Nicotine is neuroprotective to neonatal neurons of sympathetic ganglion in rat.

Sympathetic neurons of SCG are dependent on availability of nerve growth factor (NGF) for their survival. SCG neurons express nicotinic receptors (nAChR) whose expression levels are modulated by nicotine. Nicotine exerts multiple effects on neurons, including neuroprotection, through nAChR binding. Although sympathetic neurons express robust levels of nAChR, a possible neuroprotective role for nicotine in these neurons is not well-understood. Therefore we determined the effect of nicotine exposure on survival of SCG neurons during NGF withdrawal in a well-established cell culture system. NGF was withdrawn in rat neonatal SCG neuron cultures which were then treated with either 10 µM nicotine alone or with nAChR antagonists 0.1 µM α-bungarotoxin (antagonist for α7 subunit bearing nAChR) and 10 µM mecamylamine (non-specific antagonist for ganglionic nAChR) for 48 h. Apoptotic death was determined by TUNEL staining. Cell survival was also determined by MTS assay. Western blot analysis of ERK1/2 was also performed. Our results showed that exposure to 10 µM nicotine significantly reduced apoptotic cell death in SCG neurons resulting from NGF withdrawal as shown by fewer TUNEL positive cells. The MTS assay results also revealed that 10 µM nicotine concentration significantly increased cell survival thus indicating neuroprotective effect of nicotine against cell death resulting from NGF withdrawal. Nicotinic receptor antagonists (bungarotoxin & mecamylamine) attenuated the effect of nicotine's action of neuroprotection. Western blot analysis showed an increased expression of ERK1/2 in nicotine treated cultures suggesting nicotine provided neuroprotection in SCG neurons by increasing the expression of ERK1/2 through nicotinic receptor dependent mechanisms.

Dissociation of JNK Activation from Elevated Levels of Reactive Oxygen Species, Cytochrome c Release, and Cell Death in NGF-Deprived Sympathetic Neurons.

Withdrawal of nerve growth factor (NGF) from sympathetic neurons causes their apoptotic death. Activation of c-Jun NH2-terminal kinase (JNK) may contribute to this death by the induction and phosphorylation of pro-apoptotic Bcl-2 proteins, such as Bax, that are involved in cytochrome c release from mitochondria and reactive oxygen species (ROS) production. Induction of either JNK or ROS may stimulate the other, and both may regulate release of apoptogenic factors from the mitochondria. In order to discern the relationship between JNK and ROS in apoptosis, we treated NGF-deprived, mouse sympathetic neurons with a JNK inhibitor and examined the effect on several important apoptotic events. Block of JNK activation prevented induction of c-Jun expression and resulted in a dose-dependent, yet surprisingly modest, increase in cell survival after 48 h of NGF deprivation. JNK suppression was also not sufficient to prevent the elevation in ROS or the release of cytochrome c from the mitochondria in NGF-deprived sympathetic neurons. Bax deletion prevents apoptotic death of NGF-deprived neurons by preventing release of cytochrome c from their mitochondria. It also prevents increased ROS on NGF deprivation. However, we found that induction of c-Jun in cells lacking Bax was equivalent to that in wild-type neurons. Our results suggest that while JNK activation plays an important role in many forms of apoptosis, it may not be a crucial regulator of Bax-dependent events involved in the apoptotic death of mouse sympathetic neurons deprived of NGF and that ROS is not involved in its activation in these cells.

Blocking Nerve Growth Factor Signaling Reduces the Neural Invasion Potential of Pancreatic Cancer Cells.

Perineural invasion (PNI) is thought to be one of the factors responsible for the high rate of tumor recurrence after surgery and the pain generation associated with pancreatic cancer. Signaling via the nerve growth factor (NGF) pathway between pancreatic cancer cells and the surrounding nerves has been implicated in PNI, and increased levels of these proteins have been correlated to poor prognosis. In this study, we examine the molecular mechanism of the NGF signaling pathway in PNI in pancreatic cancer. We show that knocking down NGF or its receptors, TRKA and p75NTR, or treatment with GW441756, a TRKA kinase inhibitor, reduces the proliferation and migration of pancreatic cancer cells in vitro. Furthermore, pancreatic cancer cells migrate towards dorsal root ganglia (DRG) in a co-culture assay, indicating a paracrine NGF signaling between the DRGs and pancreatic cancer cells. Knocking down the expression of NGF pathway proteins or inhibiting the activity of TRKA by GW441756 reduced the migratory ability of Mia PaCa2 towards the DRGs. Finally, blocking NGF signaling by NGF neutralizing antibodies or GW441756 inhibited the neurite formation in PC-12 cells in response to conditioned media from pancreatic cancer cells, indicating a reciprocal signaling pathway between the pancreatic cancer cells and nerves. Our results indicate that NGF signaling pathway provides a potential target for developing molecularly targeted therapies to decrease PNI and reduce pain generation. Since there are several TRKA antagonists currently in early clinical trials they could now be tested in the clinical situation of pancreatic cancer induced pain.

Neuroprotection by Cocktails of Dietary Antioxidants under Conditions of Nerve Growth Factor Deprivation.

Dietary antioxidants may be useful in counteracting the chronic inflammatory status in neurodegenerative diseases by reducing oxidative stress due to accumulation of reactive oxygen species (ROS). In this study, we newly described the efficacy of a number of dietary antioxidants (polyphenols, carotenoids, thiolic compounds, and oligoelements) on viability of neuronal PC12 cells following Nerve Growth Factor (NGF) deprivation, a model of age-related decrease of neurotrophic support that triggers neuronal loss. Neuroprotection by antioxidants during NGF deprivation for 24 h was largely dependent on their concentrations: all dietary antioxidants were able to efficiently support cell viability by reducing ROS levels and restoring mitochondrial function, while preserving the neuronal morphology. Moreover, ROS reduction and neuroprotection during NGF withdrawal were also achieved with defined cocktails of 3-6 different antioxidants at concentrations 5-60 times lower than those used in single treatments, suggesting that their antioxidant activity was preserved also at very low concentrations. Overall, these data indicate the beneficial effects of antioxidants against oxidative stress induced by decreased NGF availability and suggest that defined cocktails of dietary factors at low concentrations might be a suitable strategy to reduce oxidative damage in neurodegenerative diseases, while limiting possible side effects.

Coronin-1 is a neurotrophin endosomal effector that is required for developmental competition for survival.

Retrograde communication from axonal targets to neuronal cell bodies is critical for both the development and function of the nervous system. Much progress has been made in recent years linking long-distance, retrograde signaling to a signaling endosome, yet the mechanisms governing the trafficking and signaling of these endosomes remain mostly uncharacterized. Here we report that in mouse sympathetic neurons, the target-derived nerve growth factor (NGF)-tropomyosin-related kinase type 1 (TrkA, also called Ntrk1) signaling endosome, on arrival at the cell body, induces the expression and recruitment of a new effector protein known as Coronin-1 (also called Coro1a). In the absence of Coronin-1, the NGF-TrkA signaling endosome fuses to lysosomes sixfold to tenfold faster than when Coronin-1 is intact. We also define a new Coronin-1-dependent trafficking event in which signaling endosomes recycle and re-internalize on arrival at the cell body. Beyond influencing endosomal trafficking, Coronin-1 is also required for several NGF-TrkA-dependent signaling events, including calcium release, calcineurin activation and phosphorylation of cAMP responsive element binding protein (CREB). These results establish Coronin-1 as an essential component of a feedback loop that mediates NGF-TrkA endosome stability, recycling and signaling as a critical mechanism governing developmental competition for survival.

A feed-forward loop involving Trib3, Akt and FoxO mediates death of NGF-deprived neurons.

The mechanisms governing neuron death following NGF deprivation are incompletely understood. Here, we show that Trib3, a protein induced by NGF withdrawal, has a key role in such death via a loop involving the survival kinase Akt and FoxO transcription factors. Trib3 overexpression is sufficient to induce neuron death, and silencing of endogenous Trib3 strongly protects from death when NGF is withdrawn. Mechanism studies reveal that Trib3 interferes with phosphorylation/activity of Akt and contributes to Akt inactivation after NGF deprivation. FoxO1a, a direct Akt substrate, is dephosphorylated upon NGF withdrawal and consequently undergoes nuclear translocation and activates pro-apoptotic genes. We find that Trib3 is required for FoxO1a dephosphorylation and nuclear translocation after NGF deprivation. Conversely, Trib3 induction requires FoxO transcription factors, which show enhanced occupancy of the Trib3 promoter region following NGF withdrawal. Collectively, these findings support a mechanism in which NGF deprivation, Akt dephosphorylation/inactivation, FoxO dephosphorylation/activation and Trib3 induction are linked in a self-amplifying feed-forward loop that culminates in neuron death.

Caspase-2 is essential for c-Jun transcriptional activation and Bim induction in neuron death.

Neuronal apoptotic death generally requires de novo transcription, and activation of the transcription factor c-Jun has been shown to be necessary in multiple neuronal death paradigms. Caspase-2 has been implicated in death of neuronal and non-neuronal cells, but its relationship to transcriptional activation has not been clearly elucidated. In the present study, using two different neuronal apoptotic paradigms, ß-amyloid treatment and NGF (nerve growth factor) withdrawal, we examined the hierarchical role of caspase-2 activation in the transcriptional control of neuron death. Both paradigms induce rapid activation of caspase-2 as well as activation of the transcription factor c-Jun and subsequent induction of the pro-apoptotic BH3 (Bcl-homology domain 3)-only protein Bim (Bcl-2-interacting mediator of cell death). Caspase-2 activation is dependent on the adaptor protein RAIDD {RIP (receptor-interacting protein)-associated ICH-1 [ICE (interleukin-1ß-converting enzyme)/CED-3 (cell-death determining 3) homologue 1] protein with a death domain}, and both caspase-2 and RAIDD are required for c-Jun activation and Bim induction. The present study thus shows that rapid caspase-2 activation is essential for c-Jun activation and Bim induction in neurons subjected to apoptotic stimuli. This places caspase-2 at an apical position in the apoptotic cascade and demonstrates for the first time that caspase-2 can regulate transcription.

ProNGF\NGF imbalance triggers learning and memory deficits, neurodegeneration and spontaneous epileptic-like discharges in transgenic mice.

ProNGF, the precursor of mature nerve growth factor (NGF), is the most abundant form of NGF in the brain. ProNGF and mature NGF differ significantly in their receptor interaction properties and in their bioactivity. ProNGF increases markedly in the cortex of Alzheimer's disease (AD) brains and proNGF\NGF imbalance has been postulated to play a role in neurodegeneration. However, a direct proof for a causal link between increased proNGF and AD neurodegeneration is lacking. In order to evaluate the consequences of increased levels of proNGF in the postnatal brain, transgenic mice expressing a furin cleavage-resistant form of proNGF, under the control of the neuron-specific mouse Thy1.2 promoter, were derived and characterized. Different transgenic lines displayed a phenotypic gradient of neurodegenerative severity features. We focused the analysis on the two lines TgproNGF#3 and TgproNGF#72, which shared learning and memory impairments in behavioral tests, cholinergic deficit and increased Aß-peptide immunoreactivity. In addition, TgproNGF#3 mice developed Aß oligomer immunoreactivity, as well as late diffuse astrocytosis. Both TgproNGF lines also display electrophysiological alterations related to spontaneous epileptic-like events. The results provide direct evidence that alterations in the proNGF/NGF balance in the adult brain can be an upstream driver of neurodegeneration, contributing to a circular loop linking alterations of proNGF/NGF equilibrium to excitatory/inhibitory synaptic imbalance and amyloid precursor protein (APP) dysmetabolism.

Dissecting the role of sortilin receptor signaling in neurodegeneration induced by NGF deprivation.

Sortilin is a member of the family of vacuolar protein sorting 10 protein domain receptors which has emerged as a co-receptor in cell death and neurodegeneration processes mediated by proneurotrophins. Here we tested the possibility that sortilin deficiency interferes with behavioral and neuropathological endpoints in a chronic Nerve Growth factor (NGF)-deprivation model of Alzheimer's disease (AD), the AD10 anti-NGF mouse. AD10 mice show cholinergic deficit, increased APP processing and tau hyper-phosphorylation, resulting in behavioral deficits in learning and memory paradigms assessed by novel object recognition and Morris water maze tests. Sort1(-/-) mice were crossed with AD10 anti-NGF mice and the neurodegenerative phenotype was studied. We found that the loss of sortilin partially protected AD10 anti-NGF mice from neurodegeneration. A protective effect was observed on non-spatial memory as assessed by novel object recognition, and histopathologically at the level of Aß and BFCNs, while the phosphotau increase was unaltered by knocking out sortilin. We suggest that sortilin might be involved in different aspects of neurodegeneration in a complex way, supporting the view that sortilin functions in the CNS are broader than being a co-receptor in proneurotrophin and neurotrophin signaling.

Loss of NGF-TrkA signaling from the CNS is not sufficient to induce cognitive impairments in young adult or intermediate-aged mice.

Many molecules expressed in the CNS contribute to cognitive functions either by modulating neuronal activity or by mediating neuronal trophic support and/or connectivity. An ongoing discussion is whether signaling of nerve growth factor (NGF) through its high-affinity receptor TrkA contributes to attention behavior and/or learning and memory, based on its expression in relevant regions of the CNS such as the hippocampus, cerebral cortex, amygdala and basal forebrain. Previous animal models carrying either a null allele or transgenic manipulation of Ngf or Trka have proved difficult in addressing this question. To overcome this problem, we conditionally deleted Ngf or Trka from the CNS. Our findings confirm that NGF-TrkA signaling supports survival of only a small proportion of cholinergic neurons during development; however, this signaling is not required for trophic support or connectivity of the remaining basal forebrain cholinergic neurons. Moreover, comprehensive behavioral analysis of young adult and intermediate-aged mice lacking NGF-TrkA signaling demonstrates that this signaling is dispensable for both attention behavior and various aspects of learning and memory.

Spatially coordinated kinase signaling regulates local axon degeneration.

In addition to being a hallmark of neurodegenerative disease, axon degeneration is used during development of the nervous system to prune unwanted connections. In development, axon degeneration is tightly regulated both temporally and spatially. Here, we provide evidence that degeneration cues are transduced through various kinase pathways functioning in spatially distinct compartments to regulate axon degeneration. Intriguingly, glycogen synthase kinase-3 (GSK3) acts centrally, likely modulating gene expression in the cell body to regulate distally restricted axon degeneration. Through a combination of genetic and pharmacological manipulations, including the generation of an analog-sensitive kinase allele mutant mouse for GSK3ß, we show that the ß isoform of GSK3, not the α isoform, is essential for developmental axon pruning in vitro and in vivo. Additionally, we identify the dleu2/mir15a/16-1 cluster, previously characterized as a regulator of B-cell proliferation, and the transcription factor tbx6, as likely downstream effectors of GSK3ß in axon degeneration.

Pathogen free conditions slow the onset of neurodegeneration in a mouse model of nerve growth factor deprivation.

Several studies suggest that systemic infection occurring during aging and chronic neurodegenerative diseases can evoke an exaggerated immune response that contributes to the progression of neurodegeneration and cognitive decline. However, studies directly addressing the relationship between microbial environment and the onset of neurodegeneration in Alzheimer's disease animal models are lacking. Here we show that the onset of neurodegeneration that transgenic mice develop when raised in conventional husbandry slows down when raising anti-nerve growth factor transgenic mice in a murine pathogen free condition.

Neuronal caspase 2 activity and function requires RAIDD, but not PIDD.

Caspase 2 was initially identified as a neuronally expressed developmentally down-regulated gene (HUGO gene nomenclature CASP2) and has been shown to be required for neuronal death induced by several stimuli, including NGF (nerve growth factor) deprivation and Aß (ß-amyloid). In non-neuronal cells the PIDDosome, composed of caspase 2 and two death adaptor proteins, PIDD (p53-inducible protein with a death domain) and RAIDD {RIP (receptor-interacting protein)-associated ICH-1 [ICE (interleukin-1ß-converting enzyme)/CED-3 (cell-death determining 3) homologue 1] protein with a death domain}, has been proposed as the caspase 2 activation complex, although the absolute requirement for the PIDDosome is not clear. To investigate the requirement for the PIDDosome in caspase-2-dependent neuronal death, we have examined the necessity for each component in induction of active caspase 2 and in execution of caspase-2-dependent neuronal death. We find that both NGF deprivation and Aß treatment of neurons induce active caspase 2 and that induction of this activity depends on expression of RAIDD, but is independent of PIDD expression. We show that treatment of wild-type or PIDD-null neurons with Aß or NGF deprivation induces formation of a complex of caspase 2 and RAIDD. We also show that caspase-2-dependent execution of neurons requires RAIDD, not PIDD. Caspase 2 activity can be induced in neurons from PIDD-null mice, and NGF deprivation or Aß use caspase 2 and RAIDD to execute death of these neurons.

Reduced maternal and cord nerve growth factor levels in preterm deliveries.

Nerve growth factor (NGF) is a neurotrophin, which exerts an important role in the development and function of the central and peripheral nervous system. There is limited information regarding the levels of NGF during pregnancy and its role in fetal development. We have earlier reported increased oxidative stress in pregnancy complications. The present study examines the levels of NGF in maternal and cord samples in preterm deliveries and its association with oxidative stress marker. A total number of 96 women delivering preterm (<37 weeks gestation) and 94 women delivering at term (control group) (≥37 weeks gestation) were recruited. Plasma NGF levels were measured in both mother and cord plasma using the Emax Immuno Assay System Promega kit. Maternal and cord plasma NGF levels were significantly reduced (p<0.05 for both) in women delivering preterm as compared to term. There was a positive association between maternal and cord plasma NGF levels (p=0.022). Maternal NGF levels were negatively (p=0.017) associated with maternal malondialdehyde (MDA) levels. Reduced cord NGF levels may affect fetal growth in preterm deliveries which may have implications for the neurodevelopmental pathologies in later life. Circulating maternal NGF levels in preterm pregnancies may be a useful marker to predict NGF levels in the neonate.

DLK induces developmental neuronal degeneration via selective regulation of proapoptotic JNK activity.

The c-Jun N-terminal kinase (JNK) signaling pathway is essential for neuronal degeneration in multiple contexts but also regulates neuronal homeostasis. It remains unclear how neurons are able to dissociate proapoptotic JNK signaling from physiological JNK activity. In this paper, we show that the mixed lineage kinase dual leucine zipper kinase (DLK) selectively regulates the JNK-based stress response pathway to mediate axon degeneration and neuronal apoptosis without influencing other aspects of JNK signaling. This specificity is dependent on interaction of DLK with the scaffolding protein JIP3 to form a specialized JNK signaling complex. Local activation of DLK-based signaling in the axon results in phosphorylation of c-Jun and apoptosis after redistribution of JNK to the cell body. In contrast, regulation of axon degeneration by DLK is c-Jun independent and mediated by distinct JNK substrates. DLK-null mice displayed reduced apoptosis in multiple neuronal populations during development, demonstrating that prodegenerative DLK signaling is required in vivo.

GADD45A protects against cell death in dorsal root ganglion neurons following peripheral nerve injury.

A significant loss of neurons in the dorsal root ganglia (DRG) has been reported in animal models of peripheral nerve injury. Neonatal sensory neurons are more susceptible than adult neurons to axotomy- or nerve growth factor (NGF) withdrawal-induced cell death. To develop therapies for preventing irreversible sensory cell loss, it is essential to understand the molecular mechanisms responsible for DRG cell death and survival. Here we describe how the expression of the growth arrest- and DNA damage-inducible gene 45α (GADD45A) is correlated with neuronal survival after axotomy in vivo and after NGF withdrawal in vitro. GADD45A expression is low at birth and does not change significantly after spinal nerve ligation (SNL). In contrast, GADD45A is robustly up-regulated in the adult rat DRG 24 hr after SNL, and this up-regulation persists as long as the injured fibers are prevented from regenerating. In vitro delivery of GADD45A protects neonatal rat DRG neurons from NGF withdrawal-induced cytochrome c release and cell death. In addition, in vivo knockdown of GADD45A expression in adult injured DRG by small hairpin RNA increased cell death. Our results indicate that GADD45A protects neuronal cells from SNL-induced cell death.

Mice with genetic deletion of the heparin-binding growth factor midkine exhibit early preclinical features of Parkinson's disease.

There is considerable evidence showing that the neurodegenerative processes that lead to sporadic Parkinson's disease (PD) begin many years before the appearance of the characteristic motor symptoms and that impairments in olfactory, cognitive and motor functions are associated with time-dependent disruption of dopaminergic neurotransmission in different brain areas. Midkine is a 13-kDa retinoic acid-induced heparin-binding growth factor involved in many biological processes in the central nervous system such as cell migration, neurogenesis and tissue repair. The abnormal midkine expression may be associated with neurochemical dysfunction in the dopaminergic system and cognitive impairments in rodents. Here, we employed adult midkine knockout mice (Mdk(-/-)) to further investigate the relevance of midkine in dopaminergic neurotransmission and in olfactory, cognitive and motor functions. Mdk(/-) mice displayed pronounced impairments in their olfactory discrimination ability and short-term social recognition memory with no gross motor alterations. Moreover, the genetic deletion of midkine decreased the expression of the enzyme tyrosine hydroxylase in the substantia nigra reducing partially the levels of dopamine and its metabolites in the olfactory bulb and striatum of mice. These findings indicate that the genetic deletion of midkine causes a partial loss of dopaminergic neurons and depletion of dopamine, resulting in olfactory and memory deficits with no major motor impairments. Therefore, Mdk(-/-) mice may represent a promising animal model for the study of the early stages of PD and for testing new therapeutic strategies to restore sensorial and cognitive processes in PD.

Endogenous Aß causes cell death via early tau hyperphosphorylation.

Alzheimer's disease (AD) is characterized by Aß overproduction and tau hyperphosphorylation. We report that an early, transient and site-specific AD-like tau hyperphosphorylation at Ser262 and Thr231 epitopes is temporally and causally related with an activation of the endogenous amyloidogenic pathway that we previously reported in hippocampal neurons undergoing cell death upon NGF withdrawal [Matrone, C., Ciotti, M.T., Mercanti, D., Marolda, R., Calissano, P., 2008b. NGF and BDNF signaling control amyloidogenic route and Ab production in hippocampal neurons. Proc. Natl. Acad. Sci. 105, 13138-13143]. Such tau hyperphosphorylation, as well as apoptotic death, is (i) blocked by 4G8 and 6E10 Aß antibodies or by specific ß and/or γ-secretases inhibitors; (ii) temporally precedes tau cleavage mediated by a delayed (6-12h after NGF withdrawal) activation of caspase-3 and calpain-I; (iii) under control of Akt-GSK3ß-mediated signaling. Finally, we show that such site-specific tau hyperphosphorylation causes tau detachment from microtubules and an impairment of mitochondrial trafficking. These results depict, for the first time, a rapid interplay between endogenous Aß and tau post-translational modifications which act co-ordinately to compromise neuronal functions in the same neuronal system, under physiological conditions as seen in AD brain.

Transgenic mice with chronic NGF deprivation and Alzheimer's disease-like pathology display hippocampal region-specific impairments in short- and long-term plasticities.

The etiology of Alzheimer's disease (AD) remains elusive. The "amyloid" hypothesis states that toxic action of accumulated ß-amyloid peptide (Aß) on synaptic function causes AD cognitive decline. This hypothesis is supported by analysis of familial AD (FAD)-based transgenic mouse models, where altered amyloid precursor protein (APP) processing leads to Aß accumulation correlating with hippocampal-dependent memory deficits. Some studies report prominent dentate gyrus (DG) glutamatergic plasticity alterations in these mice, while CA1 plasticity remains relatively unaffected. The "neurotrophic unbalance" hypothesis, on the other hand, states that AD-related loss of cholinergic signaling and altered APP processing are due to alterations in nerve growth factor (NGF) trophic support. This hypothesis is supported by analysis of the AD11 mouse, which exhibits chronic NGF deprivation during adulthood and displays AD-like pathology, including Aß accumulation and hippocampal-dependent memory deficits. In this study, we analyzed CA1 and DG glutamatergic plasticity in AD11 mice to evaluate whether these mice also share with FAD models a common phenotype in hippocampal synaptic dysfunction. We report that AD11 mice display age-dependent short- and long-term DG plasticity deficits, while CA1 plasticity remains relatively spared. We also report that both structures exhibit enhanced glutamatergic transmission under lower, yet physiological, neurotransmitter release conditions, a defect that should be considered when further evaluating hippocampal synaptic deficits underlying AD pathology. We conclude that severe deficits in DG plasticity represent another common denominator between these two etiologically different types of AD mouse models, independent of the initial insult (overexpression of FAD mutation or NGF deprivation).

Long-distance control of synapse assembly by target-derived NGF.

We report a role for long-distance retrograde neurotrophin signaling in the establishment of synapses in the sympathetic nervous system. Target-derived NGF is both necessary and sufficient for formation of postsynaptic specializations on dendrites of sympathetic neurons. This, in turn, is a prerequisite for formation of presynaptic specializations, but not preganglionic axonal ingrowth from the spinal cord into sympathetic ganglia. We also find that NGF-TrkA signaling endosomes travel from distal axons to cell bodies and dendrites where they promote PSD clustering. Furthermore, the p75 neurotrophin receptor restricts PSD formation, suggesting an important role for antagonistic NGF-TrkA and p75 signaling pathways during retrograde control of synapse establishment. Thus, in addition to defining the appropriate number of sympathetic neurons that survive the period of developmental cell death, target-derived NGF also exerts control over the degree of connectivity between the spinal cord and sympathetic ganglia through retrograde control of synapse assembly.