Alterations in the fine structure of nucleoli in sympathetic neurons following NGF-antiserum treatment

Lithium protects against anesthesia-induced developmental neuroapoptosis

BACKGROUND

Ethanol and anesthetic drugs trigger neuroapoptosis in the developing mouse brain. Recently, it was found that ethanol-induced neuroapoptosis is preceded by suppressed phosphorylation of extracellular signal-regulated protein kinase (ERK), and lithium counteracts both the phosphorylated ERK suppressant action and ethanol-induced neuroapoptosis. The current study was undertaken to address the following questions. (1) Do ketamine and propofol mimic ethanol in suppressing ERK phosphorylation? (2) If they do, does lithium prevent this suppressant action and also prevent these anesthetic drugs from triggering neuroapoptosis?

METHOD

Postnatal day 5 mice were treated with propofol, ketamine, lithium, a combination of propofol or ketamine with lithium or saline, and their brains were prepared for Western blot analysis or histology. For Western blot, cytosolic lysates of caudate putamen were analyzed for expression of phosphorylated ERK and phosphorylated serine/threonine-specific protein kinase. For histology, brains were stained immunohistochemically with antibodies to activated caspase-3, and the density of activated caspase-3 positive cells was determined.

RESULTS

Ketamine and propofol suppressed phosphorylated ERK, and lithium counteracted both the phosphorylated ERK suppressant action and neuroapoptotic action of these anesthetic drugs.

CONCLUSION

If further testing finds lithium to be safe for use in pediatric/obstetric medicine, administration of a single dose of lithium before anesthesia induction may be a suitable means of mitigating the risk of anesthesia-induced developmental neuroapoptosis.

Ethanol causes and lithium prevents neuroapoptosis and suppression of pERK in the infant mouse brain

Transient exposure of immature animals during the brain growth spurt period to ethanol triggers neuroapoptosis in the developing brain. Here we report that lithium, when administered in a single, well-tolerated dose to infant mice, suppresses spontaneous neuroapoptosis that occurs naturally in the developing brain, and prevents ethanol from triggering neuroapoptosis. To explore lithium's mechanism of action, we focused on kinase signaling systems (ERK, Akt, JNK) that are believed to play a regulatory role in cell survival, and found that very rapidly after ethanol administration there is a suppression of ERK phosphorylation, and that lithium stimulates ERK phosphorylation and prevents ethanol from suppressing this phosphorylation process. Ethanol also suppressed pAKT, but lithium did not counteract this effect. We also found that ethanol activates the JNK system, but this cannot explain the neurotoxic action of ethanol, because JNK activation did not occur in the same neuronal populations that are killed by ethanol.

Neuritogenic effects of T cell-derived IL-3 on mouse splenic sympathetic neurons in vivo

To determine the role played by lymphocytes and cytokines in the growth of sympathetic neurons in vivo, the innervation and cytokine levels were examined in the spleens of SCID mice that lack T and B cells. Splenic noradrenaline, nerve growth factor (NGF), and IL-1beta levels were elevated in SCID mice. Immunohistochemical examination revealed that the density of tyrosine hydroxylase-positive (TH(+)) fibers of splenic central arteries in SCID mice was increased compared with wild-type C.B-17 mice, while SCID mice had significantly fewer TH(+) fibers in their periarteriolar lymphatic sheaths (PALS). Two weeks after SCID mice were injected with C.B-17 splenic T cells, their TH(+) fiber staining increased in the PALS. IL-3 levels increased significantly in SCID mice following T cell reconstitution, and the administration of anti-IL-3 Ab blocked the above T cell-induced increase in innervation in the PALS. Anti-IL-3 treatment also inhibited the regeneration of splenic sympathetic neurons in C.B-17 mice after they were chemically sympathetomized with 6-hydroxydopamine. Depletion of NK cells by anti-asialo GM1 promoted the splenic innervation in SCID mice, while there were no significant changes in the innervation between CD8(+) T cell-deficient beta(2)-microglobulin knockout mice and their wild type. Our results suggest that T cells (probably CD4(+) Th cells but not CD8(+) CTLs) play a role in regulating the sympathetic innervation of the spleen; this effect appeared to be mediated, at least in part, by IL-3. On the contrary, NK cells may exert an inhibitory effect on the sympathetic innervation.

NAP enhances neurodevelopment of newborn apolipoprotein E-deficient mice subjected to hypoxia

Perinatal hypoxic injury is associated with significant neonatal morbidity and long-term neurodevelopmental complications. NAP, a peptide derived from ADNP (activity-dependent neuroprotective protein), has previously shown neuroprotective abilities in various adult animal models. To evaluate its neuroprotective role in neonatal hypoxic-ischemic injury, we evaluated the neurodevelopmental outcome in apolipoprotein E (ApoE)-deficient (knockout) mice (a breed prone to brain damage during hypoxic insult) exposed to postnatal global hypoxic damage with and without treatment with NAP. ApoE-deficient (n = 80) and control (C57B6) mice pups (n = 81) were exposed to postnatal global hypoxia (35 min of 8% O(2) within 24 h of birth) or room air with or without subsequent subcutaneous NAP treatment during postnatal days 1 to 14. Pups were then evaluated for neonatal motor reflex attainment, spatial learning ability in the Morris water maze, and locomotor open-field activity. The C57B6 and ApoE-deficient anoxic groups showed significantly slower achievement of neonatal reflexes, diminished locomotor activity, and diminished spatial learning ability compared with their control groups. This was more pronounced in the anoxic ApoE-deficient pups. NAP treatment had a pronounced effect on neurodevelopmental outcome in both breeds, particularly in the ApoE-deficient mice. ApoE-deficient and control mouse pups exposed to postnatal hypoxia and treated with NAP showed improvement in neurodevelopmental outcome compared with nontreated mice pups. ApoE-deficient mice show a greater susceptibility to hypoxic damage and better response to NAP treatment.

Ethanol-induced neuroapoptosis in the developing rodent cerebellum and related brain stem structures

For three decades since the fetal alcohol syndrome (FAS) was first described, researchers have been keenly interested in understanding the mechanism(s) by which ethanol damages or disrupts development of the human fetal brain. It has been reported repeatedly that exposure of infant rats to ethanol causes a reduction in brain mass and loss of cerebellar Purkinje cells, but the mechanisms underlying these effects have remained elusive. In a recent series of studies, we have demonstrated that exposure of infant rats or mice to ethanol on a single occasion during the synaptogenesis period of development causes neurons in many regions of the developing central nervous system to commit suicide (die by apoptosis), but the cerebellum was not among the brain regions focused upon in these studies. Here we show in infant rats and mice that one-time exposure to ethanol triggers acute neurodegeneration of Purkinje cells and other neurons in the cerebellar cortex, deep cerebellar nuclei, and two related brainstem nuclei (nucleus pontis, inferior olivary complex). We also describe the time course of neurodegeneration and window of vulnerability for each of these neuronal cell types and demonstrate that the cell death process in each case is unequivocally apoptotic. We conclude that exposure of infant rats or mice to ethanol on a single occasion during synaptogenesis can kill Purkinje cells, and many other neuronal populations at all levels of the developing neuraxis, and in each case the mechanism of cell death is apoptosis.

Rescue of NGF-deficient mice I: transgenic expression of NGF in skin rescues mice lacking endogenous NGF

Mice lacking a functional NGF gene (ngf-/- mice) have less than one third of the normal complement of sensory neurons, few sympathetic postganglionic neurons and die shortly after birth. We report here that transgenic expression of NGF under control of the K14 keratin promoter can rescue some elements of the peripheral nervous system and restore normal growth and viability to ngf-/- mice. While hybrid transgenic-ngf-/- mice (ngfTKOs) displayed marginal rescue of trigeminal ganglion neurons, the percentage of CGRP-positive neurons was restored to normal. Restoration of CGRP-positive terminals in skin and spinal cord was also found and accompanied by recovery of behavioral responses to noxious stimuli. ngfTKO mice displayed a normal number of superior cervical ganglion neurons and recovery of sympathetic innervation of skin. These results demonstrate that substitution of a functional NGF locus by a transgene directing expression largely to skin can result in normal growth and viability. Thus, the most vital functions of NGF are not dependent on faithful recapitulation of the normal spatiotemporal pattern of gene expression.

Ethanol-induced apoptotic neurodegeneration in the developing C57BL/6 mouse brain

Recent studies have shown that administration of ethanol to infant rats during the synaptogenesis period (first 2 weeks after birth), triggers extensive apoptotic neurodegeneration throughout many regions of the developing brain. While synaptogenesis is largely a postnatal phenomenon in rats, it occurs prenatally (last trimester of pregnancy) in humans. Recent evidence strongly supports the interpretation that ethanol exerts its apoptogenic action by a dual mechanism--blockade of NMDA glutamate receptors and hyperactivation of GABA(A) receptors. These findings in immature rats represent a significant advance in the fetal alcohol research field, in that previous in vivo animal studies had not demonstrated an apoptogenic action of ethanol, had not documented ethanol-induced cell loss from more than a very few brain regions and had not provided penetrating insight into the mechanisms underlying ethanol's neurotoxic action. To add to the mechanistic insights recently gained, it would be desirable to examine gene-regulated aspects of ethanol-induced apoptotic neurodegeneration, using genetically altered strains of mice. The feasibility of such research must first be established by demonstrating that appropriate mouse strains are sensitive to this neurotoxic mechanism. In the present study, we demonstrate that mice of the C57BL/6 strain, a strain frequently used in transgenic and gene deletion research, are exquisitely sensitive to the mechanism by which ethanol induces apoptotic neurodegeneration during the synaptogenesis period of development.

Apoptosis in the in vivo mammalian forebrain

Apoptosis is a word originally introduced by Kerr, Wyllie, and colleagues for a cell death process they defined in terms of its ultrastructural appearance in nonneuronal cells from various tissues. There are very few studies providing detailed ultrastructural criteria for recognizing neuronal apoptosis in the in vivo mammalian brain. In the absence of such criteria, the Kerr/Wyllie description pertaining to nonneuronal cells has served as a reference standard. However, contemporary neurobiologists typically rely on cell culture models for studying neuronal apoptosis, and these models are rarely validated ultrastructurally; rather they are assumed to be appropriate models based on unvalidated biochemical tests for apoptosis. Relying on evidence generated in such cell culture models or on nonspecific cytochemical tests applied to brain tissue, many authors have recently suggested that an apoptotic mechanism may mediate neuronal death in a wide variety of human neurodegenerative diseases. Whether the cell death process in neurodegenerative diseases meets ultrastructural criteria for apoptosis has been given very little consideration. Recently, several methods have been described for triggering extensive apoptotic neurodegeneration in the developing in vivo mammalian brain. These methods include head trauma or treatment with several types of drugs (NMDA antagonists, GABAA agonists, or ethanol). We have performed an ultrastructural analysis of the neuronal cell death process triggered in the cerebral cortex and thalamus by these several methods and compared it with physiological cell death (PCD), a prototypic example of neuronal apoptosis that occurs naturally in the developing brain. Our findings, which are reviewed herein, demonstrate that the types and sequence of changes induced by each of the above methods are identical to those that characterize PCD. This confirms that each of these methods produces bona fide in vivo apoptotic neurodegeneration, and it signifies that our description of this neuronal apoptotic process, which differs in some respects from the Kerr/Wyllie description of nonneuronal apoptosis, can serve as a useful reference standard for recognizing the characteristic changes that in vivo neurons undergo when they are dying by an apoptotic mechanism.

Distinct alterations in mitochondrial mass and function characterize different models of apoptosis

Recent studies have shown that reduction in mitochondrial membrane potential (delta psi m) and generation of reactive oxygen species are early events in apoptosis. In this study, we present two different models of apoptotic cell death, Chinese hamster ovary (CHO) cells treated with aphidicolin and dexamethasone-treated 2B4 T-cell hybridoma cells, which display opposing mitochondrial changes. CHO cells arrested at G1/S with aphidicolin have a progressive increase in mitochondria mass and number, assessed by flow cytometry and fluorescent microscopy with mitochondria-specific probes. The increase in mitochondrial mass was not accompanied by a gain in net cellular mitochondrial membrane potential, consistent with an accumulation of relatively depolarized mitochondria. Fluorescent microscopy demonstrated an increased content of low delta psi m mitochondria in aphidicolin-treated CHO cells, but high delta psi m mitochondria were also present and remained stable in number. Mitochondrial mass correlated with decreased clonogenicity of aphidicolin-treated CHO cells. Cycloheximide prevented both the proliferation of mitochondria and subsequent cell death. In contrast, dexamethasone treatment of 2B4 T-cell hybridoma cells caused a decrease in delta psi m without mitochondrial proliferation. Cycloheximide and Bcl-2 overexpression inhibited the loss of delta psi m, as well as apoptosis. In both models, cell death was associated with a decrease in mitochondrial potential relative to mitochondrial mass, suggesting that an accumulation of damaged or dysfunctional mitochondria had occurred.

Axotomy-induced neuronal death and reactive astrogliosis in the lateral geniculate nucleus following a lesion of the visual cortex in the rat

Following a unilateral lesion of the visual cortex (cortical areas 17, 18, and 18a) in adult rats, neurons in the ipsilateral dorsal lateral geniculate nucleus (LGN) are axotomized, which leads to their atrophy and death. The time course of this neuronal degeneration was studied quantitatively, and the astroglial response was examined with glial fibrillary acidic protein immunohistochemistry. More than 95% of the neurons in the ipsilateral LGN survive during the first 3 days following a lesion of the visual cortex. However, in the next 4 days, massive neuronal death ensues, reducing the number of surviving neurons to approximately 33% of normal by the end of the first postoperative week. Between 2 weeks and 24 weeks postoperatively, the number of neurons present in the LGN declines very gradually from 34% to 17% of normal. Three days after a lesion of the visual cortex, the mean cross-sectional areas of ipsilateral LGN neurons are 13% smaller than normal (87%). By 1 week after the operation, surviving LGN neurons have atrophied to 66% of their normal area. Subsequently, the size of surviving neurons declines slowly to approximately 50% of normal at 24 weeks after the cortical lesion. Astrocytes in the ipsilateral LGN also react to cortical damage. At 1 day after a lesion of the visual cortex, glial fibrillary acidic protein immunoreactivity in the LGN is almost undetectable, but a distinct increase in immunoreactivity is seen at 3 days. Immunoreactivity peaks between 1 week and 2 weeks postoperatively and, thereafter, remains intense for at least 24 weeks. Thus, following a lesion of the visual cortex, the somata of neurons in the LGN remain essentially normal morphologically for about 3 days before the onset of rapid atrophy and death. Moreover, most of the neural cell death that occurs in the LGN after axotomy takes place in the last half of the first postoperative week.

Ultrastructural changes of sympathetic neurons following neurotrophin 3 antiserum treatment in young rat

We have previously demonstrated that neurotrophin-3 antiserum administration to rats during the first 2 postnatal weeks results in a massive reduction of neurons in the superior cervical ganglion. In the present study, an ultrastructural analysis was undertaken to elucidate the mechanism by which neurotrophin-3 deprivation causes neuronal death. Newborn and 4-week-old rats were injected with either neurotrophin-3 antiserum or normal rabbit serum or used without injection. Superior cervical ganglia from each animal were examined by routine electron microscopy. Most neurons in the ganglia from untreated rats had a large and round nucleus with one or two nucleoli. Chromatin within the nucleus was evenly distributed. A double-layer nuclear membrane could be distinguished and the cytoplasm contained abundant organelles. Treatment with neurotrophin-3 antiserum for 24 h in neonates resulted in chromatin clumping in the nucleus of many neurons. The nuclear membrane became rough and occasionally folded. In the cytoplasm, the Golgi apparatus was disrupted. Three days after treatment, these changes became more obvious. The chromatin in the nucleus was often aggregated and marginalized. Vacuolation was present in many membranous organelles throughout the cytoplasm. Although neurotrophin-3 antiserum given to 4-week-old rats had little effect on overall neuronal numbers (Tafreshi, Zhou, and Rush, unpublished), a few neurons, undergoing either apoptotic or cytolytic cell death, were identified 7 days later. Most affected neurons were located near small blood vessels or capillaries and were associated with numerous nonneuronal cells. The debris of degenerating neurons were surrounded by the processes of glia cells. These findings support the view that loss of endogenous neurotrophin-3 following neutralization with specific antibody leads to activation of apoptotic pathways within the affected neurons. However, the presence of neurons dying as a result of cytolysis suggests that other mechanisms may also be involved.

Programmed cell death in neurons: focus on the pathway of nerve growth factor deprivation-induced death of sympathetic neurons

Extensive programmed cell death (PCD) occurs in the developing nervous system. Neuronal death occurs, at least in part, because neurons are produced in excess during development and compete with each other for the limited amounts of the survival-promoting trophic factors secreted by target tissues. Neuronal death is apoptotic and utilizes components that are conserved in other PCD pathways. In this review, we discuss the mechanism of trophic factor-dependent neuronal cell death by focusing on the pathway of nerve growth factor (NGF) deprivation-induced sympathetic neuronal death. We describe the biochemical and genetic events that occur in NGF-deprived sympathetic neurons undergoing PCD. Participation of the Bcl-2 family of proteins and the interleukin-1beta-converting enzyme family of proteases (caspases) in this and other models of neuronal death is also examined. The order and importance of these components during NGF deprivation-induced sympathetic neuronal death are discussed.

Antiserum to activity-dependent neurotrophic factor produces neuronal cell death in CNS cultures: immunological and biological specificity

Activity-dependent neurotrophic factor (ADNF) is a glia-derived protein that is neuroprotective at femtomolar concentrations. ADNF is released from astroglia after treatment with 0.1 nM vasoactive intestinal peptide (VIP). To further assess the biological role of ADNF, antiserum was produced following sequential injections of purified ADNF into mice. Anti-ADNF ascites fluid (1:10,000) decreased neuronal survival by 45-55% in comparison to untreated cultures or those treated with control ascites. The neuronal death after anti-ADNF treatment was observed in cultures derived from the spinal cord, hippocampus or cerebral cortex at similar IC50's. Using a terminal deoxynucleotidyl transferase in situ assay to estimate apoptosis in cerebral cortical cultures, anti-ADNF was shown to produce a 70% increase in the number of labeled cells in comparison to controls. In spinal cord cultures, anti-ADNF treatment produced a 20% decrease in choline acetyltransferase activity in comparison to controls. Neuronal cell death produced by the antiserum to ADNF was prevented in cultures co-treated with purified ADNF or ADNF-15, an active peptide derived from the parent ADNF. In vitro binding between the anti-ADNF and ADNF-15 was demonstrated with size exclusion chromatography. Comparative studies with other growth factors (insulin-like growth factor-1, platelet-derived growth factor, nerve growth factor, epidermal growth factor, ciliary neurotrophic growth factor, and neurotrophin-3) demonstrated that only ADNF prevented neuronal cell death associated with electrical blockade. These investigations indicated that an ADNF-like substance was present in cultures derived from multiple locations in the central nervous system and that ADNF-15 exhibited both neuroprotection and immunogenicity. ADNF appears to be both a regulator of activity-dependent neuronal survival and a neuroprotectant.

Methods of sympathetic degeneration and alteration

The role of the sympathetic nervous system in health and disease has often been elucidated by inducing changes in, or degeneration of sympathetic neural pathways. Several methods of inducing peripheral lesions have been created from surgical removal, NGF depletion, auto-immune and chemical destruction to novel approaches using immunotoxins and transgenic animals. This review compares these methods in terms of their mechanism and specificity. The advantages and disadvantages of these techniques are discussed.

Temporal analysis of events associated with programmed cell death (apoptosis) of sympathetic neurons deprived of nerve growth factor

The time course of molecular events that accompany degeneration and death after nerve growth factor (NGF) deprivation and neuroprotection by NGF and other agents was examined in cultures of NGF-dependent neonatal rat sympathetic neurons and compared to death by apoptosis. Within 12 h after onset of NGF deprivation, glucose uptake, protein synthesis, and RNA synthesis fell precipitously followed by a moderate decrease of mitochondrial function. The molecular mechanisms underlying the NGF deprivation-induced decrease of protein synthesis and neuronal death were compared and found to be different, demonstrating that this decrease of protein synthesis is insufficient to cause death subsequently. After these early changes and during the onset of neuronal atrophy, inhibition of protein synthesis ceased to halt neuronal degeneration while readdition of NGF or a cAMP analogue remained neuroprotective for 6 h. This suggests a model in which a putative killer protein reaches lethal levels several hours before the neurons cease to respond to readdition of NGF with survival and become committed to die. Preceding loss of viability by 5 h and concurrent with commitment to die, the neuronal DNA fragmented into oligonucleosomes. The temporal and pharmacological characteristics of DNA fragmentation is consistent with DNA fragmentation being part of the mechanism that commits the neuron to die. The antimitotic and neurotoxin cytosine arabinoside induced DNA fragmentation in the presence of NGF, supporting previous evidence that it mimicked NGF deprivation-induced death closely. Thus trophic factor deprivation-induced death occurs by apoptosis and is an example of programmed cell death.

Neurotrophic factor deprivation-induced death

Deprivation of sympathetic neurons of their physiological neurotrophic factor, nerve growth factor (NGF), leads to degeneration of soma and neurites, followed by loss of viability. The progression of degeneration and death are dependent upon macromolecular synthesis indicating an active participation of neuronal metabolism. Loss of viability begins only after a considerable delay after onset of NGF deprivation suggesting the presence of a sequence of degenerative events that triggers death. Such a sequence of degenerative events predicts that the activity of neuroprotective agents functioning by different mechanisms will be restricted to particular windows in time. The time-course of commitment to die as measured by the ability of NGF-deprived neurons to respond to NGF with long-term survival precedes the time-course of loss of viability by only a few hours, demonstrating that NGF displays neuroprotective properties for most of the time between onset of deprivation and death. Furthermore, NGF repairs and reverses the degenerative changes caused by prolonged periods of NGF deprivation. Because of these two aspects of NGF action, NGF demonstrates superior properties as a neuroprotective agents. NGF deprivation initiates DNA fragmentation of the neuronal genome into oligonucleosomal fragments in close temporal association with the onset of commitment to die. This is consistent with the idea that DNA fragmentation may be instrumental in causing the commitment to die. Thus, DNA fragmentation may serve as a marker of the physiologically most relevant critical step occurring during degeneration and may indicate the end of the period during which trophic factors are useful as neuroprotective agents. These results may be transferable to neurodegenerative diseases or sequelae of neuronal injury because of similarities in the phenomenology of degeneration and death.

Ultrastructural changes in the hippocampal CA1 region following transient cerebral ischemia: evidence against programmed cell death

The ultrastructural changes in the pyramidal neurons of the CA1 region of the hippocampus were studied 6 h, 24 h, 48 h, and 72 h following a transient 10 min period of cerebral ischemia induced by common carotid occlusion combined with hypotension. The pyramidal neurons showed delayed neuronal death (DND), i.e. at 24 h and 48 h postischemia few structural alterations were noted in the light microscope, while at 72 h extensive neuronal degeneration was apparent. The most prominent early ultrastructural changes were polysome disaggregation, and the appearance of electron-dense fluffy dark material associated with tubular saccules. Mitochondria and nuclear elements appeared intact until frank neuronal degeneration. The dark material accumulated with extended periods of recirculation in soma and in the main trunks of proximal dendrites, often beneath the plasma membrane, less frequently in the distal dendrites and seldom in spines. Protein synthesis inhibitors (anisomycin, cycloheximide) and an RNA synthesis inhibitor (actinomycin D), administered by intrahippocampal injections or subcutaneously, did not mitigate neuronal damage. Therefore, DND is probably not apoptosis or a form of programmed cell death. We propose that the dark material accumulating in the postischemic period represents protein complexes, possibly aggregates of proteins or internalized plasma membrane fragments, which may disrupt vital cellular structure and functions, leading to cell death.

Aurintricarboxylic acid rescues PC12 cells and sympathetic neurons from cell death caused by nerve growth factor deprivation: correlation with suppression of endonuclease activity

Past studies have shown that serum-free cultures of PC12 cells are a useful model system for studying the neuronal cell death which occurs after neurotrophic factor deprivation. In this experimental paradigm, nerve growth factor (NGF) rescues the cells from death. It is reported here that serum-deprived PC12 cells manifest an endonuclease activity that leads to internucleosomal cleavage of their cellular DNA. This activity is detected within 3 h of serum withdrawal and several hours before any morphological sign of cell degeneration or death. NGF and serum, which promote survival of the cells, inhibit the DNA fragmentation. Aurintricarboxylic acid (ATA), a general inhibitor of nucleases in vitro, suppresses the endonuclease activity and promotes long-term survival of PC12 cells in serum-free cultures. This effect appears to be independent of macromolecular synthesis. In addition, ATA promotes long-term survival of cultured sympathetic neurons after NGF withdrawal. ATA neither promotes nor maintains neurite outgrowth. It is hypothesized that the activation of an endogenous endonuclease could be responsible for neuronal cell death after neurotrophic factor deprivation and that growth factors could promote survival by leading to inhibition of constitutively present endonucleases.

Inhibitors of protein synthesis and RNA synthesis prevent neuronal death caused by nerve growth factor deprivation

We have developed an experimental paradigm to study the mechanism by which nerve growth factor (NGF) allows the survival of sympathetic neurons. Dissociated sympathetic neurons from embryonic day-21 rats were grown in vitro for 7 d in the presence of NGF. Neurons were then deprived of trophic support by adding anti-NGF antiserum, causing them to die between 24 and 48 h later. Ultrastructural changes included disruption of neurites, followed by cell body changes characterized by an accumulation of lipid droplets, changes in the nuclear membrane, and dilation of the rough endoplasmic reticulum. No primary alterations of mitochondria or lysosomes were observed. The death of NGF-deprived neurons was characterized biochemically by assessing [35S]methionine incorporation into TCA precipitable protein and by measuring the release of the cytosolic enzyme adenylate kinase into the culture medium. Methionine incorporation began to decrease approximately 18 h post-deprivation and was maximally depressed by 36 h. Adenylate kinase began to appear in the culture medium approximately 30 h after deprivation, reaching a maximum by 54 h. The death of NGF-deprived neurons was entirely prevented by inhibiting protein or RNA synthesis. Cycloheximide, puromycin, anisomycin, actinomycin-D, and dichlorobenzimidazole riboside all prevented neuronal death subsequent to NGF deprivation as assessed by the above morphologic and biochemical criteria. The fact that sympathetic neurons must synthesize protein and RNA to die when deprived of NGF indicates that NGF, and presumably other neurotrophic factors, maintains neuronal survival by suppressing an endogenous, active death program.

Decreased micrococcal nuclease sensitivity of nuclei from nerve growth factor-treated PC12 cells

Nuclei from nerve growth factor-treated PC12 cells are more resistant to digestion with micrococcal nuclease than are nuclei from control cells. The production of oligosomal fragments is decreased, as is the generation of Mg2+-soluble products. One interpretation of the data is that differentiation of these cells due to treatment with nerve growth factor involves a decrease in the total number of DNA sequences transcribed.

Nerve growth factor and neural oncology

The precise role of the nerve growth factor protein (NGF) during the growth and development of the human nervous system is not determined. Although it appears to influence a number of neural functions, its mechanism of action is poorly understood. A number of researchers have proposed that NGF may be involved in several pathological conditions including cancer. It has been shown that NGF is secreted by certain sarcoma (23), neuroblastoma (113), and glioma (7,102,136) cell lines and can bind to neuroblastoma and metastatic melanoma cell lines (42). Neuroblastoma (136,181) and pheochromocytoma (165) cells in vitro can be induced by NGF to differentiate toward a morphologically "more benign" state and appropriate NGF treatment of rats can reduce the number of chemically induced gliomas and neurinomas (174,178). NGF can also reduce the growth of intracerebrally inoculated anaplastic glioma cells (172). Anti-NGF treatment of rats (178) and mice (179) can alter the tumor distribution observed following ethylnitrosourea or benzo(a)pyrene treatment (10). In humans, it has been reported that serum levels of NGF are usually elevated in persons "at risk" for neurofibromatosis (156). The precise nature of the NGF role is not known in these instances. Further understanding of the action of NGF could be of clinical importance.

Retinal ganglion cell response to axotomy and nerve growth factor antiserum treatment in the regenerating visual system of the goldfish (Carassius auratus): an in vivo and in vitro analysis

In vitro nerve growth factor (NGF) antiserum (anti-NGF) treatment was found to significantly depress retinal ganglion cell neurite outgrowth in goldfish explant culture. Goldfish retinas, conditioned by a 14-day prior optic nerve crush, demonstrated a significant dose response inhibition of neurite outgrowth if incubated with various concentrations of the antiserum (i.e. concentrations from full strength to 1:100) before explantation for tissue culture. NGF added to the incubation medium containing antiserum partially eliminated the inhibition of neurite outgrowth during the first 4 days of explant culture. Antiserum treatment at the higher concentrations (i.e. full strength and 1:1.5 dilution) caused a cessation of nerve growth from explants between culture days 3 and 4. However, controls at this time still exhibited vigorous neurite outgrowth. In vivo treatment with anti-NGF administered intraocularly at 7 days after optic nerve crush (i.e. 7 DPA) was found to significantly reduce the size and complexity of retinal ganglion cell nucleoli when analyzed morphometrically at 14 DPA. No other cell parameters measured (i.e. cell size, nuclear size, cell/nuclear ratios and mitochondrial, Golgi and RER densities) were found to be affected by the single antiserum treatment.

Immunosympathectomy: lack of evidence for a complement-mediated cytotoxic mechanism

To determine whether the destruction of peripheral sympathetic neurons by anti-NGF-antibodies results from a complement-mediated cytotoxic action or from the deprivation of endogenous NGF or immunologically NGF-like cross-reacting molecules we investigated the time-course of the reversibility of the effect of NGF-antibodies by neutralizing doses of NGF, together with the effect of NGF-antibodies in complement-deficient mice. After administration of a single dose of 50 mg/kg of purified antibodies to newborn rats the TH level was reduced to 75% of controls after 12 h, to 48% after 24 h, 39% after 36, and 28% after 48 h. After this time no further reduction occurred and levels remained constant up to 14 days. The effect of the NGF-antibodies was reversible on addition of NGF up to 48 h after antibody administration. Although the reversibility was not complete (85% of controls) the extent of the reversibility was the same whether NGF was given 12 or 48 h after the antibodies. The incompleteness of the reversibility is reflected by the small number of degenerating neurons apparent as early as 12 h after antibody administration. Since these early degenerative effects were also seen in complement-deficient mice it is concluded that they involve a small population of neurons, sensitive to short-term NGF deprivation whereas the majority of the neurons can withstand deprivation for up to 48 h without sustaining irreversible damage.

Intracellular distribution of nerve growth factor in rat pheochromocytoma PC12 cells: evidence for a perinuclear and intranuclear location

The distribution of nerve growth factor (NGF) in rat pheochromocytoma cells (clone PC12) has been studied with two different techniques: immunofluorescence and autoradiography. It was found that NGF is progressively internalized in the cytoplasmic compartment and eventually accumulates in the form of discrete dots around the nucleus. A fraction of the internalized NGF appears within the nucleoplasm, often contiguous with the nucleolus. It is suggested that cytoplasmic and perinuclear NGF may be be in contact with a pool of tubulin or actin-like proteins in their soluble or organized form and play a key role in the process of arrest of division and neurite growth.

Retinal ganglion cell response to axotomy and nerve growth factor antiserum in the regenerating visual system of the newt (Notophthalmus viridescens): an ultrastructural morphometric analysis

One 3.0 mg dose of the nerve growth factor antiserum (anti-NGF) injected into the vitreous chamber of the eye at the time of optic nerve transection elicits significant changes in the normal newt (Notophthalmus viridescens) retinal ganglion cell body response to axotomy at 7 and 14 days postaxotomy (DPA). Light microscopic observations indicate that anti-NGF treatment significantly reduces the per cent of retinal ganglion cells demonstrating nuclear chromatin reactivity (ie., homogeneous to a more heterogeneous state) from 33.36 +/- 3.02 to 22.82 +/- 2.98%. In addition, the per cent of retinal ganglion cells demonstrating prominent nucleoli is dramatically decreased from 32.08 +/- 1.64 to 18.20 +/- 1.79% at 7 DPA. It is also important to note that the number of prominent nucleoli in the 7 DPA group is reduced to such an extent by anti-NGF treatment that the value is not significantly different from that of intact controls. Intact controls will routinely exhibit approximately half the number of prominent nucleoli that are normal for the untreated 7 DPA group. A definite dose-response relationship can be shown to exist between the per cent of nuclear reactive ganglion cells demonstrating prominent nucleoli and various anti-NGF concentrations at 14 DPA. There does not appear to be a dose-response relationship between various anti-NGF concentrations and the per cent of retinal ganglion cells demonstrating nuclear reactivity at 14 DPA. However, the degree of nuclear chromatin reactivity appears to be less at the higher anti-NGF concentrations (ie., greater than or equal to 3.0 mg/eye) at 14 DPA. Electron microscopic morphometric analysis reveals that anti-NGF treatment significantly reduces the cell perikaryal area at 7 and 14 DPA while the nuclear area remains unchanged. Therefore, there is a significant decrease in the cytoplasmic/nuclear ratios at both 7 and 14 DPA in response to anti-NGF treatment which appears more pronounced by 14 DPA. Anti-NGF treatment also significantly reduces the mitochondrial and nucleolar densities, as well as the nucleolar areas of cells at 7 and 14 DPA. There are no significant changes in Golgi field densities in response to anti-NGF treatment.

Retinal ganglion cell response to axotomy and nerve growth factor in the regenerating visual system of the newt (Notophthalmus viridescens): an ultrastructural morphometric analysis

Nerve growth factor (NGF) treatment, given as a single 200 BU intraocular injection at the time of optic nerve transection, was found to significantly accelerate the retinal ganglion cell response to axotomy in the newt (Notophthalmus viridescens). In the control series the per cent of neurons in the retinal ganglion layer demonstrating nuclear reactivity (i.e. chromatin changes) reaches a peak by 14 days post axotomy (14 DPA), plateaus through 21 DPA and falls thereafter, returning to control levels by 90 DPA. NGF treatment is shown to significantly accelerate the entrance of responding retinal ganglion cells into the reactive nuclear phase between 1 and 7 DPA, and by 7 DPA nuclear reactivity has reached a peak, in contrast to 14 DPA for control values. Consequently, NGF treatment causes retinal ganglion cells to be in the nuclear reactive state a week longer than controls but reactivity diminishes after 21 DPA as in controls. Electron microscopic morphometric analysis further substantiates these observations by demonstrating that NGF treatment can elicit certain cellular organelle changes a week earlier (i.e. at 7 DPA) than they would normally occur (i.e. at 14 DPA) in response to axotomy. In addition to eliciting cellular hypertrophy at 7 DPA, NGF treatment significantly increases Golgi field densities in the neuronal perikaryal cytoplasm as well as a doubling of the number of nucleoli per nucleus and stimulating a significant increase in nucleolar cross-sectional areas. A dose-response relationship exists between the per cent of retinal ganglion cells demonstrating nuclear reactivity at 7 DPA and various NGF concentrations which compares favorably with the dose response study involving the number of regenerating axons per nerve cross-section at 14 DPA. Studies to determine if the NGF mediated responses were a specific effect elicited by this protein molecule or whether they are also produced by other peptides which share some properties in common with NGF demonstrate that only NGF is capable of eliciting these responses.

A study of the de- and regenerative changes in the sympathetic nervous system of the adult mouse after treatment with the antiserum to nerve growth factor

In the adult mouse, the antiserum to nerve growth factor (NGF) induced marked atrophic changes of the ganglionic cell bodies in the superior cervical ganglion (SCG) and a disappearance of adrenergic nerve terminals in several peripheral tissues. By fluorescence histochemistry a lower-than-normal content of the noradrenaline (NA) transmitter was observed within the entire adrenergic neurone only 1 day after a single injection of NGF-antiserum (0.1 ml/g body weight). An atrophy of adrenergic nerve cell bodies and a disappearance of adrenergic nerve terminals were observed after 3 days, but the antiserum-induced effects did not appear maximally developed until 7 days after treatment. These fluorescence histochemical findings were paralleled by a gradual decrease of the endogenous NA levels in peripheral tissues and also of the weight of the SCG. A gradually proceeding restoration towards normal of the adrenergic innervation apparatus was observed fluorescence histochemically following a 5-day treatment with NGF-antiserum (0.1 ml/g body weight each dose), and after 6 weeks to 3 months a normal or close to normal fluorescence microscopical appearance was regained in the peripheral tissues and also in the SCG. These findings were parelleled by the results of the determinations of endogenous NA in peripheral tissues and by the results of weighing the SCG. We discuss some important differences between NGF-antiserum and 6-hydroxydopamine with respect to their mode of action on the mature sympathetic nervous system. Finally, we suggest that a decreased availability of NGF in a terminal area, due to an interference with endogenous NGF by NGF-antibodies, may temporarily result in an impaired function of the supplying adrenergic neurone, including a degeneration of nerve terminals.

Sympathetic nerve cell destruction in newborn mammals by 6-hydroxydopamine

A selective and permanent destruction of sympathetic ganglia was achieved by injecting 6-hydroxydopamine in newborn animals. A lifelong chemical sympathectomy may thus be obtained. The process of cell damage and destruction is substantially different from that produced with an antiserum to a specific nerve growth factor.