of PD, especially if viral vectors with enhanced tissue penetration are considered. Astrocytic neurotrophic factor expression may open new venues for neurotrophic factor-based gene therapy targeting severe diseases of the brain.

Development of an in vitro model to evaluate the regenerative capacity of adult brain-derived tyrosine hydroxylase-expressing dopaminergic neurons

The loss of nigral dopaminergic (DA) neurons is the disease-defining pathological change responsible for progressive motor dysfunction in Parkinson's disease. In this study, we sought to establish a culture method for adult rat tyrosine hydroxylase (TH)-immunoreactive DA neurons. In this context, we investigated the role of fibroblast growth factor 2 (FGF2), brain-derived neurotrophic factor (BDNF), transforming growth factor-β3 (TGF-β3), glial-derived neurotrophic factor (GDNF) and dibutyryl-cyclic AMP (dbcAMP) in these cultures. Culturing in the presence of FGF2, BDNF and GDNF enhanced the survival of DA neurons by 15-fold and promoted neurite growth. In contrast, dbcAMP promoted neurite growth in all neurons but did not enhance DA cell survival. This study demonstrates that long-term cultures of DA neurons can be established from the mature rat brain and that survival and regeneration of DA neurons can be manipulated by epigenetic factors such as growth factors and intracellular cAMP pathways.

Glial cell line-derived neurotrophic factor receptor-α1 expressed in striatum in trans regulates development and injury response of dopamine neurons of the substantia nigra

Many of the cellular effects of glial cell line-derived neurotrophic factor are initiated by binding to GNDF family receptor alpha-1 (GFRα1), and mediated by diverse intracellular signaling pathways, most notably through the Ret tyrosine kinase. Ret may be activated by the cell autonomous expression of GFRα1 ('in cis'), or by its non-cell autonomous presence ('in trans'), in either a soluble or immobilized state. GFRα1 is expressed in the striatum, a target of the dopaminergic projection of the substantia nigra. To determine whether post-synaptic expression of GFRα1 in striatum in trans has effects on the development or adult responses to injury of dopamine neurons, we have created transgenic mice in which GFRα1 expression is selectively increased in striatum and other forebrain targets of the dopaminergic projection. Post-synaptic GFRα1 has profound effects on the development of dopamine neurons, resulting in a 40% increase in their adult number. This morphologic effect was associated with an augmented motor response to amphetamine. In adult mice, post-synaptic GFRα1 expression did not affect neuron survival following neurotoxic lesion, but it did increase the preservation of striatal dopaminergic innervation. We conclude that post-synaptic striatal GFRα1 expression has important effects on the biology of dopamine neurons in vivo.

Distribution of glial cell line-derived neurotrophic factor receptor alpha-1 in the brain of adult zebrafish

Glial cell line-derived neurotrophic factor (GDNF) is a potent trophic factor for several types of neurons in the central and peripheral nervous systems. The biological activity of GDNF is mediated by a multicomponent receptor complex that includes a common transmembrane signaling component (the rearranged during transfection (RET) proto-oncogene product, a tyrosine kinase receptor) as well as a GDNF family receptor alpha (GFRalpha) subunit, a high-affinity glycosyl phosphatidylinositol (GPI)-linked binding element. Among the four known GFRalpha subunits, GFRalpha1 preferentially binds to GDNF. In zebrafish (Danio rerio) embryos, the expression of the GFRalpha1a and GFRalpha1b genes has been shown in primary motor neurons, the kidney, and the enteric nervous system. To examine the activity of GFRalpha in the adult brain of a lower vertebrate, we have investigated the localization of GFRalpha1a and GFRalpha1b mRNA and the GFRalpha1 protein in zebrafish. GFRalpha1a and GFRalpha1b transcripts were observed in brain extracts by reverse transcription-polymerase chain reaction. Whole-mount in-situ hybridization experiments revealed a wide distribution of GFRalpha1a and GFRalpha1b mRNAs in various regions of the adult zebrafish brain. These included the olfactory bulbs, dorsal and ventral telencephalic area (telencephalon), preoptic area, dorsal and ventral thalamus, posterior tuberculum and hypothalamus (diencephalon), optic tectum (mesencephalon), cerebellum, and medulla oblongata (rhombencephalon). Finally, expression patterns of the GFRalpha1 protein, detected immunohistochemically, correlated well with the mRNA expression and provided further insights into translational activity at the neuroanatomical level. In conclusion, the current study demonstrated that the presence of GFRalpha1 persists beyond the embryonic development of the zebrafish brain and, together with the GDNF ligand, is probably implicated in the brain physiology of an adult teleost fish.

Glial cell line-derived neurotrophic factor protects midbrain dopaminergic neurons against lipopolysaccharide neurotoxicity

Aberrant microglia activation causes dopaminergic neuronal loss and nitric oxide produced by microglia plays a critical role in dopaminergic neuronal degeneration. However, no study has determined if GDNF protects dopaminergic neurons via inhibiting nitric oxide generation in Parkinson's disease animal model. We report that GDNF not only reduces lipopolysaccharide-induced degeneration of dopaminergic neurons, suppresses microglia activation and nitric oxide generation, but also reverses the inhibition of phosphoinositide 3-kinase (PI3K) in dopaminergic neurons and microglia. It suggests that the neuroprotective effect of GDNF on dopaminergic neurons may be related to its suppression of microglia activation-mediated nitric oxide via releasing the inhibition of PI3K in both neurons and microglia.

GDNF is an endogenous negative regulator of ethanol-mediated reward and of ethanol consumption after a period of abstinence

BACKGROUND

We previously found that activation of the glial cell line-derived neurotrophic factor (GDNF) pathway in the ventral tegmental area (VTA) reduces ethanol-drinking behaviors. In this study, we set out to assess the contribution of endogenous GDNF or its receptor GFRalpha1 to the regulation of ethanol-related behaviors.

METHODS

GDNF and GFRalpha1 heterozygote mice (HET) and their wild-type littermate controls (WT) were used for the studies. Ethanol-induced hyperlocomotion, sensitization, and conditioned place preference (CPP), as well as ethanol consumption before and after a period of abstinence were evaluated. Blood ethanol concentration (BEC) was also measured.

RESULTS

We observed no differences between the GDNF HET and WT mice in the level of locomotor activity or in sensitization to ethanol-induced hyperlocomotion after systemic injection of a nonhypnotic dose of ethanol and in BEC. However, GDNF and GFRalpha1 mice exhibited increased place preference to ethanol as compared with their WT littermates. The levels of voluntary ethanol or quinine consumption were similar in the GDNF HET and WT mice, however, a small but significant increase in saccharin intake was observed in the GDNF HET mice. No changes were detected in voluntary ethanol, saccharin or quinine consumption of GFRalpha1 HET mice as compared with their WT littermates. Interestingly, however, both the GDNF and GFRalpha1 HET mice consumed much larger quantities of ethanol after a period of abstinence from ethanol as compared with their WT littermates. Furthermore, the increase in ethanol consumption after abstinence was found to be specific for ethanol as similar levels of saccharin intake were measured in the GDNF and GFRalpha1 HET and WT mice after abstinence.

CONCLUSIONS

Our results suggest that endogenous GDNF negatively regulates the rewarding effect of ethanol and ethanol-drinking behaviors after a period of abstinence.

Excessive alcohol consumption is blocked by glial cell line-derived neurotrophic factor

We previously found that activation of the glial cell line-derived neurotrophic factor (GDNF) pathway in the ventral tegmental area (VTA) reduces moderate alcohol (ethanol) intake in a rat operant self-administration paradigm. Here, we set out to assess the effect of GDNF in the VTA on excessive voluntary consumption of ethanol. Long-Evans rats were trained to drink large quantities of a 20% ethanol solution in an intermittent-access two-bottle choice drinking paradigm. The rats were given three 24-h sessions per week, and GDNF's actions were measured when rats achieved a baseline of ethanol consumption of 5.5g/kg/24h. We found that microinjection of GDNF into the VTA 10min before the beginning of an ethanol-drinking session significantly reduced ethanol intake and preference, but did not affect total fluid intake. We further show that GDNF greatly decreased both the first bout of excessive ethanol intake at the beginning of the session, and the later consummatory activity occurring during the dark cycle. These data suggest that GDNF is a rapid and long-lasting inhibitor of "binge-like" ethanol consumption.

The nigrostriatal dopamine system of aging GFRalpha-1 heterozygous mice: neurochemistry, morphology and behavior

Given the established importance of glial cell line-derived neurotrophic factor (GDNF) in maintaining dopaminergic neurotransmitter systems, the nigrostriatal system and associated behaviors of mice with genetic reduction of its high-affinity receptor, GDNF receptor (GFR)alpha-1 (GFRalpha-1(+/-)), were compared with wild-type controls. Motor activity and the stimulatory effects of a dopamine (DA) D1 receptor agonist (SKF 82958) were assessed longitudinally at 8 and 18 months of age. Monoamine concentrations and dopaminergic nerve terminals in the striatum and the number of dopaminergic neurons in the substantia nigra (SN) were assessed. The results support the importance of GFRalpha-1 in maintaining normal function of the nigrostriatal dopaminergic system, with deficits being observed for GFRalpha-1(+/-) mice at both ages. Motor activity was lower and the stimulatory effects of the DA agonist were enhanced for the older GFRalpha-1(+/-) mice. DA in the striatum was reduced in the GFRalpha-1(+/-) mice at both ages, and tyrosine hydroxylase-positive cell numbers in the SN were reduced most substantially in the older GFRalpha-1(+/-) mice. The combined behavioral, pharmacological probe, neurochemical and morphological measures provide evidence of abnormalities in GFRalpha-1(+/-) mice that are indicative of an exacerbated aging-related decline in dopaminergic system function. The noted deficiencies, in turn, suggest that GFRalpha-1 is necessary for GDNF to maintain normal function of the nigrostriatal dopaminergic system. Although the precise mechanism(s) for the aging-related changes in the dopaminergic system remain to be established, the present study clearly establishes that genetic reductions in GFRalpha-1 can contribute to the degenerative changes observed in this system during the aging process.

GDNF--a potential target to treat addiction

The glial cell line-derived neurotrophic factor (GDNF) is a secreted protein, best known for its role in the development of the central and peripheral nervous systems and the survival of adult dopaminergic neurons. More recently, accumulating evidence suggests that GDNF plays a unique role in negatively regulating the actions of drugs of abuse. In this article, we review these data and highlight the possibility that the GDNF pathway may be a promising target for the treatment of addiction.

Direct muscle delivery of GDNF with human mesenchymal stem cells improves motor neuron survival and function in a rat model of familial ALS

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease in which there is a progressive loss of motor neurons and their connections to muscle, leading to paralysis. In order to maintain muscle connections in a rat model of familial ALS (FALS), we performed intramuscular transplantation with human mesenchymal stem cells (hMSCs) used as "Trojan horses" to deliver growth factors to the terminals of motor neurons and to the skeletal muscles. hMSCs engineered to secrete glial cell line-derived neurotrophic factor (hMSC-GDNF) were transplanted bilaterally into three muscle groups. The cells survived within the muscle, released GDNF, and significantly increased the number of neuromuscular connections and motor neuron cell bodies in the spinal cord at mid-stages of the disease. Further, intramuscular transplantation with hMSC-GDNF was found to ameliorate motor neuron loss within the spinal cord where it connects with the limb muscles receiving transplants. While disease onset was similar in all the animals, hMSC-GDNF significantly delayed disease progression, increasing overall lifespan by up to 28 days, which is one of the largest effects on survival noted for this rat model of FALS. This preclinical data provides a novel and practical approach toward ex vivo gene therapy for ALS.

Altered glial cell line-derived neurotrophic factor (GDNF) concentrations in the brain of patients with depressive disorder: a comparative post-mortem study

INTRODUCTION

A growing body of evidence suggests that the glial cell line-derived neurotrophic factor (GDNF) is involved in the aetiopathology of mood disorders. GDNF is a neurotrophic factor from the transforming growth factor-beta-family, playing a role in cell development and function in the limbic system. This is the first study to examine GDNF concentration in different brain regions of patients with depressive disorder (DD).

MATERIAL AND METHODS

We used sandwich-ELISA-technique to ascertain GDNF concentration and Lowry assay for overall protein levels in post-mortem brain tissue of 7 patients with recurrent depressive disorder and 14 individuals without any neurological or psychiatric diagnoses. We included cortical regions as well as limbic area's (hippocampus, entorhinal cortex) basal ganglia (putamen, caudate nucleus), thalamus and cingulated gyrus.

RESULTS

We found a significant increase in GDNF concentration in the parietal cortex of patients with DD compared to the control group. In other regions the trend of an increased GDNF concentration did not reach statistical difference.

DISCUSSION

This proof of concept study supports previous findings of an alteration of the GDNF in patients with depressive disorder. However, for the first time a significant increase of GDNF in a cortical brain area was found in DD.

Changes in Glial cell line-derived neurotrophic factor expression in the rostral and caudal stumps of the transected adult rat spinal cord

Limited information is available regarding the role of endogenous Glial cell line-derived neurotrophic factor (GDNF) in the spinal cord following transection injury. The present study investigated the possible role of GDNF in injured spinal cords following transection injury (T(9)-T(10)) in adult rats. The locomotor function recovery of animals by the BBB (Basso, Beattie, Bresnahan) scale score showed that hindlimb support and stepping function increased gradually from 7 days post operation (dpo) to 21 dpo. However, the locomotion function in the hindlimbs decreased effectively in GDNF-antibody treated rats. GDNF immunoreactivty in neurons in the ventral horn of the rostral stump was stained strongly at 3 and 7 dpo, and in the caudal stump at 14 dpo, while immunostaining in astrocytes was also seen at all time-points after transection injury. Western blot showed that the level of GDNF protein underwent a rapid decrease at 7 dpo in both stumps, and was followed by a partial recovery at a later time-point, when compared with the sham-operated group. GDNF mRNA-positive signals were detected in neurons of the ventral horn, especially in lamina IX. No regenerative fibers from corticospinal tract can be seen in the caudal segment near the injury site using BDA tracing technique. No somatosensory evoked potentials (SEP) could be recorded throughout the experimental period as well. These findings suggested that intrinsic GDNF in the spinal cord could play an essential role in neuroplasticity. The mechanism may be that GDNF is involved in the regulation of local circuitry in transected spinal cords of adult rats.

Nigrostriatal neurons in rat express the glial cell line-derived neurotrophic factor receptor subunit c-RET

The substantia nigra neurons expressing c-RET, a glial cell line-derived neurotrophic factor (GDNF) receptor intracellular tyrosine kinase subunit, were investigated in rats by using a double labeling method which combined retrograde horseradish peroxidase (HRP) labeling after injection into the striatum with immunohistochemistry to c-RET. It was revealed that the distribution of c-RET-immunoreactive neurons and HRP-labeled nigrostriatal neurons overlapped. Numerous double-labeled HRP/c-RET neurons were found in the substantia nigra pars compacta with predominate distribution ipsilateral to the injected striatum. Semiquantitative cell count indicated that a large percentage (97%) of HRP-labeled neurons showed c-RET immunoreactivity. Furthermore, double-labeled HRP/c-RET ones constituted only 61% of total c-RET-immunoreactive neurons in the substantia nigra ipsolateral to the injected striatum. Taken together with previous observations on glial cell line-derived neurotrophic factor in the basal ganglia, this study provides evidence that the c-RET protein may mediate biological activity of GDNF family ligands in most of projecting neurons in the substantia nigra pars compacta where the dopaminergic neurons are numerously distributed. Specially, it suggests that c-RET-mediating signaling cascades may play important roles in neuron-glial interaction that support and sustain nigrostriatal neuronal circuits in the basal ganglia.

Retrograde signaling onto Ret during motor nerve terminal maturation

Establishment of the neuromuscular synapse requires bidirectional signaling between the nerve and muscle. Although much is known on nerve-released signals onto the muscle, less is known of signals important for presynaptic maturation of the nerve terminal. Our results suggest that the Ret tyrosine kinase receptor transmits a signal in motor neuron synapses that contribute to motor neuron survival and synapse maturation at postnatal stages. Ret is localized specifically to the presynaptic membrane with its ligands, GDNF (glial cell line-derived neurotrophic factor)/NTN (neurturin), expressed in skeletal muscle tissue. Lack of Ret conditionally in cranial motor neurons results in a developmental deficit of maturation and specialization of presynaptic neuromuscular terminals. Regeneration of Ret-deficient adult hypoglossal motor neurons is unperturbed, but despite contact with the unaffected postsynaptic specializations, presynaptic axon terminal maturation is severely compromised in the absence of Ret signaling. Thus, Ret transmits a signal in motor nerve terminals that participate in the organization and maturation of presynaptic specializations during development and during regeneration in the adult.

Aspiration of a cervical spinal contusion injury in preparation for delayed peripheral nerve grafting does not impair forelimb behavior or axon regeneration

A peripheral nerve graft model was used to examine axonal growth after a unilateral cervical (C) contusion injury in adult rats and to determine if manipulation of an injury site prior to transplantation affects spontaneous behavioral recovery. After a short delay (7 d) the epicenter of a C4 contusion was exposed and aspirated without harming the cavity walls followed by apposition with one end of a pre-degenerated tibial nerve to the rostral cavity wall. After a longer delay (28 d) the aspirated cavity was treated with GDNF to promote regeneration by chronically injured neurons. In both groups forelimb and hindlimb locomotor scores decreased significantly 2 d after lesion site manipulation, but by 7 d, the forelimb score was not different from the pre-manipulation score. There was no significant difference in grid walking or grip strength scores for the affected forelimb in either group 7 d after contusion vs. 7 d after manipulation. Over 1500 brain stem and propriospinal neurons grew axons into the graft with either delay. These results demonstrate that a contusion injury site can be manipulated prior to transplantation without causing long-lasting forelimb or hindlimb behavioral deficits and that peripheral nerve grafts support axonal growth after acute or chronic contusion injury.

Tissue distribution of Ret, GFRalpha-1, GFRalpha-2 and GFRalpha-3 receptors in the human brainstem at fetal, neonatal and adult age

Occurrence and localization of receptor components of the glial cell line-derived neurotrophic factor (GDNF) family ligands, the Ret receptor tyrosine kinase and the GDNF family receptor (GFR) alpha-1 to -3, were examined by immunohistochemistry in the normal human brainstem at fetal, neonatal, and adult age. Immunoreactive elements were detectable at all examined ages with uneven distribution and consistent pattern for each receptor. As a rule, the GFRalpha-1 and GFRalpha-2 antisera produced the most abundant and diffuse tissue labelling. Immunoreactive perikarya were observed within sensory and motor nuclei of cranial nerves, dorsal column nuclei, olivary nuclear complex, reticular formation, pontine nuclei, locus caeruleus, raphe nuclei, substantia nigra, and quadrigeminal plate. Nerve fibers occurred within gracile and cuneate fasciculi, trigeminal spinal tract and nucleus, facial, trigeminal, vestibular and oculomotor nerves, solitary tract, medial longitudinal fasciculus, medial lemniscus, and inferior and superior cerebellar peduncles. Occasionally, glial cells were stained. Age changes were appreciable in the distribution pattern of each receptor. On the whole, in the grey matter, labelled perikarya were more frequently observed in pre- and perinatal than in adult specimens; on the other hand, in discrete regions, nerve fibers and terminals were abundant and showed a plexiform arrangement only in adult tissue; finally, distinct fiber systems in the white matter were immunolabelled only at pre- and perinatal ages. The results obtained suggest the involvement of Ret and GFRalpha receptors signalling in processes subserving both the organization of discrete brainstem neuronal systems during development and their functional activity and maintenance in adult life.

Constitutive Ret activity in knock-in multiple endocrine neoplasia type B mice induces profound elevation of brain dopamine concentration via enhanced synthesis and increases the number of TH-positive cells in the substantia nigra

Ret is the common signaling receptor for glial cell line-derived neurotrophic factor (GDNF) and other ligands of the GDNF family that have potent effects on brain dopaminergic neurons. The Met918Thr mutation leads to constitutive activity of Ret receptor tyrosine kinase, causing the cancer syndrome called multiple endocrine neoplasia type B (MEN2B). We used knock-in MEN2B mice with the Ret-MEN2B mutation to study the effects of constitutive Ret activity on the brain dopaminergic system and found robustly increased concentrations of dopamine (DA) and its metabolites in the striatum, cortex, and hypothalamus. The concentrations of brain serotonin were not affected and those of noradrenaline were slightly increased only in the lower brainstem. Tyrosine hydroxylase (TH) protein levels were increased in the striatum and substantia nigra/ventral tegmental area (SN/VTA), and TH mRNA levels were increased in SN/VTA of MEN2B mice, suggesting that constitutive Ret activity increases DA levels by increasing its synthesis. Also, the striatal DA transporter protein levels in the MEN2B mice were increased, which agrees with increased sensitivity of these mice to the stimulatory effects of cocaine. In the SN pars compacta of homozygous MEN2B mice, we found a 26% increase in the number of TH-positive cells, but no differences were found in the VTA. Thus, we show here that the constitutive Ret activity in mice is sufficient to increase the number of dopaminergic neurons and leads to profound elevation of brain DA concentration. These data clearly suggest that Ret activity per se can have a direct biological function that actively changes and shapes the brain dopaminergic system.

Tissue distribution of neurturin, persephin and artemin in the human brainstem at fetal, neonatal and adult age

The occurrence of the glial cell line-derived neurotrophic factor (GDNF) family ligands neurturin (NTN), persephin (PSP), and artemin (ART) was examined by immunohistochemistry in the normal human brainstem at pre-, perinatal and adult age. Immunolabelled neurons were unevenly distributed and each trophin had a consistent distribution pattern. As a rule, the NTN antiserum produced the most abundant and diffuse tissue labelling, whereas the lowest density of positive elements was observed after ART immunostaining. Labelling for NTN, PSP, and ART occurred at all examined ages. For each trophin, neuronal perikarya were observed within sensory and motor nuclei of cranial nerves, dorsal column nuclei, olivary nuclear complex, reticular formation, pontine nuclei, locus caeruleus, raphe nuclei, substantia nigra, and quadrigeminal plate. Nerve fibers occurred within gracile and cuneate fasciculi, trigeminal spinal tract and nucleus, oculomotor and facial nerves, solitary tract, vestibular nerve, medial longitudinal fasciculus, medial and lateral lemnisci, and inferior and superior cerebellar peduncles. Age changes were detected in the distribution pattern for each trophin. On the whole, in the grey matter, labelled perikarya were more frequently observed in pre- and perinatal than in adult specimens; on the other hand, in discrete regions, nerve fibers and terminals were abundant and showed a definite arrangement only in adult tissue; finally, distinct fiber systems in the white matter were immunolabelled only at pre- and perinatal ages. The results support the concept of a trophic involvement of NTN, PSP, and ART in the development, functional activity and maintenance of a variety of human brainstem neuronal systems.

Distribution of RET immunoreactivity in the rodent spinal cord and changes after nerve injury

RET (for "rearranged during transfection") is a transmembrane tyrosine kinase signaling receptor for members of the glial cell line-derived neurotrophic factor (GDNF) family of ligands. We used RET immunohistochemistry (IHC), double-labeling immunofluorescence (IF), and in situ hybridization (ISH) in adult naïve and nerve-injured rats to study the distribution of RET in the spinal cord. In the dorsal horn, strong RET-immunoreactive (-ir) fibers were abundant in lamina II-inner (II(i)), although this labeling was preferentially observed after an antigen-unmasking procedure. After dorsal rhizotomy, RET-ir fibers in lamina II(i) completely disappeared from the dorsal horn, indicating that they were all primary afferents. After peripheral axotomy, RET-ir in primary afferents decreased in lamina II(i) and appeared to increase slightly in laminae III and IV. RET-ir was also observed in neurons and dendrites throughout the dorsal horn. Some RET-ir neurons in lamina I had the morphological appearance of nociceptive projection neurons, which was confirmed by the finding that 53% of RET-ir neurons in lamina I colocalized with neurokinin-1. GDNF-ir terminals were in close proximity to RET-ir neurons in the superficial dorsal horn. In the ventral horn, RET-ir was strongly expressed by motoneurons, with the strongest staining in small, presumably gamma-motoneurons. Increased RET expression following peripheral axotomy was most pronounced in alpha-motoneurons. The expression and regulation pattern of RET in the spinal cord are in line with its involvement in regenerative processes following nerve injury. The presence of RET in dorsal horn neurons, including nociceptive projection neurons, suggests that RET also has a role in signal transduction at the spinal level. This role may include mediating the effects of GDNF released from nociceptive afferent fibers.

A glial cell line-derived neurotrophic factor (GDNF):tetanus toxin fragment C protein conjugate improves delivery of GDNF to spinal cord motor neurons in mice

Glial cell line-derived neurotrophic factor (GDNF) has shown robust neuroprotective and neuroreparative activities in various animal models of Parkinson's Disease or amyotrophic lateral sclerosis (ALS). The successful use of GDNF as a therapeutic in humans, however, appears to have been hindered by its poor bioavailability to target neurons in the central nervous system (CNS). To improve delivery of exogenous GDNF protein to CNS motor neurons, we employed chemical conjugation techniques to link recombinant human GDNF to the neuronal binding fragment of tetanus toxin (tetanus toxin fragment C, or TTC). The predominant species present in the purified conjugate sample, GDNF:TTC, had a molecular weight of approximately 80 kDa as determined by non-reducing SDS-PAGE. Like GDNF, addition of GDNF:TTC to culture media of neuroblastoma cells expressing GFRalpha-1/c-RET produced a dose-dependent increase in cellular phospho-c-RET levels. Treatment of cultured midbrain dopaminergic neurons with either GDNF or the conjugate similarly promoted both DA neuron survival and neurite outgrowth. However, in contrast to mice treated with GDNF by intramuscular injection, mice receiving GDNF:TTC revealed intense GDNF immunostaining associated with spinal cord motor neurons in fixed tissue sections. That GDNF:TTC provided neuroprotection of axotomized motor neurons in neonatal rats further revealed that the conjugate retained its GDNF activity in vivo. These results indicate that TTC can serve as a non-viral vehicle to substantially improve the delivery of functionally active growth factors to motor neurons in the mammalian CNS.

Dynamic expression of neurotrophic factor receptors in postnatal spinal motoneurons and in mouse model of ALS

Neurotrophic factors support the survival of spinal motoneurons (MNs) and have been considered as strong candidates for treating motoneuron diseases. However, it is unclear if the right combination of neurotrophic factor receptors is present in postnatal spinal MNs. In this study, we show that the level of c-ret expression remains relatively stable in embryonic and postnatal spinal MNs. In contrast, the mRNA and protein of GFRalpha1 and -2 are progressively down-regulated in postnatal life. By 3 and 6 months of age, both receptors are barely detectable in spinal MNs. The down-regulation of GFRalpha1 appears accelerated in transgenic mice expressing mutant SOD1(G93A). Despite the progressive loss of GFRalpha1 and -2, phosphorylation of c-ret shows no detectable reduction on tyrosine residues or on serine 696. In addition to the GFRalpha subunits, expression of TrkB also shows a dynamic change. During embryogenesis, there is twice as much full-length TrkB as the truncated TrkB isoform. However, this ratio is reversed in postnatal spinal cord. Expression of the mutant SOD1(G93A) appears to have no effect on the TrkB receptor ratio. Taken together, our data indicate that the expression of neurotrophic factor receptors, GFRalpha1, -2, and TrkB, is not static, but undergoes dynamic changes in postnatal spinal MNs. These results provide insights into the use of neurotrophic factors as therapeutic agents for ALS.

Glial cell line-derived neurotrophic factor mediates the desirable actions of the anti-addiction drug ibogaine against alcohol consumption

Alcohol addiction manifests as uncontrolled drinking despite negative consequences. Few medications are available to treat the disorder. Anecdotal reports suggest that ibogaine, a natural alkaloid, reverses behaviors associated with addiction including alcoholism; however, because of side effects, ibogaine is not used clinically. In this study, we first characterized the actions of ibogaine on ethanol self-administration in rodents. Ibogaine decreased ethanol intake by rats in two-bottle choice and operant self-administration paradigms. Ibogaine also reduced operant self-administration of ethanol in a relapse model. Next, we identified a molecular mechanism that mediates the desirable activities of ibogaine on ethanol intake. Microinjection of ibogaine into the ventral tegmental area (VTA), but not the substantia nigra, reduced self-administration of ethanol, and systemic administration of ibogaine increased the expression of glial cell line-derived neurotrophic factor (GDNF) in a midbrain region that includes the VTA. In dopaminergic neuron-like SHSY5Y cells, ibogaine treatment upregulated the GDNF pathway as indicated by increases in phosphorylation of the GDNF receptor, Ret, and the downstream kinase, ERK1 (extracellular signal-regulated kinase 1). Finally, the ibogaine-mediated decrease in ethanol self-administration was mimicked by intra-VTA microinjection of GDNF and was reduced by intra-VTA delivery of anti-GDNF neutralizing antibodies. Together, these results suggest that GDNF in the VTA mediates the action of ibogaine on ethanol consumption. These findings highlight the importance of GDNF as a new target for drug development for alcoholism that may mimic the effect of ibogaine against alcohol consumption but avoid the negative side effects.

Intrathecal injection of GDNF and BDNF induces immediate early gene expression in rat spinal dorsal horn

Glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) are potent trophic factors for dorsal root ganglion cells. In addition, these factors are produced in subsets of dorsal root ganglion cells and transported anterogradely to their terminals in the superficial dorsal horn of the spinal cord, where they constitute the only source of GDNF and BDNF. We investigated the effect of 10 mug GDNF and BDNF injected by lumbar puncture on the expression of the immediate early gene (IEG) products c-Fos, c-Jun, and Krox-24 in the adult rat dorsal horn. In the dorsal horn of S1 spinal segments, GDNF and BDNF induced a strong increase in IEG expression, which was most pronounced in laminae I and II (2.9- to 4.5-fold). More distal from the injection site, in the dorsal horn of L1/L2 spinal segments, the increase in IEG expression was less pronounced, suggesting a concentration-dependent effect. In order to explain the effects of intrathecally injected GDNF, we investigated whether lumbo-sacral dorsal horn neurons expressed RET protein, the signal-transducing element of the receptor complex for GDNF. It was found that several of these neurons contained RET immunoreactivity and that some of the RET-labeled neurons had the appearance of nociceptive-specific cells, confirming their presumed role in pain transmission. Additionally, using double-labeling immunofluorescence combined with confocal microscopy, it was found that after intrathecal GDNF injection 35% of c-Fos-labeled cells were also labeled for RET. These results demonstrate that intrathecally administered GDNF and BDNF induce IEG expression in dorsal horn neurons in the adult rat, supposedly by way of their cognate receptors, which are present on these neurons. We further suggest that the endogenous release of GDNF and BDNF, triggered by nociceptive stimuli, is involved in the induction of changes in spinal nociceptive transmission as in various pain states.

Ret, GFRalpha‐1, GFRalpha‐2 and GFRalpha‐3 receptors in the human hippocampus and fascia dentata

The immunohistochemical occurrence and localization of the receptor components of the glial cell line-derived neurotrophic factor (GDNF) family ligands, the Ret receptor tyrosine kinase and GDNF family receptor (GFR) alpha-1 to -3, is described in the human post-mortem hippocampal formation at pre- and full-term newborn, and adult age. Two different antibodies for each of the four-receptor molecules were used. Western blot analysis indicates that the availability of GFRalpha receptor proteins may vary with age and post-mortem delay. The immunohistochemical detectability of GFRalpha-1, GFRalpha-2, GFRalpha-3 and Ret receptor molecules is shown in the rat up to 72 h post-mortem. In the human specimens, labelled neuronal perikarya were detectable for each receptor protein at all examined ages, with prevalent localization in the pyramidal layer of the Ammon's horn and hilus and granular layer of the fascia dentata. In the adult subjects, abundant punctate-like structures were also present. Labelled glial elements were identifiable. Comparison of the pattern of immunoreactive elements among young and adult subjects suggests that the intracellular distribution of the GDNF family ligands may vary between pre- and perinatal life and adult age. The results obtained suggest the involvement of the Ret and GFRalpha receptors signalling in processes subserving both the organization of this cortical region during development and the functional activity and maintenance of the mature hippocampal neurons.

Anatomical basis of glial cell line-derived neurotrophic factor expression in the striatum and related basal ganglia during postnatal development of the rat

There is increasing evidence that glial cell line-derived neurotrophic factor (GDNF) plays a role as a limiting, striatal target-derived neurotrophic factor for dopamine neurons of the substantia nigra pars compacta (SNpc) by regulating the magnitude of the first phase of postnatal natural cell death which occurs in these neurons. While it has been shown that GDNF mRNA is relatively abundant in postnatal striatum, the cellular basis of its expression has been unknown. We therefore used nonradioactive in situ hybridization and immunohistochemistry to examine the cellular basis of GDNF mRNA and protein expression, respectively, in postnatal striatum and related structures. We found that GDNF mRNA is expressed within medium-sized striatal neurons. Expression in glia was not observed. At the protein level, regionally, GDNF expression in striatum was observed in striosomal patches, as previously described. At a cellular level a few neurons were observed, but they do not account for the striosomal pattern. This pattern is predominantly due to GDNF-positive neuropil. Some of this neuropil arises from tyrosine hydroxylase-positive nigro-striatal dopaminergic afferents. Astrocytic processes do not appear to contribute to the striosomal pattern. GDNF-positive fibers are identified not only within intrinsic striatal neuropil, but also in fibers within the major striatal efferent targets: the globus pallidus, the entopeduncular nucleus, and the SN pars reticulata. We conclude that during normal postnatal development, medium-sized neurons are the principal source of GDNF within the striatum.

Glial cell line-derived neurotrophic factor (GDNF) is required for differentiation of pontine noradrenergic neurons and patterning of central respiratory output

Genetic mutations affecting signaling by glial cell line-derived neurotrophic factor (GDNF) perturb development of breathing in mice and are associated with congenital central hypoventilation syndrome in humans. However, the role of GDNF in development of brainstem neurons that control breathing is largely unknown. The present study demonstrates that genetic loss of GDNF decreases the number of tyrosine hydroxylase (TH) neurons in the pontine A5 noradrenergic cell group, a major source of inhibitory input to the medullary respiratory pattern generator. This phenotype is associated with a significant increase in the frequency of central respiratory output recorded from the fetal medulla-spinal cord in vitro. In dissociate cultures of the A5 region from rat embryos, GDNF increases TH cell number and neurite growth without affecting total neuronal survival or proliferation of TH neurons. These effects of GDNF are inhibited by function blocking antibodies against endogenous brain-derived neurotrophic factor (BDNF), indicating that GDNF requires BDNF as a cofactor to stimulate differentiation of A5 neurons. Our findings demonstrate that GDNF is required for development of pontine noradrenergic neurons in vivo and indicate that defects in the A5 cell group may contribute to the effects of genetic disruption of GDNF signaling on respiratory control.

Dopaminergic innervation of forebrain by ventral mesencephalon in organotypic slice co-cultures: Effects of GDNF

Numerous studies have verified the ability of glial cell line-derived neurotrophic factor (GDNF) to protect or rescue neurons in models of Parkinson's disease. However, the role of GDNF in the development of dopaminergic (DA) neurons remains unclear. We investigated the hypothesis that GDNF is a target protein for the DA neurons of the mesencephalon forming the nigrostriatal pathway in an in vitro rat model. Organotypic slice cultures were prepared from tissue isolated from postnatal rat pups including but not limited to the substantia nigra (SN), striatum, and cerebral cortex. These cultures were maintained for up to 100 days in vitro. In the absence of exogenous GDNF, DA neurons from the SN grew into the striatum but not the cerebral cortex or hippocampus as determined by immunostaining for tyrosine hydroxylase. The addition of exogenous GDNF increased the survival of DA neurons and also enhanced the number of dopaminergic processes innervating the striatum. GDNF also induced DA innervation of the cerebral cortex but not hippocampus. In conclusion, our studies indicate that the normal pattern of innervation by DA neurons of the mesencephalon can be recapitulated with organotypic co-cultures and that this pattern can be altered by GDNF.

Differential effects of growth/differentiation factor 5 and glial cell line-derived neurotrophic factor on dopaminergic neurons and astroglia in cultures of embryonic rat midbrain

Parkinson's disease is characterized by the progressive degeneration of midbrain dopaminergic neurons. Several studies have examined the effects of the dopaminergic neurotrophins growth/differentiation factor 5 (GDF5) and glial cell line-derived neurotrophic factor (GDNF) on these neurons in vitro. However, there is little information regarding their effects on astroglial cells. Here, the effects of GDF5 and GDNF on dopaminergic neuronal and astroglial survival and differentiation in embryonic rat midbrain cultures were examined. Both GDF5 and GDNF enhanced the survival and differentiation of dopaminergic neurons. GDF5 significantly increased the survival of astroglial cells, whereas GDNF had no significant effect on these cells. The possible involvement of astroglia in the dopaminergic neurotrophic effect induced by GDF5 was investigated by examining the effect of GDF5 on the survival of dopaminergic neurons in glia-depleted midbrain cultures. There was no significant difference between the survival of dopaminergic neurons in glia-depleted cultures treated with GDF5 and that in mixed cell cultures treated with GDF5, suggesting that GDF5 acts directly on dopaminergic neurons in exerting its neurotrophic effect. GDF5 and GDNF have been established as potent neurotrophic factors for dopaminergic neurons. However, the effects of adding a combination of these neurotrophins to midbrain cultures have not been previously examined. The present study found that combined treatment with GDF5 and GDNF significantly increased the survival of dopaminergic neurons in cultures compared with that in cultures treated with either neurotrophin alone. This was an additive effect, indicating that these neurotrophins act on separate subpopulations of dopaminergic neurons.

GDNF and Addiction

Biochemical adaptations to drugs of abuse and alcohol are especially profound in midbrain dopaminergic neurons. Long-lasting molecular and structural changes in mesolimbic dopaminergic neurons that result from chronic exposure to drugs of abuse and alcohol are thought to underlie adverse behaviors such as compulsive drug seeking and relapse. Recent studies suggest that a subset of these changes is prevented/reversed by activation of the glial cell line-derived neurotrophic factor (GDNF) signaling pathway. Behavioral effects of drugs of abuse such as cocaine and alcohol are also negatively regulated by GDNF: inhibition of the endogenous GDNF pathway enhances the activity of drugs of abuse, while administration of GDNF reduces the severity of the effects. In this review, we summarize the data implicating GDNF as a negative regulator of drug and alcohol addiction. We also provide evidence to suggest that therapies that activate GDNF signaling may be useful for the treatment of drug and alcohol addiction.

Overexpression of glial cell line-derived neurotrophic factor in the CNS rescues motoneurons from programmed cell death and promotes their long-term survival following axotomy

To study the role of one of the most potent motoneuron (MN) survival factors, glial cell line-derived neurotrophic factor (GDNF) derived from the CNS, we generated transgenic animals overexpressing GDNF under the control of an astrocyte-specific GFAP promoter. In situ hybridization revealed that GDNF was expressed at high levels in astrocytes throughout the brain and spinal cord. We analyzed the effects of CNS-derived GDNF on MN survival during the period of programmed cell death (PCD) and after nerve axotomy. In GFAP-GDNF mice at E15, E18, and P1, the survival of brachial MNs was increased on average by 30%, lumbar MNs by 20%, and thoracic MNs at P1 by 33%. GDNF also prevented MN PCD in several cranial motor nuclei. We demonstrated for the first time that the number of MNs in the mouse abducens nucleus was also increased by 40%, thus extending known MN populations that are responsive to GDNF. Next, we tested if GDNF could support complete and relatively long-term survival of MNs following neonatal facial nerve axotomy. We found that virtually all MNs (91%) in GFAP-GDNF mice survived for up to 18 weeks post-axotomy. This is the longest GDNF-mediated survival of neonatal MNs reported following axotomy. Most of surviving MNs were not atrophic, and MN-specific ChAT and neurofilament immunoreactivity (IR) were preserved. Furthermore, GDNF attenuated axotomy-induced astroglial activation. These data demonstrate that overexpression of GDNF in the CNS has very profound effects on MN survival both during the PCD period and after neuronal injury. GFAP-GDNF mice will be valuable to study the effects of CNS-derived GDNF in mouse models of MN degenerative diseases and axonal regeneration in vivo.

Stroke and TGF-beta proteins: glial cell line-derived neurotrophic factor and bone morphogenetic protein

Recent studies have indicated that proteins in the transforming growth factor-beta superfamily alter damage induced by various neuronal injuries. Of these proteins, glial cell line-derived neurotrophic factor (GDNF) and bone morphogenetic protein-7 (BMP-7) have unique protective and regenerative effects in stroke animals. Delivery of GDNF or BMP-7 to brain tissue reduced cerebral infarction and improved motor functions in stroke animals. Pretreatment with these factors reduced caspase-3 activity and DNA fragmentation in the ischemic brain region, suggesting that antiapoptotic effects are involved. Beside the protective effects, BMP-7 given after stroke improves locomotor function. These regenerative effects of BMP-7 may involve the enhancement of dendritic growth and remodeling. In this review, we illustrate the neuroprotective and neuroregenerative properties of GDNF and BMP-7 and emphasize their therapeutic potential for stroke.

Quantitative analyses of GFRα-1 and GFRα-2 mRNAs and tyrosine hydroxylase protein in the nigrostriatal system reveal bilateral compensatory changes following unilateral 6-OHDA lesions in the rat

Copy numbers of mRNAs for GFRalpha-1 and GFRalpha-2, the preferred receptors for glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) were determined by real-time quantitative RT-PCR (QRT-PCR). Receptor expression was assessed in striatum (ST) and substantia nigra (SN) of normal rats and rats acutely or progressively lesioned by 6-OHDA injected into the medial forebrain bundle or ST, respectively. GFRalpha-1 mRNA was clearly detected in normal ST. In normal SN, significantly higher expression of both receptors was observed. At 4 weeks after acute lesion, GFRalpha-2 mRNA was markedly decreased in SN bilaterally, whereas GFRalpha-1 mRNA in SN and ST was not affected. A progressive lesion resulted in a progressive decrease of GFRalpha1 mRNA in ST bilaterally. In SN, levels of GFRalpha-1 mRNA were not significantly affected by a progressive lesion, whereas GFRalpha-2 mRNA was markedly decreased bilaterally. Quantitative western blotting standardized against tyrosine hydroxylase (TH) protein from PC12 cells revealed the expected decrease in TH protein in lesioned SN, but also significant increases in TH protein in contralateral, unlesioned SNs at 4 weeks after both acute and progressive lesions. These data suggest that previously unrecognized compensatory changes in the nigrostriatal system occur in response to unilateral dopamine depletion. Since the changes observed in receptor expression did not always parallel loss of dopamine neurons, cells in addition to the nigral dopamine neurons appear to be affected by a 6-OHDA insult and are potential targets for the neurotrophic factors, GDNF and NTN.

Glial cell line-derived neurotrophic factor receptor GFRα1 is expressed in the rat striatum during postnatal development

Dopamine neurons of the substantia nigra (SN) undergo a natural cell death event which is biphasic, with peaks at postnatal days (PNDs) 2 and 14. There is growing evidence that GDNF functions as a striatal target-derived neurotrophic factor to regulate the first phase. It has been unknown whether the GDNF receptor, GFRalpha1, may play a role in regulating either phase. To evaluate a possible role for GFRalpha1 we have examined its expression throughout postnatal development in the SN and particularly in the striatum, where its expression has been uncertain. GFRalpha1 mRNA is highly expressed in SN, as previously shown, with highest levels at PND14-28. We find that it is also expressed in striatum with a similar time course, but with a more discrete period of maximal expression between PND10 and PND14. The cellular basis of this maximum of expression is an increased number of GFRalpha1 mRNA-positive medium-sized neurons evenly distributed within the striatum. Immunostaining reveals GFRalpha1 protein-positive neurons with a similar morphology and distribution. We conclude that GFRalpha1 is expressed in striatum maximally late in postnatal development. In this location it may act in trans to influence the viability and development of nigral dopamine neurons.

Local GDNF expression mediated by lentiviral vector protects facial nerve motoneurons but not spinal motoneurons in SOD1G93A transgenic mice

Approximately 2% of amyotrophic lateral sclerosis (ALS) cases are associated with mutations in the cytosolic Cu/Zn superoxide dismutase 1 (SOD1) gene. Transgenic SOD1 mice constitute useful models of ALS to screen therapeutical approaches. Glial cell line-derived neurotrophic factor (GDNF) holds promises for the treatment of motoneuron disease. In the present study, GDNF expression in motoneurons of SOD1(G93A) transgenic mice was assessed by facial nucleus or intraspinal injection of lentiviral vectors (LV) encoding GDNF. We show that lentiviral vectors allow the expression for at least 12 weeks of GDNF that was clearly detected in motoneurons. This robust intraspinal expression did, however, not prevent the loss of motoneurons and muscle denervation of transgenic mice. In contrast, LV-GDNF induced a significant rescue of motoneurons in the facial nucleus and prevented motoneuron atrophy. The differential effect of GDNF on facial nucleus versus spinal motoneurons suggests different vulnerability of motoneurons in ALS.