Kainate-induced apoptotic cell death in hippocampal neurons

Kainic acid-induced excitotoxic hippocampal neurodegeneration in C57BL/6 mice: B cell and T cell subsets may contribute differently to the pathogenesis

The roles of T cells and B cells in kainic acid (KA)-induced hippocampal lesions were studied in C57BL/6 mice lacking specific T cell populations (CD4, CD8, and CD4/CD8 cells) and B cells [Igh-6(-/-)]. At 48 mg/kg of KA administrated intranasally, KA-induced convulsions were seen in all groups. However, CD4/CD8(-/-) mice exhibited the mildest seizures; the responses of CD8(-/-), Igh-6(-/-) and wild-type mice were intermediate, whereas CD4(-/-) mice displayed much more severe clinical signs and 100% early mortality, indicating that a deficiency of CD4 T cells obviously increased susceptibility to KA-induced brain damage. Histopathological analysis of the mice that survived 7 days after KA administration revealed that CD4/CD8(-/-) mice had the fewest pathologic changes but Igh-6(-/-) mice showed more severe lesions in area CA3 of the hippocampus than CD8(-/-) and wild-type mice. Reactive astrogliosis were prominent in all KA-treated mice. Locomotor activity as assessed by open-field test increased after KA administration in Igh-6(-/-) and wild-type mice only. These results denote the influence of the adaptive immune response on KA-induced hippocampal neurodegeneration and suggest that B cell and T cell subsets may contribute differently to the pathogenesis.

PARP cleavage, DNA fragmentation, and pyknosis during excitotoxin-induced neuronal death

Poly(ADP-ribose)polymerase-1 (PARP-1) is a nuclear enzyme activated by DNA breaks and serves a role in DNA repair through the formation of polymers (poly(ADP)ribosylation) at sites of DNA damage. PARP-1 is activated by DNA damage in neurons of the hippocampus and cerebral cortex following excessive exposure to glutamate receptor agonists such as NMDA or kainic acid. In addition, recent studies suggest that degradation of PARP-1 occurs in cells that undergo apoptotic versus nonapoptotic forms of cell death. To investigate this process further, we examined the spatiotemporal aspects of excitotoxic injury in the rodent visual cortex by making focal intracerebral injections of kainic acid. These injections resulted in DNA damage, PARP-1 activation, and neuronal cell death over a 5-day period. Rapid neuronal cell injury assessed by Fluoro-Jade staining appeared within hours, but increased TUNEL staining occurred only after 24 h. A dramatic increase in caspase-3 activity, as well as an increase in the number of neurons containing active caspase-3, peaked 2 days after injury. Last, increased PARP-1 immunoreactivity and PARP-1 cleavage reached peak levels 2 to 3 days after delivering the excitotoxin. These findings suggest that increased caspase-3 activity may regulate the degradation of PARP-1 in subsets of cortical neurons during excitotoxic cell death.

Neurotoxins and neurotoxic species implicated in neurodegeneration

Neurotoxins, in the general sense, represent novel chemical structures which when administered in vivo or in vitro, are capable of producing neuronal damage or neurodegeneration--with some degree of specificity relating to neuronal phenotype or populations of neurons with specific characteristics (i.e., receptor type, ion channel type, astrocyte-dependence, etc.). The broader term 'neurotoxin' includes this categorization but extends the term to include intra- or extracellular mediators involved in the neurodegenerative event, including necrotic and apoptotic factors. Moreover, as it is recognized that astrocytes are essential supportive satellite cells for neurons, and because damage to these cells ultimately affects neuronal function, the term 'neurotoxin' might reasonably be extended to include those chemical species which also adversely affect astrocytes. This review is intended to highlight developments that have occurred in the field of 'neurotoxins' during the past 5 years, including MPTP/MPP+, 6-hydroxydopamine (6-OHDA), methamphetamine; salsolinol; leukoaminochrome-o-semiquinone; rotenone; iron; paraquat; HPP+; veratridine; soman; glutamate; kainate; 3-nitropropionic acid; peroxynitrite anion; and metals (copper, manganese, lead, mercury). Neurotoxins represent tools to help elucidate intra- and extra-cellular processes involved in neuronal necrosis and apoptosis, so that drugs can be developed towards targets that interrupt the processes leading towards neuronal death.

Cell cycle regulation of neuronal apoptosis in development and disease

Apoptosis of neurons is indispensable to the normal development of the nervous system and contributes to neuronal loss in neurologic injury and disease. Life and death decisions are imposed upon neurons by extracellular and intracellular stimuli including the lack of trophic support, exposure to neurotoxins, oxidative stress, and DNA damage. These stimuli induce signaling pathways that are integrated at the mitochondrial apoptotic machinery culminating in cell survival or death. Growing evidence suggests that cell cycle proteins are expressed in dying neurons in the developing and adult brain. However, the role and mechanisms by which re-activation of cell cycle pathways in postmitotic neurons propagates an apoptotic signal to the cell death machinery are just beginning to be characterized. Here, we will review the molecular mechanisms of neuronal cell death and survival with a focus on recent findings on cell cycle regulation of neuronal apoptosis in primary cultures of neurons, mouse models of neuronal diseases, and human neurodegenerative diseases.

Cellular expression of connexins in the rat brain: neuronal localization, effects of kainate-induced seizures and expression in apoptotic neuronal cells

The identification of connexins (Cxs) expressed in neuronal cells represents a crucial step for understanding the direct communication between neurons and between neuron and glia. In the present work, using a double-labelling method combining in situ hybridization for Cx mRNAs with immunohistochemical detection for neuronal markers, we provide evidence that, among cerebral connexins (Cx26, Cx32, Cx36, Cx37, Cx40, Cx43, Cx45 and Cx47), only Cx45 and Cx36 mRNAs are localized in neuronal cells in both developing and adult rat brain. In order to establish whether connexin expression is influenced in vivo by abnormal neuronal activity, we examined the short-term effects of kainate-induced seizures. The results revealed an unexpected expression of Cx26 and Cx45 mRNA in neuronal cells undergoing apoptotic cell death in the CA3-CA4, in the hilus of the hippocampus and in other brain regions involved in seizure-induced lesion. However, the expression of Cx26 and Cx45 mRNAs was not associated with detectable expression of corresponding proteins as evaluated by immunohistochemistry with specific antibodies. Moreover, in the same brain regions Cx32 and Cx43 were up-regulated in non-neruronal cells whereas the neuronal Cx36 was down-regulated. Taken together the present results provide novel information regarding the specific subpopulation of neurons expressing Cx45 and raise the question of the meaning of connexin mRNA expression in the neuronal apoptotic process.

Temporal and spatial distribution of activated caspase-3 after subdural kainic acid infusions in rat spinal cord

The molecular events initiating apoptosis following traumatic spinal cord injury (SCI) remain poorly understood. Soon after injury, the spinal cord is exposed to numerous secondary insults, including elevated levels of glutamate, that contribute to cell dysfunction and death. In the present study, we attempted to mimic the actions of glutamate by subdural infusion of the selective glutamate receptor agonist, kainic acid, into the uninjured rat spinal cord. Immunohistochemical colocalization studies revealed that activated caspase-3 was present in ventral horn motor neurons at 24 hours, but not 4 hours or 96 hours, following kainic acid treatment. However, at no time point examined was there evidence of significant neuronal loss. Kainic acid resulted in caspase-3 activation in several glial cell populations at all time points examined, with the most pronounced effect occurring at 24 hours following infusion. In particular, caspase-3 activation was observed in a significant number of oligodendroglia in the dorsal and ventral funiculi, and there was a pronounced loss of oligodendroglia at 96 hours following treatment. The results of these experiments indicate a role for glutamate as a mediator of oligodendroglial apoptosis in traumatic SCI. In addition, understanding the apoptotic signaling events activated by glutamate will be important for developing therapies targeting this cell death process.

Increase in Bcl-2 phosphorylation and reduced levels of BH3-only Bcl-2 family proteins in kainic acid-mediated neuronal death in the rat brain

Kainic acid induces excitotoxicity and nerve cell degeneration in vulnerable regions of rat brain, most markedly in hippocampus and amygdala. Part of the cell death following kainic acid is apoptotic as shown by caspase 3 activation and chromatin condensation. Here we have studied the regulation of pro- and anti-apoptotic proteins belonging to the Bcl-2 family in rat hippocampus and amygdala by kainic acid in relationship to ensuing neuronal death. The pro-apoptotic protein Bax was up-regulated in hippocampus 6 h after kainic acid administration. The increase in Bax was followed by the appearance of TdT-mediated dUTP nick end labelling-positive cells which were prominent at 24 h. Immunohistochemistry for active Bax revealed a punctuated labelling of neurons in the CA3 and hilar regions of hippocampus as well as in amygdala. Double staining for NeuN, a marker for nerve cells, and TdT-mediated dUTP nick end labelling showed that mainly neurons undergo degeneration after kainic acid treatment. In contrast to Bax, the pro-apoptotic BH3-only Bcl-2 proteins Bim and Harakiri/DP5 were down-regulated by kainic acid. This was also observed for the anti-apoptotic proteins Bcl-x and Bcl-w. Immunoreactive Bcl-2 was up-regulated in hippocampus after kainic acid together with an increase in the phosphorylation of serine-87 in Bcl-2, suggesting a post-transcriptional modification of the protein. This was confirmed using immunoprecipitation of total Bcl-2 from hippocampus and amygdala which revealed an increase in serine-87 phospho-Bcl-2 after kainic acid. Inhibition of the c-jun N-terminal protein kinase pathway reduced both serine-87 phosphorylation and cell death after kainic acid. This indicates an important role of Bcl-2 phosphorylation in controlling neuronal death after kainic acid. In contrast to the situation in trophic factor-deprived neurons, no up-regulation of Bim or Harakiri/DP5 proteins occurred after kainic acid, suggesting alternative pathways for regulation of cell death in excitotoxicity. The results indicate that not only the relative levels of Bcl-2 family proteins but also conformation changes and post-translational modifications contribute to neuronal death following kainic acid.

N-methyl-D-aspartate receptor blockade after status epilepticus protects against limbic brain damage but not against epilepsy in the kainate model of temporal lobe epilepsy

Most patients with temporal lobe epilepsy (TLE), the most common type of epilepsy, show pronounced loss of neurons in limbic brain regions, including the hippocampus. The massive neurodegeneration in the hippocampus is known as hippocampal sclerosis, and is considered one of the hallmarks of this type of difficult-to-treat epilepsy. There is a long and ongoing debate on whether this sclerosis is the result of an initial pathological event, such as a status epilepticus (S.E.), stroke or head trauma, which often precedes the development of TLE, or is caused by the spontaneous recurrent seizures (SRS) once epilepsy has developed. At present, pharmacological prevention of limbic sclerosis is not available. In a clinical situation, such prevention would only be possible if delayed cell death developing after an initial pathological event is involved. Assuming that sclerotic brain lesions provoke epileptogenesis and that delayed cell death is involved in these lesions, it should be possible to prevent both the lesions and the epilepsy by a prophylactic treatment after an initial insult such as an S.E. In order to test this hypothesis, we used a rat model of TLE in which limbic brain lesions and epilepsy with SRS develop after a kainate-induced S.E. A single low dose of the N-methyl-D-aspartate (NMDA) receptor blocker dizocilpine (MK-801) significantly reduced the damage in limbic regions, including the hippocampus and piriform cortex, and completely protected several rats from such damage when given after an S.E. of 90 min induced by kainate, strongly suggesting that delayed cell death is involved in the damage. This was substantiated by the use of molecular and immunohistochemical markers of delayed active ("programmed") cell death. However, the neuroprotection by dizocilpine did not prevent the development of SRS after the S.E., suggesting that structures not protected by dizocilpine may play a role in the genesis of SRS or that epileptogenesis is not the consequence of structural lesions in the limbic system. The only brain regions that exhibited neuronal damage in all rats with SRS were the hilus of the dentate gyrus and the mediodorsal thalamus, although treatment with dizocilpine reduced the severity of damage in the latter region. The data indicate that NMDA receptor blockade immediately after a prolonged S.E. is an effective means to reduce the damage produced by a sustained S.E. in several brain regions, including the hippocampus, but show that this partial neuroprotection of the limbic system does not prevent the development of epilepsy.

Purines and neuroprotection

The activation of adenosine A1, A2 andA3 receptors can protect neurones against damage generated by mechanical or hypoxic/ischaemic insults as well as excitotoxins. A1 receptors are probably effective by suppressing transmitter release and producing neuronal hyperpolarisation. They are less likely to be of therapeutic importance due to the plethora of side effects resulting from A1 agonism, although the existence of receptor subtypes and recent synthetic chemistry efforts to increase ligand selectivity, may yet yield clinically viable compounds. Activation of A2A receptors can protect neurons, although there is much uncertainty as to whether agonists are acting centrally or via a peripheral mechanism such as altering blood flow or immune cell function. Selective antagonists at the A2A receptor, such as 4-(2-[7-amino-2-(2-furyl)(1,2,4)triazolo(2,3-a)(1,3,5)triazin-5-yl-amino]ethyl)phenol (ZM 241385) and 7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3e]-1,2,4-triazolo[1,5-c]pyrimidine (SCH 58261), can also protect against neuronal death produced by ischaemia or excitotoxicity. In addition, A2A receptor antagonists can reduce damage produced by combinations of subthreshold doses of the endogenous excitotoxin quinolinic acid and free radicals. Since the A2A receptors do not seem to be activated by normal endogenous levels of adenosine, their blockade should not generate significant side effects, so that A2A receptor antagonists appear to be promising candidates as new drugs for the prevention of neuronal damage. Adenosine A3 receptors have received less attention to date, but agonists are clearly able to afford protection against damage when administered chronically. Given the disappointing lack of success of NMDA receptor antagonists in human stroke patients, despite their early promise in animal models, it is possible that A2A receptor antagonists could have a far greater clinical utility.

Is the cell death in mesial temporal sclerosis apoptotic?

PURPOSE

Mesial temporal sclerosis (MTS) is characterized by neuronal loss in the hippocampus. Studies on experimental models and patients with intractable epilepsy suggest that apoptosis may be involved in neuronal death induced by recurrent seizures.

METHODS

We searched evidence for apoptotic cell death in temporal lobes resected from drug-resistant epilepsy patients with MTS by using the terminal deoxynucleotidyl transferase (TdT) and digoxigenin-11-dUTP (TUNEL) method and immunohistochemistry for Bcl-2, Bax, and caspase-cleaved actin fragment, fractin. The temporal lobe specimens were obtained from 15 patients (six women and nine men; mean age, 29 +/- 8 years).

RESULTS

Unlike that in normal adult brain, we observed Bcl-2 immunoreactivity in some of the remaining neurons dispersed throughout the hippocampus proper as well as in most of the reactive astroglia. Bax immunopositivity was increased in almost all neurons. Fractin immunostaining, an indicator of caspase activity, was detected in approximately 10% of these neurons. Despite increased Bax expression and activation of caspases, we could not find evidence for DNA fragmentation by TUNEL staining. We also could not detect typical apoptotic changes in nuclear morphology by Hoechst-33258 or hematoxylin counterstaining.

CONCLUSIONS

These data suggest that either apoptosis is not involved in cell loss in MTS, or a very slow rate of cell demise may have precluded detecting TUNEL-positive neurons dying through apoptosis. Increased Bax expression and activation of caspases support the latter possibility.

The neuroprotective effects of heat shock protein 27 overexpression in transgenic animals against kainate-induced seizures and hippocampal cell death

The 27-kDa heat shock protein (HSP27) has a potent ability to increase cell survival in response to a wide range of cellular challenges. In order to investigate the mode of action of HSP27 in vivo, we have developed transgenic lines, which express human HSP27 at high levels throughout the brain, spinal cord, and other tissues. In view of the particular property of HSP27 compared with other HSPs to protect neurons against apoptosis, we have tested these transgenic lines in a well established in vivo model of neurotoxicity produced by kainic acid, where apoptotic cell death occurs. Our results demonstrate for the first time the marked protective effects of HSP27 overexpression in vivo, which significantly reduces kainate-induced seizure severity and mortality rate (>50%) in two independent lines and markedly reduces neuronal cell death in the CA3 region of hippocampus. This reduced seizure severity in HSP27 transgenic animals was associated with a marked attenuation of caspase 3 induction and apoptotic features. These studies clearly demonstrate that HSP27 has a major neuroprotective effect in the central nervous system in keeping with its properties demonstrated in culture and highlight an early stage in the cell death pathway that is affected by HSP27.

Seizure-like activity leads to the release of BAD from 14-3-3 protein and cell death in hippocampal neurons in vitro

Seizure-induced neuronal death may involve engagement of the BCL-2 family of apoptosis-regulating proteins. In the present study we examined the activation of proapoptotic BAD in cultured hippocampal neurons following seizures induced by removal of chronic glutamatergic transmission blockade. Kynurenic acid withdrawal elicited an increase in seizure-like electrical activity, which was inhibited by blockers of AMPA (CNQX) and NMDA (MK801 and AP5) receptor function. However, only NMDA receptor antagonists inhibited calcium entry as assessed by fura-2, and cell death of hippocampal neurons. Seizures increased proteolysis of caspase-3 and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) of cells. Seizure-like activity induced dephosphorylation of BAD and the disruption of its constitutive interaction with 14-3-3 proteins. In turn, BAD dimerized with antiapoptotic BCL-Xl after seizures. However, the absence of neuroprotective effects of pathway intervention suggests that BAD may perform a reinforcement rather than instigator role in cell death following seizures in vitro.

Glutamate enhances caspase-3 immunoreactivity in cultured spinal cord neurons of newborn rats

The role of glutamate in the mechanism of spinal neuron death is not fully understood. With addition of glutamate to primary culture of 11-day-old rat spinal cord, the number of caspase-3 positive small neurons of the dorsal horn greatly increased at 6-24 h in contrast to the case with vehicle. The addition of glutamate made caspase-3 immunoreactivity stronger in the cytoplasm of large motor neurons in the ventral horn. The present results show that excessive amount of glutamate enhances apoptotic pathway through caspase-3 in cultured spinal neurons of newborn rat.

Topiramate protects against glutamate- and kainate-induced neurotoxicity in primary neuronal-astroglial cultures

Potential neuroprotective effects of the antiepileptic drug (AED) topiramate (TPM) were evaluated using primary neuronal-astroglial cultures or astroglial-enriched cultures from newborn rats exposed to excitotoxic concentrations of glutamate (Glu) or kainate. Neurons expressed functional Glu receptors of the NMDA and AMPA/kainate types as evaluated by immunocytochemistry and Ca(2+) imaging. When Glu (10 mM) was added to 9-10-day cultures incubated with the fluorescent dye calcein/AM for 5h, there was a marked cell loss in both culture types, but was more pronounced in the neuronal-astroglial cultures. When TPM (5-10 microM) was included in the medium together with Glu, the amount of surviving cells was significantly higher in the neuronal-astroglial cultures, but not in the astroglial-enriched cultures. Immuno-labeling of the cultures revealed an enhanced survival of MAP positive neuronal cells when TPM was included in the Glu containing medium. As TPM has a proven negative modulatory effect on kainate activated receptors, neuronal-astroglial cultures were further exposed to excitotoxic concentrations of kainate (100 microM) and analyzed immunohistochemically. Significantly more MAP positive neurons survived in the TPM containing medium and showed a morphology similar to untreated cells. Valproate and phenytoin were used as reference AEDs. In conclusion, our results demonstrate a protective effect of TPM upon neuronal cells in primary culture, exposed to excitotoxic levels of Glu or kainate.

Heat shock protein 27 delivered via a herpes simplex virus vector can protect neurons of the hippocampus against kainic-acid-induced cell loss

Heat shock proteins are expressed in response to cellular stress and can protect cells from further stress and facilitate recovery. Heat shock protein 27 is of particular interest because it has been implicated in a range of protective roles including protein chaperoning, stabilising elements of the cytoskeleton and as an active inhibitor of apoptosis. In the present study, we have examined the potential of administration of exogenous HSP27 to confer protection against KA-induced neuronal cell death in vivo. We aimed to exploit the neurotropic specificity of herpes simplex virus-1 based virus vectors, which have been rendered replication-incompetent, to infect neurons of the hippocampus. The systemic administration of kainic acid, an analogue of glutamate, causes seizures resulting in neuronal damage and is an established animal model of epilepsy. Neuron loss is particularly prominent in the hippocampus and the mode of death is at least partly apoptotic in nature. We show that the overexpression of HSP27 in these neurons can significantly augment their survival following kainic acid administration. In contrast, injection of a control virus expressing beta-galactosidase does not confer protection. This is the first time that protection by exogenously expressed HSP27 has been demonstrated in an in vivo model of neuronal cell death.

The protective effect of a ketogenic diet on kainic acid-induced hippocampal cell death in the male ICR mice

This study was designed to evaluate the antiapoptotic effects of a ketogenic diet (KD) through histological (cresyl violet staining, TUNEL staining and immunohistochemistry) and behavioral studies using kainic acid (KA, 25mg/kg i.p.)-induced seizures in male ICR mice. KA-induced seizure in rodents is widely used as an experimental model for human temporal lobe epilepsy because of their behavioral and pathological similarities. A KA-induced seizure causes neuronal damage in hippocampal pyramidal neurons and involves a caspase-3-mediated apoptotic pathway. In this study, the seizure onset time of the KD-fed group was delayed compared to that of the group fed a normal diet (ND) after a systemic KA injection. Histological studies revealed that KA caused pyknosis in most of the hippocampal areas in the ND-fed group, however, well-preserved pyramidal neurons were detected in the hippocampus of mice that had been on KD for 1 month, which began on postnatal day 21. The number of TUNEL-positive cells and caspase-3-positive cells in the hippocampus of the KD-fed group was lower than that of the ND-fed group. These findings indicate that KD has an antiepileptic effect via a neuroprotective action that involves the inhibition of caspase-3-mediated apoptosis of hippocampal neurons.

Morphologic study of neuronal death, glial activation, and progenitor cell division in the hippocampus of rat models of epilepsy

PURPOSE

To clarify the relationship of neuronal death to cellular responses, we studied neuronal death as well as reactions of glia and progenitor cells in the hippocampus of two rat models of epilepsy.

METHODS

Seizures were induced by either kainic acid (KA) administration or electrical kindling. Neuronal degeneration was assessed by in situ DNA fragmentation analysis. Reactions of glial cells were studied by immunohistochemistry. Progenitor cell division was evaluated using the bromodeoxyuridine (BrdU) labeling method.

RESULTS

DNA fragmentation and reactive microglia were observed in the CA1, CA3, and hilus region for 24 h to 4 weeks after KA injection, but not detected in the kindling model. Reactive astrocytes and enhancement of progenitor cell division were seen in both animal models. The number of BrdU-positive cells began to increase on day 3 after KA injection, peaked on day 5, and returned to baseline on day 10. After kindling, the number of BrdU-positive cells began to increase after five consecutive experience of stage I seizures.

CONCLUSIONS

These observations show that neuronal degeneration is not necessary for triggering the upregulation. Microglial activation is closely related to the neuronal death process induced by KA.

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.

Passive immunization against beta-amyloid peptide protects central nervous system (CNS) neurons from increased vulnerability associated with an Alzheimer's disease-causing mutation

To characterize the effects of the familial Alzheimer's disease-causing Swedish mutations of amyloid precursor protein (SwAPP) on the vulnerability of central nervous system neurons, we induced epileptic seizures in transgenic mice expressing SwAPP. The transgene expression did not change the seizure threshold, but consistently more neurons degenerated in brains of SwAPP mice as compared with wild-type littermates. The degenerating neurons were stained both by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling and by Gallyas silver impregnation. A susceptible population of neurons accumulated intracellular Abeta and immunoreacted with antibodies against activated caspase-3. To demonstrate that increased Abeta levels mediated the increased vulnerability, we infused antibodies against Abeta and found a significant reduction in neuronal loss that was paralleled by decreased brain levels of Abeta. Because the SwAPP mice exhibited no amyloid plaques at the age of these experiments, transgenic overproduction of Abeta in brain rendered neurons susceptible to damage much earlier than the onset of amyloid plaque formation. Our data underscore the possibility that Abeta is toxic, that it increases the vulnerability of neurons to excitotoxic events produced by seizures, and that lowering Abeta by passive immunization can protect neurons from Abeta-related toxicity.

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.

Connexin-30 mRNA is up-regulated in astrocytes and expressed in apoptotic neuronal cells of rat brain following kainate-induced seizures

Glial connexins (Cxs) make an extensively interconnected functional syncytium created by a network of gap junctions between astrocytes and oligodendrocytes. Among Cxs expressed in the brain, Cx30 is expressed in grey matter astrocytes, as shown at the protein level by immunoistochemistry. In the present study we aimed to perform a detailed study of the regional distribution of Cx30 mRNA in the adult and postnatal developing rat brain, analyzing its expression by in situ hybridization, and determining its cell type localization by double labeling. Recently, it has been suggested that neuronal activity may control the level of intercellular communication between astrocytes through gap junctions channels. Thus, a second aim of the present study was to investigate the short-term effects of kainate-induced seizures on Cx30 expression. The results showed that, in basal condition, Cx30 was expressed only in grey matter astrocytes with distinct regional patterns in developing and adult brain. Kainate treatment induced strong and region-specific changes of astroglial Cx30 mRNA levels and expression of Cx30 mRNA in neuronal cells undergoing cell death, suggesting a direct or indirect involvement of this connexin in the neuronal apoptotic process.

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.

Relations between brain pathology and temporal lobe epilepsy

Temporal lobe epilepsy, the most common type of epilepsy in adult humans, is characterized clinically by the progressive development of spontaneous recurrent seizures of temporal lobe origin and pathologically by hippocampal neuronal loss and mossy fiber sprouting. In this study, we sought to test the prominent hypothesis that neuronal loss and mossy fiber sprouting play a critical role in the genesis and progression of temporal lobe epilepsy. Rats receiving a single kainic acid injection experienced a single sustained episode of epileptic status with massive neuronal loss and mossy fiber sprouting, whereas rats receiving triple kainic acid injections experienced two priming episodes and one sustained episode of epileptic status with no detectable neuronal loss and mossy fiber sprouting. Early in the process of chronic seizure development, primed rats that failed to show detectable neuronal loss and mossy fiber sprouting exhibited a starting date and a frequency of spontaneous recurrent seizures similar to those of nonprimed rats that showed massive neuronal loss and mossy fiber sprouting. However, nonprimed rats displayed significantly prolonged episodes of spontaneous recurrent seizures over the whole process of chronic seizure development and more frequent severe seizures later in the process. Similar results were observed in both Fischer-344 and Wistar rats as well as in the rat pilocarpine preparation of temporal lobe epilepsy. These results fail to reveal a relation between neuronal loss-mossy fiber sprouting and the genesis of temporal lobe epilepsy but suggest that neuronal loss, mossy fiber sprouting, or both contribute to the intensification of chronic seizures.

Immediate and delayed hippocampal neuronal loss induced by kainic acid during early postnatal development in the rat

The degree to which the neonatal hippocampus is resistant to the effects of excitotoxins, such as kainic acid (KA) remains uncertain. Previously, we showed delayed loss of hippocampal neurons during pubescence in neonatal rats subjected to intracerebroventricular (i.c.v.) KA administration (10 nmol) at postnatal day 7 (P7). To further characterize the time course as well as the underlying mechanisms of this neuronal loss, we administered i.c.v. KA (10 or 50 nmol) to P7 preweanling rats. Brain sections were then examined at several neurodevelopmental time points (i.e., P8, P14, P25, P40, P60 and P75) using thionin staining and three-dimensional, non-biased cell counting to assess neuronal loss, and immunohistochemistry and electron microscopy to search for evidence of necrosis and apoptosis. Dose-dependent acute neuronal loss was observed at P8-P14 in hippocampal subfields CA3a and CA3c. Transient heat shock protein (HSP-70) immunostaining accompanied this acute neuronal loss. Progressive neuronal loss then continued in CA3 until P75, but without concomitant HSP-70 immunostaining. Progressive neuronal cell loss was also observed in the CA1 subfield of the hippocampus beginning at pubescence (i.e., P40) and continuing until P75. The appearance of TUNEL-positive hippocampal neurons accompanied the delayed neuronal loss in both CA3 and CA1 and electron micrographs confirmed that neurons in these subfields were undergoing apoptosis. KA administration (i.c.v.) to preweanling rats caused both immediate and delayed damage to hippocampal neurons. The effect of KA was dose-dependent, and the delayed neuronal damage occurred through an apoptosis-mediated mechanism. These findings may be relevant to the pathogenesis of some neuropsychiatric disorders, where early CNS injury is not apparent until the onset of clinical symptoms in young adulthood.

Expression and differential processing of caspases 6 and 7 in relation to specific epileptiform EEG patterns following limbic seizures

The caspase family of cell death proteases has been implicated in the mechanism of neuronal death following seizures. We investigated the expression and processing of caspases 6 and 7, putative executioner caspases. Brief limbic seizures were evoked by intraamygdala kainic acid to elicit unilateral death of target hippocampal CA3 neurons in the rat. Seizures rapidly induced cleavage of constitutively expressed caspase-6, followed by elevated VEIDase activity and the proteolysis of lamin A. Neuronal caspase-6 immunoreactivity was markedly upregulated within cortex and hippocampus in relation to bursts of polyspike paroxysmal discharges. In contrast, while caspase-7 expression also increased within cortical and hippocampal neuronal populations in response to the same seizure patterns, caspase-7 was not proteolytically activated. These data highlight differences in expression and activation of caspases 6 and 7 in response to identifiable seizure patterns, focusing potential therapeutic targets for neuroprotection in epilepsy.

Reduced postischemic apoptosis in the hippocampus of mice deficient in interleukin-1

The cytokine interleukin-1 (IL-1) has been implicated in ischemic brain damage, because the IL-1 receptor antagonist markedly inhibits experimentally induced neuronal loss. However, to date, no studies have demonstrated the involvement of endogenous IL-1alpha and IL- 1beta in neurodegeneration. We report here, for the first time, that mice lacking IL-1alpha/beta (double knockout) exhibit markedly reduced neuronal loss and apoptotic cell death when exposed to transient cardiac arrest. Furthermore, we show that, despite the reduced neuronal loss, phosphorylation of JNK/SAPK (c-Jun NH2- terminal protein kinase/stress activated protein kinase) and p38 enzymes remain elevated in IL-1 knockout mice. In contrast, the inducible nitric oxide (iNOS) immunoreactivity after global ischemia was reduced in IL-1 knockout mice as compared with wild-type mice. The levels of nitrite (NO(2) (-)) and nitrate (NO(3) (-)) in the hippocampus of wild-type mice were increased with time after ischemia-reperfusion, whereas the increase was significantly inhibited in IL-1 knockout mice. These observations strongly suggest that endogenous IL-1 contributes to ischemic brain damage, and this influence may act through the release of nitric oxide by iNOS.

Induction of neuronal type-specific neurogenesis in the cerebral cortex of adult mice: manipulation of neural precursors in situ

Over the past 3 decades, research exploring potential neuronal replacement therapies have focused on replacing lost neurons by transplanting cells or grafting tissue into diseased regions of the brain [Nat. Neurosci. 3 (2000) 67-78]. Over most of the past century of modern neuroscience, it was thought that the adult brain was completely incapable of generating new neurons. However, in the last decade, the development of new techniques has resulted in an explosion of new research showing that neurogenesis, the birth of new neurons, normally occurs in two limited and specific regions of the adult mammalian brain, and that there are significant numbers of multipotent neural precursors in many parts of the adult mammalian brain [Mol. Cell. Neurosci. 19 (1999) 474-486]. Recent findings from our laboratory demonstrate that it is possible to induce neurogenesis de novo in the adult mammalian brain, particularly in the neocortex where it does not normally occur, and that it may become possible to manipulate endogenous multipotent precursors in situ to replace lost or damaged neurons [Nature 405 (2000) 951-955; Neuron 25 (2000) 481-492]. Recruitment of new neurons can be induced in a region-specific, layer-specific, and neuronal type-specific manner, and newly recruited neurons can form long-distance connections to appropriate targets. Elucidation of the relevant molecular controls may both allow control over transplanted precursor cells and potentially allow the development of neuronal replacement therapies for neurodegenerative disease and other central nervous system injuries that do not require transplantation of exogenous cells.

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.

The lizard cerebral cortex as a model to study neuronal regeneration

The medial cerebral cortex of lizards, an area homologous to the hippocampal fascia dentata, shows delayed postnatal neurogenesis, i.e., cells in the medial cortex ependyma proliferate and give rise to immature neurons, which migrate to the cell layer. There, recruited neurons differentiate and give rise to zinc containing axons directed to the rest of cortical areas, thus resulting in a continuous growth of the medial cortex and its zinc-enriched axonal projection. This happens along the lizard life span, even in adult lizards, thus allowing one of their most important characteristics: neuronal regeneration. Experiments in our laboratory have shown that chemical lesion of the medial cortex (affecting up to 95% of its neurons) results in a cascade of events: first, massive neuronal death and axonal-dendritic retraction and, secondly, triggered ependymal-neuroblast proliferation and subsequent neo-histogenesis and regeneration of an almost new medial cortex, indistinguishable from a normal undamaged one. This is the only case to our knowledge of the regeneration of an amniote central nervous centre by new neuron production and neo-histogenesis. Thus the lizard cerebral cortex is a good model to study neuronal regeneration and the complex factors that regulate its neurogenetic, migratory and neo-synaptogenetic events.

Matrix metalloproteinase-9 undergoes expression and activation during dendritic remodeling in adult hippocampus

Neurons of adult brain are able to remodel their synaptic connections in response to various stimuli. Modifications of the peridendritic environment, including the extracellular matrix, are likely to play a role during synapse remodeling. Proteolytic disassembly of ECM is a complex process using the regulated actions of specific extracellular proteinases. One of best-characterized families of matrix-modifying enzymes is the matrix metalloproteinase (MMP) family. Here, we describe changes in the expression and function of two well known MMPs, MMP-9 and MMP-2, in adult rat brain before and after systemic administration of the glutamate receptor agonist kainate. Kainate application results in enhanced synaptic transmission and seizures followed by selective tissue remodeling, primarily in hippocampal dentate gyrus. MMP-9 but not MMP-2 was highly expressed by neurons in normal adult rat brain. MMP-9 protein was localized in neuronal cell bodies and dendrites. Kainate upregulated the level of MMP-9 mRNA and protein within hours after drug administration. This was followed several hours later by MMP-9 enzymatic activation. Within hippocampus, MMP-9 mRNA and activity were increased selectively in dentate gyrus, including its dendritic layer. In addition, MMP-9 mRNA levels decreased in areas undergoing neuronal cell loss. This unique spatiotemporal pattern of MMP-9 expression suggests its involvement in activity-dependent remodeling of dendritic architecture with possible effects on synaptic physiology.

Role of K(+) efflux in apoptosis induced by AMPA and kainate in mouse cortical neurons

Activation of ionotropic glutamate receptors can induce neuronal apoptosis in vitro and in vivo. We showed previously that activation of the N-methyl-D-aspartic acid (NMDA) subtype of glutamate receptors in a low Ca(2+) and low Na(+) condition induced apoptotic neuronal death, and that the K(+) efflux via NMDA receptor channels was likely a key event in NMDA-induced apoptosis. Since non-NMDA receptors, alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) and kainate receptors, are also permeable to K(+), we tested the hypothesis that stimulating K(+) efflux via non-NMDA receptor channels could induce apoptosis in cultured cortical neurons. Using a Ca(2+)-free and Na(+)-free external solution, application of kainate revealed outward membrane currents carried by K(+) efflux. In a low Ca(2+)/low Na(+) medium, a 5-h exposure to 50-500 microM AMPA in the presence of the NMDA receptor antagonist MK801 induced dose-dependent neuronal death 24 h after the onset of the insult, accompanied by intracellular K(+) reduction and caspase-3 activation. The AMPA-induced cell death was attenuated by the caspase inhibitor Z-Val-Ala-Asp(OMe)-fluoromethyl ketone (Z-VAD-FMK) and by the protein synthesis inhibitor cycloheximide. Reducing K(+) efflux by raising extracellular K(+) concentration from 5 to 25 mM attenuated AMPA-triggered cell death, the Ca(2+) channel antagonist nifedipine showed no effect on the AMPA toxicity. Kainate induced similar neuronal death sensitive to attenuation by Z-VAD-FMK or elevated extracellular K(+).We suggest that the non-NMDA receptor-mediated K(+) efflux may participate in apoptotic process and that blocking excessive K(+) efflux mediated by NMDA and non-NMDA receptors may selectively prevent neuronal apoptosis under certain pathological conditions.

HSV-mediated delivery of virally derived anti-apoptotic genes protects the rat hippocampus from damage following excitotoxicity, but not metabolic disruption

Studies utilizing gene delivery to the nervous system indicate that various strategies are protective following acute neurological insults such as seizure and stroke. We have found that inhibitors of apoptosis are protective against excitotoxicity and heat stress but not energetic impairment in vitro. Here we studied the neuroprotective efficacy in vivo of these mediators: viral genes (crmA, p35, gamma34.5 KsBcl-2) that have evolved to suppress suicidal host responses to infection, by inhibiting apoptosis. We investigated these effects by utilizing modified herpes vectors to deliver the anti-apoptotic agents intracerebrally and examined them in the face of excitotoxic and metabolic insults. We found that p35 and gamma34.5 reduced by 45% a hippocampal CA3 lesion caused by kainic acid, while crmA and KsBcl-2 did not. None of the inhibitors protected the dentate gyrus of the hippocampus following 3-acetylpyridine, a hypoglycemia model, but we found crmA to worsen the damage. These data are similar to our results in neuronal cultures where the inhibitors protected against the excitotoxin domoic acid, but not against the metabolic poison, cyanide. Together, the results suggest that inhibitors of various apoptotic elements are capable of protecting under acute insult conditions both in vitro and in vivo, suggesting possible future therapeutic applications.

Is neuronal death required for seizure-induced epileptogenesis in the immature brain?

Do seizures cause neuronal death? At least in the immature hippocampus, this may not be the critical question for determining the mechanisms of epileptogenesis. Neuronal injury and death have clearly been shown to occur in most epilepsy models in the mature brain, and are widely considered a prerequisite to seizure-induced epilepsy. In contrast, little neuronal death occurs after even a severe and prolonged seizure prior to the third postnatal week. However, seizures early in life, for example prolonged experimental febrile seizures, can profoundly and permanently change the hippocampal circuit in a pro-epileptogenic direction. These seizure-induced alterations of limbic excitability may require transient structural injury, but are mainly due to functional changes in expression of gene coding for specific receptors and channels, leading to altered functional properties of hippocampal neurons. Thus, in some pro-epileptogenic models in the developing brain, neither the death of neurons nor death-induced abnormalities of surviving neurons may underlie the formation of an epileptic circuit. Rather, findings in the experimental prolonged febrile seizure model suggest that persistent functional alterations of gene expression ('neuroplasticity') in diverse hippocampal neuronal populations may promote pro-epileptogenic processes induced by these seizures. These findings also suggest that during development, relatively short, intense bursts of neuronal activity may disrupt 'normal' programmed maturational processes to result in permanent, selective alterations of gene expression, with profound functional consequences. Therefore, determining the cascade of changes in the programmed expression of pertinent genes, including their temporal and cell-specific spatial profiles, may provide important information for understanding the process of transformation of an evolving, maturing hippocampal network into one which is hyperexcitable.

Apoptosis: a guide for the perplexed

The term 'apoptosis' describes an active process of cellular deconstruction originally contrasted morphologically with necrosis. The mistaken equivalence of the terms apoptosis and 'programmed cell death' has caused confusion and implied that apoptosis is an identifiable therapeutic target rather than a name of a type of cell death. The roots of confusion are suggested to lie not in superficial disagreements about the morphology and biochemistry of cell death, but in the lamentable disconnection of modern science from its philosophical foundations (i.e. Socratic definition, nominalism versus realism, and William of Ockham's advocacy of Aristotelian metaphysics over Plato's Theory of Forms). Renewed awareness of these issues might be the key to understanding that apoptosis is a created concept, not a real entity, and that the use of terms that defy definition has become an obstacle to clear thinking about preventable cell death.

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.

Amygdala kindling develops without mossy fiber sprouting and hippocampal neuronal degeneration in rats

Repeated electrical stimulation of limbic structures has been reported to produce the kindling effect together with morphological changes in the hippocampus such as mossy fiber sprouting and/or neuronal loss. However, to argue against a causal role of these neuropathological changes in the development of kindling-associated seizures, we examined mossy fiber sprouting in amygdala (AM)-kindled rats using Timm histochemical staining, and evaluated the hippocampal neuronal degeneration in AM-kindled rats by terminal deoxynucleotidyl transferase-mediated digoxigenin-11-dUTP nick end labelling (TUNEL). Amygdala kindling was established by 10.3 +/- 0.7 electrical stimulations, and no increase in Timm granules (neuronal sprouting) was observed up to the time of acquisition of a fully kindled state. However, the density and distribution of Timm granules increased significantly in the dentate gyrus compared with unkindled rats after 29 after-discharges or more than 10 kindled convulsions. In addition, no significant increase in TUNEL-positive cells was found in the hilar polymorphic neurons or in CA3 pyramidal neurons of the kindled rats that had fewer than 29 after-discharges. However, a significant increase of TUNEL-positive cells was found in the granule cell layer in the dentate gyrus of the stimulated side after 18 after-discharges or 10 kindled convulsions. Our result show that AM kindling develops without evidence of mossy fiber sprouting, and that mossy fiber sprouting may appear after repeated kindled convulsions, following death of the granule cells in the dentate gyrus.

Formation of the Apaf-1/cytochrome c complex precedes activation of caspase-9 during seizure-induced neuronal death

In this study we examine the in vivo formation of the Apaf-1/cytochrome c complex and activation of caspase-9 following limbic seizures in the rat. Seizures were elicited by unilateral intraamygdala microinjection of kainic acid to induce death of CA3 neurons within the hippocampus of the rat. Apaf-1 was found to interact with cytochrome c within the injured hippocampus 0-24 h following seizures by co-immunoprecipitation analysis and immunohistochemistry demonstrated Apaf-1/cytochrome c co-localization. Cleavage of caspase-9 was detected approximately 4 h following seizure cessation within ipsilateral hippocampus and was accompanied by increased cleavage of the substrate Leu-Glu-His-Asp-p-nitroanilide (LEHDpNA) and subsequent strong caspase-9 immunoreactivity within neurons exhibiting DNA fragmentation. Finally, intracerebral infusion of z-LEHD-fluoromethyl ketone increased numbers of surviving CA3 neurons. These data suggest seizures induce formation of the Apaf-1/cytochrome c complex prior to caspase-9 activation and caspase-9 may be a potential therapeutic target in the treatment of brain injury associated with seizures.

Glutathione in blood of patients with Friedreich's ataxia

BACKGROUND

Oxidative stress and mitochondrial dysfunction have long been considered to play a role in Friedreich's ataxia, a neurodegenerative disease due to a GAA expansion in a gene coding for a mitochondrial protein (frataxin), implicated in the regulation of iron metabolism. Since glutathione is an important antioxidant whose role has been recently proposed in the pathogenesis of some neurodegenerative diseases, we investigated glutathione metabolism in the blood of 14 patients with Friedreich's ataxia by measuring total, free and protein-bound glutathione concentrations.

MATERIALS AND METHODS

Blood samples were obtained from 14 unrelated patients with Friedreich's ataxia (nine males, five females) and 20 age-matched healthy controls (10 males, 10 females). Total and free glutathione concentrations were determined by reverse-phase liquid chromatography with fluorescence detection; the glutathionyl-haemoglobin separation from healthy and pathological subjects was obtained by electrospray ionization-mass spectrometry.

RESULTS

We consistently found a reduction of free glutathione levels (0.55 +/- 0.06 nmol mg(-1) haemoglobin, vs. 8.4 +/- 1.79 nmol mg(-1) haemoglobin, P < 0.001) in the blood of patients with Friedreich's ataxia, a total glutathione concentration comparable to the controls (15 +/- 2.6 nmol mg(-1) haemoglobin, vs. 15.4 +/- 1.4 nmol mg(-1) haemoglobin), and a significant increase of glutathione bound to haemoglobin (15 +/- 1.5 vs. 8 +/- 1.8%, P < 0.05) in erythrocytes.

CONCLUSIONS

Our findings give evidence of an impairment in vivo of glutathione homeostasis in Friedreich's ataxia, suggesting a relevant role of free radical cytotoxicity in the pathophysiology of the disease; this study may also prove useful in the search for an oxidative stress marker in neurodegeneration.

Caspase-mediated cleavage of the Ca2+/calmodulin-dependent protein kinase-like kinase facilitates neuronal apoptosis

This study was designed to identify the role of a recently identified Ca(2+)/calmodulin-dependent protein kinase (CaMK)-like kinase (CaMKLK) in neuronal apoptosis. For this purpose, we studied proteolytic cleavage of CaMKLK by caspases in vitro and in neuronal NG108 cells. In addition, we have investigated the effect of overexpression of wild type and mutant CaMKLK proteins on staurosporine- and serum deprivation-induced apoptosis of NG108 cells. We found that CaMKLK is a substrate for caspase-3 and -8, both in vitro and in NG108 cells during staurosporine- and serum withdrawal-induced apoptosis. Substitution of an aspartic acid residue at position 62 in an asparagine residue within a putative caspase cleavage site completely blocked cleavage of CaMKLK, strongly indicating that (59)DEND(62) is the caspase recognition site. Overexpression of an Asp(62) --> Asn CaMKLK mutant protected NG108 cells from staurosporine-induced apoptosis to a similar extent as Bcl-x(L). In contrast, overexpression of wild type CaMKLK did not lead to protection. Moreover, microinjection of Asp(62) --> Asn CaMKLK protected NG108 cells from serum deprivation-induced apoptosis, while overexpression of a caspase-generated noncatalytic N-terminal CaMKLK fragment exacerbated apoptosis. Together, our data suggest that cleavage of CaMKLK and generation of the noncatalytic N-terminal domain of CaMKLK facilitate neuronal apoptosis.

Differential expression of active, phosphorylation-dependent MAP kinases, MAPK/ERK, SAPK/JNK and p38, and specific transcription factor substrates following quinolinic acid excitotoxicity in the rat

Excitotoxicity is considered a major cell death inductor in neurodegeneration. Yet mechanisms involved in cell death and cell survival following excitotoxic insults are poorly understood. Expression of active, phosphorylation-dependent mitogen-activated extracellular signal-regulated kinases (MAPK/ERKs), stress activated c-Jun N-terminal kinases (SAPK/JNKs) and p38 kinases, as well as their putative active specific transcriptional factor substrates CREB, Elk-1, ATF-2, c-Myc and c-Jun, have been examined following intracortical injection of the glutamate analogue quinolinic acid (QA). Increased JNK(P) and p38(P) immunoreactivity has been found in the core at 1 h following QA injection, whereas increased MAPK(P) immunoreactivity occurs in neurons and glial cells localised around the lesion and in neurons in remote cortical regions. This is accompanied by strong phosphorylated Ser63 c-Jun (c-Jun(P)) immunoreactivity in the core at 3 h, and by strong phosphorylated CREB, Elk-1 and ATF-2 (CREB(P), Elk-1(P) and ATF-2(P)) immunoreactivity mainly in neurons around the core at 24 h following QA injection. Examination with the method of in situ end-labelling of nuclear DNA fragmentation has revealed large numbers of positive cells with no apoptotic morphology in the core at 24 h, thus indicating that JNK(P), p38(P) and c-Jun(P) over-expression precedes cell death. In contrast, MAPK(P), CREB(P), Elk-1(P) and ATF-2(P), but not phosphorylated c-Myc (c-Myc(P)), over-expression correlates with cell survival. Examination of cleaved, active caspase-3 has shown specific immunoreactivity restricted to a few hematogenous cells in the area of injection. Since cleaved caspase-3 is not expressed by dying cells in the present paradigm, JNK(P), p38(P) and c-Jun(P) expression is not associated with caspase-3 activation. The present results demonstrate selective activation of specific MAPK signals which are involved either in cell death or cell survival triggered by excitotoxic insult.

Heat shock protein 27 shows a distinctive widespread spatial and temporal pattern of induction in CNS glial and neuronal cells compared to heat shock protein 70 and caspase 3 following kainate administration

Kainate-induced status epilepticus is associated with both apoptotic and necrotic cell death and induction of heat shock proteins (HSPs) in hippocampal and cortical regions of the rodent brain. In the present study we have examined the temporal, spatial and cellular expression patterns of mRNAs for the highly inducible HSPs, HSP70 and HSP27, together with the apoptotic marker, caspase 3 (CPP32) in rat brain after systemic administration of kainate. HSP70 mRNA was transiently induced in the forebrain by kainate, principally in the CA1, CA3 and hilar cells of the hippocampal formation, in piriform cortex and discrete thalamic nuclei. Maximal expression was seen at 8 h after kainate which then declined to background levels by 7 days. Labelling was predominantly neuronal. In contrast, HSP27 mRNA expression was more widespread. Intense labelling was observed in CA1, CA3 and the hilar region at 8 h after kainate but the expression profile for HSP27 mRNA expanded considerably with intense signals seen in corpus callosum, cortex and thalamus at 24 h post kainate. Emulsion autoradiographs indicated a predominantly glial localisation for HSP27 mRNA. In the hilus, a distinct subpopulation of interneurones were found to express HSP27 mRNA. CPP32 mRNA was upregulated in CA1, CA3 and hilus of the hippocampal formation and in piriform cortex. CPP32 mRNA expression was more restricted and similar in distribution to HSP70 mRNA being localised to neurones. The present study demonstrates the unique early expression of HSP27 mRNA by glial cells and distinct populations of neurones which extends beyond those in which HSP70 and CPP32 induction occurs with subsequent cell loss.

Role of kainate receptor activation and desensitization on the [Ca(2+)](i) changes in cultured rat hippocampal neurons

We investigated the role of kainate (KA) receptor activation and desensitization in inducing the increase in the intracellular free Ca(2+) concentration ([Ca(2+)](i)) in individual cultured rat hippocampal neurons. The rat hippocampal neurons in the cultures were shown to express kainate receptor subunits, KA2 and GluR6/7, either by immunocytochemistry or by immunoblot analysis. The effect of LY303070, an alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) receptor antagonist, on the alterations in the [Ca(2+)](i) caused by kainate showed cell-to-cell variability. The [Ca(2+)](i) increase caused by kainate was mostly mediated by the activation of AMPA receptors because LY303070 inhibited the response to kainate in a high percentage of neurons. The response to kainate was potentiated by concanavalin A (Con A), which inhibits kainate receptor desensitization, in 82.1% of the neurons, and this potentiation was not reversed by LY303070 in about 38% of the neurons. Also, upon stimulation of the cells with 4-methylglutamate (MGA), a selective kainate receptor agonist, in the presence of Con A, it was possible to observe [Ca(2+)](i) changes induced by kainate receptor activation, because LY303070 did not inhibit the response in all neurons analyzed. In toxicity studies, cultured rat hippocampal neurons were exposed to the drugs for 30 min, and the cell viability was evaluated at 24 hr using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The selective activation of kainate receptors with MGA, in the presence of Con A, induced a toxic effect, which was not prevented by LY303070, revealing a contribution of a small subpopulation of neurons expressing kainate receptors that independently mediate cytotoxicity. Taken together, these results indicate that cultured hippocampal neurons express not only AMPA receptors, but also kainate receptors, which can modulate the [Ca(2+)](i) and toxicity.

Caspase inhibitors increase short-term survival of progenitor-cell progeny in the adult rat dentate gyrus following status epilepticus

The dentate gyrus (DG) is one of the few regions in the brain that continues to produce new neurons throughout adulthood. Seizures not only increase neurogenesis, but also lead to death of DG neurons. We investigated the relationship between cell death and neurogenesis following seizures in the DG of adult rats by blocking caspases, which are key components of apoptotic cell death. Multiple intracerebroventricular infusions of caspase inhibitors (pancaspase inhibitor zVADfmk, and caspase 3 and 9 inhibitor) prior to, just after, 1 day after, and 1 week following 2 h of lithium-pilocarpine-induced status epilepticus reduced the number of terminal deoxynucleotidyl transferase-mediated fluorescein-dUTP nick-end labelled (TUNEL) cells and increased the number of bromodeoxyuridine (BrdU) -stained proliferated cells in the subgranular zone at 1 week. The caspase inhibitor-treated group did not differ from control at 2 days or 5 weeks following the epileptic insult. Our findings suggest that caspases modulate seizure-induced neurogenesis in the DG, probably by regulating apoptosis of newly born neurons, and that this action can be suppressed transiently by caspase inhibitors. Furthermore, although previous studies have indicated that increased neuronal death can trigger neurogenesis, we show here that reduction in apoptotic death may be associated with increased neurogenesis.

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.

Somatostatin type 2 receptor expression in the rat hippocampus following cerebral ischemia

We examined how transient cerebral ischemia affects the mRNA expression, and the immunoreactive distribution, of the somatostatin type 2 (sst2) receptor in the adult rat hippocampus. Following reperfusion, sst2 mRNA levels increased significantly in the CA1 region by 3 h, and were also increased in the CA3 and CA4/hilus subfields at 6 and 12 h. At 24 h, however, sst2 receptor mRNA levels returned to baseline throughout the hippocampus. At the protein level, we found the regional immunoreactivity of the sst2a receptor was maintained, or slightly elevated, throughout the hippocampus at 6 h, but not different from control at 24 h. These results suggest that sst2 receptors maintain their normal distribution and prevalence in the post-ischemic hippocampus before the deterioration of the vulnerable CA1 neurons. Thus, they represent attractive targets for neuroprotective interventions.

Increased expression of Fas (CD95/APO-1) in adult rat brain after kainate-induced seizures

Fas (CD95/APO-1), a transmembrane glycoprotein and receptor for the Fas ligand, plays an important role in apoptosis. The present study examined whether excitotoxic cell death induces Fas expression in the adult rat brain. Although relatively light immunostaining was observed in control brain sections, significantly increased Fas immunoreactivity was seen from 4 h to 5 days after the onset of kainic acid-induced seizures. Increased expression of both Fas mRNA and protein were also evident by reverse transcription polymerase chain reaction and Western blotting, respectively. Fas induction was correlated with neuronal apoptosis as demonstrated by colocalization of Fas and terminal dT-mediated dUTP nick end-labeling (TUNEL). Cells with increased Fas-expression were also immunoreactive for tumor suppressor p53 and neuronal specific nuclear protein (NeuN). These results suggest that Fas receptor may contribute to excitotoxic neuronal death in cooperation with p53, and further implicates the Fas pathway in the pathophysiology of neurodegenerative diseases.

Long-lasting induction of brain-derived neurotrophic factor is restricted to resistant cell populations in an animal model of status epilepticus

We have recently characterized an animal model of status epilepticus induced by a single intraseptal injection of kainate. Under these conditions, there is a delayed expanding apoptotic hippocampal and amygdalar cell death. In order to further characterize this animal model, we have performed a detailed time-course analysis of the appearance of cell death, brain-derived neurotrophic factor messenger RNA expression and astroglial and microglial response in different brain areas related to the limbic system. We found a long-lasting delayed apoptotic cell death in the hippocampal formation, amygdala, medial thalamus, dorsal endopiriform nucleus and multiple cortical areas from two to 21 days post-injection. There was a spatiotemporal correlation between the appearance of cell death and induction of brain-derived neurotrophic factor messenger RNA expression in the areas studied, and interestingly this induction was found in non-degenerating cells. We conclude that our animal model of status epilepticus exhibits remarkable features of recurrent seizure activity and provides evidence for a neuroprotective role of brain-derived neurotrophic factor against seizure-induced apoptotic cell death.