Spreading depression induces expression of calcium-independent protein kinase C subspecies in ischaemia-sensitive cortical layers: regulation by N-methyl-D-aspartate receptors and glucocorticoids

Metabolic Pathophysiology of Cortical Spreading Depression: A Review

Cortical spreading depression (CSD) is an electrophysiologic pathological state in which a wave of depolarization in the cerebral cortex is followed by the suppression of spontaneous neuronal activity. This transient spread of neuronal depolarization on the surface of the cortex is the hallmark of CSD. Numerous investigations have demonstrated that transmembrane ion transport, astrocytic ion clearing and fatigue, glucose metabolism, the presence of certain genetic markers, point mutations, and the expression of the enzyme responsible for the production of various arachidonic acid derivatives that participate in the inflammatory response, namely, cyclooxygenase (COX), all influence CSD. Here, we explore the associations between CSD occurrence in the cortex and various factors, including how CSD is related to migraines, how the glucose state affects CSD, the effect of TBI and its relationship with CSD and glucose metabolism, how different markers can be measured to determine the severity of CSD, and possible connections to oligemia, orexin, and leptin.

17-β-Estradiol induces spreading depression and pain behavior in alert female rats

AIMS

Test the putative contribution of 17-β-estradiol in the development of spreading depression (SD) events and head pain in awake, non-restrained rats.

MAIN METHODS

Female, Sprague-Dawley rats were intact or underwent ovariectomy followed one week later by surgery to place electrodes onto the dura to detect epidural electroencephalographic activity (dEEG). dEEG activity was recorded two days later for 12 hours after systemic administration of 17-β-estradiol (180 μg/kg, i.p.). A separate set of rats were observed for changes in exploratory, ambulatory, fine, and rearing behaviors; periorbital allodynia was also assessed.

KEY FINDINGS

A bolus of 17-β-estradiol significantly elevated serum estrogen levels, increased SD episodes over a 12-hour recording period and decreased rearing behaviors in ovariectomized rats. Pre-administration of ICI 182,780, an estrogen receptor antagonist, blocked 17-β-estradiol-evoked SD events and pain behaviors; similar results were observed when the antimigraine therapeutic sumatriptan was used.

SIGNIFICANCE

These data indicate that an estrogen receptor-mediated mechanism contributes to SD events in ovariectomized rats and pain behaviors in both ovariectomized -and intact- rats. This suggests that estrogen plays a different role in each phenomenon of migraine where intense fluctuations in concentration may influence SD susceptibility. This is the first study to relate estrogen peaks to SD development and pain behaviors in awake, freely moving female rats, establishing a framework for future preclinical migraine studies.

Cortical spreading depression-induced preconditioning in the brain

Cortical spreading depression is a technique used to depolarize neurons. During focal or global ischemia, cortical spreading depression-induced preconditioning can enhance tolerance of further injury. However, the underlying mechanism for this phenomenon remains relatively unclear. To date, numerous issues exist regarding the experimental model used to precondition the brain with cortical spreading depression, such as the administration route, concentration of potassium chloride, induction time, duration of the protection provided by the treatment, the regional distribution of the protective effect, and the types of neurons responsible for the greater tolerance. In this review, we focus on the mechanisms underlying cortical spreading depression-induced tolerance in the brain, considering excitatory neurotransmission and metabolism, nitric oxide, genomic reprogramming, inflammation, neurotropic factors, and cellular stress response. Specifically, we clarify the procedures and detailed information regarding cortical spreading depression-induced preconditioning and build a foundation for more comprehensive investigations in the field of neural regeneration and clinical application in the future.

Presynaptic NMDA receptor mechanisms for enhancing spontaneous neurotransmitter release

NMDA receptors (NMDARs) are required for experience-driven plasticity during formative periods of brain development and are critical for neurotransmission throughout postnatal life. Most NMDAR functions have been ascribed to postsynaptic sites of action, but there is now an appreciation that presynaptic NMDARs (preNMDARs) can modulate neurotransmitter release in many brain regions, including the neocortex. Despite these advances, the cellular mechanisms by which preNMDARs can affect neurotransmitter release are largely unknown. Here we interrogated preNMDAR functions pharmacologically to determine how these receptors promote spontaneous neurotransmitter release in mouse primary visual cortex. Our results provide three new insights into the mechanisms by which preNMDARs can function. First, preNMDARs can enhance spontaneous neurotransmitter release tonically with minimal extracellular Ca(2+) or with major sources of intracellular Ca(2+) blocked. Second, lowering extracellular Na(+) levels reduces the contribution of preNMDARs to spontaneous transmitter release significantly. Third, preNMDAR enhance transmitter release in part through protein kinase C signaling. These data demonstrate that preNMDARs can act through novel pathways to promote neurotransmitter release in the absence of action potentials.

epsilonPKC confers acute tolerance to cerebral ischemic reperfusion injury

In response to mild ischemic stress, the brain elicits endogenous survival mechanisms to protect cells against a subsequent lethal ischemic stress, referred to as ischemic tolerance. The molecular signals that mediate this protection are thought to involve the expression and activation of multiple kinases, including protein kinase C (PKC). Here we demonstrate that epsilonPKC mediates cerebral ischemic tolerance in vivo. Systemic delivery of psiepsilonRACK, an epsilonPKC-selective peptide activator, confers neuroprotection against a subsequent cerebral ischemic event when delivered immediately prior to stroke. In addition, activation of epsilonPKC by psiepsilonRACK treatment decreases vascular tone in vivo, as demonstrated by a reduction in microvascular cerebral blood flow. Here we demonstrate the role of acute and transient epsilonPKC in early cerebral tolerance in vivo and suggest that extra-parenchymal mechanisms, such as vasoconstriction, may contribute to the conferred protection.

The Role of Protein Kinase C in Cerebral Ischemic and Reperfusion Injury

Background and Purpose— Stroke is a leading cause of disability and death in the United States, yet limited therapeutic options exist. The need for novel neuroprotective agents has spurred efforts to understand the intracellular signaling pathways that mediate cellular response to stroke. Protein kinase C (PKC) plays a central role in mediating ischemic and reperfusion damage in multiple tissues, including the brain. However, because of conflicting reports, it remains unclear whether PKC is involved in cell survival signaling, or mediates detrimental processes.

Summary of Review— This review will examine the role of PKC activity in stroke. In particular, we will focus on more recent insights into the PKC isozyme-specific responses in neuronal preconditioning and in ischemia and reperfusion-induced stress.

Conclusion— Examination of PKC isozyme activities during stroke demonstrates the clinical promise of PKC isozyme-specific modulators for the treatment of cerebral ischemia.

Energy failure in astrocytes increases the vulnerability of neurons to spreading depression

A neuroprotective role of astrocytes has been hypothesized, but the mechanism is debated and in vivo evidence is limited. To test this hypothesis, a sublethal stressor (spreading depression) and fluorocitrate (FC), a selective inhibitor of the astrocytic Krebs cycle, were used in urethane-anaesthetized adult rats. Neuronal damage was assessed 24 h after treatment with silver stain and immunoreactivity for a 72-kDa heat-shock protein. ATP levels and mitochondrial aconitase activity, a marker indicating exposure to reactive oxygen species, were measured after 4 and 24 h. Spreading depression alone did not affect ATP levels, mitochondrial aconitase activity, or induce neuronal injury in the cortex. Local or intraventricular injection of FC significantly decreased ATP levels and mitochondrial aconitase activity, but did not produce neuronal damage. In animals receiving injections of FC and then spreading depression, there was evidence of significant neuronal stress and damage. Isocitrate, which bypasses the metabolic inhibition produced by FC, prevented all of the changes seen after the combination of FC and spreading depression. One-hour pretreatment with dimethyl sulfoxide (a scavenger of hydroxyl radicals), deferoxamine (an iron chelator) or fructose-1,6-bisphosphate also blocked inactivation of mitochondrial aconitase, ATP depletion and the neuronal damage induced by FC and spreading depression. These experiments demonstrate that inhibition of the metabolism of astrocytes, with a decrease in ATP levels, will increase the susceptibility of neurons to the stress induced by spreading depression. The neuroprotective effects of dimethyl sulfoxide, deferoxamine and fructose-1,6-bisphosphate suggest that oxidative stress contributes to the neurotoxicity in this situation.

Atrial natriuretic peptide expression is increased in rat cerebral cortex following spreading depression: possible contribution to sd-induced neuroprotection

Cortical spreading depression (CSD) is characterised by slowly propagating waves of cellular depolarization and depression and involves transient changes in blood flow, ion balance and metabolism. In cerebral ischaemia, peri-infarct CSD-like depolarization potentiates infarct growth, whereas preconditioning with a CSD episode protects against subsequent ischaemic insult. Thus, many of the long-lasting molecular changes that occur in CSD-affected tissue are presumed to be part of a 'neuroprotective cascade.' 3',5'-Cyclic guanosine monophosphate (cGMP) has been shown to be a neuroprotective mediator and the nitric oxide system, which increases cGMP production by soluble guanylate cyclase, is up-regulated by CSD. Atrial and C-type natriuretic peptide (ANP/CNP) are present in cerebral cortex and their actions are mediated via particulate guanylate cyclase receptors and cGMP production. Therefore, in further efforts to characterise the role of cGMP-related systems in CSD and neuroprotection, this study investigated possible changes in cortical natriuretic peptide expression following acute, unilateral CSD in rats. Using in situ hybridisation, significant 20-80% increases in ANP mRNA were detected in layers II and VI of ipsilateral cortex at 6 h and 1-14 days after CSD. Ipsilateral cortical levels were again equivalent to control contralateral values after 28 days. Assessment of cortical concentrations of ANP immunoreactivity by radioimmunoassay revealed a significant 57% increase at 7 days after CSD. Despite using a sensitive signal-amplification protocol, authentic ANP-like immunostaining was readily detected in subcortical nerve fibres, but was not reliably detected in normal or CSD-affected neocortex, suggesting the presence of very low levels, and/or active or differential processing of the peptide. Cortical CNP mRNA levels are not altered by CSD, indicating the specificity of the observed effects.Overall, these novel findings demonstrate a prolonged increase in cortical ANP expression after an acute episode of CSD. The overlap between the described time course of CSD-induced protection against ischaemic insult and demonstrated increases in ANP levels, suggest that ANP (like nitric oxide) may contribute to CSD-induced neuroprotection, via effects on cGMP production and other signal-transduction pathways.

Prevention of NMDA-induced death of cortical neurons by inhibition of protein kinase Czeta

Excitotoxicity through stimulation of N-methyl-d-aspartate (NMDA) receptors contributes to neuronal death in brain injuries, including stroke. Several lines of evidence suggest a role for protein kinase C (PKC) isoforms in NMDA excitotoxicity. We have used specific peptide inhibitors of classical PKCs (alpha, beta, and gamma), novel PKCs delta and epsilon, and an atypical PKCzeta in order to delineate which subspecies are involved in NMDA-induced cell death. Neuronal cell cultures were prepared from 15-day-old mouse embryos and plated onto the astrocytic monolayer. After 2 weeks in vitro the neurons were exposed to 100 micro m NMDA for 5 min, and 24 h later the cell viability was examined by measuring the lactate dehydrogenase release and bis-benzimide staining. While inhibitors directed to classical (alpha, beta, and gamma) or novel PKCs (delta or epsilon) had no effect, the PKCzeta inhibitor completely prevented the NMDA-induced necrotic neuronal death. Confocal microscopy confirmed that NMDA induced PKCzeta translocation, which was blocked by the PKCzeta inhibitor. The NMDA-induced changes in intracellular free Ca2+ were not affected by the peptides. In situ hybridization experiments demonstrated that PKCzeta mRNA is induced in the cortex after focal brain ischemia. Altogether, the results indicate that PKCzeta activation is a downstream signal in NMDA-induced death of cortical neurons.

Spreading depression-induced preconditioning in the mouse cortex: differential changes in the protein expression of ionotropic nicotinic acetylcholine and glutamate receptors

Preconditioning of the cerebral cortex was induced in mice by repeated cortical spreading depression (CSD), and the major ionotropic glutamate (GluRs) and nicotinic acetylcholine receptor (nAChRs) subunits were compared by quantitative immunoblotting between sham- and preconditioned cortex, 24 h after treatment. A 30% reduction in alpha-amino-3-hydroxy-5-methyl-4-iso- xazolepropionate (AMPA) GluR1 and 2 subunit immunoreactivities was observed in the preconditioned cortex (p < 0.03), but there was no significant change in the NMDA receptor subunits, NR1, NR2A and NR2B. A 12-15-fold increase in alpha7 nAChR subunit expression following in vivo CSD (p < 0.001) was by far the most remarkable change associated with preconditioning. In contrast, the alpha4 nAChR subunit was not altered. These data point to the alpha7 nAChR as a potential new target for neuroprotection because preconditioning increases consistently the tolerance of the brain to acute insults such as ischaemia. These data complement recent studies implicating alpha7 nAChR overexpression in the amelioration of chronic neuropathologies, notably Alzheimer's disease (AD).

Cortical spreading depression transiently activates MAP kinases

Cortical spreading depression (CSD) has been shown to have neuroprotective effects when administered in advance of cerebral ischemia. The mechanism by which CSD induces its neuroprotective effect however remains to be elucidated. Since MAP kinases have been shown to impart neuroprotection in ischemic preconditioning paradigms, we attempted to determine the role CSD may have in the activation of MAPK. We show that CSD is capable of increasing the phosphorylation of ERK in a MEK-dependent manner. This phosphorylation is, however, transient, as phosphorylated ERK levels return to control levels 45 min after 2 h of CSD elicitation. Immunohistochemical analysis reveals that the phosphorylated form of ERK is located ubiquitously in cells of the CSD-treated cortex while CSD-elicited MEK phosphorylation resides solely in the nuclei. These data suggest that CSD may act via the MAP kinase pathways to mediate preconditioning.

Isoform-specific membrane translocation of protein kinase C after ischemic preconditioning

Mild cerebral anoxic/ischemic/stress insults promote 'tolerance' and thereby protect the brain from subsequent 'lethal' anoxic/ischemic insults. We examined whether specific activation of PKC alpha, delta, epsilon, or zeta isoforms is associated with ischemic preconditioning (IPC) in rat brain. IPC was produced by a 2-minute global cerebral ischemia. Membrane and cytosolic fractions of the hippocampi were immunoblotted using specific antibodies for PKCalpha, delta, epsilon, and zeta. PKCalpha showed a significant translocation to the membrane fraction from 30 min to 4 h and PKCdelta at 4 h following IPC. In contrast, the membrane/cytosol ratio of PKCepsilon showed a tendency to decrease at 30 min and 8 h, and the membrane/cytosol ratio of PKCzeta was significantly decreased from 30 min to 24 h following IPC. These findings indicate PKC isoform-specific membrane translocations in the hippocampus after brief global brain ischemia and suggest that activation of PKCalpha and PKCdelta may be associated with IPC-induced tolerance in the rat hippocampus.

Preconditioning with spreading depression activates specifically protein kinase Cdelta

Preconditioning with brief ischemia or spreading depression (SD) confers tolerance in cortical neurons to subsequent episode of ischemia. In myocardium a similar preconditioning is achieved by mechanisms, which are mediated by protein kinase C (PKC) alpha, delta, epsilon or zeta isoform. We induced SD by cortical application of KCl in the rat and analyzed cortical tissues after recovery of 30 min, 4 h and 12 h. While no changes at protein levels or activity of PKCalpha, epsilon or zeta were detected, a considerable increase in membrane translocation of PKCdelta was seen at 30 min and 12 h. A significant increase at mRNA level, protein amount and autophosphorylation at 12 h confirmed the late activation of PKCdelta, which may be involved in neuronal protection by preconditioning.

Cerebral ischemia and seizures induce tyrosine phosphorylation of PYK2 in neurons and microglial cells

The nonreceptor tyrosine kinase PYK2 represents a stress-sensitive mediator of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase (MAPK) signaling pathways in many cell types. In the present study, we assessed the tyrosine phosphorylation of PYK2 under normal and pathological conditions in the CNS. We generated a polyclonal antibody that selectively recognizes tyrosine-phosphorylated PYK2 at its major autophosphorylation site. By using this antibody, we demonstrate that the phosphorylation profile of PYK2 after focal cerebral ischemia is biphasic. The first phase occurs within 1 hr, when most of the phospho-PYK2 immunoreactivity was observed in cortical neurons, whereas 24-72 hr after ischemia, a striking induction of phospho-PYK2 immunoreactivity was evident in microglia around the necrotic infarcted area. Double-immunostaining analysis using both anti-phospho-PYK2 antibody and antibody against the double-phosphorylated active form of p38MAPK revealed that the two phosphorylated protein kinases exhibit strikingly similar distribution patterns after ischemia. A short time after ischemia, phosphorylation of p38MAPK was evident in the cortical neurons as demonstrated by both immunohistochemistry and immunoblotting analysis, whereas 24-72 hr after ischemia, phospho-p38MAPK was found in activated microglia and colocalized with phospho-PYK2. In contrast to cortical neurons, basal phospho-PYK2 immunoreactivity was observed in hippocampal pyramidal neurons, which was markedly decreased after kainate acid-induced status epilepticus. However, 24 hr after the epileptic onset, a pronounced upregulation of PYK2 and phospho-PYK2 immunoreactivities was evident in microglial cells, as demonstrated by double-immunostaining with the microglial marker OX42. These results provide, for the first time, in situ localization of tyrosine-phosphorylated PYK2 in neuronal stress pathways in the adult rat brain and are consistent with the role of PYK2 as an upstream regulator of p38MAPK signaling cascades in response to stress signals.

Functional differentiation of multiple perilesional zones after focal cerebral ischemia

Transient and permanent focal cerebral ischemia results in a series of typical pathophysiologic events. These consequences evolve in time and space and are not limited to the lesion itself, but they can be observed in perilesional (penumbra) and widespread ipsi- and sometimes contralateral remote areas (diaschisis). The extent of these areas is variable depending on factors such as the type of ischemia, the model, and the functional modality investigated. This review describes some typical alterations attributable to focal cerebral ischemia using the following classification scheme to separate different lesioned and perilesional areas: (1) The lesion core is the brain area with irreversible ischemic damage. (2) The penumbra is a brain region that suffers from ischemia, but in which the ischemic damage is potentially, or at least partially, reversible. (3) Remote brain areas are brain areas that are not directly affected by ischemia. With respect to the etiology, several broad categories of remote changes may be differentiated: (3a) remote changes caused by brain edema; (3b) remote changes caused by waves of spreading depression; (3c) remote changes in projection areas; and (3d) remote changes because of reactive plasticity and systemic effects. The various perilesional areas are not necessarily homogeneous; but a broad differentiation of separate topographic perilesional areas according to their functional state and sequelae allows segregation into several signaling cascades, and may help to understand the functional consequences and adaptive processes after focal brain ischemia.

Multiple molecular penumbras after focal cerebral ischemia

Though the ischemic penumbra has been classically described on the basis of blood flow and physiologic parameters, a variety of ischemic penumbras can be described in molecular terms. Apoptosis-related genes induced after focal ischemia may contribute to cell death in the core and the selective cell death adjacent to an infarct. The HSP70 heat shock protein is induced in glia at the edges of an infarct and in neurons often at some distance from the infarct. HSP70 proteins are induced in cells in response to denatured proteins that occur as a result of temporary energy failure. Hypoxia-inducible factor (HIF) is also induced after focal ischemia in regions that can extend beyond the HSP70 induction. The region of HIF induction is proposed to represent the areas of decreased cerebral blood flow and decreased oxygen delivery. Immediate early genes are induced in cortex, hippocampus, thalamus, and other brain regions. These distant changes in gene expression occur because of ischemia-induced spreading depression or depolarization and could contribute to plastic changes in brain after stroke.

Effects of nitric oxide donors on the afferent resting activity in the cephalopod statocyst

The effects of bath applications of the nitric oxide (NO) donors sodium nitroprusside (SNP), diethylamine sodium (DEA), 3-morpholinosydnonimine (SIN-1), and S-nitroso-N-acetyl-penicillamine (SNAP) on the resting activity (RA) of afferent crista fibers were studied in isolated statocysts of the cuttlefish Sepia officinalis. The NO donors had three different effects: inhibition, excitation, and excitation followed by an inhibition. The SNAP analog N-acetyl-DL-penicillamine (xSNAP; with no NO moiety) had no effect. When the preparation was pre-treated with the NO synthase inhibitor N(G)-nitric-L-arginine methyl ester HCl (L-NAME), the NO donors were still effective. When the preparation was pre-treated with the guanylate cyclase inhibitors methylene blue (M-BLU) or cystamine (CYS), NO donors had only excitatory effects, whereas their effects were inhibitory only when pre-treatment was with the adenylate cyclase inhibitors nicotinic acid (NIC-A), 2',3'-dideoxyadenosine (DDA), or MDL-12330A. When pre-treatment was with a guanylate and an adenylate cyclase inhibitor combined, NO donors had no effect; in that situation, the RA of the afferent fibers remained and the preparation still responded to bath applications of GABA. Selective experiments with statocysts from the squid Sepioteuthis lessoniana and the octopod Octopus vulgaris gave comparable results. These data indicate that in cephalopod statocysts an inhibitory NO-cGMP and an excitatory NO-cAMP signal transduction pathway exist, that these two pathways are the key pathways for the action of NO, and that they have only modulatory effects on, and are not essential for the generation of, the RA.

Genomic structure and chromosomal localization of the rat protein kinase Cdelta-gene

Protein kinase Cdelta (PKCdelta) is a widely expressed calcium-independent PKC isozyme that is induced at mRNA and protein levels upon stimulation of different cellular pathways. We found the rat PKCdelta gene to consist of 19 exons and to span approximately 29 kb. The exon-intron junctions follow the GT/AG rule. The 5' untranslated region is nearly 12 kb in length, and the transcription initiation site is surrounded by CG-rich sequences. The 5' flanking region contains putative binding sites for activator protein 1 (AP-1), nuclear factor kappa B (NFkappaB), stimulatory protein-1 (Sp-1) and nerve growth factor induced-C (NGFI-C) transcription factors. The PKCdelta gene is localized at the rat chromosome 19p14. The cloned gene will help to elucidate the role of PKCdelta in growth, differentiation and death of mammalian cells.