Up-regulation of bax and down-regulation of bcl-2 is associated with kainate-induced apoptosis in mouse brain

Activation of Bcl-2-associated death protein and counter-response of Akt within cell populations during seizure-induced neuronal death

Bcl-2 family gene products are critical to the integration of cell death stimuli that target the mitochondrion. Proapoptotic BAD (Bcl-2-associated death protein) has been shown to dissociate from its sequestered site with the molecular chaperone protein 14-3-3 and displace proapoptotic BAX (Bcl-2-associated X protein) from antiapoptotic BCL-Xl. BAX subsequently translocates to the mitochondrion and induces cytochrome c release and caspase activation. Herein we report the response of the key members of this proposed pathway after seizures. Seizures evoked by microinjection of kainic acid into the amygdala of the rat induced unilateral CA3 pyramidal neuron death with features of apoptosis. In control hippocampus and cortex, BAD was found constitutively bound to 14-3-3, whereas BCL-Xl bound BAX. Within damaged hippocampus, seizures induced the dissociation of BAD from 14-3-3 and the subsequent dimerization of BAD with BCL-Xl as determined by immunoprecipitation and immunohistochemical colocalization. 14-3-3 was found to translocate to the nucleus of degenerating neurons, whereas BAX accumulated at mitochondrial membranes. In contrast, the primarily uninjured cortex exhibited increased phosphorylation of Akt (protein kinase B), which may phosphorylate and inhibit BAD, and no altered binding of BAD to BCL-Xl. Finally, administration of an inhibitor of phosphatidylinositol 3-kinase (LY294002), thought to be an upstream activator of Akt, exacerbated cortical apoptosis after seizures. These data suggest that seizures elicit divergent cell death and survival responses within neuronal populations and that the BAD cell death pathway may perform an instigator or reinforcement role in seizure-induced neuronal death.

Delayed sclerosis, neuroprotection, and limbic epileptogenesis after status epilepticus in the rat

PURPOSE

Hippocampal sclerosis and massive neurodegeneration in other parts of the limbic system are considered hallmarks of temporal lobe epilepsy. Using the rat model of kainate-induced status epilepticus, we sought to determine if limbic sclerosis after an excitotoxic insult follows a delayed type of neurodegeneration and is thus accessible to neuroprotective intervention after the insult. Effective pharmacologic neuroprotection after status epilepticus also addresses the old question of whether degenerative morphologic changes after an epilepsy-inducing event like status epilepticus are the primary cause of epileptogenesis (i.e., the development of recurrent spontaneous seizures) during the following weeks.

METHODS

Female Wistar rats after 90 min of generalized status epilepticus were used. Molecular biologic and histologic techniques were used to demonstrate markers of delayed cell death (apoptosis) 48 h after the status. The neuroprotective effects of i.c.v. injections of caspase inhibitors and systemic injections of the anticonvulsant drugs (AEDs) dizocilpine and retigabine after the status epilepticus were studied. The effect of neuroprotective intervention on the development of recurrent spontaneous seizures was investigated by behavioral observation of the rats.

RESULTS

After generalized status epilepticus in Wistar rats, massive sclerosis of the hippocampus and the piriform cortex occurred. TUNEL labeling and electron microscopy revealed that apoptosis is involved in the degenerative processes. Immunohistochemical analysis of the time course of the expression of the proapoptotic protein Bax suggested a maximal induction of apoptosis 24-48 h after the status. Application of caspase inhibitors before or after the status did not reduce lesions, although Bax labeling was reduced. Injection of dizocilpine and to a lower extent also of retigabine after the status prevented limbic neurodegeneration and expression of markers of apoptosis. However, the neuroprotection by dizocilpine did not prevent the development of recurrent spontaneous seizures.

CONCLUSIONS

Prolonged seizure activity can induce delayed sclerosis in the hippocampus and other parts of the limbic system. This delayed cell loss can be prevented by neuroprotective drugs after a status epilepticus. However, the damage in limbic brain regions is not the main reason for limbic epileptogenesis and the occurrence of recurrent spontaneous seizures.

Characterization of neuronal death induced by focally evoked limbic seizures in the C57BL/6 mouse

Research into the molecular mechanisms of epileptic brain injury is hampered by the resistance of key mouse strains to seizure-induced neuronal death evoked by systemically administered excitotoxins such as kainic acid. Because C57BL/6 mice are extensively employed as the genetic background for transgenic/knockout modeling in cell death research but are seizure resistant, we sought to develop a seizure model in this strain characterized by injury to the hippocampal CA subfields. Adult male C57BL/6 mice underwent focally evoked seizures induced by intraamygdala microinjection of kainic acid. Kainic acid (KA) effectively elicited ipsilateral CA3 pyramidal neuronal death within a narrow dose range of 0.1-0.3 microg, with mortality < 10%. With employment of the most consistent (0.3 microg) dose, seizures were terminated 15, 30, 60, or 90 min after KA by diazepam. Damage was largely restricted to the ipsilateral CA3 subfield of the hippocampus, but injury was also consistent within CA1, suggesting that this mouse model better reflects the hippocampal neuropathology of human temporal lobe epilepsy than does the rat, in which CA1 is typically spared. Confirming this CA1 injury as seizure specific and not a consequence of ischemia, we used laser-Doppler flowmetry to determine that cerebral perfusion did not significantly change (97% to 118%) over control. Degenerating cells were > 95% neuronal as determined by neuron-specific nuclear protein (NeuN) counterstaining of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeled (TUNEL) brain sections. Furthermore, TUNEL-positive cells often exhibited the morphological features of apoptosis, and small numbers were positive for cleaved caspase-3. These data establish a mouse model of focally evoked seizures in the C57BL/6 strain associated with a restricted pattern of apoptotic neurodegeneration within the hippocampal subfields that may be applied to research into the molecular basis of neuronal death after seizures.

Human Meissner corpuscles express Bcl-2 but not Bax protein

Bcl-2 and Bax proteins play major roles in the control of apoptosis. The Bcl-2/Bax ratio is considered a marker of a cell's susceptibility to apoptotic stimuli. Immunohistochemical expression of Bcl-2 and Bax in Meissner corpuscles was investigated in 30 human skin samples. All of the Meissner corpuscles showed immunoreactivity for Bcl-2 and Bax was negative. These data support a role for Bcl-2 as a resistance mechanism of these mechanoreceptors to apoptosis.

Neuronal apoptosis after brief and prolonged seizures

Evidence has accumulated that apoptotic cell death contributes to brain damage following experimental seizures. A substantial number of degenerating neurons within limbic regions display morphological features of apoptosis following prolonged seizures evoked by systemic or local injections of kainic acid, systemic injections of pilocarpine and sustained stimulation of the perforant path. Although longer periods of seizures consistently result in brain damage, it has previously not been clear whether brief single or intermittent seizures lead to cell death. However, recent results indicate that also single seizures lead to apoptotic neuronal death. A brief, non-convulsive seizure evoked by kindling stimulation was found to produce apoptotic neurons bilaterally in the rat dentate gyrus. The mechanism triggering and mediating apoptotic degeneration is at present being studied. Alterations in the expression and activity of cell-death regulatory proteins such as members of the Bcl-2 family and the cysteinyl aspartate-specific proteinase (caspase) family occur in regions vulnerable to cell degeneration, suggesting an involvement of these factors in mediating apoptosis following seizures. Findings of decreased apoptotic cell death following administration of caspase inhibitors prior to and following experimentally induced status epilepticus, further suggest a role for caspases in seizure-evoked neuronal degeneration. Intermediate forms of cell death with both necrotic and apoptotic features have been found after seizures and investigation into the detailed mechanisms of the different forms of cell degeneration is needed before attempts to specific prevention can be made.

Mifepristone protects CA1 hippocampal neurons following traumatic brain injury in rat

The present study addresses mineralocorticoid receptor and glucocorticoid receptor effects on hippocampal neuron viability after experimental traumatic brain injury. Rats were pretreated for 48 h with vehicle, the mineralocorticoid receptor antagonist spironolactone, or the glucocorticoid receptor antagonist mifepristone (RU486) and subsequently subjected to sham operation or unilateral controlled cortical impact injury. To determine the effects of receptor antagonist pretreatments on cell survival, neurons in regions CA1, CA3, and dentate gyrus of the hippocampal formation were counted 24 h post-injury using the optical fractionator method. Injury decreased the number of viable neurons in CA1 and CA3 of vehicle-pretreated animals. Notably, this cell loss was prevented in CA1 by RU486 pretreatment. Neuronal loss was also observed in dentate gyrus. The effects of receptor blockade and injury on the expression of viability-related genes were also assessed by comparing relative bcl-2, bax, and p53 messenger RNA levels using in situ hybridization analysis. Spironolactone and RU486 decreased basal bcl-2 messenger RNA levels in CA1 and dentate gyrus but did not affect basal bax or p53 levels. Injury decreased bcl-2 messenger RNA levels in dentate gyrus but did not affect bax or p53 levels in vehicle-pretreated animals. These data demonstrate that RU486 pretreatment prevents the loss of CA1 pyramidal neurons 24 h after traumatic brain injury. RU486 modulation of bcl-2, bax, or p53 messenger RNA expression does not predict neuronal viability at this time point, suggesting that RU486-mediated preservation of CA1 neurons does not involve transcriptional regulation of these cell death-related genes.

Caspase-3-associated apoptotic cell death in excitotoxic necrosis of the entorhinal cortex following intraperitoneal injection of kainic acid in the rat

The present study is directed to study: (a) bax translocation and cytochrome c release as mediators of the mitochondrial pathway of apoptosis; (b) Fas-L (Fas-ligand) expression as an indicator of the possible involvement of the Fas/Fas-L signaling pathway; and (c) active caspase-3 expression as the main executioner of caspase-mediated apoptosis, in rats receiving an intraperitoneal injection of the glutamate analogue kainic acid (KA) at a dose of 9 mg/kg, which is sufficient to produce generalized seizures and excitotoxic cell death in the entorhinal cortex. Sub-fractionation studies of entorhinal cortex homogenates have shown cytochrome c and cytochrome oxidase IV localized in the mitochondrial fraction, and Bax localized in the cytosolic fraction. No modifications in the sub-cellular distribution of cytochrome c and Bax have been observed at 6 h and 24 h in KA-treated rats. Morphological studies have shown cytoplasmic shrinkage and nuclear condensation consistent with necrosis in the entorhinal cortex. Many neurons (about 30% of dying cells) are stained with the method of in situ end-labeling of nuclear DNA fragmentation. Yet only about 5% of dying cells have apoptotic morphology. A percentage of dying cells (5% at 6 h and 40% at 24 h) over-express Fas-L but only about 2% of dying cells at 24 h post-injection express cleaved caspase-3 (17 kD). The present data further support the concept that necrosis is the predominant form of cell death in the entorhinal cortex, although caspase-3-dependent apoptotic cell death may play a limited role, in the present paradigm of KA-induced excitotoxicity.

Status epilepticus leads to the degradation of the endogenous inhibitor of caspase-activated DNase in rats

Specific biochemical hallmarks of apoptosis, namely internucleosomal DNA fragmentation and caspase-3 activation, appear in the aftermath of status epilepticus (SE). This led us to hypothesize that caspase-activated DNase (CAD) is involved in DNA fragmentation and apoptotic neuronal cell death following SE. The present study aimed to determine whether SE is associated with an activation of CAD, as reflected in the degradation of the CAD inhibitor, ICAD. SE was induced in adult male Sprague-Dawley rats by kainic acid (12 mg/kg i.p.) and seizures were terminated with diazepam after 2 h. At 24, 48, or 72 h after SE termination, protein levels of CAD and ICAD were measured by Western blotting (after sodium dodecyl sulfate-polyacrylamide gel electrophoresis) using specific antibodies. At 48 and 72 h after SE termination, ICAD protein levels significantly decreased (by more than 60%) in rhinal cortex and hippocampus as compared with those in the same tissue from animals not experiencing SE. No changes were detected in total CAD protein levels at any time point, resulting in an increase in the ratio of CAD to its inhibitor. The loss of ICAD following SE is indicative of a disinhibition of CAD, leading to DNA fragmentation. Consistent with this, we observed that the decrease in ICAD between 24 and 48 h was accompanied by a marked increase in DNA fragmentation. Our results support the proposal that CAD participates in caspase-3-mediated internucleosomal DNA fragmentation in the aftermath of SE.

Neuronal expression and regulation of rat inhibitor of apoptosis protein-2 by kainic acid in the rat brain

Inhibitors of apoptosis proteins (IAPs) define a protein family with the ability to counteract cell death by the inhibition of different caspases activated during apoptosis. These proteins are present in different cells, however, the function and roles of IAPs in brain tissue are not fully understood. We report here that RIAP-2, the rat homologue of human cIAP-1/HIAP-2, is expressed in different areas of rat brain as shown by in situ hybridization and immunohistochemistry. Brain regions with relatively high expression of RIAP-2 mRNA included cortex, cerebellum and different subregions of rat hippocampus. Double labelling using a specific anti-RIAP antibody and markers for neurons and glial cells, showed that RIAP-2 is predominantly expressed by nerve cells. Kainic acid treatment, which induces seizures, transiently up-regulated RIAP-2 mRNA levels in cerebral cortex, in the CA1 and dentate gyrus regions of hippocampus, which returned to normal levels at 24 h. However in the CA3 region, RIAP-2 mRNA was decreased at 6 h following an early up-regulation. This region contains neurons particularly vulnerable to kainic acid induced cell degeneration. The decrease in RIAP-2 following kainic acid was also observed using immunohistochemistry. RIAP-2 protein did not colocalize with TUNEL labelling present in cells undergoing cell death. The results show that in the adult rat brain RIAP-2 is expressed mainly by neurons, and that the levels are regulated by kainic acid, which activates glutamate receptors. The decrease in RIAP-2 in specific neuronal populations may contribute to cell degeneration in vulnerable brain regions observed after kainic acid treatment.

Effect of graded hypoxia on high-affinity Ca2+-ATPase activity in cortical neuronal nuclei of newborn piglets

Previous studies have shown that nuclear calcium signals control a variety of nuclear functions including gene transcription, DNA synthesis, DNA repair and nuclear envelope breakdown. The present study tested the hypothesis that the activity of the neuronal nuclear high affinity Ca2+-ATPase increases as a function of decreased energy metabolism in the cerebral cortex. Studies were performed in 11 ventilated newborn piglets, age 3-5 days, divided into normoxic (Nx, n = 4) and hypoxic (Hx, n = 7) groups. The animals were exposed to a single FiO2 in the range from 0.21 to 0.05 for one hr. Cerebral tissue hypoxia was confirmed biochemically by determining brain tissue ATP and phosphocreatine levels. Neuronal nuclei were isolated and the high-affinity Ca2+-ATPase activity determined. During graded hypoxia, cerebral tissue ATP decreased from 4.80 +/- 0.58 (normoxic) to 1.03 +/- 0.38 (ranging from 0.61-1.63) micromol/g brain (p < 0.05) and PCr decreased from 3.94 +/- 0.75 (normoxic) to 0.99 +/- 0.27 (ranging from 0.50 to 1.31) micromol/g brain (p < 0.05). The total high affinity Ca2+-ATPase activity in the hypoxic nuclei increased and ranged from 541 to 662 nmol/mg protein/hr, compared to activity in normoxic group of 327 to 446 nmol/mg protein/hr. During graded hypoxia, the level of nuclear high affinity Ca2+-ATPase activity correlated inversely with ATP (r = 0.91) and PCr levels (r = 0.82), with activity increasing as tissue high energy phosphates decreased. The results demonstrate that the decrease in cerebral energy metabolism during hypoxia is linearly correlated with an increase in activity of high affinity Ca2+-ATPase in cerebral cortical nuclei from immature brain. We propose that increased nuclear membrane high affinity Ca2+-ATPase activity, leading to increased nuclear Ca2+, will result in altered expression of apoptotic genes that could initiate programmed neuronal death.

Vasoactive intestinal peptide stimulation modulates the expression of Bcl-2 family members in the adrenal gland of the lizard Podarcis sicula

The adrenal gland of the lizard Podarcis sicula is formed by a dorsal ribbon of chromaffin cells, generally defined as medullary tissue, arranged along a central part of steroidogenic cells considered as cortical tissue. These two tissues produce catecholamines and steroids as part of the hypothalamo-hypophyseal-adrenal gland axis. Recent studies have demonstrated that Podarcis sicula adrenal gland is not only under hypothalamo-hypophyseal axis control but that several peptides may influence the physiological activity of the gland; among these, vasoactive intestinal peptide is able to enhance strongly both catecholamine and steroid hormone production. The aim of the present study was to verify whether vasoactive intestinal peptide administration could become deleterious. For this reason, we monitored the pattern of expression of two members of the Bcl-2 family, Bcl-2 and Bax, in control and vasoactive intestinal peptide treated specimens. Furthermore, we also tested if peptide treatment induces apoptosis by TUNEL assay.

Kainate excitotoxicity in organotypic hippocampal slice cultures: evidence for multiple apoptotic pathways

The mechanisms underlying kainate (KA) neurotoxicity are still not well understood. We previously reported that KA-mediated neuronal damage in organotypic cultures of hippocampal slices was associated with p53 induction. Recently, both bax and caspase-3 have been demonstrated to be key components of the p53-dependent neuronal death pathway. Caspase activation has also been causally related to the release of mitochondrial cytochrome c (Cyto C) in the cytoplasm as a result of the collapse of the mitochondrial membrane potential (Deltapsi(M)) and the opening of mitochondrial permeability transition pores (mPTP). In the present study, we observed a rapid induction of bax in hippocampal slice cultures after KA treatment. In addition, the levels of Cyto C and caspase-3 were increased in the cytosol while the level of the caspase-9 precursor was decreased. There was also a complete reduction of Rhodamine 123 fluorescence after KA treatment, an indication of Deltapsi(M) dissipation. Furthermore, inhibition of mPTP opening by cyclosporin A partially prevented Cyto C release, caspase activation and neuronal death. These data suggest the involvement of bax, several caspases, as well as Cyto C release in KA-elicited neuronal death. Finally, inhibition of caspase-3 activity by z-VAD-fmk only partially protected neurons from KA toxicity, implying that multiple mechanisms may be involved in KA excitotoxicity.

Molecular events involved in neuronal death induced in the mouse hippocampus by in-vivo injection of kainic acid

Apoptosis results from the activation of a programmed cellular cascade involving several mechanisms. In the present study, we have investigated the implication of three molecules of this cascade, p53, Bax and caspase-3, in neuronal death induced by kainic acid (KA) administration in mouse hippocampus. Using immunocytochemistry, western blot and quantification of enzyme activity, we observed in p53+/+ and p53-/- animals that KA induced neuronal death by both p53-dependent and independent pathways. Moreover, apoptosis (labeled by TUNEL) and the increase of bax and caspase-3 protein expression after the neurotoxic insult appeared to clearly depend on p53 expression.

Expression of Bax and Bcl-2 proteins during hypoxia in cerebral cortical neuronal nuclei of newborn piglets: effect of administration of magnesium sulfate

This study tests the hypothesis that administration of magnesium sulfate, an antagonist of the NMDA receptor ion-channel, will prevent the hypoxia-induced alteration in the expression and the ratio of Bax and Bcl-2 proteins in cerebral cortical neuronal nuclear membranes. Anesthetized, ventilated and instrumented newborn piglets were divided into three groups: normoxic controls (Nx), untreated hypoxic (Hx), and magnesium sulfate-treated hypoxic (Mg-Hx) groups. Cerebral hypoxia was induced by lowering the FiO2 (0.05-0.07) for 1 h and the cerebral cortex was harvested immediately for isolation of neuronal nuclei and hypoxia was confirmed biochemically by a decrease in the tissue levels of ATP and phosphocreatine (PCr). Brain tissue PCr (micromol/g brain) was 2.74+/-0.77 (Nx), 0.38+/-0.09 (Hx, P<0.05 vs. Nx) and 0.69+/-0.60 (Mg-Hx, P<0.05 vs. Nx). The density of immunoblotted proteins was expressed as absorbance (Axmm(2)). The expression of Bax protein (Axmm(2)) was 222+/-31 (Nx), 279+/-32 (Hx), and 148+/-44 (Mg-Hx, P<0.05 vs. Hx). Bcl-2 protein expression was 77+/-1.0 (Nx), 37+/-5.0 (Hx) and 46+/-15 (Mg-Hx, P<0.05 vs. Nx). The ratio of Bax to Bcl-2 proteins increased more than twofold during hypoxia as compared to normoxia (7:1 Hx vs. 3:1 Nx). However, in the magnesium sulfate-treated group the Bax:Bcl-2 ratio was similar to normoxic controls. The data demonstrate that magnesium sulfate treatment prevents both the hypoxia-induced increase in Bax protein expression and the alteration of Bax:Bcl-2 protein ratios. We suggest that magnesium sulfate treatment before and during hypoxia may decrease hypoxia-induced programmed cell death by maintaining the normal ratio of Bax to Bcl-2 proteins.

Cleavage of bid may amplify caspase-8-induced neuronal death following focally evoked limbic seizures

The mechanism by which seizures induce neuronal death is not completely understood. Caspase-8 is a key initiator of apoptosis via extrinsic, death receptor-mediated pathways; we therefore investigated its role in mediating seizure-induced neuronal death evoked by unilateral kainic acid injection into the amygdala of the rat, terminated after 40 min by diazepam. We demonstrate that cleaved (p18) caspase-8 was detectable immediately following seizure termination coincident with an increase in cleavage of the substrate Ile-Glu-Thr-Asp (IETD)-p-nitroanilide and the appearance of cleaved (p15) Bid. Expression of Fas and FADD, components of death receptor signaling, was increased following seizures. In vivo intracerebroventricular z-IETD-fluoromethyl ketone administration significantly reduced seizure-induced activities of caspases 8, 9, and 3 as well as reducing Bid and caspase-9 cleavage, cytochrome c release, DNA fragmentation, and neuronal death. These data suggest that intervention in caspase-8 and/or death receptor signaling may confer protection on the brain from the injurious effects of seizures.

Electroconvulsive shock exposure prevents neuronal apoptosis after kainic acid-evoked status epilepticus

In the aftermath of prolonged continuous seizure activity (status epilepticus, SE), neuronal cell death occurs in the brain regions through which the seizure propagates. The vulnerability to adrenalectomy-induced apoptotic neuronal death was recently reported to be reduced by prior exposure to repeated daily noninjurious electroconvulsive shock (ECS). The present studies identified apoptosis and apoptosis-associated gene products in the neurodegenerative response to experimentally controlled periods (1 or 2 h) of SE in the rat, and determined whether exposure to ECS can interrupt these apoptotic responses mechanisms. Internucleosomal DNA fragmentation and the presence of apoptotic-like neurons (as assessed by in situ double labeling technique) was detected in hippocampus and rhinal cortex at 24 h after SE. Under these conditions, levels of both mRNA and protein encoded by the 'death promoting' bcl-XS gene were increased in the same brain areas. Pretreatment of animals for 7 days with low intensity (minimal) ECS conferred resistance to SE-evoked neurodegeneration, as assessed histopathologically by silver staining. Associated with this neuroprotective action was a reduction in the incidence of apoptosis-like neuronal morphology and DNA fragmentation, and a prevention of the increase in Bcl-XS protein and mRNA in hippocampus and rhinal cortex. These data suggest that pre-exposure to controlled, brief noninjurious seizures decreases vulnerability to programmed neuronal cell death, that this neuroprotective action occurs upstream from Bcl-XS, and that increases in bcl-XS gene expression may serve as a sensitive indicator of neurodegeneration following SE.

Effect of graded hypoxia on cerebral cortical genomic DNA fragmentation in newborn piglets

Previous studies have shown that hypoxia is associated with modification of the cerebral cortical nuclear membrane, leading to increased intranuclear calcium. The increased intranuclear calcium activates calcium-dependent endonucleases, resulting in DNA fragmentation. The present study tests the hypothesis that the fragmentation of neuronal genomic DNA increases with an increase in the degree of cerebral tissue hypoxia. Sixteen newborn piglets were anesthetized, ventilated and divided into normoxic and hypoxic groups with varying degrees of hypoxia. Cerebral hypoxia was documented biochemically by measuring tissue levels of ATP and phosphocreatine. Isolation of cerebral cortical neuronal nuclei and DNA and their purity was confirmed by standard techniques. DNA samples were separated by electrophoresis on 1% agarose gel and stained with ethidium bromide. In the hypoxic samples, multiple low-molecular-weight DNA fragments were present as a smear pattern from 200 to 2,000 base pairs. Levels of high-energy phosphates were compared to the area of each smear for each animal to correlate the degree of hypoxia with the degree of DNA fragmentation. DNA fragmentation increased when high-energy phosphate levels decreased. We conclude that there is a critical threshold value of oxidative metabolism beyond which there are progressive changes in the cortical neuronal cells, leading to DNA fragmentation.

Increased Bcl-w expression following focally evoked limbic seizures in the rat

Control of seizure-induced neuronal death may involve members of the Bcl-2 family of cell death regulating proteins. Bcl-w is a newly described anti-apoptotic member of this family that may confer neuroprotective effects. We therefore investigated Bcl-w expression in rat brain following focally evoked limbic seizures. Seizures were induced by unilateral microinjection of kainic acid into the amygdala of the rat and terminated after 40 min by diazepam. Constitutive Bcl-w expression was detected by Western blotting and immunohistochemistry. Bcl-w expression was increased 4-72 h following seizures within the injured hippocampus. Immunohistochemistry determined Bcl-w was predominantly expressed in neurons and seizures increased Bcl-w immunoreactivity within piriform cortex and surviving regions of the injured hippocampus. These data suggest Bcl-w may be involved in the modulation of seizure-induced brain injury.

Bax kappa, a novel Bax splice variant from ischemic rat brain lacking an ART domain, promotes neuronal cell death

Bax is a pro-apoptotic Bcl-2 family protein that regulates programmed cell death through homodimerization and through heterodimerization with Bcl-2. Bax alpha is encoded by six exons and undergoes alternative splicing. Bax kappa, a splice variant of Bax with conserved BH1, BH2 and BH3 binding domains and a C-terminal transmembrane domain (TM), but with an extra 446-bp insert between exons 1 and 2 leading to loss of an N-terminal ART domain, was identified from an ischemic rat brain cDNA library. Expression of Bax kappa mRNA and protein was up-regulated in hippocampus after cerebral ischemic injury. The increased Bax kappa mRNA was distributed mainly in selectively vulnerable hippocampal CA1 neurons that are destined to die after global ischemia. Overexpression of Bax kappa protein in HN33 mouse hippocampal neuronal cells induced cell death, which was partially abrogated by co-overexpression of Bcl-2. Moreover, co-overexpression of Bax kappa and Bax alpha increased HN33 cell death. The results suggest that the Bax kappa may have a role in ischemic neuronal death.

Caspase-2 activation is redundant during seizure-induced neuronal death

Seizure-induced neuronal death may be under the control of the caspase family of cell death proteases. We examined the role of caspase-2 in a model of focally evoked limbic seizures with continuous EEG recording. Seizures were elicited by microinjection of kainic acid into the amygdala of the rat and terminated after 40 min by diazepam. Caspase-2 was constitutively present in brain, mostly within neurons, and was detected in both cytoplasm and nucleus. Cleaved caspase-2 (12 kDa) was detected immediately following seizure termination within injured ipsilateral hippocampus, contiguous with increased Val-Asp-Val-Ala-Asp (VDVADase) activity, a putative measure of activated caspase-2. Expression of receptor interacting protein (RIP)-associated Ich-1-homologous protein with death domain (RAIDD) was increased following seizures, whereas expression of RIP and tumor necrosis factor receptor associated protein with death domain (TRADD), other components thought to be linked to the caspase-2 activation and signaling mechanism, were unchanged. Intracerebroventricular administration of z-VDVAD-fluoromethyl ketone blocked seizure-induced caspase-2 activity but did not alter caspase-8 activity and failed to affect DNA fragmentation or neuronal death. These data support activation of caspase-2 following seizures but suggest that parallel caspase pathways may circumvent deficits in caspase-2 function to complete the cell death process.

Alteration of Bcl-2 expression in the nigrostriatal system after kainate injection with or without melatonin co-treatment

In order to understand further the role of the anti-apoptotic Bcl-2 proto-oncogene protein in excitotoxin-induced brain injury and possible interaction between Bcl-2 and the antioxidant melatonin, the expression of Bcl-2 in various brain parts was studied after intrastriatal injection of kainate (KA, 2.5 nmol) with or without co-treatment of melatonin (10 mg/kg, intraperitoneally (i.p.)). Three days after unilateral injection of KA to the striatum in the rat, a dramatic direct cytotoxic effect was observed, as indicated an expression of Bcl-2 immunoreactivity in TUNEL- and OX-42-positive cells in the KA-injected striatum and traumatized cortical region. A less severe detrimental effect was also observed in the ipsilateral substantia nigra and peritraumatic cortex, as reflected by an upregulation of Bcl-2-immunostained neurons. Surprisingly, a reduction in Bcl-2-immunoreactive neurons that was accompanied by a less severe loss of tyrosine hydroxylase-immunoreactive neurons in the nigrostriatal pathway was observed after co-treatment with melatonin. Western blot analysis confirmed that Bcl-2 expression is elevated in striatum and cortex on the lesioned side, and that its expression was attenuated substantially after systemic administration of melatonin. The results showing an upregulation of Bcl-2 in nigral neurons and reactive microglia after KA lesion are consistent with the view that Bcl-2 is protective in function in the central nervous system.

Insulin-like growth factor-I overexpression attenuates cerebellar apoptosis by altering the expression of Bcl family proteins in a developmentally specific manner

In studies of transgenic (Tg) mice that overexpress insulin-like growth factor-I (IGF-I) exclusively in the CNS, we demonstrated a dramatic increase in cerebellar granule cell number that appeared to be attributable predominantly to enhanced survival. IGF-I anti-apoptotic actions are well established in cultured neurons, but comparable studies in vivo are few. Using the same Tg mice, therefore, we set out to document IGF-I anti-apoptotic effects during cerebellar development and to probe IGF-I signaling mechanisms. Compared with cerebella (CBs) of non-Tg littermates, those of Tg mice had fewer apoptotic cells at postnatal day 7 (P7) and showed a similar tendency at P14 and P21. At each age studied, procaspase-3 and caspase-3 were decreased in CBs of Tg mice. The caspase-3 decline was accompanied by decreases in the 85 kDa fragment of Poly(ADP-ribose) polymerase, a known product of caspase cleavage, suggesting decreased caspase activity. At P7 decreased apoptosis in Tg mice was associated with increased expression of the anti-apoptotic Bcl genes, Bcl-x(L) and Bcl-2. The mRNA expression of the proapoptotic Bcl genes, Bax and Bad, also was increased, but no changes were observed in the abundance of their proteins. At P14 Bcl-xL and Bcl-2 expression were similar in normal and Tg mice; Bax mRNA was unchanged in Tg mice, but its protein abundance was decreased, and both Bad mRNA and protein abundance were decreased. At P21 Bcl-xL and Bcl-2 expression were unchanged, but Bax and Bad expression were decreased. Our data show that IGF-I exerts anti-apoptotic actions during cerebellar development, and thereby alters the magnitude of naturally occurring apoptosis. IGF-I appears to affect multiple steps in the apoptotic pathway in a developmentally specific manner. IGF-I decreases caspase-3 availability and activity, increases the expression of anti-apoptotic Bcl-x(L) and Bcl-2 during early postnatal development, and decreases proapoptotic Bax and Bad expression at later developmental stages.

Uteroplacental insufficiency lowers the threshold towards hypoxia-induced cerebral apoptosis in growth-retarded fetal rats

Infants suffering uteroplacental insufficiency and hypoxic ischemic injury often demonstrate cerebral apoptosis. Our objective was to determine the global effects of uteroplacental insufficiency upon cerebral gene expression of the apoptosis related proteins Bcl-2 and Bax and their role in increasing vulnerability to hypoxia-induced cerebral apoptosis. We therefore caused uteroplacental insufficiency and growth retardation by performing bilateral uterine artery ligation upon pregnant rats 2 days prior to term delivery and elicited further perinatal fetal hypoxia by placing maternal rats in 14% FiO(2) 3 h prior to delivery. We quantified cerebral levels of Bcl-2 and Bax mRNA, lipid peroxidation, caspase-3 activity, and cAMP in control and growth retarded term rat pups that experienced either normoxia or hypoxia. Uteroplacental insufficiency alone caused a significant decrease in cerebral Bcl-2 mRNA levels without altering cerebral Bax mRNA levels, malondialdehyde levels, or caspase-3 activity. In contrast, uteroplacental insufficiency and subsequent fetal hypoxia significantly increased cerebral Bax mRNA levels, lipid peroxidation and caspase-3 activity; Bcl-2 mRNA levels continued to be decreased. Hypoxia alone increased cerebral cAMP levels, whereas uteroplacental insufficiency and subsequent hypoxia decreased cerebral cAMP levels. We speculate that the decrease in Bcl-2 gene expression increases the vulnerability towards cerebral apoptosis in fetal rats exposed initially to uteroplacental insufficiency and subsequent hypoxic stress.

Role of anti-apoptotic Bcl-2 protein in spinal muscular atrophy

Apoptosis is an essential physiological cell death for selective elimination of cells, involved in a variety of biological events including morphogenesis, cell turn over and removal of harmful cells. Disruption of the regulation of apoptosis may result in various diseases, including cancer and autoimmune diseases both associated with inhibition of apoptosis and various degenerative disorders associated with enhancement of apoptosis, and therefore, apoptosis is an important theme in the medical field. Apoptosis is driven by a family of cysteine proteases, called caspases and regulated by a Bcl-2 family of proteins, which is the best characterized apoptosis regulators. The Bcl-2 family consists of anti-apoptotic and pro-apoptotic members, and some members are implicated in cancer and nuronal diseases. Here, I overview the mechanism of how Bcl-2 family proteins regulate cell death, and how they are implicated in human diseases, particularly focusing on role of Bcl-2 in spinal muscular atropy.

Bax-induced apoptosis not demonstrated in the congenital toxoplasmosis in mice

A prominent neuropathological change observed in a murine model of congenital toxoplasmosis is cerebral cortical hypoplasia. In the early embryonic life of toxoplasmosis mice, the number of apoptotic cell observed in cerebral cortex is increased, indicating that increased number of apoptotic cells might relate to the pathogenetic mechanism of the cortical hypoplasia. Immunohistochemical expression of apoptosis-related factors, Bcl-2 and Bax has been studied in fetal murine brains infected with toxoplasma and in controls. Paraffin sections of the fetal brains on embryonic day (ED) 10, 12, 14, 16 and 18 were applied for the immunostains of Bcl-2 and Bax. Totally, 47 experimental animals (ED10: n=8, ED12: n=6, ED14: n=12, ED16: n=6, ED18: n=15) and 48 control animals (ED10: n=6, ED12: n=8, ED14: n=9, ED16: n=9, ED18: n=16) were examined. Bcl-2 positive cells were detected on ED10, whereas Bax positive cells appeared on ED14. No difference of Bcl-2 and Bax expression between toxoplasmosis and control groups was detected, suggesting that there is no clear relation between Bax-induced apoptosis and cortical dysplasia in congenital toxoplasmosis.

Neuroprotective role of dopamine against hippocampal cell death

Glutamate excitotoxicity plays a key role in the induction of neuronal cell death occurring in many neuropathologies, including epilepsy. Systemic administration of the glutamatergic agonist kainic acid (KA) is a well characterized model to study epilepsy-induced brain damage. KA-evoked seizures in mice result in hippocampal cell death, with the exception of some strains that are resistant to KA excitotoxicity. Little is known about the factors that prevent epilepsy-related neurodegeneration. Here we show that dopamine has such a function through the activation of the D2 receptor (D2R). D2R gene inactivation confers susceptibility to KA excitotoxicity in two mouse strains known to be resistant to KA-induced neurodegeneration. D2R-/- mice develop seizures when administered KA doses that are not epileptogenic for wild-type (WT) littermates. The spatiotemporal pattern of c-fos and c-jun mRNA induction well correlates with the occurrence of seizures in D2R-/- mice. Moreover, KA-induced seizures result in extensive hippocampal cell death in D2R-/- but not WT mice. In KA-treated D2R-/- mice, hippocampal neurons die by apoptosis, as indicated by the presence of fragmented DNA and the induction of the proapoptotic protein BAX. These results reveal a central role of D2Rs in the inhibitory control of glutamate neurotransmission and excitotoxicity.

Lovastatin induces apoptosis of spontaneously immortalized rat brain neuroblasts: involvement of nonsterol isoprenoid biosynthesis inhibition

We have examined the effects of lovastatin and pravastatin (competitive HMG-CoA reductase inhibitors) on the growth and survival of rat brain neuroblasts. Lovastatin, but not pravastatin, suppressed cell growth by inducing apoptosis of neuroblasts in a dose- and time-dependent manner. Apoptosis was accompanied by a decrease in both Bcl-2 and Bcl-xL protein levels, suggesting that changes in the expression of these genes may contribute to apoptosis following lovastatin treatment. Lovastatin treatment was also associated with decreased prenylation of both Ras and Rho A proteins whereas Rac 1 geranylgeranylation was not affected. Lovastatin effects were fully prevented by mevalonate. The present data suggest that lovastatin induces apoptosis of rat brain neuroblasts by its capacity to decrease the prenylation of specific proteins involved in signal transduction pathways that control growth and survival of neuronal cells.

Neuronal death is an active, caspase-dependent process after moderate but not severe DNA damage

Mild insults to neurons caused by ischemia or glutamate induce apoptosis, whereas severe insults induce non apoptotic death, such as necrosis. The molecular targets that are damaged by these insults and ultimately induce cell death are not fully established. To determine if DNA damage can induce apoptotic or non apoptotic death depending on the severity, neurons were treated with up to 128 Gy of ionizing radiation. Such treatment induced a dose-related increase in DNA single-strand breaks but no immediate membrane disruption or lipid peroxidation. Following moderate doses of < or = 32 Gy, neuronal death had many characteristics of apoptosis including nuclear fragmentation and DNA laddering. Nuclear fragmentation and membrane breakdown after moderate DNA damage could be blocked by inhibition of active protein synthesis with cycloheximide and by inhibition of caspases. In contrast, cell death after doses of > 32 Gy was not blocked by cycloheximide or caspase inhibitors, and membrane breakdown occurred relatively early in the cell death process. These data suggest that cell death after high dose irradiation and severe DNA damage can occur by non apoptotic mechanisms and that blocking apoptotic pathways may not prevent death after severe damage.

Expression of bcl-2, bax, and caspase-3 in the brain of the developing rat

Naturally occurring neuronal death (NOND) is generally considered to be apoptotic. Apoptosis is an active form of cell death in which the regulation of specific proteins produces anti- or pro-apoptotic signals. Two of the protein families involved in this regulation are the bcl proteins and caspases. A quantitative immunoblotting technique was used to examine the temporal expression of bcl-2, bax, and two isoforms of caspase 3 (an active 20 kDa isoform and the inactive 32 kDa precursor) throughout the developing neuraxis. Long-Evans rat fetuses were collected on gestational day (G) 16 and G19, and pups were harvested on postnatal day (P) 0, P3, P6, P12, P21, and P30. Brains were divided into five segments: cortex, thalamus, midbrain, medulla/pons, and cerebellum. In general, the expression of bax increased and the ratio of bcl-2 expression to bax expression decreased concurrent with published data on the onset of NOND in a given area. The timing of these events was paralleled by an increase in the expression of active caspase 3. Unlike the bcl proteins, caspase 3 expression returned toward fetal levels as the brain matured. The timing of the changes in bcl protein and caspase expression show that both protein families are involved in promoting neuronal death. Reductions in caspase expression (and not bcl-2 and bax expression) are key to ending the period of NOND.

Seizure-induced neuronal necrosis: implications for programmed cell death mechanisms

PURPOSE

To determine definitively the morphology of neuronal death from lithium-pilocarpine (LPC)-and kainic acid (KA)-induced status epilepticus (SE), and to correlate this with markers of DNA fragmentation that have been associated with cellular apoptosis. Endogenous glutamate release is probably responsible for neuronal death in both seizure models, because neuronal death in both is N-methyl-D-aspartate receptor-mediated.

METHODS

SE was induced for 3 hours in adult male Wistar rats with either LPC or KA, and 24 or 72 hours later the rats were killed. One group of rats had brain sections, stained with hematoxylin and eosin and the terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) technique, examined by light microscopy and by electron microscopy. A separate group of rats had DNA extracted from the same brain regions examined by electron microscopy in the first group. The extracted DNA was electrophoresed on an agarose gel with ethidium bromide and was examined for the presence or absence of internucleosomal DNA cleavage (DNA "laddering").

RESULTS

Twenty-four and 72 hours after 3 hours of LPC- or KA-induced SE, neuronal death in the hippocampus, amygdala, and piriform, entorhinal, and frontal cortices was morphologically necrotic, in spite of DNA laddering in these regions 24 and 72 hours after SE and positive TUNEL staining in some of the regions 72 hours after SE. Ultrastructurally, necrotic neurons were dark and shrunken, with cytoplasmic vacuoles and pyknotic nuclei with small, irregular, dispersed chromatin clumps.

CONCLUSIONS

Our results, together with those of other reports, suggest that programmed cell death-promoting mechanisms are activated by SE in neurons that become necrotic rather than apoptotic and point to the possibility that such mechanisms may contribute to SE-induced neuronal necrosis.

Prevention of death of axotomized hypoglossal neurones and promotion of regeneration by chitin grafting

1. Chitin is known to promote skin wound healing. In this study, chitin, prepared from Zuwai crab shell, was used as a bridge between the proximal and distal stumps of cut hypoglossal nerves in shrews. We compared the effects of chitin on the regeneration of transected right hypoglossal nerve axons, with those of porcine dermis, bovine dermal aterocollagen, and autologous nerve bundles. 2. To assess the survival of neurones, the size of neuronal cell body, and number of motoneurones were determined in the absence of any bridged material and in the presence of porcine dermis, bovine dermal aterocollagen, chitin, or autologous nerve bundles as a bridge. 3. Our results revealed a significantly better outcome in chitin and autologous nerve bridged groups; the size of neuronal cell body and number of hypoglossal neurones were higher than in the other groups. Chitin also enhanced the regeneration of neurones; the number of horseradish peroxide positive neurones indicative of repaired axonal processes was significantly higher in chitin and autologous nerve-bridged groups than in other groups. 4. Our results demonstrated that the use of chitin sheet or autograft successfully prevented the death of severed neurones and promoted the regeneration of the lesioned nerve. Although the mechanisms underlying the effects of chitin are still unknown, chitin seems to be a potentially useful biocompatible material for nerve repair and regeneration.

Kainic acid-induced seizures produce necrotic, not apoptotic, neurons with internucleosomal DNA cleavage: implications for programmed cell death mechanisms

Prolonged seizures (status epilepticus) induced by kainic acid activate programmed cell death mechanisms, and it is believed that kainic acid-induced status epilepticus induces neuronal apoptosis. In order to test this hypothesis, adult rats were subjected to 3-h kainic acid-induced seizures, with 24- or 72-h recovery periods. Neuronal death was assessed by light microscopy with the Hematoxylin and Eosin stain and with in situ terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL stain), by electron microscopy, and by agarose gel electrophoresis of DNA extracted from five vulnerable brain regions. Spontaneous and MK-801-induced apoptotic neurons from retrosplenial cortex of neonatal rats, evaluated by light and electron microscopy, were used as positive controls for apoptosis. Surprisingly, the large chromatin clumps of apoptotic neurons were TUNEL negative, whereas the cytoplasm showed light-to-moderate TUNEL staining, consistent with a lack of identifiable nuclear membranes ultrastructurally, and with intermingling of nuclear and cytoplasmic contents. Ultrastructurally, the acidophilic neurons produced by kainic acid-induced status epilepticus, identified with Hematoxylin and Eosin stain, were dark, shrunken and necrotic, with pyknotic nuclei containing small, dispersed chromatin clumps, and with cytoplasmic vacuoles, some of which were swollen, disrupted mitochondria. No apoptotic cells were seen. Acidophilic neurons were found in up to 20 of 23 brain regions examined and comprised 10-25% of the total number of neurons examined. A subset of these neurons (<10% of the total number of neurons in five of 23 regions) had TUNEL-positive nuclei 72h but not 24h after status epilepticus. Internucleosomal DNA cleavage (DNA "laddering") occurred in the four most damaged brain regions examined by electron microscopy 24h after SE and the three most damaged regions 72h after status epilepticus. Our results demonstrate that kainic acid-induced status epilepticus produces neuronal necrosis and not apoptosis in adult rats. The necrotic neurons show nuclear pyknosis, chromatin condensation and DNA laddering. Programmed cell death mechanisms activated by kainic acid-induced status epilepticus occur in neurons which become necrotic and could contribute to necrotic, as well as apoptotic, neuronal death.

Alterations in bcl-2 and caspase gene family protein expression in human temporal lobe epilepsy

OBJECTIVE

To address the role of cell death regulatory genes of the bcl-2 and caspase families in the neuropathology of human epilepsy using tissue extracted from patients undergoing temporal lobectomy for intractable seizures.

METHODS

Using Western blotting and immunohistochemistry, the authors investigated the expression of bcl-2, bcl-xL, bax, caspase-1,and caspase-3 in temporal cortex samples from patients who had undergone temporal lobectomy surgery for intractable epilepsy (n = 19). Nonepileptic postmortem tissue from a brain bank served as control (n = 6).

RESULTS

Western blot analysis demonstrated significant increases in levels of bcl-2 and bcl-xL protein in seizure brain compared to control. Cleavage of caspase-1 was evidenced by a reduction in levels of the 45 kDa proenzyme form and an increase in levels of the p10 fragment. Levels of the 32 kDa proenzyme form of caspase-3 were elevated in seizure patients, as were levels of the 12 kDa cleaved fragment. Bcl-2, bax, and caspase-3 immunoreactivity was increased predominantly in cells with the morphologic appearance of neurons, whereas bcl-xL immunoreactivity was increased in cells with the appearance of glia. DNA fragmentation was detected in some but not all sections from epileptic brain samples.

CONCLUSIONS

Cell death regulatory genes of the bcl-2 and caspase families may play a role in ongoing neuropathologic processes in human epilepsy, and offer novel targets as an adjunct to anticonvulsant therapy.

Carbachol blocks beta-amyloid fragment 31-35-induced apoptosis in cultured cortical neurons

We reported previously that many neurodegenerative changes characteristic of apoptosis could be induced by a short fragment of beta-amyloid protein, A(beta31-35), in cultured newborn mice cortical neurons, and that these changes were accompanied with alterations in expression of some genes. This study was designed to examine whether the apoptotic processes and related gene modulations in this model could be affected by coadministration of carbachol by electrophoretic analysis for DNA ladder formation and by RT-PCR assays for genomic modulation. The results showed that (1) simultaneous incubation with carbachol dose- and time-dependently blocked the specific DNA ladder formation induced by exposure to A(beta31-35) and (2) the A(beta31-35)-induced downregulation of bcl-2 and upregulations of bax, p53, and c-fos genes were reversed or ameliorated by the coadministration of carbachol. It is proposed that A(beta31-35)-induced apoptosis can be prevented by carbachol through mechanisms that modulate the expression of related genes.

Deltamethrin induces delayed apoptosis and altered expression of p53 and bax in rat brain

Our previous work indicates that deltamethrin induces degeneration and apoptosis in rat brain at 24 and 48 h after treatment. To determine whether molecular characteristics of apoptosis is involved in neurodegeneration in rat brain after deltamethrin treatment, we investigated the effects of deltamethrin on the mRNA expression of p53 and bax and their correlation with deltamethrin-induced apoptotic cell death in rat brain. Hematoxylin-eosin and cresyl violet staining revealed numerous degenerative cells in cortex and hippocampus at 5 and 24 h after deltamethrin treatment. Apoptotic cells were detected in cortex and hippocampus of treated rats at 24 h by in situ end labeling, whereas no apoptotic cells were observed in the same brain regions at 5 h after treatment. By using in situ hybridization, it was demonstrated that the increase of p53 and bax mRNA levels appeared at 5 and also at 24 h after treatment. The alterations in mRNA expression of p53 and bax preceded the occurrence of delayed apoptotic cell death in the same brain regions after deltamethrin treatment. These results indicate that (1) deltamethrin induces delayed apoptotic cell death, which may play an important role in deltamethrin-elicited neurodegeneration; (2) deltamethrin leads to the persistent increase of p53 and bax mRNA levels, which may contribute to delayed apoptosis in rat brain following deltamethrin treatment.

Co-stimulation of cyclic-AMP-linked metabotropic glutamate receptors in rat striatum attenuates excitotoxin-induced nuclear factor-kappaB activation and apoptosis

Interactions between glutamatergic mechanisms mediated by receptors of the ionotropic and metabotropic classes in the central nervous system are complex and incompletely understood. To explore the consequences of these interactions on excitotoxicity, we examined the influence of group II and group III selective metabotropic glutamate receptor agonists on the N-methyl-D-aspartate-induced apoptotic destruction of GABAergic neurons in rat striatum. The intrastriatal administration of a group III metabotropic glutamate receptor agonist (amino-4-phosphonobutyric acid, 900-1800 nmol), but not of a group II agonist [(2S,1'S,2'S)-(carboxycyclopropyl)glycine, 100-1800 nmol] produced internucleosomal DNA fragmentation. Similarly, amino-4-phosphonobutyric acid (600 nmol) but not (2S,1'S,2'S)-(carboxycyclopropyl)glycine (100-1800 nmol) destroyed some striatal neurons as indicated by a loss of D1 dopamine receptors and 67,000 mol. wt glutamate decarboxylase (glutamate decarboxylase-67) messenger RNA. On the other hand, the intensity of internucleosomal DNA fragmentation induced by N-methyl-D aspartate (150 nmol) was substantially decreased by the intrastriatal co-administration of either (2S,1'S,2'S)-(carboxycyclopropyl)glycine or amino-4-phosphonobutyric acid (100-600 nmol). Both (2S, 1'S,2'S)-(carboxycyclopropyl)glycine and amino-4-phosphonobutyric acid also reduced the N-methyl-D-aspartate-induced loss of striatal D1 dopamine receptors by 67% and 68% (both P < 0.001), and glutamate decarboxylase-67 messenger RNA by 68% and 61%, respectively. Furthermore, both (2S,1'S,2'S)-(carboxycyclopropyl)glycine and amino-4-phosphonobutyric acid also attenuated the N-methyl-D-aspartate-induced decline in striatal IKB-alpha protein levels by 62% and 37%, as well as the increase in nuclear transcription factor nuclear factor-kappaB binding activity by 135% and 94% (both P < 0.001), and the subsequent rise in p53 and c-Myc protein levels. These results suggest that stimulation of cyclic-AMP-linked metabotropic glutamate receptors inhibits ionotropic glutamate receptor-mediated activation of apoptotic cascades involving IkappaB-alpha degradation and nuclear factor-kappaB nuclear translocation, as well as p53 and c-Myc induction. Certain selective metabotropic glutamate receptor agonists might thus find utility as adjuncts to N-methyl-D-aspartate antagonists in the protection against the neurotoxicity initiated by excessive ionotropic glutamate receptor stimulation.

Kainic acid-induced apoptosis in rat striatum is associated with nuclear factor-kappaB activation

The present study evaluated whether nuclear factor-kappaB (NF-kappaB) activation contributes to the apoptotic-like death of striatal neurons induced by kainic acid (KA) receptor stimulation. Intrastriatally infused KA (1.25-5.0 nmol) produced substantial neuronal loss as indicated by an 8-73% decrease in 67-kDa glutamic acid decarboxylase (p<0.05). KA (1.25-5.0 nmol) elicited internucleosomal DNA fragmentation that was inhibited by the AMPA/KA receptor antagonist NBQX (1,2,3,4-tetrahydro-6-nitro-2,3-dibenzo[f]quinoxaline-7-sulfonamide) but not by the NMDA receptor antagonist MK-801. A decrease in IkappaB-alpha protein levels, which was accompanied by an increase in NF-kappaB binding activity, was found from 6 to 72 h after KA (2.5 nmol) infusion. NF-kappaB was composed mainly of p65 and c-Rel as revealed by supershift assay. In addition, c-Myc and p53 increased from five- to sevenfold from 24 to 72 h after KA (2.5 nmol) administration. Immunohistochemistry revealed high levels of c-Myc and p53 immunoreactivity, mainly in medium-sized striatal neurons. Pretreatment with the cell-permeable recombinant peptide NF-kappaB SN50 (5-20 microg) blocked NF-kappaB nuclear translocation, but had no effect on AP-1 binding. NF-kappaB SN50 also inhibited the KA-induced up-regulation of c-Myc and p53, as well as internucleosomal DNA fragmentation. The apoptotic-like destruction of rat striatal neurons induced by KA receptor stimulation thus appears to involve biochemical mechanisms similar to those mediating the excitotoxic response to NMDA receptor stimulation. The present results provide additional support for the view that NF-kappaB activation contributes to c-Myc and p53 induction and subsequent apoptosis in an excitotoxic model of Huntington's disease.

Overexpression of neurotrophin receptor p75 contributes to the excitotoxin-induced cholinergic neuronal death in rat basal forebrain

Both excitotoxicity and altered trophic factor support have been implicated in the pathogenesis of Alzheimer's disease. To determine whether stimulation of p75, the low-affinity receptor for nerve growth factor, contributes to the excitotoxin-induced apoptotic death of cholinergic neurons, we examined the effect of unilateral kainic acid (KA; PBS vehicle, 1.25, 2.5 and 5.0 nmol) administration into rat basal forebrain on neuronal loss and p75 expression. KA (2. 5 nmol) destroyed 43% of Nissl-stained neurons and 70% of choline acetyltransferase (ChAT)-positive neurons 5 days after injection. Agarose gel electrophoresis revealed that KA (2.5 nmol) induced local internucleosomal DNA fragmentation after 6-48 h. Immunohistochemical analysis further showed that KA (2.5 nmol) augmented p75 immunoreactivity at a time when terminal transferase-mediated deoxyuridine trophosphate (d-UTP)-digoxigenin nick end labeling (TUNEL)-positive nuclei were increased. Many fragmented nuclei were co-labeled with ChAT antibody. The chronic administration of anti-rat p75 or the protein synthesis inhibitor, cycloheximide, but not anti-human p75, substantially reduced the KA-induced destruction of cholinergic neurons and the induction of internucleosomal DNA fragmentation. Anti-rat p75, but not cycloheximide, also reversed the spatial memory impairment produced by KA. These findings suggest that overexpression of p75 contributes to the excitotoxin-induced death of rat basal forebrain cholinergic neurons by an apoptotic-like mechanism.

Apoptosis and the nervous system

Apoptosis is now recognized as a normal feature in the development of the nervous system and may also play a role in neurodegenerative diseases and aging. This phenomenon has been investigated intensively during the last 6-7 years, and the progress made in this field is reviewed here. Besides a few in vivo studies, a variety of neuronal preparations from various parts of the brain, the majority of which were primary cultures, and some cell lines have been investigated. Several apoptosis-inducing agents have been identified, and these include lack of neurotrophic support, neurotransmitters, neurotoxicants, modulators of protein phosphorylation and calcium homeostasis, DNA-damaging agents, oxidative stress, nitric oxide, and ceramides. The precise signaling cascade is not well established, and there are lacunae in many suggested pathways. However, it appears certain that the Bcl family of proteins is involved in the apoptotic pathway, and these proteins in turn affect the processing of interleukin-1beta converting enzyme (ICE)/caspases. The available evidence suggests that there may be several apoptotic pathways that may depend on the cell type and the inducing agent, and most of the pathways may converge at the ICE/caspases step.

Status epilepticus-induced neuronal damage in the rat amygdaloid complex: distribution, time-course and mechanisms

The present study was designed to elucidate the distribution, time-course and mechanism(s) of status epilepticus-induced neuronal damage in the rat amygdaloid complex. Status epilepticus was induced with kainate (9 mg/kg, i.p.), and the behavioral and electrographic seizure activity of each rat was monitored via cortical electrodes attached to a continuous video electrocorticogram system. Rats were subsequently perfused 1, 2, 4, 8, 16, 24 or 48 h after kainate injection. The first signs of amygdaloid damage were seen in rats perfused 4 h after kainate injection, though the severity and temporal appearance of damage varied substantially between the different amygdaloid nuclei and their subdivisions. Second, terminal transferase dUTP nick-end labeling (TUNEL)-positive nuclei and laddering of DNA in gel electrophoresis appeared in the amygdala 8 and 16 h after kainate, respectively. The distribution and density of TUNEL-positive nuclei in the different amygdaloid nuclei correlated with the distribution of neuronal damage in Thionin- and silver-stained sections. Third, the immunoreactivity of Bax protein, a promoter of apoptotic neuronal death, increased in the vulnerable medial division of the lateral nucleus prior to the appearance of argyrophilic neurons and TUNEL-positive nuclei. Fourth, the severity of neuronal damage progressed in some, but not all, amygdaloid regions throughout the 48-h follow-up, even though the occurrence of high-amplitude and frequency discharges, which are typically associated with behavioral seizure activity, extinguished after 7 h. These data show that status epilepticus-induced neuronal damage in the amygdala is a dynamic region-specific process, the severity of which depends on the duration of seizure activity. At least one mechanism underlying the damage involves apoptosis, which continues long after the behavioral and electrographic seizures have subsided.

Resistance to excitotoxin-induced seizures and neuronal death in mice lacking the preprotachykinin A gene

Epileptic seizures are associated with increases in hippocampal excitability, but the mechanisms that render the hippocampus hyperexcitable chronically (in epilepsy) or acutely (in status epilepticus) are poorly understood. Recent evidence suggests that substance P (SP), a peptide that has been implicated in cardiovascular function, inflammatory responses, and nociception, also contributes to hippocampal excitability and status epilepticus, in part by enhancing glutamate release. Here we report that mice with disruption of the preprotachykinin A gene, which encodes SP and neurokinin A, are resistant to kainate excitoxicity. The mice show a reduction in the duration and severity of seizures induced by kainate or pentylenetetrazole, and both necrosis and apoptosis of hippocampal neurons are prevented. Although kainate induced the expression of bax and caspase 3 in the hippocampus of wild-type mice, these critical intracellular mediators of cell death pathways were not altered by kainate injection in the mutant mice. These results indicate that the reduction of seizure activity and the neuroprotection observed in preprotachykinin A null mice are caused by the extinction of a SP/neurokinin A-mediated signaling pathway that is activated by seizures. They suggest that these neurokinins are critical to the control of hippocampal excitability, hippocampal seizures, and hippocampal vulnerability.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Bcl-2, Bax and Bcl-x expression following kainic acid administration at convulsant doses in the rat

Neuronal death was produced in the CA1 and CA3 areas of the hippocampus, amygdala, and piriform and entorhinal cortices after intraperitioneal administration of kainic acid at convulsant doses to adult rats. To assess the involvement of members of the Bcl-2 family in cell death or survival, immunohistochemistry, western and northern blotting to Bcl-2, Bcl-x and Bax, and in situ hybridization to Bax were examined at different time-points after kainic acid treatment. Members of the Bcl-2 family were expressed in the cytoplasm of pyramidal neurons in the hippocampus, and in a subset of neurons of the piriform and the entorhinal cortices, amygdala and neocortex in the normal adult brain. Dying neurons in the pyramidal cell layer of CA1 and CA3 areas, entorhinal and piriform cortices, and amygdala also expressed Bcl-2, Bax and Bcl-x following excitotoxicity, although many dying cells did not. In addition, a number of cells in the affected areas showed Bax immunoreactivity in their nuclei at 24-48 h following kainic acid administration, thus indicating Bax nuclear translocation in a subset of dying cells. Western blots disclosed no modifications in the intensity of the bands corresponding to Bcl-2, Bcl-x and Bax, between control and kainic acid-treated rats. No modifications in the intensity of the bcl-2 messenger RNA band on northern blots was observed in kainic acid-treated rats. However, a progressive increase in the intensity of the bax messenger RNA band was found in kainic acid-treated rats at 6 h, 12 h and 24 h following kainic acid administration. Interestingly, a slight increase in Bax immunoreactivity was observed in the cytoplasm of neurons of the dentate gyrus at 24-48 h, a feature which matches the increase of bax messenger RNA in the same area, as shown by in situ hybridization at 12-24 h following kainic acid injection. The present results suggest that cell death or survival does not correlate with modifications of Bcl-2, Bax and Bcl-x protein, and messenger RNA expression, but rather that kainic acid excitotoxicity is associated with Bax translocation to the nucleus in a subset of dying cells.

Impact of neonatal kainate treatment on hippocampal insulin-like growth factor receptors

The insulin-like growth factors-I and -II have neurotrophic properties and act through specific membrane receptors. High levels of binding sites for these growth factors are distributed discretely throughout the brain, being concentrated in the hippocampal formation. Functionally, the insulin-like growth factors, in addition to their growth-promoting actions, are considered to play important roles in normal cell functions, as well as in response to pharmacological or surgical manipulations. In adult rats, we have previously shown that systemic injection of kainate produces an overall decrease, in a time-dependent manner, in insulin-like growth factor-I and -II receptor binding sites in the hippocampus [Kar S. et al. (1997) Neuroscience 80, 1041-1055]. Given the evidence that insulin-like growth factors play a critical role during the early stages of brain development, the present study is a logical extension of this earlier report and established the effect of neonatal kainate injection on the developmental profile of insulin-like growth factor receptors. We have evaluated the time-course alteration of these receptors following systemic injection of kainate to newborn rats. After injection of a sublethal dose of kainate (5 mg/kg, i.p.) to postnatal one-day-old pups, [125I]insulin-like growth factor-I, [125I]insulin-like growth factor-II and [125I]insulin binding sites were studied at different postnatal days (7, 14, 21, 28 and 35) using receptor autoradiography. In the developing hippocampus, insulin-like growth factor-I and insulin binding sites are concentrated primarily in the dentate gyrus and the CA2/CA3 subfields, whereas insulin-like growth factor-II binding is discretely localized to the pyramidal layer and the granular layer of the dentate gyrus. Following kainate injection, we observed a slight increase in insulin-like growth factor-I binding sites in given hippocampal subfields starting at postnatal day 14, being significant at day 21. At later days, a progressive decrease was noted. This transient increase may represent an attempt for neuronal plasticity by up-regulating receptor levels. In contrast, insulin-like growth factor-II and insulin receptor binding sites are found to be decreased in various regions of the hippocampus in kainate-treated pups. Taken together, these results provide further evidence for the existence and differential alterations of insulin-like growth factor-I, insulin-like growth factor-II and insulin receptors in the developing rat hippocampus following kainate-induced lesion, suggesting possible involvement of these growth factors in brain plasticity.

Neonatal ethanol exposure alters bcl-2 family mRNA levels in the rat cerebellar vermis

BACKGROUND

The objective of the present work was to determine whether ethanol-induced cerebellar cell death during development is related to alterations in the expression of bcl-2 family genes.

METHODS

Rats were exposed to ethanol or control conditions during the neonatal period and transcript levels of bcl-2 family members relative to cyclophilin were determined. Pups exposed in parallel were taken for cerebellar cell counts.

RESULTS

Ethanol exposure during the first postnatal week significantly reduced Purkinje and granule cell numbers by postnatal day 21 (P21). Acute first postnatal week ethanol exposure up-regulated mRNA transcripts encoding the cell death-promoting molecules bax and bcl-xs as measured on P4. An additional day of exposure on P5 resulted in no further alterations in bcl-2 family transcripts, likely because Purkinje cell death was detectable as early as P5. To determine whether proapoptotic gene expression changes were specific to first postnatal week ethanol neurotoxicity, we examined bcl-2 family mRNA levels in rats exposed to ethanol during a developmental period of cerebellar insusceptibility, the second postnatal week. Exposure on P7 to P8 produced no change in cerebellar cell number, but also resulted in increased levels of bax, although only after 2-day ethanol exposure and not after acute exposure on P7.

CONCLUSIONS

These data implicate altered expression of proapoptotic members of the bcl-2 gene family in acute ethanol-mediated cerebellar cell death during the first postnatal week. They also suggest that the differential survival of cerebellar neurons after ethanol exposure during more mature developmental stages may be related to more successful suppression of proapoptotic processes.

Reciprocal changes in the expression of Bcl-2 and Bax in hypoglossal nucleus after axotomy in adult rats: possible involvement in the induction of neuronal cell death

Numerous studies of neonatal neuronal development in mammals have revealed that neuronal cell death following axotomy is apoptotic in nature. In adult animals, however, neuronal cell death following axonal injury may or may not exhibit features of apoptosis. Bcl-2 and Bax have been identified as inhibitor and promoter proteins, respectively, of apoptosis. To investigate the relationship between these proteins and neuronal cell death following axotomy in adult animals, we performed axotomy of the right hypoglossal nerve in adult male Wistar rats, and sacrificed the rats at various intervals after axotomy. We analyzed the expression of Bcl-2 and Bax immunohistochemically in the hypoglossal nuclei of the adult rats following axotomy. Our analysis showed an increase in the percentage of Bax-positive motoneurons relative to the total number of motoneurons in the hypoglossal nucleus on the axotomy side at three days after axotomy. In contrast, a low percentage of Bcl-2-positive motoneurons to the total number of motoneurons was noted at the same time interval after axotomy. Quantitative analysis of the signal intensity for Bcl-2 and Bax in individual neurons showed that Bax immunostaining significantly increased 7 days after axotomy, while the intensity of Bcl-2 immunostaining decreased in most of Bcl-2-positive neurons. Our results confirmed the occurrence of motoneuron cell death in adult rats after axotomy, and that a close temporal relationship exists between the reciprocal changes in Bcl-2/Bax expression and the loss of motoneurons. These results indicate the possible involvement of the Bcl-2/Bax system in the induction of neuronal cell apoptosis after axotomy in adult rats.

Lithium-pilocarpine-induced status epilepticus produces necrotic neurons with internucleosomal DNA fragmentation in adult rats

Prolonged and continuous epileptic seizures [status epilepticus (SE)] produce a widespread pattern of neuronal death, primarily in limbic brain regions. Because it has been suggested that seizure-induced neuronal death may be apoptotic in nature, we tested the hypothesis that lithium-pilocarpine-induced status epilepticus (LPCSE) produces apoptotic neurons. LPCSE lasting 3 h was induced in male Wistar rats which were allowed to recover for 24 or 72 h before perfusion-fixation. Neuronal death was assessed by light microscopy with the haematoxylin-and-eosin stain (H&E), with in situ DNA nick-end labelling (TUNEL stain), by electron microscopy, and by agarose gel electrophoresis of DNA extracted from vulnerable brain regions. Ultrastructurally, acidophilic neurons identified with H&E were dark, shrunken and necrotic in appearance, exhibiting pyknotic nuclei, irregular, dispersed chromatin clumps and cytoplasmic vacuolization. No cells with apoptotic features were seen. Acidophilic neurons were found in 21 out of 23 brain regions examined, and comprised 26-45% of the total number of neurons examined. A subset of these neurons (< 10% of the total number of neurons) were TUNEL-positive at 72 h, but not 24 h, after SE. Internucleosomal DNA cleavage (DNA 'laddering') was found in the six brain regions examined ultrastructurally 24 and 72 h after SE. These results indicate that, in adult rats, LPCSE produces neuronal injury with the appearance of necrosis rather than apoptosis. The necrotic neurons show nuclear pyknosis, chromatin condensation and internucleosomal DNA fragmentation, confirming the nonspecificity of these nuclear changes. Internucleosomal DNA cleavage and other programmed cell death mechanisms can be activated by SE in neurons which become necrotic.

Apoptosis in neurodegenerative diseases: the role of mitochondria

Nerve cell death is the central feature of the human neurodegenerative diseases. It has long been thought that nerve cell death in these disorders occurs by way of necrosis, a process characterized by massive transmembrane ion currents, compromise of mitochondrial ATP production, and the formation of high levels of reactive oxygen species combining to induce rapid disruption of organelles, cell swelling, and plasma membrane rupture with a secondary inflammatory response. Nuclear DNA is relatively preserved. Recent evidence now indicates that the process of apoptosis rather than necrosis primarily contributes to nerve cell death in neurodegeneration. This has opened up new avenues for understanding the pathogenesis of neurodegeneration and may lead to new and more effective therapeutic approaches to these diseases.