HGF promotes survival and growth of maturing sympathetic neurons by PI-3 kinase- and MAP kinase-dependent mechanisms

Hepatocyte growth factor (HGF) is a pleiotrophic factor whose many functions include promoting neuronal survival and growth. Hitherto, these effects have been observed in the presence of other neurotrophic factors like NGF and CNTF, and this requirement for an accessory factor has made it difficult to elucidate the signaling pathways that mediate its survival and growth-enhancing effects. Here, we show that HGF promotes the survival of mature sympathetic neurons of the superior cervical ganglion (SCG) grown at low density in defined medium lacking other neurotrophic factors. This effect was first clearly observed in cultures established from postnatal day 20 (P20) mice and became maximal by P40. HGF also enhanced the growth of neurite arbors from neurons throughout postnatal development and in the adult. HGF treatment resulted in phosphorylation of Akt and ERK1/ERK2. Preventing Akt activation with the phosphatidylinositol-3 (PI-3) kinase inhibitor LY294002 blocked the HGF survival response, and inhibition of ERK activation with the MEK inhibitors PD98059 or U0126 reduced the HGF survival response and the neurite growth-promoting effects of HGF. These results indicate that HGF promotes the survival and growth of maturing sympathetic neurons by both PI-3 kinase- and MAP kinase-dependent mechanisms.     

Neurotrophin-3-induced PI-3 kinase/Akt signaling rescues cortical neurons from apoptosis

A number of cytokines including neurotrophins have been tested for their neuroprotective activity against different paradigms of neuronal death. However, as for neurotrophin-3 (NT-3), their mechanisms of action have not been fully identified. By using cultures of mouse cortical neurons, we have investigated the molecular mechanisms by which neurotrophin-3 could protect cortical neurons against apoptosis. In a model of caspase-dependent apoptosis leading to the recruitment of active initiators caspase-8 and -9 and of executioner caspase-3, we have evidenced that NT-3 displayed an anti-apoptotic effect in a dose-dependent manner. First, we showed that, in cultured cortical neurons, NT-3 could promote extracellular signal-regulated protein kinase/mitogen-activated protein kinase (ERK/MAPK) and phosphatidylinositol-3' (PI-3) kinase/Akt phosphorylation. Second, we showed that although the blockade of the Akt pathway prevented the anti-apoptotic effect of NT-3, blockade of the ERK pathway did not. Altogether, our data demonstrate that NT-3 displayed an anti-apoptotic effect on cultured cortical neurons through a mechanism involving the recruitment of the PI-3 kinase/Akt signaling pathway.     

Membrane depolarization-mediated survival of sympathetic neurons occurs through both phosphatidylinositol 3-kinase- and CaM kinase II-dependent pathways

It has been well established that the NGF-mediated survival of sympathetic neurons in culture occurs through the phosphatidylinositol (PI) 3-kinase/Akt-dependent pathway. In contrast, the mechanism by which membrane depolarization promotes neuronal survival independently of NGF remains unresolved. Here we show that LY294002, a specific inhibitor of PI 3-kinase, induced cell death of sympathetic neurons under depolarizing conditions with elevated K(+) (IC(50)= approximately 30 microM). Interestingly, lower concentrations of this agent (< or =10 microM) were sufficient to suppress Akt phosphorylation at Ser-473, a putative downstream target of PI 3-kinase, under these conditions. We also show that KN-62, a specific inhibitor of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) suppressed depolarization-mediated survival in a does-dependent manner (IC(50)= approximately 2 microM) that paralleled attenuation of sustained levels of intracellular Ca(2+) evoked by depolarization. This IC(50) value is greater than that for CaMKII ( approximately 0.8 microM). These findings led us to hypothesize that depolarization-mediated survival occurs through both the PI 3-kinase/Akt and the CaMKII pathways. Indeed, combined treatment with LY294002 (25 microM) and KN-62 (0.5 microM) dramatically abolished depolarization-mediated survival, whereas each alone did not significantly attenuate it. Under these conditions, KN-62 neither impaired sustained levels of intracellular Ca(2+), nor inhibited the phosphorylation of Akt. It is thus likely that PI 3-kinase and CaMKII independently promote the membrane depolarization-mediated survival of sympathetic neurons in culture.     

Increased truncated TrkB receptor expression and decreased BDNF/TrkB signaling in the frontal cortex of reeler mouse model of schizophrenia

Heterozygous reeler mouse has been used as an animal model for schizophrenia based on several neuropathological and behavioral abnormalities homologous to schizophrenia. Since some of these abnormalities are primarily associated with altered BDNF signaling we investigated BDNF signaling in the frontal cortex of reeler mice in order to shed some light on the neuropathology and treatment of schizophrenia. BDNF, TrkB receptor isoforms (full-length and truncated), reelin, GAD67, GAD65, p75NTR, and NRH-2 levels were measured in the frontal cortex samples from reeler (B6C3Fe a/a-Reln^rl/+) and wild-type (WT) mice. BDNF protein levels were significantly higher in reeler compared to WT. The protein levels of full-length TrkB were not altered in reeler mice, but both mRNA and protein levels of truncated TrkB were significantly higher. Protein analysis showed that TrkB activity, as indicated by the levels of tyrosine-phosphorylated TrkB, was lower in reeler mice. We did not find any significant change in the levels of p75NTR and NRH-2, regulatory proteins of TrkB signaling, in the reeler mice. Furthermore, we found significant reduction in reelin and GAD67 expressions, but not GAD65 expression in reeler compared to WT mice. In summary, molecular processes associated with defective BDNF signaling in reeler mice provide new therapeutic targets for neuroprotective pharmacotherapy for schizophrenia.     

BDNF and CNTF regulate cholinergic properties of sympathetic neurons through independent mechanisms

Cultured neonatal sympathetic neurons can synthesize and corelease norepinephrine (NE) and acetylcholine (ACh). Evoked release of NE has an excitatory effect on the beat rate of cocultured cardiac myocytes while ACh release results in myocyte inhibition. Here we show that the cholinergic properties of the neurons and the relative level of NE and ACh corelease are modulated by neurotrophic factors. Brain-derived neurotrophic factor (BDNF) rapidly promoted ACh release in the absence of cholinergic differentiation activity and even in neurons that were predominantly noradrenergic. This increase in the cholinergic component of sympathetic cotransmission was sufficient for myocytes to display an overall inhibitory response to neuronal stimulation. In contrast, short-term growth in ciliary neurotrophic factor (CNTF) resulted in the upregulation of cholinergic and downregulation of noradrenergic markers without an effect on normal excitatory neurotransmission. Only once the cells had acquired a cholinergic phenotype did CNTF acutely promote the evoked release of the cholinergic vesicle pool. The results of this study indicate that BDNF and CNTF, acting through independent pathways, modulate NE and ACh cotransmission to regulate the level of sympathetic excitation or inhibition of cardiac myocytes.     

BDNF/TrkB signaling regulates HNK-1 carbohydrate expression in regenerating motor nerves and promotes functional recovery after peripheral nerve repair

Functional recovery after peripheral nerve injury is often poor despite high regenerative capacity of peripheral neurons. In search for novel treatments, brief electrical stimulation of the acutely lesioned nerve has recently been identified as a clinically feasible approach increasing precision of axonal regrowth. The effects of this stimulation appear to be mediated by BDNF and its receptor, TrkB, but the down-stream effectors are unknown. A potential candidate is the HNK-1 carbohydrate known to be selectively reexpressed in motor but not sensory nerve branches of the mouse femoral nerve and to enhance growth of motor but not sensory axons in vitro. Here, we show that short-term low-frequency electrical stimulation (1 h, 20 Hz) of the lesioned and surgically repaired femoral nerve in wild-type mice causes a motor nerve-specific enhancement of HNK-1 expression correlating with previously reported acceleration of muscle reinnervation. Such enhanced HNK-1 expression was not observed after electrical stimulation in heterozygous BDNF or TrkB-deficient mice. Accordingly, the degree of proper reinnervation of the quadriceps muscle, as indicated by retrograde labeling of motoneurons, was reduced in TrkB+/- mice compared to wild-type littermates. Also, recovery of quadriceps muscle function, evaluated by a novel single-frame motion analysis approach, and axonal regrowth into the distal nerve stump, assessed morphologically, were considerably delayed in TrkB+/- mice. These findings indicate that BDNF/TrkB signaling is important for functional recovery after nerve repair and suggest that up-regulation of the HNK-1 glycan is linked to this phenomenon.     

Sirt1 overexpression in neurons promotes neurite outgrowth and cell survival through inhibition of the mTOR signaling

The mammalian nicotinamide-adenine dinucleotide (NAD)-dependent deacetylase Sirt1 impacts different processes involved in the maintenance of brain integrity and in the pathogenic pathways associated with several neurodegenerative disorders, including Alzheimer's disease. Here we used human Sirt1 transgenic mice to demonstrate that neuron-specific Sirt1 overexpression promoted neurite outgrowth and improved cell viability under normal and nutrient-limiting conditions in primary culture systems and that Sirt1-overexpressing neurons exhibited higher tolerance to cell death or degeneration induced by amyloid-β1-42 oligomers. Coincidentally, we found that enhanced Sirt1 expression in neurons downregulated the mammalian target of rapamycin (mTOR) protein levels and its phosphorylation without changes in its mRNA levels, which was accompanied by concomitant inhibition of the mTOR downstream signaling activity as revealed by decreased p70S6 kinase (p70S6K) phosphorylation at Thr389. Consistently with this, using a Sirt1 siRNA transfection approach, we observed that reduction of endogenous mouse Sirt1 led to increased levels of mTOR and phosphorylation of itself and p70S6K as well as impaired cell survival and neurite outgrowth in wild-type mouse primary neurons, corroborating a suppressing effect of mTOR by Sirt1. Correspondingly, the mTOR inhibitor rapamycin markedly improved neuronal cell survival in response to nutrient deprivation and significantly enhanced neurite outgrowth in wild-type mouse neurons. The protective effect of rapamycin was extended to neurons even with Sirt1 siRNA knockdown that displayed developmental abnormalities compared with siRNA control-treated cells. Collectively, our findings suggest that Sirt1 may act to promote growth and survival of neurons in the central nervous system via its negative modulation of mTOR signaling.     

头痛宁胶囊对偏头痛大鼠BDNF/TrkB信号通路表达的影响

目的观察头痛宁胶囊对偏头痛大鼠模型中脑源性神经营养因子(BDNF)及其信号通路上酪氨酸激酶(TrkB)受体、下游信号分子细胞外调节蛋白激酶(ERK)、磷酸化cAMP反应结合蛋白(p-CREB)表达的影响。方法将60只SD大鼠随机分为正常对照组、模型组、头痛宁干预组,依照Tassorelli法建立硝酸甘油实验性偏头痛SD大鼠模型,观察各组大鼠的行为学变化,第五次建模后用ELISA法检测血清BDNF水平及免疫组化法检测三叉神经组织中BDNF、TrkB受体、下游信号分子ERK和p-CREB的蛋白表达变化及其定位。结果行为学观察结果显示:模型组及干预组大鼠造模后出现挠头增多、双耳发红、爬笼活动频繁,但干预组大鼠的持续时间及挠头爬笼次数较模型组减少,差异具有统计学意义(P<0.05);对照组未出现上述行为学改变。ELISA结果显示:模型组大鼠发作期及间歇期血清BDNF水平高于干预组发作期及间歇期和对照组(P<0.05),无性别差异(P>0.05)。免疫组化结果显示:模型组大鼠发作期三叉神经节细胞内BDNF、TrkB、p-ERK、p-CREB的蛋白水平高于干预组发作期及间歇期和对照组(P<0.05),无性别差异(P>0.05)。结论头痛宁胶囊可能通过下调BDNF、TrkB、p-ERK、p-CREB蛋白的表达水平来达到防治偏头痛的作用。     

BDNF, but not NT-3, promotes long-term survival of axotomized adult rat corticospinal neurons in vivo

Axotomy-induced death of corticospinal neurons (CSN) is prevented by intracotrical infusions of BDNF or NT-3 within the first week after axotomy. The present study examined whether this represents merely a delay of CSN death or whether BDNF and NT-3 can promote long-term survival of these neurons in vivo. The neurotrophins were infused for an initial period of 14 days to lesioned CSN which was followed by 28 days without treatment. BDNF was able to promote CSN survival for at least 42 days while NT-3 had no significant effect. These results suggest that initial BDNF treatment induces an endogamous mechanism that promotes survival of axotomized CSN without further exogenous neurotrophic factor supply. These findings may be important for the design of therapeutic strategies for motoneuron disease.     

Activity-dependent modulation of the BDNF receptor TrkB: mechanisms and implications

Although brain-derived neurotrophic factor (BDNF) has emerged as a key regulator of activity-dependent synaptic plasticity, a conceptually challenging question is how this diffusible molecule achieves local and synapse-specific modulation. One hypothesis is that neuronal activity enhances BDNF signaling by selectively modulating TrkB receptors at active neurons or synapses without affecting receptors on neighboring, less-active ones. Growing evidence suggests that neuronal activity facilitates cell-surface expression of TrkB. BDNF secreted from active synapses and neurons recruits TrkB from extrasynaptic sites into lipid rafts, microdomains of membrane that are enriched at synapses. Postsynaptic rises in cAMP concentrations facilitate translocation of TrkB into the postsynaptic density. Finally, neuronal activity promotes BDNF-induced TrkB endocytosis, a signaling event important for many long-term BDNF functions. These mechanisms could collectively underlie synapse-specific regulation by BDNF.     

BDNF/NT4-5 receptor TrkB and cadherin participate in cell-cell adhesion

The neurotrophin receptor TrkB plays a key role in promoting cell survival and differentiation in the nervous system. Two adhesive motifs in the extracelluar domain of TrkB have been proposed based on its predicted secondary structure. To investigate the potential adhesive function of trkB, a full length trkB cDNA was stably transfected into NIH 3T3 cells and TrkB-expressing clones isolated. Transfectant clones producing different levels of TrkB protein were subjected to a homotypic aggregation assay. Results showed that parental cells were non-adhesive during the assay while TrkB-expressing cells displayed varying degrees of aggregation depending on the amount of TrkB protein expressed. The observed adhesion was Ca²⁺-, Mg²⁺-, and temperature-dependent, characteristics shared by the cadherin family of adhesion molecules. The transfected cell lines also expressed cadherin in proportion to TrkB expression and both molecules were required for cell adhesion. Double immunofluorescence staining studies showed that TrkB was colocalized with cadherin and catenin at cell-cell contact sites. Whether TrkB and cadherin mediate adhesion separately or synergistically remains to be determined. J. Neurosci. Res. 49:281–291, 1997. © 1997 Wiley-Liss, Inc.     

Subtoxic N-methyl-D-aspartate delayed neuronal death in ischemic brain injury through TrkB receptor- and calmodulin-mediated PI-3K/Akt pathway activation

Previous studies have shown that subtoxic NMDA moderated the neuronal survival in vitro and vivo. We performed this experiment to clarify the precise mechanism underlie subtoxic NMDA delayed neuronal death in ischemic brain injury. We found that pretreatment of NMDA (100 mg/kg) increased the number of the surviving CA1 pyramidal cells of hippocampus at 5 days of reperfusion. This dose of NMDA could also enhance Akt activation after ischemia/reperfusion (I/R). Here, we examined the possible mechanism that NMDA induced Akt activation. On the one hand, we found NMDA receptor-mediated Akt activation was associated with increased expression of BDNF (brain-derived neurotrophic factor) and activation of its high-affinity receptor TrkB after I/R in the hippocampus CA1 region, which could be held down by TrkB receptor antagonist K252a. On the other hand, we found that NMDA enhanced the binding of Ca2+-dependent calmodulin (CaM) to p85 (the regulation subunit of PI-3K), which led to the activation of Akt. W-13, an active CaM inhibitor, prevented the combination of CaM and p85 and subsequent Akt activation. Furthermore, NMDA receptor-mediated Akt activation was reversed by combined treatment with LY294002, the specific blockade of PI-3K. Taken together, our results suggested that subtoxic NMDA exerts the neuroprotective effect via activation of prosurvival PI-3K/Akt pathway against ischemic brain injury, and BDNF-TrkB signaling and Ca2+-dependent CaM cascade might contribute to NMDA induced activation of PI-3K/Akt pathway.     

Ischemic preconditioning is mediated by erythropoietin through PI-3 kinase signaling in an animal model of transient ischemic attack

Ischemic preconditioning (IP) protects the brain from subsequent, prolonged, and lethal ischemia in experimental studies. Erythropoietin (EPO) participates in the brain's intrinsic response to injury and may play a role in preconditioning. By using a middle cerebral artery occlusion (MCAo) model of transient ischemic attack (TIA), we sought to determine whether EPO is required for IP in the protective response against focal ischemic stroke. Rats underwent three 10-min MCA occlusions or sham surgery. Three days later, animals underwent 2 hr of MCAo and 22 hr of reperfusion. Experimental TIAs reduced infarct volumes by 55% (P < 0.05), inhibited DNA fragmentation, and improved neurological outcome by 50% (P < 0.05) after ischemic stroke. EPO and its receptor were up-regulated by IP in the ipsilateral hemisphere by 24 hr after IP, before ischemic stroke and soluble EPO receptor attenuated neuroprotection by IP (88% reduction, P < 0.05). Pretreatment with the PI-3 kinase inhibitor wortmannin abolished the protective effect of IP against ischemic injury (P < 0.05). IP may be mediated in part by EPO through a PI-3 kinase pathway.     

N-methyl-D-aspartate and TrkB receptors protect neurons against glutamate excitotoxicity through an extracellular signal-regulated kinase pathway

N-Methyl-D-aspartate (NMDA) at a subtoxic concentration (100 microM) promotes neuronal survival against glutamate-mediated excitotoxicity via a brain-derived neurotrophic factor (BDNF) autocrine loop in cultured cerebellar granule cells. The signal transduction mechanism(s) underlying NMDA neuroprotection, however, remains elusive. The mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI3-K) pathways alter gene expression and are involved in synaptic plasticity and neuronal survival. This study tested whether neuroprotective activation of NMDA receptors, together with TrkB receptors, coactivated the MAPK or PI3-K pathways to protect rat cerebellar neurons. NMDA receptor activation caused a concentration- and time-dependent activation of MAPK lasting 24 hr. This activation was blocked by the NMDA receptor antagonist MK-801 but was attenuated only partially by the tyrosine kinase inhibitor k252a, suggesting that activation of both NMDA and TrkB receptors are required for maximal neuroprotection. The MAPK kinase (MEK) inhibitor U0126 (10 microM) partially blocked NMDA neuroprotection, whereas LY294002, a selective inhibitor of the PI3-K pathway, did not affect the neuroprotective activity of NMDA. Glutamate excitotoxicity decreased bcl-2, bcl-X(L), and bax mRNA levels,. NMDA increases Bcl-2 and Bcl-X(L) protein levels and decreases Bax protein levels. NMDA and TrkB receptor activation thus converge on the extracellular signal-regulated kinase (ERK) 1/2 signaling pathway to protect neurons against glutamate-mediated excitotoxicity. By increasing antiapoptotic proteins of the Bcl-2 family, NMDA receptor activation may also promote neuronal survival by preventing apoptosis.     

Autocrine signaling through Ras regulates cell survival activity in human glioma cells: potential cross-talk between Ras and the phosphatidylinositol 3-kinase-Akt pathway

Autocrine fibroblast growth factor (FGF) signaling mediates an uncontrollable growth of human gliomas. We investigated the intracellular signaling of FGF on cell survival activity. U251MG human glioma cells were infected with adenovirus vectors expressing dominant negative type I FGF receptor (DNFR), constitutive active Ras (RasL61), or dominant negative Ras (RasN17). DNFR reduced glioma cell accumulation with apoptosis and this reduction was alleviated with exogenous epidermal growth factor (EGF), which can activate Ras independent of FGFR but not with bFGF. RasL61 prevented but RasN17-enhanced DNFR-induced apoptosis. Reportedly, cell survival signaling through Akt was constitutively active in U251MG cells and this effect may be dependent on autocrine signaling and dysfunction of PTEN, a tumor suppressor gene limiting phosphatidylinositol 3-kinase (PI3K) activity. DNFR dose-dependently inhibited Akt activity and this inhibition was recovered by RasL61, whereas RasN17 inhibited Akt activity. Wortmannin (a PI3K inhibitor) inhibited Akt activity and mildly promoted apoptosis. RasL61 prevented the down-regulation of Akt activity and apoptosis induced by wortmannin, but RasN17 plus wortmannin strongly inhibited Akt activity and promoted marked apoptosis. Our data suggested that the cell survival activity of human gliomas is largely dependent on cross-talk between Ras and the PI3K-Akt pathway, and this cross-talk could be a potential target for molecular-based therapeutics.     

Neurotrophism without neurotropism: BDNF promotes survival but not growth of lesioned corticospinal neurons.

Neurotrophic factors exert many effects on the intact and lesioned adult central nervous system (CNS). Among these effects are prevention of neuronal death (neurotrophism) and promotion of axonal growth (neurotropism) after injury. To date, however, it has not been established whether survival and axonal growth functions of neurotrophins can be independently modulated in injured adult neurons in vivo. To address this question, the ability of brain-derived neurotrophic factor (BDNF) to influence corticospinal motor neuronal survival and axonal growth was examined in two injury paradigms. In the first paradigm, a survival assay, adult Fischer 344 rats underwent subcortical lesions followed by grafts to the lesion cavity of syngenic fibroblasts genetically modified to secrete high amounts BDNF or, in control subjects, the reporter gene green fluorescent protein. In control subjects, only 36.2 +/- 7.0% of the retrogradely labeled corticospinal neurons survived the lesion, whereas 89.8 +/- 5.9% (P < 0.001) of the corticospinal neurons survived in animals that received BDNF-secreting grafts. However, in an axonal growth assay, BDNF-secreting cell grafts that were placed into either subcortical lesion sites or sites of thoracic spinal cord injury failed to elicit corticospinal axonal growth. Despite this lack of a neurotropic effect on lesioned corticospinal axons, BDNF-secreting cell grafts placed in the injured spinal cord significantly augmented the growth of other types of axons, including local motor, sensory, and coerulospinal axons. Immunolabeling for tyrosine kinase B (trkB) demonstrated that BDNF receptors were present on corticospinal neuronal somata and apical dendrites but were not detected on their projecting axons. Thus, single classes of neurons in the adult CNS appear to exhibit disparate survival and growth sensitivity to neurotrophic factors, potentially attributable at least in part to differential trafficking of neurotrophin receptors. The possibility of tropic/trophic divergence must be considered when designing strategies to promote CNS recovery from injury.     

Prelimbic BDNF and TrkB signaling regulates consolidation of both appetitive and aversive emotional learning

The medial prefrontal cortex (mPFC) is known to regulate executive decisions and the expression of emotional memories. More specifically, the prelimbic cortex (PL) of the mPFC is implicated in driving emotional responses via downstream targets including the nucleus accumbens and amygdala, but mechanisms are yet to be fully understood. Therefore, we investigated whether prelimbic cortical brain-derived neurotrophic factor (BDNF) signaling through the high-affinity tyrosine kinase receptor B (TrkB) receptor may serve as a molecular mechanism underlying emotional memory encoding. Here, we utilized viral-mediated inducible bdnf deletion within the PL, as well as TrkB^F616A mutant mice, wherein TrkB receptor point mutation results in its being highly sensitive to inhibition by small PP1-derivative molecules, serving as a specific TrkB inhibitor. The site-specific TrkB antagonism and viral-mediated bdnf deletion within the PL resulted in deficits in both cocaine-dependent associative learning and fear expression. Deficiencies were rescued by the novel TrkB agonist 7,8-dihydroxyflavone, indicating that PL BDNF expression and downstream signaling through the TrkB receptor are required for memory formation in both appetitive and aversive domains.     

Roles of brain-derived neurotrophic factor/tropomyosin-related kinase B (BDNF/TrkB) signalling in Alzheimer's disease

Alzheimer's disease (AD) is one of the most common causes of dementia in the elderly. It is characterized by extracellular deposition of the neurotoxic peptide, amyloid-beta (Aβ) peptide fibrils, and is accompanied by extensive loss of neurons in the brains of affected individuals. However, the pathogenesis of AD is not fully understood. The aim of this review is to discuss the possible role of brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB) signalling in the development of AD, focusing on BDNF/TrkB signalling in the production of Aβ, tau hyperphosphorylation and cognition decline, and exploring new possibilities for AD intervention.     

Hypertonicity promotes survival of corticospinal motoneurons via mitogen-activated protein kinase p38 signaling

Extracellular hypertonicity can induce the phosphorylation of mitogen-activated protein kinases (MAPKs). Of these, both extracellular signal-regulated kinases (ERKs) and the stress-activated kinase p38 have been implicated in neuronal cell survival. Resuscitation with hypertonic saline decreases secondary brain injury after trauma, as well as neuronal damage, after ischemia. Since hypertonicity has been shown to support somatic cell survival, we investigated if hypertonicity can also prevent neuronal cell death via MAPK signaling. Death of postnatal rat corticospinal motoneurons (CSMNs) was induced by serum deprivation, and survival in both isotonic and hypertonic media was assessed after 20 h. Addition of NaCl (4–250 mM) to isotonic medium significantly and dose dependently protected CSMN in enriched cultures, increasing cell survival by up to 70% over that in isotonic medium. This response was not restricted to NaCl; addition of KCl, choline chloride, and sucrose had similar effects on cell survival. In addition, hypertonicity supported the survival of pure CSMN populations, albeit with lower potency. In cortical cell suspensions, hypertonic NaCl (20–100 mM) increased basal phosphorylation of p38 and ERK. The activation of both MAPKs, which was induced by 40 mM NaCl, was transient. Cultivation of CSMNs in media containing the specific p38 inhibitor SB203580 abolished the protective effect of hypertonic NaCl, indicating a central role for p38. We therefore conclude that hypertonicity can prevent neuronal cell death via MAPK signaling.