Central nervous system DNA fragmentation induced by the inhibition of nuclear factor kappa B

Ageing of the central nervous system (CNS) is characterized by a progressive apoptotic loss of neurons that may be in part due to impaired neurotrophin signaling mediated by such elements as the transcription factor nuclear factor kappa B (NFkappaB). To support this hypothesis, we inhibited nuclear translocation of NFkappaB in vivo by injecting a proteasome inhibitor (PSI) directly in the CNS lateral ventricle of rats and then measured fragmented DNA in various CNS areas as an index of ongoing apoptosis. Our results show that after PSI injection there was a significant inhibition of NFkappaB activity in vivo that resulted in the appearance of fragmented (apoptotic) DNA in the CNS of rats. These results suggest that alteration of NFkappaB may cause apoptotic cell death in the rat CNS during ageing.

MAP2, synaptophysin immunostaining in rat brain and behavioral modifications after cerebral postischemic reperfusion

Plasticity in the central nervous system after cerebral ischemia is a controversial issue; focal cerebral ischemia produces an area of infarction that is surrounded by neurons that may respond to nearby damage by creating new synapses. In the present study the expression of the postsynaptic microtubule-associated protein 2 (MAP2) and the presynaptic marker protein, synaptophysin, was investigated by immunocytochemical techniques in the CA1 sector of hippocampus and in cerebellum of rats made ischemic by bilateral clamping of common carotid arteries and reperfused for 7 and 30 days. In addition, ischemia-induced behavioral alterations were also evaluated after 7 and 30 days of reperfusion. The present study demonstrates a decreased postsynaptic MAP2 immunoreactivity, representative of neuronal loss, particularly in CA1 sector of hippocampus and in cerebellum of ischemic rats reperfused for 7 days. After 30 days of reperfusion, MAP2 immunostaining was similar to control. In the same brain sections an increased presynaptic synaptophysin immunoreactivity has been observed only after 30 days of reperfusion. These data suggest compensatory regenerative changes associated with synaptic remodelling and are supported by behavioral recovery observed under the same experimental conditions.

In vivo regulation of amyloid precursor protein secretion in rat neocortex by cholinergic activity

The proteolytic cleavage of the amyloid precursor protein (APP) has been shown to be modulated through specific muscarinic receptor activation in vitro in both transfected cell lines and native brain slices, whereas a demonstration of receptor-mediated control of APP processing under in vivo conditions is still lacking. To simulate alterations in muscarinic receptor stimulation in vivo, we have (i) specifically reduced the cortical cholinergic innervation in rats using partial immunolesions with 192IgG-saporin, and (ii) restored cholinergic function in lesioned rats by transplantation of nerve growth factor producing fibroblasts. While total APP levels in cortical homogenates were unaffected by cholinergic deafferentation, we observed a significant reduction in the abundance of secreted APP and a concomitant increase in membrane-bound APP. These changes were reversed in immunolesioned rats with nerve growth factor-producing fibroblasts. There was a strong positive correlation between the ratio of secreted APP to membrane-bound APP and the activity of choline acetyltransferase and M1 muscarinic acetylcholine receptor density (measured by [3H]pirenzepine binding) in experimental groups. Additionally, we observed a transient decrease in the ratio of cortical APP transcripts containing the Kunitz protease inhibitor domain (APP 770 and APP 751) versus APP 695 in rats with cholinergic hypoactivity. The data presented suggest that cortical APP processing is under basal forebrain cholinergic control, presumably mediated through M1 muscarinic acetylcholine receptors on cholinoceptive cortical target cells.

Effect of a long-term nerve growth factor treatment on body weight, blood pressure, and serum corticosterone in rats

Nerve growth factor is a well-characterized neurotrophin essential for the development and maintenance of certain central and peripheral neurons. As many neurons affected by aging depend for their survival on a constant supply of neurotrophins, nerve growth factor has been proposed as a possible treatment to prevent aging-associated neurodegeneration. There is evidence that nerve growth factor also plays a role in the immune system and modulates certain aspects of endocrine function. Here we have determined the effects of prolonged peripheral (intraperitoneal) treatment with nerve growth factor on body weight, blood pressure, and serum corticosterone levels in the rat. Our data indicate that intraperitoneally-injected nerve growth factor can affect body weight gain in rats. This effect may not be mediated by nerve growth factor-induced increases in serum corticosterone levels, as exogenous administration of corticosterone did not result in a similar body weight loss. These results show that, as previously reported for intracerebroventricular treatment with nerve growth factor, intraperitoneally-injected nerve growth factor also reduces body weight gain in rats. The data also suggest that exogenous delivery of nerve growth factor as part of therapeutic regimens is likely to have several effects.

Cholinergic control of nerve growth factor in adult rats: evidence from cortical cholinergic deafferentation and chronic drug treatment

It is well documented that nerve growth factor (NGF) plays an important role in maintaining functions of cholinergic basal forebrain neurons. In the present study, we tested the hypothesis that cholinergic activity controls NGF levels in cholinoceptive neurons of the cerebral cortex and hippocampus. To address that question, we used both cholinergic deafferentation of cerebral cortex and hippocampus by cholinergic immunolesion with 192IgG-saporin and chronic pharmacological treatment of sham-treated and immunolesioned rats with the cholinergic agonist pilocarpine and the cholinergic antagonist scopolamine. We observed an increase in NGF protein levels in the cortex and hippocampus after cholinergic immunolesions and also after muscarinic receptor blockade by chronic intracerebroventricular scopolamine infusion in sham-treated rats after 2 weeks. There was no further increase in the accumulation of NGF after scopolamine treatment of immunolesioned rats. Chronic infusion of pilocarpine had no effect on cortical and hippocampal NGF protein levels in sham-treated rats. In rats with cholinergic immunolesions, however, pilocarpine did prevent the lesion-induced accumulation of NGF. There was no effect of cholinergic lesion and drug treatment on cortical or hippocampal NGF mRNA levels, consistent with the importance of NGF retrograde transport as opposed to its de novo synthesis. This study provides strong evidence for the hypothesis that there is cholinergic control of cortical and hippocampal NGF protein but not mRNA levels in adult rats.

Ornithine decarboxylase activity in cerebral post-ischemic reperfusion damage: effect of methionine sulfoximine

Excessive activation of glutamate receptors via the N-methyl-D-aspartate (NMDA) subtype appears to play a role in the sequence of cellular events which lead to irreversible ischemic damage to neurons. Furthermore, NMDA receptor activation induces a stimulation of ornithine decarboxylase (ODC), the rate-limiting enzyme for polyamine (PA) biosynthesis. In order to better understand the role of PA we have measured ODC activity and the effect of methionine sulfoximine (MSO), a molecule able to stimulate ODC, on a model of transient cerebral ischemia. There was a significant increase in ODC activity in the rat cerebral cortex during post-ischemic reperfusion. The treatment with MSO induced a significant decrease in cerebral glutamine synthetase activity accompanied by a marked increase in ODC activity. In MSO-pretreated rats there was a significant decrease in the survival rate when compared to untreated ischemic rats.

BCL-2-related protein expression in apoptosis: oxidative stress versus serum deprivation in PC12 cells

Expression of the BCL-2 protein family members, BAX, BAK, BAD, BCL-xL, BCL-xS, and BCL-2, was measured (by western blotting using specific antibodies) in PC12 cells before and during apoptosis induced by either H2O2 treatment or by serum deprivation and during rescue from apoptosis by nerve growth factor (NGF). H2O2-induced apoptosis, as measured by DNA fragmentation, caused: (a) a dose-dependent increase in BAX, (b) a dose-independent increase in BAK, and (c) a dose-dependent inhibition of BAD expression. By comparison, apoptosis induced by serum deprivation resulted in a time-dependent decrease in both BAX and BAK, along with a dramatic and sudden decrease in BAD expression. However, when PC12 cells were incubated in an apoptosis-sparing medium (i.e., NGF-supplemented serum-free medium), both BAX and BAK were increased significantly, whereas BAD expression remained inhibited. BCL-xL expression was increased by H2O2 but unaffected by serum deprivation or long-term NGF treatment. Neither BCL-2 nor BCL-xS expression could be detected in PC12 cells under the experimental conditions tested. Our results show that the expression of BAX, BAK, BAD, and BCL-xL is altered in a stimulus-dependent manner but cannot be used to define whether a cell will undergo or survive apoptosis. The similarity between changes in expression of BCL-2-related proteins induced by H2O2 exposure and NGF rescue could reflect activation in part of a common antioxidant pathway.

Selective induction of c-Jun and NGF in reactive astrocytes after cholinergic degenerations in rat basal forebrain

Cholinergic basal forebrain neurons are the major source of cortical cholinergic innervation. The number of these neurons is regulated by the availability of nerve growth factor (NGF) during development while in adulthood their cholinergic activity is modulated by NGF. In previous studies we have shown that cholinergic immunolesions of basal forebrain neurons increase local immediate early gene expression and NGF synthesis in the regions of degeneration. In this study we identify the cellular source of c-Jun and NGF expression using dual immunolabeling of c-Jun and NGF in combination with neuronal and glial markers. We demonstrate that both c-Jun and NGF are exclusively expressed in reactive astrocytes but not in microglia or in GABAergic basal forebrain neurons. These observations support the hypothesis that reactive astrocytes synthesize neurotrophic substances in vivo in response to neuronal degeneration in the basal forebrain.

NG-nitro-L-arginine methyl ester modifies the input function measured by dynamic susceptibility contrast magnetic resonance imaging

In rat brain dynamic susceptibility contrast magnetic resonance (MR) images, vessels visible on the same scan plane as the brain tissue were used to measure the characteristics of the input function of the MR contrast agent gadopentetate dimeglumine. MR images were acquired 30 and 60 minutes after intravenous injections of 3 mg/kg and 15 mg/kg NG-Nitro-L-arginine methyl ester (L-NAME) (n = 9). The time of arrival (TOA) and the mean transit time corrected for TOA of the input function were increased by 3 mg/kg or 15 mg/kg L-NAME. The area of the input function was increased by 15 mg/kg L-NAME. In two animals, similar modifications of the input function induced by 20 mg/kg L-NAME were reversed by infusion of sodium nitroprusside. In two other animals, MABP was increased by phenylephrine to a similar extent as in L-NAME experiments, but did not induce the same modifications of the input function, showing that the action of L-NAME on the input function was not simply caused by an effect on MABP. These results show that the input function can be significantly altered by manipulations widely used in cerebrovascular studies. These input function changes have important implications for calculation of cerebral blood flow.

Insulin-like growth factor-I liposomal gene transfer and systemic growth hormone stimulate wound healing

Many of the anabolic effects of growth hormone (GH) act through insulin-like growth factor-I (IGF-I). Systemic administration of GH in combination with IGF-I has been shown to stimulate wound reepithelialization, however, it causes hyperglycemia or hypoglycemia, respectively. We hypothesize that very low doses of IGF-I in a liposome form will have the same positive wound-healing effect when administered locally as the higher doses of GH plus IGF-I given systemically. To test this hypothesis, rats were given a 40% TBSA full-thickness scald injury and received either placebo IGF-I (5.0 mg/kg/day, subcutaneously), IGF-I liposome (0.9 microgram/kg/week, subcutaneously), or a combination of GH and IGF-I, or IGF-I liposomes for 8 weeks. GH in combination with IGF-I showed a significant increase in postburn weight. Wound reepithelialization, measured by computerized planimetry as percentage original wound area, was significantly increased in rats receiving GH plus IGF-I, GH plus IGF-I liposomes, and IGF-I liposomes when compared to sham, or IGF-I (p < 0.05). Results indicate that small doses of IGF-I, delivered in the form of liposomes, are equally effective in increasing burn wound reepithelialization as the higher doses of GH plus IGF-I, or GH plus IGF-I liposomes.

Age-associated alterations in hippocampal and basal forebrain nuclear factor kappa B activity

Age-related cognitive deficits are often associated with loss of cholinergic activity within the neurotrophin-dependent cholinergic neurons that project from the basal forebrain to the hippocampus. The cause of reduced cholinergic function is unknown, but alterations in transcription factor-signaling pathways causing altered gene expression may cause decreased specific tissue function, resulting in loss of cholinergic activity. We measured transcription factor Nuclear Factor kappa B by electrophoretic mobility shift assay and Western analysis in young and aged rat brain tissues and report that basal levels of Nuclear Factor kappa B DNA-binding activity increase in the hippocampus and basal forebrain with age to significantly higher levels at 30 months of age. This age-associated increase in binding activity is associated with increased translocation of p65 to the nucleus. These data show an age-associated alteration in Nuclear Factor kappa B signal transduction pathways that may contribute to age-associated decreases in specific tissue function.

Retinoic acid induces apoptosis in PC12 cells independent of neurotrophic factors

PC12 cells are known to undergo programmed cell death (apoptosis) when they are deprived of serum. Nerve growth factor (NGF) rescues PC12 cells from serum deprivation-induced apoptosis. In the present study, we examined the effects of retinoic acid (RA), a classic morphogen, on apoptosis in PC12 cells after serum deprivation and NGF-mediated rescue. In naive PC12 cells, all trans-RA treatment induced cell death in the presence of NGF. RA also abolished the protective effects of dibutyryl cyclic AMP or insulin under serum-free conditions. The death process was accompanied by nuclear condensation and DNA fragmentation, typical of apoptosis. In addition, RA also increased the extent of apoptosis in PC12 cells after serum deprivation. Cycloheximide, an inhibitor of protein synthesis, did not abolish the effects of RA on serum-deprived PC12 cells. RA also decreased thymidine incorporation and proliferation in NGF-treated PC12 cells. Furthermore, although the total DNA binding activity of the AP-1 transcription factor was not changed after RA treatment, RA decreased a specific AP-1 transcriptional activity. It is surprising that differentiated PC12 cells resisted the toxic effects of RA. These data suggest that RA might function as an endogenous inducer of apoptosis during neural differentiation by a mechanism distinct from that of serum deprivation.

Inhibition of nuclear factor kappa B (NFkappaB) activity induces nerve growth factor-resistant apoptosis in PC12 cells

The mechanism(s) underlying nerve growth factor (NGF)-mediated rescue of neurons from apoptosis is poorly understood, although it is well established that the high-affinity NGF receptor (TrkA) plays a pivotal role in mediating NGF effects. The report that the low-affinity NGF receptor (p75NGFR) can induce apoptosis prompted us to analyze the role played by a putative p75NGFR-associated signal-transduction element, the transcription factor nuclear factor kappa B (NFkappaB), in the modulation of apoptosis in PC12 cells. Here, we report that inhibition of NFkappaB function results in apoptosis of rat PC12 cells, a neuroblast-like cell line model of NGF-responsive neural tissues. Furthermore, NGF did not protect PC12 cells from cell death induced by the inhibition of NFkappaB. These results indicate that NFkappaB function is essential to maintain PC12 cell survival and to permit NGF-mediated rescue, consistent with the idea that signaling elements potentially associated with both TrkA- and p75NGFR are involved in the regulation of apoptosis.

Nerve growth factor, central nervous system apoptosis, and adrenocortical activity in aged Fischer-344/brown Norway F1 hybrid rats

During aging there is a progressive loss of neuronal function in the basal forebrain that results in cognitive impairment and cholinergic deficits. While altered neurotrophin (NT)-mediated signal transduction may account for some age-associated deficits, there are differences in the extent of NT responsiveness among different laboratory rat strains. Here we measured nerve growth factor (NGF) protein levels and fragmented DNA in the CNS, and basal and NGF-stimulated activity levels of the hypothalamus-pituitary-adrenocortical axis (HPAA) in 3-, 18-, and 30-month-old Fischer-344/Brown Norway rats. Our results show that while there is no age-associated differences in NGF protein levels, in aged Fischer-344/Brown Norway rats, there are increases in levels of immunoreactive fragmented DNA in the CNS and in adrenocortical responses to the peripheral administration of NGF. These data contribute to the characterization of the Fischer-344/Brown Norway F1 hybrid rat and provide baseline values useful for future studies on aged CNS.

Cationic lipid-mediated NGF gene transfection increases neurofilament phosphorylation

We examined the effect of cationic lipid-mediated gene transfection of nerve growth factor (NGF) in primary septo-hippocampal cell cultures. Rat NGF cDNA was subcloned into a pUC19-based plasmid containing a CMV promoter. Two days after NGF gene transfection in primary cell cultures, ELISA confirmed increases in NGF protein secretion from transfected cells. To study the biological effect of cationic lipid-mediated NGF gene transfection, we analyzed the amount of neurofilament protein from NGF-transfected cell cultures. Western blot and immunohistochemical analyses detected significant increases in the phosphorylated form of neurofilament proteins in the cultures after cationic lipid-mediated NGF cDNA transfection. Cationic lipid-mediated NGF cDNA transfection did rot cause significant changes in the total amount of neurofilament protein. Our studies suggest that cationic lipid-mediated NGF gene transfection can increase neurofilament phosphorylation but not total neurofilament protein.

Effects of nerve growth factor on splenic norepinephrine and pineal N-acetyl-transferase in neonate rats exposed to alcohol in utero: neuroimmune correlates

Prenatal alcohol exposure (FAE) has been associated with multiple anomalies, including a selective developmental delay of sympathetic innervation in lymphoid organs. Sympathetic neurons require nerve growth factor (NGF) for their development and maintenance, and recent evidence has suggested that alcohol impairs the synthesis and/or biological activity of NGF in selected central and peripheral neurons. Thus, the present study examined the hypothesis that NGF administration to FAE rats during early postnatal development would reverse some of the peripheral sympathetic deficits. Neonate rats, FAE and the corresponding control cohorts, received daily treatments of NGF or cytochrome C (0.3 mg/kg; s.c.) for various time intervals, and were killed 24 hr or 10 days after the last treatment. The measured parameters included norepinephrine (NE) concentrations in the spleen and heart, which receive nor-adrenergic innervation from the coeliac ganglion and the superior cervical ganglion (SCG), respectively. In addition, we measured the activity of pineal N-acetyltransferase (NAT), the rate-limiting enzyme of melatonin biosynthesis, which depends on sympathetic innervation from the SCG. The data show that chronic, but not acute, NGF treatments reversed the FAE-related deficits in splenic NE concentrations as well as in pineal NAT activity in a time- and age-dependent manner. Sympathetic neurons play an important role in immune modulation. Thus, the altered splenic NE levels and pineal NAT activity may play a role in immune deficits associated with exposure to alcohol in utero.

Early signaling events by endotoxin in PC12 cells: involvement of tyrosine kinase, constitutive nitric oxide synthase, cGMP-dependent protein kinase, and Ca2+ channels

We studied the effects of endotoxin from Escherichia coli (E. coli) on Ca2+ channel activity in PC12 cells using the cell-attached patch clamp technique. Endotoxin (1-100 ng/ml) decreased channel availability (n x Po) to about one third of control values, an effect that required 3.5 +/- 1 min (mean +/- SD; n = 13) to reach steady state. The biophysical properties of the channel, including slope conductance (22 pS; 40 mM Ba2+), voltage dependence of n x Po, and open times (tau 1 = 0.78 ms, tau 2 = 8.9 ms) for the two open states at 0 mV, were not altered. The effect of endotoxin was blocked by polymyxin-B, indicating involvement of the lipid-A moiety of lipopolysaccharide, and by the tyrosine kinase (tk) inhibitor, tyrphostin. The effect of endotoxin was mimicked by 8-bromo-cGMP (100 microM), and was blocked by the inhibitor of cGMP-dependent protein kinase (PKG), H-8, suggesting involvement of the cGMP/PKG pathway. The effect of endotoxin also was blocked by the nitric oxide (NO) synthase inhibitor, NG-monomethyl-L-arginine monoacetate, suggesting involvement of nitric oxide synthase (NOS). The rapidity of the effect of endotoxin on Ca2+ channel activity suggested that constitutive NOS (cNOS) was involved, in accordance with our finding that endotoxin-induced transcriptional induction of NOS, as measured by nitrite production, required > 6 hr. We conclude that early signaling events by endotoxin in PC12 cells involve tk, cNOS, cGMP/PKG, and Ca2+ channels.

Effect of nerve growth factor on AP-1, NF-kappa B, and Oct DNA binding activity in apoptotic PC12 cells: extrinsic and intrinsic elements

Both intrinsic signals, such as serum and neurotrophic factor deprivation, and extrinsic events or agents, such as oxidative stress and glucose deprivation, can induce cell death in pheochromocytoma (PC12) cells. Also, treatment with nerve growth factor (NGF) reduces cell death due to the treatments mentioned. Serumless-induced cell death, as a model of apoptosis, has been intensively investigated in PC12 cells. In the present study, we investigated the molecular components of H2O2-induced cell death and compared it with serumless-induced cell death. Exposure of PC12 cells to intermediate concentrations of H2O2 (100 microM) induced nuclear condensation and DNA fragmentation, indicating that there is an apoptotic component in H2O2-induced cell death. Since transcription factors have been shown to play an essential role in the control of cellular proliferation, differentiation, and survival, we measured changes in the DNA binding activities of the transcription factors activator protein-1 (AP-1), nuclear factor kappa B (NF-kappa B), and octamer-binding protein (Oct) by electrophoretic mobility shift assay (EMSA) after H2O2 treatment and serum deprivation, both in the absence and presence of exogenous NGF in PC12 cells. AP-1 DNA binding activity transiently increased during apoptosis due to serum deprivation, and NGF treatment further stimulated AP-1 DNA binding activity in a more persistent fashion. NF-kappa B DNA binding activity only increased slightly after serum deprivation, and NGF treatment of PC12 cells decreased NF-kappa B binding activity in the late stages of serum deprivation. Oct DNA binding activity decreased after serum deprivation, while NGF had an opposite effect. AP-1 DNA binding activity also transiently increased after H2O2 treatment, as did NF-kappa B DNA binding activity. Our results suggest that AP-1 is likely to be a common component of signaling pathways associated with both the induction or suppression of apoptosis induced by intrinsic or extrinsic stimuli.

Effects of intraventricular transplantation of NGF-secreting cells on cholinergic basal forebrain neurons after partial immunolesion

The aim of the present study was to examine the effects of nerve growth factor on brain cholinergic function after a partial immunolesion to the rat cholinergic basal forebrain neurons (CBFNs) by 192 IgG-saporin. Two weeks after intraventricular injections of 1.3 micrograms of 192 IgG-saporin, about 50% of CBFNs were lost which was associated with 40-60% reductions of choline acetyltransferase (ChAT) and high-affinity choline uptake (HACU) activities throughout the basal forebrain cholinergic system. Two groups of lesioned animals received intraventricular transplantations of mouse 3T3 fibroblasts retrovirally transfected with either the rat NGF gene (3T3NGF+) or the retrovirus alone (3T3NGF-) and were sacrificed eight weeks later. In vivo production of NGF by 3T3NGF+ cells was confirmed by NGF immunohistochemistry on the grafts and NGF immunoassay on cerebrospinal fluid (CSF) samples. Both ChAT and HACU activities returned to normal control levels in the basal forebrain and cortex after 3T3NGF+ transplants, whereas no recovery was observed in 3T3NGF- transplanted animals. There was a 25% increase in the size of remaining CBFNs and an increased staining intensity for NGF immunoreactivity in these cells after NGF treatments. Acetylcholinesterase (AChE) histochemistry revealed that the optical density of AChE-positive fibers in the cerebral cortex and hippocampus were reduced by about 60% in immunolesioned rats which were completely restored by 3T3NGF+ grafts. In addition, decreases in growth-associated protein (GAP)-43 immunoreactivity after immunolesion and increases in synaptophysin immunoreactivity after 3T3NGF+ grafts were observed in the hippocampus. Our results further confirm the notion that transfected NGF-secreting cells are useful in long-term in vivo NGF treatment and NGF can upregulate CBFN function. They also highly suggest that NGF induces terminal sprouting from remaining CBFNs.

Neuronal lesions and behavioral modifications in rat following cerebral ischemia and reperfusion

Neurons of the mammalian CNS differ in their vulnerability to various disease processes and other insults, particularly in their response to total anoxia/ischemia. In this study we have tested the histological and behavioral modifications induced by experimental conditions of partial cerebral ischemia in the rats. The specific morphological and histological alterations, observed in our experimental conditions of reversible partial cerebral ischemia, confirm the selective vulnerability of certain neuronal populations to ischemic injury and are also evidenced by behavioral modifications which may mirror the functional impairment observed in humans after a transitory ischemic attack.

Suppression of p140trkA does not abolish nerve growth factor-mediated rescue of serum-free PC12 cells

Programmed cell death, the intrinsic form of apoptosis, plays an integral role in those neurodegenerative events associated with age-related neuropathology. Neurotrophins (NTs), such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and NT-3, are required for survival of certain neurons, and thus their clinical use to counteract age- and pathology-associated neurodegeneration has been suggested, although mechanistic descriptions for NT cell rescue from apoptosis are not definitive. Here we attempted to isolate the individual actions of high-affinity tyrosine kinase (Trk) receptors and p75NGFR, the common low-affinity NT receptor, in NT rescue of apoptotic PC12 cells. Our results showed that whereas inhibiting Trk receptor phosphorylation abolishes NGF rescue of serum-deprived PC12 cells from apoptosis, TrkA suppression with antisense oligonucleotides did not. Also, although BDNF did not rescue naive serumless PC12 cells, which lack the BDNF-specific TrkB receptor, it significantly increased survival of TrkA-suppressed serum-starved PC12 cells. These data confirm the hypothesis that binding of any NT to Trk-free p75NGFR-bearing cells blocks apoptosis but also suggest that if Trk receptors are expressed, prohibiting Trk phosphorylation also blocks NT-mediated rescue from apoptosis.

Increased expression of brain-derived neurotrophic factor but not neurotrophin-3 mRNA in rat brain after cortical impact injury

Levels of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) mRNA expression were measured in a rodent model of traumatic brain injury (TBI) following unilateral injury to the cerebral cortex. To obtain reliable data on the co-expression of neurotrophin genes, adjacent coronal sections from the same rat brains were hybridized in situ with BDNF and NT3 cRNA probes. BDNF mRNA increased at 1,3, and 5 hr after unilateral cortical injury in the cortex ipsilateral to the injury site and bilaterally in the dorsal hippocampus. NT3 mRNA did not change significantly following injury. Our results suggest that TBI produces rapid increases in BDNF mRNA expression in rat brain without changes in NT3 mRNA expression, a finding which differs from studies of ischemia and seizures. It is possible that increased levels of BDNF mRNA rather than NT3 are important components of pathophysiological responses to TBI.

Evidence for DNA fragmentation in the CNS of aged Fischer-344 rats

The aged central nervous system (CNS) is characterized by a loss of neurons. Apoptosis has been reported to be responsible for neuronal death during development and may also be involved in some age-related neurodegenerative diseases of the CNS. No evidence is currently available as to whether apoptosis is also responsible for the loss of neurons associated with physiological aging. In this study, we have found fragmented DNA, a characteristic trait of cells undergoing apoptosis, in the hippocampus and, to a minor extent, in the frontal cortex and basal forebrain of aged (24-month-old) Fisher-344 rats, but not in the cerebellum. These data represent important evidence to support the idea that apoptosis may be associated with the neuronal death observed during normal aging.

Rapid neurite formation in a human cortical neuronal cell line

The subclone HCN-1 was derived from parental cell lines from cortical tissue of a patient with unilateral megalencephaly growth and immunochemistry staining characteristics [G. V. Ronnett et al. (1990) Human cortical neuronal cell line: establishment from a patient with unilateral megalencephaly. Science 248, 603-605]. As we and others have shown, HCN-1A cells can be induced to differentiate to a neuronal-like morphology. HCN-1A cells stain positively for neurofilament, neuron-specific enolase and the low-affinity neurotrophin receptors, p75NGFR, but not for myelin basic protein, S-100, or glial fibrillary acidic protein (GFAP). HCN-1A cells also stain positively for gamma-aminobutyric acid and glutamate. In the present study, we examine the effects of cell density on the requirements for efficient induction of differentiation of HCN-1A cells and analyze the time course of this induction and its reversion. We also characterize the changes in cytoskeletal proteins of HCN-1A cells in response to their differentiation neuronal phenotype.