Nerve Growth Factor is Required for Induction of c-Fos Immunoreactivity by Serum, Depolarization, Cyclic AMP or Trauma in Cultured Rat Sympathetic Neurons

Cytoplasmic inclusions of Htt exon1 containing an expanded polyglutamine tract suppress execution of apoptosis in sympathetic neurons

Proteins containing extended polyglutamine repeats cause at least nine neurodegenerative disorders, but the mechanisms of disease-related neuronal death remain uncertain. We show that sympathetic neurons containing cytoplasmic inclusions formed by 97 glutamines expressed within human huntingtin exon1-enhanced green fluorescent protein (Q97) undergo a protracted form of nonapoptotic death that is insensitive to Bax deletion or caspase inhibition but is characterized by mitochondrial dysfunction. By treating the neurons with combined cytosine arabinoside and NGF withdrawal, we demonstrate that Q97 confers a powerful resistance to apoptosis at multiple levels: despite normal proapoptotic signaling (elevation of P-ser15-p53 and BimEL), there is no increase of Puma mRNA or Bax activation, both necessary for apoptosis. Even restoration of Bax translocation with overexpressed Puma does not activate apoptosis. We demonstrate that this robust inhibition of apoptosis is caused by Q97-mediated accumulation of Hsp70, which occurs through inhibition of proteasomal activity. Thus, apoptosis is reinstated by short hairpin RNA-mediated knockdown of Hsp70. These findings explain the rarity of apoptotic death in Q97-expressing neurons. Given the proteasomal blockade, we test whether enhancing lysosomal-mediated degradation with rapamycin reduces Q97 accumulation. Rapamycin reduces the amount of nonpathological Q25 by 70% over 3 d, but Q97 accumulation is unaffected. Interestingly, Q47 inclusions form more slowly as a result of constitutive lysosomal degradation, but faster-forming Q97 inclusions escape lysosomal control. Thus, cytoplasmic Q97 inclusions are refractory to clearance by proteasomal and lysosomal systems, leading to a toxicity that dominates over neuroprotective Hsp70. Our findings may explain the rarity of apoptosis but the inevitable cell death associated with polyQ inclusion diseases.

Temporal coupling of cyclic AMP and Ca/calmodulin-stimulated adenylyl cyclase to the circadian clock in chick retinal photoreceptor cells

cAMP signaling pathways play crucial roles in photoreceptor cells and other retinal cell types. Previous studies demonstrated a circadian rhythm of cAMP level in chick photoreceptor cell cultures that drives the rhythm of activity of the melatonin synthesizing enzyme arylalkylamine N-acetyltransferase and the rhythm of affinity of the cyclic nucleotide-gated channel for cGMP. Here, we report that the photoreceptor circadian clock generates a rhythm in Ca(2+)/calmodulin-stimulated adenylyl cyclase activity, which accounts for the temporal changes in the cAMP levels in the photoreceptors. The circadian rhythm of cAMP in photoreceptor cell cultures is abolished by treatment with the l-type Ca(2+) channel antagonist nitrendipine, while the Ca(2+) channel agonist, Bay K 8644, increased cAMP levels with continued circadian rhythmicity in constant darkness. These results indicate that the circadian rhythm of cAMP is dependent, in part, on Ca(2+) influx. Photoreceptor cell cultures exhibit a circadian rhythm in Ca(2+)/calmodulin-stimulated adenylyl cyclase enzyme activity with high levels at night and low levels during the day, correlating with the temporal changes of cAMP in these cells. Transcripts encoding two of the Ca(2+)/calmodulin-stimulated adenylyl cyclases, type 1 and type 8 (Adcy1 and Adcy8), displayed significant daily rhythms of mRNA expression under a light-dark cycle, but only the Adcy1 transcript rhythm persisted in constant darkness. Similar rhythms of Adcy1 mRNA level and Ca(2+)/calmodulin-stimulated adenylyl cyclase activity were observed in retinas of 2-week-old chickens. These results indicate that a circadian clock controls the expression of Adcy1 mRNA and Ca(2+)/calmodulin-stimulated adenylyl cyclase activity; and calcium influx into these cells gates the circadian rhythm of cAMP, a key component in the regulation of photoreceptor function.

The BH3-only protein Puma is both necessary and sufficient for neuronal apoptosis induced by DNA damage in sympathetic neurons

DNA damage activates apoptosis in several neuronal populations and is an important component of neuropathological conditions. While it is well established that neuronal apoptosis, induced by DNA damage, is dependent on the key cell death regulators p53 and Bax, it is unknown which proteins link the p53 signal to Bax. Using rat sympathetic neurons as an in vitro model of neuronal apoptosis, we show that cytosine arabinoside is a DNA damaging drug that induces the expression of the BH3-only pro-apoptotic genes Noxa, Puma and Bim. Increased expression occurred after p53 activation, measured by its phosphorylation at serine 15, but prior to the conformational change of Bax at the mitochondria, cytochrome c (cyt c) release and apoptosis. Hence Noxa, Puma and Bim could potentially link p53 to Bax. We directly tested this hypothesis by the use of nullizygous mice. We show that Puma, but not Bim or Noxa, is a crucial mediator of DNA damage-induced neuronal apoptosis. Despite the powerful pro-apoptotic effects of overexpressed Puma in Bax-expressing neurons, Bax nullizygous neurons were resistant to Puma-induced death. Therefore, Puma provides the critical link between p53 and Bax, and is both necessary and sufficient to mediate DNA damage-induced apoptosis of sympathetic neurons.

Differential phosphoprotein labeling (DIPPL), a method for comparing live cell phosphoproteomes using simultaneous analysis of (33)P- and (32)P-labeled proteins

We developed a differential method to reveal kinase-specific phosphorylation events in live cells. In this method, cells in which the specified kinase is inactive are labeled with (32)Pi, whereas cells in which the kinase is active are labeled with (33)Pi. The two cell extracts are then mixed, and proteins are separated on a single two-dimensional gel. The dried gel is exposed twice. The first exposure reveals both (32)P- and (33)P-labeled proteins; the kinase-specific spots are revealed because of (33)P labeling. The second exposure is conducted with two acetate sheets intervening between the gel and the detection plate. This maneuver screens out the less energetic (33)P-labeled proteins while allowing the more energetic (32)P-labeled proteins to be detected, thus leaving only those spots that were phosphorylated independently of the specified kinase. We demonstrate the utility of this method for detecting kinase substrates in rare tissue by focusing on extracellular signal-regulated kinase-specific phosphorylation of stathmin/OP18 in primary rat sympathetic neurons.

Death commitment point is advanced by axotomy in sympathetic neurons

Axotomized neurons have several characteristics that are different from intact neurons. Here we show that, unlike established cultures, the axotomized sympathetic neurons deprived of NGF become committed to die before caspase activation, since the same proportion of NGF-deprived neurons are rescued by NGF regardless of whether caspases are inhibited by the pan-caspase inhibitor Boc-Asp(O-methyl)-CH(2)F (BAF). Despite prolonged Akt and ERK signaling induced by NGF after BAF treatment has prevented death, the neurons fail to increase protein synthesis, recover ATP levels, or grow. Within 3 d, all the mitochondria disappear without apparent removal of any other organelles or loss of membrane integrity. Although NGF does rescue intact BAF-treated 6-d cultures after NGF deprivation, rescue by NGF fails when these neurons are axotomized before NGF deprivation and BAF treatment. Moreover, cytosolic cytochrome c rapidly kills axotomized neurons. We propose that axotomy induces signals that make sympathetic neurons competent to die prematurely. NGF cannot repair these NGF-deprived, BAF-treated neurons because receptor signaling (which is normal) is uncoupled from protein renewal, and the mitochondria (which are damaged) go on to be eliminated. Hence, the order of steps underlying neuronal death commitment is mutable and open to regulation.

Nerve growth factor-induced PKB/Akt activity is sustained by phosphoinositide 3-kinase dependent and independent signals in sympathetic neurons

Phosphoinositide 3-kinase and its downstream effector kinase PKB/Akt have been suggested to have crucial roles in suppressing apoptosis in several classes of neurons. However, few studies have conducted a long-term investigation of either kinase activity, many studies relying instead on use of the phosphoinositide 3-kinase inhibitors wortmannin and LY294002. When we added LY294002 or wortmannin to sympathetic neurons, apoptosis in the presence of nerve growth factor (NGF) was very slow compared to that obtained by NGF deprivation. However, expression of a kinase-inactive mutant of PKB/Akt in the presence of NGF induced apoptosis in a significant proportion of the neurons. To understand this discrepancy, we investigated more closely the regulation of PKB/Akt activity by NGF. NGF stimulation induced a rapid increase in PKB/Akt activity which was sustained at approximately 6-fold up to 24 h. Phosphoinositide 3-kinase was also rapidly activated by NGF. However, concentrations of wortmannin which completely blocked phosphoinositide 3-kinase activity in the neurons inhibited no more than 50-70% of cellular PKB/Akt activity. Similarly, approximately 50% of maximal NGF-stimulated PKB/Akt activity remained elevated at concentrations of LY294002 which completely blocked neurite outgrowth, a process known to be phosphoinositide 3-kinase dependent. We suggest that a proportion of the sustained PKB/Akt activity induced by NGF is mediated by phosphoinositide 3-kinase-independent pathways. These results raise a cautionary note as to the usefulness of LY294002 or wortmannin as tools to dissect the role of PKB/Akt in neuronal survival.

A role for MAPK/ERK in sympathetic neuron survival: protection against a p53-dependent, JNK-independent induction of apoptosis by cytosine arabinoside

The antimitotic nucleoside cytosine arabinoside (araC) causes apoptosis in postmitotic neurons for which two mechanisms have been suggested: (1) araC directly inhibits a trophic factor-maintained signaling pathway required for survival, effectively mimicking trophic factor withdrawal; and (2) araC induces apoptosis by a p53-dependent mechanism distinct from trophic factor withdrawal. In rat sympathetic neurons, we found that araC treatment for 12 hr induced approximately 25% apoptosis without affecting NGF-maintained signaling; there was neither reduction in the activity of mitogen activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) or protein kinase B/Akt, a kinase implicated in NGF-mediated survival, nor was there c-Jun N-terminal kinase (JNK) activation or c-Jun N-terminal phosphorylation, events implicated in apoptosis induced by NGF withdrawal. However, araC treatment, but not NGF-withdrawal, elevated expression of p53 protein before and during apoptosis. Additionally, araC-induced apoptosis was suppressed in sympathetic neurons from p53 null mice. Although MAPK/ERK activity is not necessary for NGF-induced survival, it protected against toxicity by araC, because inhibition of the MAPK pathway by PD98059 resulted in a significant increase in the rate of apoptosis induced by araC in the presence of NGF. Consistent with this finding, ciliary neurotrophic factor, which does not cause sustained activation of MAPK/ERK, did not protect against araC toxicity. Our data show that, in contrast to NGF deprivation, araC induces apoptosis via a p53-dependent, JNK-independent mechanism, against which MAPK/ERK plays a substantial protective role. Thus, NGF can suppress apoptotic mechanisms in addition to those caused by its own deprivation.

Active p21Ras is sufficient for rescue of NGF-dependent rat sympathetic neurons

We have examined whether p21Ras proteins can rescue nerve growth factor-deprived rat sympathetic neurons from death, to test further our hypothesis that p21Ras is a central mediator in the nerve growth factor-to-survival signalling pathway. After crosslinking [125I]nerve growth factor to live neurons, two forms of Trk (molecular weight approximately 140,000 and 115,000) were immunoprecipitated with anti-Trk antibodies. Nerve growth factor induced tyrosine phosphorylation of both Trk forms and at least two additional proteins. When these phosphorylations were prevented by staurosporine (in a protein kinase C-independent manner) the neurons died. However, neurons were rescued from death due to staurosporine treatment by intracellular loading of oncogenic Ha-Ras(val12) protein. Both Ha-Ras(val12) and cellular Ha-Ras proteins maintained survival for several days in the absence of nerve growth factor and mimicked other actions of nerve growth factor, inducing rapid c-Fos protein expression and robust neurite outgrowth. Conversely, Fab fragments of neutralizing antibodies to p21Ras which blocked the capacity of nerve growth factor to promote neuron survival were also found to inhibit the early expression of c-Fos protein in these neurons. The close correspondence observed between the timing of onset of c-Fos responsiveness and acquisition of nerve growth factor-dependence in embryonic day 17 sympathetic neurons, and the coordinate increase found in both parameters until embryonic day 19 indicates that c-Fos protein expression is a good biochemical indicator of the presence of a functional nerve growth factor-to-survival signal transduction pathway. Nevertheless, expression of c-Fos is not sufficient for survival since phorbol esters induce c-Fos with no effect on survival. These data strengthen our proposal that p21Ras proteins are crucial anti-apoptotic mediators of survival in rat sympathetic neurons by demonstrating that p21Ras is both necessary and sufficient to rescue neurons which are disabled from signalling through Trk receptors.

Activation of p44 and p42 MAP kinases is not essential for the survival of rat sympathetic neurons

We have examined whether activation of MAP kinases [or extracellular signal-regulated kinases (ERKs)] is required for the survival of rat sympathetic neurons by comparing the actions of three survival factors whose survival-promoting actions can be blocked by neutralizing Fab fragments to p21 ras (Nobes and Tolkovsky, 1995, Eur. J. Neurosci., 7, 344-350), nerve growth factor (NGF), the cytokines ciliary neurotrophic factor (CNTF) and leukaemia inhibitory factor (LIF), and the cyclic AMP analogue 4-(8-chlorophenylthio)cAMP (CPTcAMP). NGF-induced survival was accompanied by an intense (15- to 30-fold) and steady (> 24 h) activation of p44 and p42 ERKs which waned rapidly (t1/2 approximately 30 min) upon NGF withdrawal. However, concentrations of NGF that induced a weak (4- to 5-fold) stimulation of the ERKs were not sufficient to maintain long-term survival. Moreover, prolonged and intense stimulation of the ERKs by NGF for up to 15.5 h was unable to confer long-term survival, since withdrawal of NGF after this time resulted in neuronal death that was kinetically indistinguishable from the death of neurons that had not been exposed to NGF. By contrast, CNTF and LIF continued to support survival for up to 3 days after eliciting only transient (< 30 min and 1 h respectively) activation of p44 and p42 ERKs, while CPTcAMP induced survival for several days without any measurable activation of the ERKs. Taken together, these data suggest that ERK activation per se is neither necessary nor sufficient for survival and that alternative pathways exist for effecting long-term survival of rat sympathetic neurons.

Programmed cell death in sympathetic neurons: a study by two-dimensional polyacrylamide gel electrophoresis using computer image analysis

The technique of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) coupled with computer image analysis was used in this study to examine changes in protein expression occurring during the onset of programmed cell death (PCD) in rat sympathetic neurons following withdrawal of nerve growth factor (NGF). Sympathetic neurons from superior cervical ganglia of postnatal day-one Wistar rats were cultured in the presence of NGF for 24 h and then either maintained in the presence of NGF or deprived of NGF for a period of 8 h. To label the proteins being synthesised, neurons were cultured in the presence of L-[35S]methionine for a further 2 h under the same conditions but with 3% of the normal methionine concentration. Neuronal proteins were then analysed by 2-D PAGE using immobilised pH gradient (IPG) gel strips in the first dimension. For the second dimension a custom-built electrophoresis system capable of running multiple sodium dodecyl sulfate (SDS)-PAGE slab gels in a vertical configuration, with good temperature control (+/- 0.7 degrees C) was used and is described in this paper. Proteins resolved on the dried gels were visualised using storage phosphor technology and the digitised images subjected to rigorous analysis using the QUEST II software system. Seventeen proteins whose relative synthesis decreased and four proteins that increased upon NGF withdrawal were located and are documented.

The rate of Wallerian degeneration in cultured neurons from wild type and C57BL/WldS mice depends on time in culture and may be extended in the presence of elevated K+ levels

Wallerian degeneration of severed axons is delayed in C57BL/WldS mice. We have examined this further in cultured sympathetic, sensory and CNS neurons using superior cervical ganglion (SCG), dorsal root ganglion (DRG) and cerebellar granule neurons respectively from neonatal mice. We found that the time taken for the neurites to degenerate depends upon the length of time in culture before cutting, reaching a maximum by approximately 7 days when C57BL/WldS neurites survive for > 6 days after axotomy. The onset of degeneration could also be extended in SCG and DRG neurites from wild type C57BL/6J mice. After 7 days in culture these neurites normally degenerate within approximately 12-16 h of axotomy, but in the presence of raised K+ (50 mM) degeneration often did not begin until a further 2 days had lapsed. Under similar conditions degeneration of neurites from C57BL/WldS mice was also found to be further delayed, extending survival from approximately 5-6 days to > 7 days. The L-type Ca2+ channel blockers nifedipine (5 microM) and verapamil (10 microM) both blocked the effect of raised [K+], although not completely. Thapsigargin, which raises cytoplasmic [Ca2+], and the cAMP analogue 8-(4-chlorophenyl-thio)cAMP were also able to delay degeneration, but only when added 24 h prior to axotomy. These results show that it is possible to influence the course of Wallerian degeneration and that increases in levels of cytoplasmic Ca2+ can protect neurites from its onset.

Neutralizing anti-p21ras Fabs suppress rat sympathetic neuron survival induced by NGF, LIF, CNTF and cAMP

In purified cultures of newly isolated rat sympathetic neurons plated on laminin, apoptosis is suppressed by the cytokines leukaemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF), by the permeant cAMP analogue 8-(4-chlorophenylthio)cAMP, and by nerve growth factor. Whilst nerve growth factor, 8-(4-chlorophenylthio)cAMP and LIF/CNTF initiate survival by using different kinases, in each case survival is inhibited by a Fab fragment of Y13-259, a neutralizing antibody to p21ras proteins, but not by rat IgG Fab. The inhibitory effect of Y13-259 could be partially attenuated by cotrituration of the Fab with T'24(inactive)ras. Thus, prevention of apoptosis in rat sympathetic neurons by several different survival factors appears to be critically dependent on p21ras protein activity.

Expression of the cyclic AMP-dependent protein kinase (PKA) catalytic subunit from a herpes simplex virus vector extends the survival of rat sympathetic neurons in the absence of NGF

Superior cervical ganglion neurons from neonatal rats are dependent on nerve growth factor for their survival both in vivo and in vitro. In culture this requirement can be largely replaced by cAMP or its analogues. Since activation of protein kinase A by cAMP is likely to be the pathway by which it exerts its survival-promoting effect, we have tested the feasibility of using herpes simplex virus (HSV) as a vector for expressing survival-promoting genes in neurons by cloning the catalytic subunit of the cAMP-dependent protein kinase (PKAcat) with a metallothionein gene promoter into the HSV thymidine kinase gene by homologous recombination. About 95% of the neurons became infected using 2.5 p.f.u. per cell. When this construct was used to express PKAcat in superior cervical ganglion neurons, in the presence of nerve growth factor (NGF) increases of 1.9- to 2.4-fold in PKA activity were found 8-10 h after infection; levels remained elevated (1.4- to 2.1-fold) up to 18 h, returning to basal by 24 h. After infection in the absence of NGF, cumulative activity over 24 h was approximately 3.5-fold lower in the first 24 h. Although the level of the inhibitory regulatory subunit type I was raised by 18 h, this is unlikely to completely explain the transient activity of PKAcat. When neurons were induced to express maximum PKAcat levels in the presence of NGF and then deprived of NGF, survival was extended by up to 2 days, demonstrating a direct role for PKA in promoting survival. By this time, some neurite degeneration was beginning which appeared to be partly due to toxic effects of the virus. However, replenishment with NGF supported further survival, showing that at this time the neurons were still viable. Similar rates of survival were obtained using a tsK-based PKAcat vector, but no significant survival was obtained with parental HSV or tsK virus strains. These data demonstrate the feasibility, and highlight some of the problems, of using HSV-based vectors as tools for expressing functional survival proteins in sympathetic neurons.

Apoptosis is induced in post-mitotic rat sympathetic neurons by arabinosides and topoisomerase II inhibitors in the presence of NGF

Sympathetic neurons depend on nerve growth factor (NGF) for their survival and die by apoptosis when NGF is withdrawn, despite their post-mitotic state. Martin et al. (1990, J. Neurosci. 10, 184–193) showed that cytosine arabinoside, but no other arabinofuranosyl nucleoside, could induce cell death in the presence of NGF and they suggested that it may block a critical step in the NGF-signalling pathway. We show that cytosine arabinoside is not the only nucleoside capable of inducing apoptosis in sympathetic neurons in the presence of NGF. In newly isolated neurons from P0 rat pups cultured in the presence of NGF, all the arabinose nucleosides (adenine, cytosine, guanine and thymine) induce apoptosis at 10 microM when combined with 5-fluorodeoxyuridine treatment. Because 1-beta-arabinofuranosylcytosine is associated with double-strand breaks and chromosomal abberrations, we examined whether topoisomerase II inhibitors, which also cause double-strand breaks by stabilising the enzyme-DNA ‘cleavable complex’, were capable of promoting apoptosis in these neurons. Although P0 rat neurons are strictly postmitotic, topoisomerase II inhibitors teniposide and mitoxantrone induced them to die by apoptosis in the presence of NGF with the same apparent time-course as arabinose treatment or NGF withdrawal. By contrast, ICRF 193, a catalytic inhibitor of topoisomerase II, reduced the extent of apoptosis induced by mitoxantrone or teniposide by 80% if added simultaneously with the latter but by 2 hours it had no rescue effect, suggesting that topoisomerase II is highly active in these neurons. ICRF 193 also partially reduced the induction of fluorodeoxyuridine-dependent apoptosis by the arabinose nucleosides.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of apoptosis in cultured rat sympathetic neurons after nerve growth factor withdrawal

Sympathetic neurons depend on nerve growth factor (NGF) for their survival both in vivo and in vitro. In culture, the neurons die after NGF withdrawal by an autonomous cell death program but whether these neurons die by apoptosis is under debate. Using vital DNA stains and in situ nick translation, we show here that extensive chromatin condensation and DNA fragmentation occur before plasma membrane breakdown during the death of NGF-deprived rat sympathetic neurons in culture. Furthermore, kinetic analysis of chromatin condensation events within the cell population is consistent with a model which postulates that after NGF deprivation nearly all of the neurons die in this manner. Although the dying neurons display membrane blebbing, cell fragmentation into apoptotic bodies does not occur. Apoptotic events proceed rapidly at around the time neurons become committed to die, regardless of neuronal culture age. However the duration of NGF deprivation required to commit neurons to die, and the rate at which apoptosis occurs, increase with culture age. Thus, within the first week of culture, apoptosis is the predominant form of cell death in sympathetic neurons.

Cell-type-specific expression and regulation of a c-fos-NGF fusion gene in neurons and astrocytes of transgenic mice

A mouse line transgenic for nerve growth factor (NGF) was developed using the mouse prepro-NGF cDNA inserted within a plasmid containing the proximal region (-10 to -550 bp) of the c-fos promoter and the transcription termination and polyadenylation signals of the rabbit beta-globin gene. No significant modification of gross behavior or central nervous system anatomy was detected in adult animals as assessed by immunohistochemistry and in situ hybridization for NGF and choline acetyltransferase. The expression of the transgene and the possible regulation of its expression by agents acting on the promoter were investigated in vitro. Despite the presence of an additional pool of NGF mRNA specific to the transgene, basal levels of NGF in the supernatant of transgenic astrocytes were similar to normal ones. On the other hand, transgenic neurons spontaneously synthesized and released levels of NGF two to three times higher than normal neurons, while mRNA levels were barely detectable by conventional Northern blotting. The tissue-specificity of NGF expression was respected, with higher levels in hippocampal than neocortical neurons. Increases of NGF mRNA by agents acting on the promoter could be observed in normal and transgenic astrocytes only after inhibition of the protein synthesis by cycloheximide, suggesting a similar rapid turnover of normal and transgenic transcripts. Cyclic AMP agonists specifically increased the secretion of NGF protein by transgenic astrocytes and neurons, while activators of the protein kinase C had a similar effect on transgenic and normal cells. Differences between amounts of NGF secreted by neurons and astrocytes with regards to their respective content in mRNA suggest that transgenic transcripts are subject to normal cell- and tissue-specific post-transcriptional regulations. Agents acting on the c-fos promoter through the protein kinase C or cyclic AMP routes differentially increased the secretion of NGF by transgenic astrocytes or neurons, supporting this hypothesis.

Fos induction by nerve growth factor in the adult rat brain

The distribution of Fos, the protein product of the immediate early gene c-fos, was studied with immunocytochemistry in the adult male rat brain after nerve growth factor (NGF) administration. NGF was injected in the lateral cerebral ventricle through a previously implanted cannula. The total number of Fos-immunoreactive (ir) neurons in the brain was 2-3 times higher after NGF administration than in control animals (untreated or injected with cytochrome c). With respect to control rats, in the NGF-treated cases Fos-ir cells were more numerous in the anterior olfactory nucleus, in the medial prefrontal and anterior cingulate cortices, in the basal forebrain, in the preoptic and ventromedial nuclei of the hypothalamus, as well as anterior hypothalamic area, in the thalamic midline nuclei, and in some brainstem structures, such as the parabrachial nucleus. The relative quantitative increase of Fos-ir neurons varied in the different structures. In addition, Fos-ir neurons were evident after NGF administration in areas devoid of immunopositive cells in control animals. These included: frontoparietal and occipital cortical fields, the hypothalamic arcuate nucleus, and many brainstem structures, such as the dorsal nucleus of the lateral lemniscus, posterodorsal tegmental, medial and lateral vestibular, ventral cochlear, and prepositus hypoglossal nuclei. These findings demonstrate that the intracerebroventricular administration of NGF can induce c-fos expression in neurons in vivo. The distribution of Fos-ir neurons indicates that NGF can induce activation of functionally and chemically heterogeneous neuronal subsets in the brain.

Early nerve growth factor-induced events in developing rat septal neurons

A culture system enriched for nerve growth factor (NGF) receptor bearing cells was developed to investigate signal transduction events activated by NGF in postmitotic central nervous system neurons. Cells from the septal region of embryonic rats at 16 days of gestation were grown on glass coverslips above a glial cell layer established from postnatal rat cortex. The separation of glial and neuronal planes in this "bilaminar" system permits the diffusion of glial-derived factors required by septal neurons for survival yet allows the investigation of NGF responses in a pure neuronal population. Approximately 15% of the neurons in this culture system were immunoreactive for the low affinity NGF receptor. NGF rapidly increased MAP kinase activity (2-5 min) and transiently induced expression of c-fos in septal neurons. NGF treatment also increased choline acetyltransferase activity, while the number of cholinergic neurons remained constant. Septal neuron survival depended on the presence of glial cells, but neuronal viability in the bilaminar system was unaffected by anti-NGF antiserum, indicating that glial-derived neurotrophic support is not mediated by NGF alone. These data suggest that the bilaminar culture system is a useful system for the study of early events in NGF-activated signal transduction and the nature of glial-derived trophic support of developing basal forebrain neurons.

c-fos expression in gracilothalamic tract neurons after electrical stimulation of the injured sciatic nerve in the adult rat

The number of c-fos protein-like immunoreactive (Fos-LI) cells in the gracile nucleus was determined after electrical stimulation at A alpha/A beta-fiber strength of the normal and of the previously injured sciatic nerve in adult rats. No Fos-LI cells were seen after electrical stimulation of the noninjured sciatic nerve, or after sciatic nerve injury without electrical stimulation. However, stimulation 21 days after sciatic nerve transection resulted in numerous Fos-LI cells in the ipsilateral gracile nucleus. Combined Fos immunocytochemistry and retrograde labeling from the thalamus showed that the majority (76%; range = 70-80%) of the cells in the gracile nucleus that expressed Fos-LI after nerve injury projected to the thalamus. The results indicate that morphological, biochemical, and physiological alterations in primary sensory central endings and second-order neurons, which have earlier been demonstrated in the dorsal column nuclei after peripheral nerve injury, are accompanied by changes in the c-fos gene activation pattern after stimulation of the injured sciatic nerve. A substantial number of the c-fos-expressing neurons project to the thalamus.

Neuronal specificity and plasticity in the autonomic nervous system

The autonomic nervous system is divided into the sympathetic, parasympathetic and enteric subdivisions. The present review is focussed upon the highly specialized reflex organization and neurochemistry of sympathetic parasympathetic neurons. The currently available informations allow to conclude that autonomic control of each peripheral target tissue is specifically regulated under normal conditions but nevertheless able to respond to altered conditions by changes in neural activity and mediator expression.

Changing pattern of c-FOS expression in spinal cord neurons after electrical stimulation of the chronically injured sciatic nerve in the rat

Immunocytochemical technique was used to study the distribution of c-FOS protein immunoreactive cells in the spinal cord and gracile nuclei 2 h after electrical stimulation of the sciatic nerve in ketamine/xylazine/acepromazine-anesthetized adult rats. Quantitative examination of the c-fos-labeled cells in the spinal cord laminae was made in unoperated and sham operated controls, after sciatic nerve transection without electrical stimulation, and after electrical stimulation at C-fiber or A alpha/beta-fiber intensity, both in normal animals and at various survival times after chronic sciatic nerve injury (transection and ligation) or crush. Unoperated animals showed very few c-fos-labeled cells, and sham operated controls showed labeled cells located mainly outside the sciatic nerve projection territory. A small increase in number of c-fos protein positive cells was seen after sciatic nerve transection without electrical stimulation. Stimulation of the normal sciatic nerve at C-fiber intensity resulted in c-fos protein-positive cells within the sciatic projection territory in the ipsilateral dorsal horn. Labeled cells were seen in all spinal cord laminae except lamina IX, with the vast majority in lamina I and outer lamina II. No labeled cells were seen in the gracile nucleus. Stimulation at A alpha/beta fiber intensity resulted in no or only a very small number of c-fos-positive neurons. Electrical stimulation of the injured sciatic nerve at C-fiber intensity, using the uninjured contralateral side as control, resulted in significant decreases in c-fos-immunoreactive cells in lamina I plus the outer portion of lamina II at 12 and 39 days survival after injury. A non-significant decrease was seen in these laminae also after 21 days. Significant increases were seen in laminae III and IV at 21 days. Decreases in laminae V, VI and more ventral laminae were significant at 21 and 39 days after injury. At longer survival times, the difference between the normal and injured side seen weeks after injury tended to disappear. Stimulation at A alpha/beta fiber intensity 21 days after injury resulted in increases in the numbers of labeled cells in ipsilateral laminae II, III and IV and in the gracile nucleus. Sciatic nerve stimulation after crush injury resulted in more variable side differences, with tendencies for the same alterations as those noted after chronic transection-ligation.(ABSTRACT TRUNCATED AT 400 WORDS)

Nerve growth factor transcriptional control of c-fos promoter transfected in cultured spinal sensory neurons

High efficiency gene transfer (greater than 90%) in chicken dorsal root ganglion neurons has been obtained by DNA calcium phosphate co-precipitation, hence providing an important tool to study control of gene expression in primary neurons. Transfection with c-fos promoter sequences linked to the chloramphenicol acetyltransferase reporter gene showed that the serum responsive element functions as a strong transcriptional enhancer. Transcription from this element is developmentally regulated, and mediates the genetic response to nerve growth factor (NGF) in developing avian sensory neurons. Furthermore, NGF exerts a negative effect on transcription from the cyclic AMP responsive element, thereby supporting the involvement of tyrosine kinase activation by NGF in primary sensory neurons.

The death programme in cultured sympathetic neurones can be suppressed at the posttranslational level by nerve growth factor, cyclic AMP, and depolarization

We have examined whether sympathetic neurones that have lost the potential to be rescued by protein and RNA synthesis inhibitors after a period of nerve growth factor (NGF) deprivation are irreversibly committed to die. We found that 15 h after withdrawal of NGF from 7-day cultures of neonatal rat superior cervical ganglion neurones, 50% of the neurones lost the potential to be rescued by cycloheximide but that NGF rescued most of the neurones. By 22 h after NGF withdrawal, only 10% of the neurones were rescued by inhibition of macromolecular synthesis with cycloheximide, puromycin, or actinomycin D, but as many as 60-80% of the neurones were rescued by NGF. This is after the time at which a DNA "ladder," consistent with cell death by apoptosis, was first detected (18 h). As long as 27 h of NGF withdrawal was required before 50% of the neurones lost the potential to be rescued by NGF. The survival-promoting agent 8-(4-chlorophenylthio)cyclic AMP (CPTcAMP) or depolarization with 50 mM KCl (HK) rescued neurones with kinetics similar to those of NGF, and rescue by all three agents did not require protein synthesis. Thus, NGF, CPTcAMP, and HK can rescue neurones deprived of NGF at much later times than either protein or RNA synthesis inhibitors by acting at the posttranslational level, a finding suggesting that initiation of the cell death programme in sympathetic neurones is not an irreversible step.