Aurintricarboxylic acid prevents GLUR2 mRNA down-regulation and delayed neurodegeneration in hippocampal CA1 neurons of gerbil after global ischemia

Caloxin-derived peptides for the inhibition of plasma membrane calcium ATPases

Plasma membrane calcium ATPases (PMCAs) are a family of transmembrane proteins responsible for the extrusion of cytosolic Ca²⁺ to the extracellular milieu. They are important players of the calcium homeostasis possibly implicated in some important diseases. The reference inhibitors of PMCA extruding activity are on one hand ortho-vanadate (IC₅₀ in the 30 mM range), and on the other a series of 12- to 20-mer peptides named caloxins (IC₅₀ in the 100 µM scale). As for all integral membrane proteins, biochemistry and pharmacology are difficult to study on isolated and/or purified proteins. Using a series of reference blockers, we assessed a pharmacological window with which we could study the functionality of PMCAs in living cells. Using this system, we screened for alternative versions of caloxins, aiming at shortening the peptide backbone, introducing non-natural amino acids, and overall trying to get a glimpse at the structure-activity relationship between those new peptides and the protein in a cellular context. We describe a short series of equipotent 5-residue long analogues with IC₅₀ in the low µM range.

Dynamic volumetric changes of hippocampal subfields in clinically isolated syndrome patients: A 2-year MRI study

Background:

Different subregional patterns of hippocampal involvement have been observed in diverse multiple sclerosis (MS) phenotypes.

Objective:

To evaluate the occurrence of regional hippocampal variations in clinically isolated syndrome (CIS) patients, their relationships with focal white matter (WM) lesions, and their prognostic implications.

Methods:

Brain dual-echo and three-dimensional (3D) T1-weighted scans were acquired from 14 healthy controls and 36 CIS patients within 2 months from clinical onset and after 3, 12, and 24 months. Radial distance distribution was assessed using 3D parametric surface mesh models. A cognitive screening was also performed.

Results:

Patients showed clusters of reduced radial distance in the Cornu Ammonis 1 from month 3, progressively extending to the subiculum, negatively correlated with ipsilateral T2 and T1 lesion volume. Increased radial distance appeared in the right dentate gyrus after 3 ( p < 0.05), 12, and 24 ( p < 0.001) months, and in the left one after 3 and 24 months ( p < 0.001), positively correlated with lesional measures. Hippocampal volume variations were more pronounced in patients converting to MS after 24 months and did not correlate with cognitive performance.

Conclusion:

Regional hippocampal changes occur in CIS, are more pronounced in patients converting to MS, and are modulated by focal WM lesions.

Review : Gene Expression after Cerebral Ischemia

Global and focal ischemias induce a variety of gene families, including immediate early genes, cytokines, neurotransmitter receptors, and heat-shock proteins. The Janus-like effects of several of these gene prod ucts promote neuronal survival and degeneration. Therefore, determining the molecular pathways respon sible for the differential regulation of these genes is of paramount importance. The discovery of apoptosis as a mediator of delayed neuronal death has led to the identification of a number of other genes involved in postischemic brain damage. Future neuroprotective therapies for cerebral ischemia may be directed at preventing alterations in gene expression. NEUROSCIENTIST 5:238-253, 1999

Involvement of GluR2 up-regulation in neuroprotection by electroacupuncture pretreatment via cannabinoid CB1 receptor in mice

We investigated whether glutamate receptor subunit 2 (GluR2) is involved in EA pretreatment-induced neuroprotection via cannabinoid CB1 receptors (CB1R) after global cerebral ischemia in mice. Two hours after electric acupuncture (EA) pretreatment, global cerebral ischemia (GCI) was induced by bilateral common carotid artery occlusion (BCCAO) for 20 min. The GluR2 expression was examined in the hippocampus after reperfusion. Cell survival, neuronal apoptosis, the Bax/Bcl-2 ratio and neurological scores were evaluated at 24 h after BCCAO in the presence or absence of the GluR2 inhibitor. Furthermore, the GluR2 was determined in the presence and absence of CB1R inhibitor. Our results showed EA pretreatment enhanced expression of GluR2 in the hippocampus 2 h after reperfusion. Moreover, EA pretreatment improved neurological outcome, promoted cell survival, inhibited neuronal apoptosis, and decreased the Bax/Bcl-2 ratio after reperfusion. GluR2 knockdown by GluR2 siRNA effectively reversed the beneficial effects of EA pretreatment. Furthermore, CB1R siRNA and two CB1R antagonists blocked the elevation of GluR2 expression by EA pretreatment, whereas the two CB1R agonists up-regulated GluR2 expression as EA pretreatment. In conclusion, GluR2 up-regulation is involved in neuroprotection of EA pretreatment against GCI through CB1R, suggesting that GluR2 may be a novel target for stroke intervention.

PTEN regulates AMPA receptor-mediated cell viability in iPS-derived motor neurons

Excitatory transmission in the brain is commonly mediated by the α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors. In amyotrophic lateral sclerosis (ALS), AMPA receptors allow cytotoxic levels of calcium into neurons, contributing to motor neuron injury. We have previously shown that oculomotor neurons resistant to the disease process in ALS show reduced AMPA-mediated inward calcium currents compared with vulnerable spinal motor neurons. We have also shown that PTEN (phosphatase and tensin homolog deleted on chromosome 10) knockdown via siRNA promotes motor neuron survival in models of spinal muscular atrophy (SMA) and ALS. It has been reported that inhibition of PTEN attenuates the death of hippocampal neurons post injury by decreasing the effective translocation of the GluR2 subunit into the membrane. In addition, leptin can regulate AMPA receptor trafficking via PTEN inhibition. Thus, we speculate that manipulation of AMPA receptors by PTEN may represent a potential therapeutic strategy for neuroprotective intervention in ALS and other neurodegenerative disorders. To this end, the first step is to establish a fibroblast-iPS-motor neuron in vitro cell model to study AMPA receptor manipulation. Here we report that iPS-derived motor neurons from human fibroblasts express AMPA receptors. PTEN depletion decreases AMPA receptor expression and AMPA-mediated whole-cell currents, resulting in inhibition of AMPA-induced neuronal death in primary cultured and iPS-derived motor neurons. Taken together, our results imply that PTEN depletion may protect motor neurons by inhibition of excitatory transmission that represents a therapeutic strategy of potential benefit for the amelioration of excitotoxicity in ALS and other neurodegenerative disorders.

Application of aurintricarboxylic acid for the adherence of mouse P19 neurons and primary hippocampal neurons to noncoated surface in serum-free culture

Dissociated primary neuron culture has been the most widely used model systems for neuroscience research. Most of these primary neurons are cultured on adhesion matrix-coated surface to provide a proper environment for cell anchorage under serum-free conditions. In this study, we provide an alternative technique to promote the adhesions of these neurons using aurintricarboxylic acid (ATA), a nonpeptide compound, without surface manipulations. We first demonstrated that ATA could promote Chinese hamster ovary cell attachment and proliferation in serum-free medium in a dosage-dependent manner. We later showed that ATA significantly enhanced the attachment of the retinoic acid differentiated P19 mouse embryonal carcinoma (P19) neurons, with an optimal concentration around 30 μg/mL. A similar result was seen in primary hippocampal neurons, with an optimal ATA concentration around 15 μg/mL. Further morphological assessments revealed that the average neurite length and neuronal polarization were almost identical to that obtained using a conventional method with poly-L-lysine surface. The advantages of using the ATA treatment technique for immunochemical analysis are discussed.

Astrocytes regulate GluR2 expression in motor neurons and their vulnerability to excitotoxicity

Influx of Ca(2+) ions through alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors contributes to neuronal damage in stroke, epilepsy, and neurodegenerative disorders such as ALS. The Ca(2+) permeability of AMPA receptors is largely determined by the glutamate receptor 2 (GluR2) subunit, receptors lacking GluR2 being permeable to Ca(2+) ions. We identified a difference in GluR2 expression in motor neurons from two rat strains, resulting in a difference in vulnerability to AMPA receptor-mediated excitotoxicity both in vitro and in vivo. Astrocytes from the ventral spinal cord were found to mediate this difference in GluR2 expression in motor neurons. The presence of ALS-causing mutant superoxide dismutase 1 in astrocytes abolished their GluR2-regulating capacity and thus affected motor neuron vulnerability to AMPA receptor-mediated excitotoxicity. These results reveal a mechanism through which astrocytes influence neuronal functioning in health and disease.

Extensive Hippocampal Demyelination in Multiple Sclerosis

Memory impairment is especially prominent within the spectrum of cognitive deficits in multiple sclerosis (MS), and a crucial role for hippocampal pathology may therefore be expected in this disease. This study is the first to systematically assess hippocampal demyelination in MS. Hippocampal tissue samples of 19 chronic MS cases and 7 controls with non-neurologic disease were stained immunohistochemically for myelin proteolipid protein. Subsequently, number, location, and size of demyelinated lesions were assessed. Furthermore, the specimens were stained for HLA-DR to investigate microglia/macrophage activity. An unexpectedly high number of lesions (n = 37) was found in 15 of the 19 MS cases. Mixed intrahippocampal-perihippocampal lesions, which were more often found in cases with cognitive decline, were large and did not respect anatomical borders. Moderate microglial activation was frequently observed at the edges of these mixed lesions. Isolated intrahippocampal lesions were also frequently found. These were smaller than the mixed lesions and had a specific anatomical predilection: the cornu ammonis 2 subregion and the hilus of the dentate gyrus were consistently spared. Microglial activation was rare in isolated intrahippocampal lesions. Our results indicate that hippocampal demyelination is frequent and extensive in MS and that anatomical localization, size, and inflammatory activity vary for different lesion types.

Differential localization of the GluR1 and GluR2 subunits of the AMPA-type glutamate receptor among striatal neuron types in rats

Differences among the various striatal projection neuron and interneuron types in cortical input, function, and vulnerability to degenerative insults may be related to differences among them in AMPA-type glutamate receptor abundance and subunit configuration. We therefore used immunolabeling to assess the frequency and abundance of GluR1 and GluR2, the most common AMPA subunits in striatum, in the main striatal neuron types. All neurons projecting to the external pallidum (GPe), internal pallidum (GPi) or substantia nigra, as identified by retrograde labeling, possessed perikaryal GluR2, while GluR1 was more common in striato-GPe than striato-GPi perikarya. The frequency and intensity of immunostaining indicated the rank order of their perikaryal GluR1:GluR2 ratio to be striato-GPe>striatonigral>striato-GPi. Ultrastructural studies suggested a differential localization of GluR1 and GluR2 to striatal projection neuron dendritic spines as well, with GluR1 seemingly more common in striato-GPe spines and GluR2 more common in striato-GPi and/or striatonigral spines. Comparisons among projection neurons and interneurons revealed GluR1 to be most common and abundant in parvalbuminergic interneurons, and GluR2 most common and abundant in projection neurons, with the rank order for the GluR1:GluR2 ratio being parvalbuminergic interneurons>calretinergic interneurons>cholinergic interneurons>projection neurons>somatostatinergic interneurons. Striosomal projection neurons had a higher GluR1:GluR2 ratio than did matrix projection neurons. The abundance of both GluR1 and GluR2 in striatal parvalbuminergic interneurons and projection neurons is consistent with their prominent cortical input and susceptibility to excitotoxic insult, while differences in GluR1:GluR2 ratio among projection neurons are likely to yield differences in Ca(2+) permeability, desensitization, and single channel current, which may contribute to differences among them in plasticity, synaptic integration, and excitotoxic vulnerability. The apparent association of the GluR1 subunit with synaptic plasticity, in particular, suggests striato-GPe neuron spines as a particular site of corticostriatal synaptic plasticity, presumably associated with motor learning.

Differential effects of sublethal ischemia and chemical preconditioning with 3-nitropropionic acid on protein expression in gerbil hippocampus

Pretreatment with a low dose of 3-nitropropionic acid (3-NPA) has been shown to induce ischemic tolerance in the gerbil hippocampus. It is well known that sublethal (2-min) ischemia also induces ischemic tolerance. To investigate the acquisition of ischemic tolerance with 3-NPA, we examined the protein expression after 3-NPA treatment in comparison with sublethal ischemia. Immunohistochemical studies revealed intense expression of Bcl-2 and Bcl-xL in the hippocampal CA1 area after 3-NPA treatment. Furthermore, the time course of the expression of Bcl-xL showed a similar pattern to the acquisition of ischemic tolerance by 3-NPA treatment. The induction of Bcl-xL occurred in the hippocampal CA1 area at 24 h after 3-NPA treatment, and significant induction was observed at 48 h. Western blot analysis of hippocampus harvested 48 h after the pretreatment, showed that the expression of Bcl-2 and Bcl-xL was significantly increased by either 3-NPA treatment or 2-min ischemia. However, PMCA1 and HSP70 protein expression increased only in the sublethal ischemia treated group. The difference between 3-NPA treated group and control group was not statistically significant. These results suggest that Bcl-2 and Bcl-xL are essential for acquisition of ischemic tolerance, while HSP70 and PMCA1 play important roles in the enhancement of ischemic tolerance.

p66ShcA and ageing: modulation by longevity-promoting agent aurintricarboxylic acid

Many mutations that extend the lifespan of the lower organisms such as C. elegans and Drosophila, are associated with signaling or apoptotic pathways. Recently, such a possibility was shown in mammals: p66ShcA-deficient mice were more resistant to oxidative stress and lived longer than the wild-type animals [Migliaccio, E., Giorgio, M., Mele, S., Pelicci, G., Reboldi, P., Randolfi, P.P., Lanfrancone, L., Pelicci, P.G., 1999. The p66Shc adaptor protein controls oxidative stress response and life span in mammals. Nature 402, 309-313]. There is evidence to implicate p66ShcA in age-related degenerative pathology, including atherosclerosis, sarcopenia, and Alzheimer's disease. We hypothesized that a low level expression of p66ShcA could be associated with longevity. Also, we suggested that the level of p66ShcA could be modulated by a putative longevity-promoting agent aurintricarboxylic acid [aurintricarboxylic acid (ATA); Fraifeld, V., Wolfson, M., Sagi, O., Seidman, R., Asraf, H., Utko, N., Muradian, K., 2002. Effects of anti-apoptotic agent aurintricarboxylic acid on longevity and longevity-associated processes. Biogerontology 3, 48]. We have found that: (i) the level of p66ShcA decreases with advanced age. Thirty-six-month-old mice have the lowest, whereas newborns have the highest p66ShcA levels; (ii) ATA significantly decreases the p66ShcA level in mouse lungs. In addition, the lifespan-prolongation effect of ATA in a Drosophila model was further validated. The results support the suggested role for the p66ShcA as one of the lifespan determinants in mammals; p66ShcA therefore represents a potential target for pharmacological longevity-promoting intervention.

Ischemia-induced alterations of AMPA-type glutamate receptor subunit. Expression patterns in the rat retina--an immunocytochemical study

This study investigates whether retinal ischemia/reperfusion leads to alterations in the expression of AMPA-type glutamate receptor (AMPAR) subunits GluR1-4. In ischemia-vulnerable hippocampal neurons, a subunit-specific downregulation of GluR2 precedes the actual neurodegeneration. Our purpose was to study whether retinal ischemia induces a similar downregulation of GluR2 preceding the loss of ganglion and amacrine cells. A 60-min ischemic period was followed by reperfusion lasting between 2 h and 7 days. Changes in the expression patterns of GluR1-4 were assessed using immunocytochemistry. In the same sections, alterations in cell density, thickness of retinal layers, and density of apoptotic cells were investigated. Two-hour post-ischemia, GluR1 immunoreactivity was nearly absent from the inner plexiform layer (IPL). Thereafter, labeling intensity recovered slowly and was close to control levels at 7 days, albeit in a thinner IPL. The decrease in GluR2/3 labeling intensity was most profound at 4 h. The recovery of GluR2/3 staining intensity was slow, and staining was still decreased at 7 days. GluR2 immunoreactivity was not attenuated after ischemia. GluR4 labeling showed a similar time course as observed for GluR1, but the decrease in immunoreactivity was less profound and the recovery was nearly complete. The immunostaining of PKCalpha, a rod bipolar cell marker, was unaffected at all reperfusion times. The reduction of GluR staining preceded both the typical thinning of the IPL and the peak of cell loss, but coincided with a significant swelling of the IPL. In conclusion, retinal ischemia/reperfusion leads to differential changes in the expression of the different AMPA-type GluR subunits, which may affect excitatory synaptic transmission in the inner retina. However, no evidence was found for a preferential loss of GluR2 immunoreactivity that could account for selective neurodegeneration of amacrine and ganglion cells after retinal ischemia.

Ventral root avulsion leads to downregulation of GluR2 subunit in spinal motoneurons in adult rats

It has been observed that motor neuron death is induced in adult rats by ventral root avulsion which involves pulling out the spinal cord root. Since motor neurons are reported to be selectively vulnerable to alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor-mediated injury in vitro, we investigated changes in the expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate-receptor subunits in rat spinal motor neurons after ventral root avulsion. The L4-L5 ventral roots of adult Sprague-Dawley rats were avulsed by an extravertebral extraction procedure. After an appropriate survival time, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate-receptor subunits were detected immunohistochemically in the L4-L5 segments. Ventral root avulsion resulted in a 60% loss of motor neurons by 14 days after surgery. GluR2 labeling in motor neurons was markedly decreased after avulsion, but before the onset of motor neuron death, while the GluR1 and GluR4 labeling of motor neurons remained unchanged. Intrathecal administration of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate-receptor antagonists rescued a significant number of injured motor neurons from cell death. In contrast, N-methyl-D-aspartate-receptor antagonists did not prevent motor neuron death. Since the presence of GluR2 subunit renders heteromeric alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors Ca(2+)-impermeable, the downregulation of GluR2 may result in increased formation of GluR2-lacking, Ca(2+)-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors in motor neurons and could contribute to motor neuron death after ventral root avulsion.

Discovery of diaminobutane derivatives as Ca(2+)-permeable AMPA receptor antagonists

We designed and synthesized a series of the polyamine derivatives as potent Ca(2+)-permeable AMPA receptor antagonists. In the course of this study, we found that the polyamine derivatives exhibited strong hypotensive activity which was undesirable activity for neuroprotective agents. Therefore, we tried to find non-hypotensive antagonists by structural modification of such compounds. Through this derivatization, we obtained the diamine compounds having desired profiles. Especially, compound 8f, which was non-hypotensive and potent Ca(2+)-permeable AMPA receptor antagonist, showed neuroprotective effects in transient global ischemia models in gerbils.

Synthesis of diaminobutane derivatives as potent Ca(2+)-permeable AMPA receptor antagonists

We synthesized diaminobutane derivatives as potent Ca(2+)-permeable AMPA receptor antagonists with non-hypotensive activity. Compound 10c showed selective Ca(2+)-permeable AMPA receptor antagonist activity and neuroprotective effects in transient global ischemia models in gerbils.

The AMPAR subunit GluR2: still front and center-stage

Abnormal influx of Ca(2+) through AMPA-type glutamate receptors (AMPARs) is thought to contribute to the neuronal death associated with a number of brain disorders. AMPARs exist as both Ca(2+)-impermeable and Ca(2+)-permeable channels. AMPARs are encoded by four genes designated GluR1 (GluR-A) through GluR4 (GluR-D). The presence of the GluR2 subunit renders heteromeric AMPA receptor assemblies Ca(2+)-impermeable. Molecular diversity of AMPARs under physiological and pathological conditions is generated by differential spatio-temporal patterns of GluR expression, by alternative RNA splicing and editing and by targeting and trafficking of receptor subunits at dendritic spines. The GluR2 gene is under transcriptional control by the RE1 element specific transcription factor, a gene silencing factor which renders it neuron-specific. GluR2 transcripts are edited by ADAR2 (double-stranded RNA-specific editase 1). AMPAR targeting and trafficking to spines are regulated by synaptic activity and are critical to synaptic plasticity. Recent studies involving animal models of transient forebrain ischemia and epilepsy show that GluR2 mRNA and GluR2 subunit expression are downregulated in vulnerable neurons prior to cell death. Ca(2+) imaging and electrical recording from individual pyramidal neurons in hippocampal slices reveal changes in AMPAR functional properties after ischemia. In slices from post-ischemia animals, CA1 neurons with robust action potentials exhibit greatly enhanced AMPA-elicited rises in intracellular Ca(2+). Excitatory postsynaptic currents in post-ischemic CA1 exhibit an enhanced Ca(2+)-dependent component that appears to be mediated by Ca(2+)-permeable AMPARs. These studies provide evidence for Ca(2+) influx through AMPARs in neurons destined to die. To examine whether acute GluR2 downregulation, even in the absence of a neurological insult, can induce neuronal death, we performed knockdown experiments in rats and gerbils with antisense oligonucleotides targeted to GluR2 mRNA. GluR2 antisense oligonucleotide induced neuronal cell death of pyramidal neurons and enhanced pathogenicity of brief ischemic episodes. These observations provide evidence for Ca(2+) influx through AMPARs in neurons destined to die and implicate Ca(2+)-permeable AMPARs in the pathogenesis of ischemia-induced neuronal death.

NMDA and AMPA/kainate glutamate receptors modulate dentate neurogenesis and CA3 synapsin-I in normal and ischemic hippocampus

The effect of N-methyl-D-aspartate (NMDA) and 2-(aminomethyl)phenylacetic acid/kainate (AMPA/kainate) glutamate receptors on dentate cell proliferation and hippocampal synapsin-I induction was examined after global ischemia. Cell proliferation was assessed using BrdU labeling, and synaptic responses were assessed using synapsin-I expression. Systemic glutamate receptor antagonists (MK-801 and NBQX) increased BrdU-labeled cells in the dentate subgranular zone (SGZ) of control adult gerbils (30% to 90%, P < 0.05). After global ischemia (at 15 days after 10 minutes of ischemia), most CA1 pyramidal neurons died, whereas the numbers of BrdU-labeled cells in the SGZ increased dramatically (>1000%, P < 0.0001). Systemic injections of MK801 or NBQX, as well as intrahippocampal injections of either drug, when given at the time of ischemia completely blocked the birth of cells in the SGZ and the death of CA1 pyramidal neurons at 15 days after ischemia. Glutamate receptor antagonists had little effect on cell birth and death when administered 7 days after ischemia. The induction of synapsin-I protein in stratum moleculare of CA3 at 7 and 15 days after global ischemia was blocked by pretreatment with systemic or intrahippocampal MK-801 or NBQX. It is proposed that decreased dentate glutamate receptor activation--produced by glutamate receptor antagonists in normal animals and by chronic ischemic hippocampal injury--may trigger dentate neurogenesis and synaptogenesis. The synapsin-I induction in mossy fiber terminals most likely represents re-modeling of dentate granule cell neuron presynaptic elements in CA3 in response to the ischemia. The dentate neurogenesis and synaptogenesis that occur after ischemia may contribute to memory recovery after hippocampal injury caused by global ischemia.

Absence of the GluR2 receptor sensitizes mouse sympathetic neurons to nerve growth factor deprivation

Over-activation of glutamate receptors is implicated in neurodegeneration. Using mice with a deletion in the GluR2 gene, we studied the sensitivity of sympathetic neurons to reduced levels of nerve growth factor (NGF), which can cause neuronal cell death. Under standard culture conditions of 50 ng/ml NGF, neurons from the superior cervical ganglion survived and grew equally well compared with wild type controls. However, the subsequent reduction of NGF levels caused significantly poorer survival among mutant neurons by 48 h, at 44+/-13% of control at 10 ng/ml NGF, and dropping further to 14+/-6% at 0.05 ng/ml NGF. These results suggest that the absence of GluR2 impairs the ability of these NGF-sensitive neurons to survive under limiting amounts of this neurotrophic factor.

Aurintricarboxylic acid promotes survival and regeneration of axotomised retinal ganglion cells in vivo

Aurintricarboxylic acid (ATA) has been used as an anti-apoptotic drug to counteract ischemic or cytotoxic injury to neurons. We investigated whether ATA has a neuroprotective effect on axotomized, adult retinal ganglion cells (RGC) as a model for traumatic neuronal cell death. A solution of ATA was injected into the vitreous body of rat eyes whose optic nerves had been cut. In controls, 14% of RGC survived 14 days after axotomy, whereas 44% of RGC survived after a single injection of ATA solution, and 59% survived when the injection was repeated after 7 days. A single injection of ATA 1 day after axotomy rescued 58% of RGC. However, injection of ATA 4 days after axotomy did not influence the survival of RGC, indicating that crucial, irreversible cascades of death are initiated prior to this point in time. The TUNEL technique was used to visualise apoptotic ganglion cells and revealed that 4 days after axotomy their number was significantly less in retinas whose optic nerves were axotomized and treated with ATA, than those of controls. As a consequence of neuroprotection, more RGC were recruited to regenerate into a peripheral nerve graft used to replace the cut optic nerve. In this paradigm, ATA-treated RGC extended significantly more axons within the graft than control RGC. This number could be increased by a second injection of ATA 7 days after axotomy. These data show that ATA is not only able to delay post-traumatic neuronal death but also enhances the extent of axonal regeneration in vivo.

Pharmacology of AMPA/kainate receptor ligands and their therapeutic potential in neurological and psychiatric disorders

It has been postulated, consistent with the ubiquitous presence of glutamatergic neurons in the brain, that defects in glutamatergic neurotransmission are associated with many human neurological and psychiatric disorders. This review evaluates the possible application of ligands acting on glutamate alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and kainate (KA) receptors to minimise the pathology and/or symptoms of various diseases. Glutamate activation of AMPA receptors is thought to mediate most fast synaptic neurotransmission in the brain, while transmission via KA receptors contributes only a minor component. Variants of the protein subunits forming these receptors greatly extend the pharmacological and electrophysiological properties of AMPA/KA receptors. Disease and drug use can differentially affect the expression of the subunits and their variants. Ligands bind to AMPA receptors by competing with glutamate at the glutamate binding site, or non-competitively at other sites on the proteins (allosteric modulators). Ligands showing selective competitive antagonist actions at the AMPA/ KA class of glutamate receptors were first reported in 1988, and the systemically active antagonist 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (NBQX) was first shown to have useful therapeutic effects on animal models of neurological diseases in 1990. Since then, newer antagonists with increased potency, higher specificity, increased water solubility, and a longer duration of action in vivo have been developed. Negative allosteric modulators such as the prototype GYKI-52466 also block AMPA receptors but have little action at KA receptors. Positive allosteric modulators enhance glutamatergic neurotransmission at AMPA receptors. Polyamines and adamantane derivatives bind within the ion channel of calcium-permeable AMPA receptors. The latest developments include ligands selective for KA receptors containing Glu-R5 subunits. Evidence for advantages of AMPA receptor antagonists over N-methyl-D-aspartate (NMDA) receptor antagonists for symptomatic treatment of neurological and psychiatric conditions, and for minimising neuronal loss occurring after acute neurological diseases, such as physical trauma, ischaemia or status epilepticus, have been shown in animal models. However, as yet AMPA receptor antagonists have not been shown to be effective in clinical trials. On the other hand, a limited number of clinical trials have been reported for AMPA receptor ligands that enhance glutamatergic neurotransmission by extending the ion channel opening time (positive allosteric modulators). These acute studies demonstrate enhanced memory capability in both young and aged humans, without any apparent serious adverse effects. The use of these allosteric modulators as antipsychotic drugs is also possible. However, the long term use of both direct agonists and positive allosteric modulators must be approached with considerable caution because of potential adverse effects.

Role of endogenous endonucleases and tissue site in transfection and CpG-mediated immune activation after naked DNA injection

DNA degradation is a fundamental problem for any gene therapy or genetic immunization approach, since destruction of incoming genes translates into loss of gene expression. To characterize the biology of DNA degradation after naked DNA injection, the location and levels of tissue nucleases were assessed. Extracts from the serum, kidney, and liver of mice had high levels of calcium-dependent endonuclease activity. High levels of acidic endonuclease activity were identified in the spleen, liver, kidney, and skin with little activity in skeletal or cardiac muscle. Relatively little exonuclease activity was observed in any tissue. The presence of endonucleases in the skin and muscle mediated degradation of 99% of naked DNA within 90 min of injection. This degradation most likely occurred in the extracellular space upstream of other cellular events. Despite this massive destruction, gross tissue nuclease levels did not determine skin-to-muscle transfection efficiency, or site-to-site transfection efficiency in the skin. While gross tissue nuclease levels do not appear to determine differences in transfection efficiency, the presence of robust tissue nuclease activity still necessitates that massive amounts of DNA be used to overcome the loss of 99% of expressible DNA. In addition to destroying genes, the nucleases may play a second role in genetic immunization by converting large plasmids into small oligonucleotides that can be taken up more easily by immune cells to stimulate CpG-dependent Th1 immune responses. For genetic immunization, vaccine outcome may depend on striking the right balance of nuclease effects to allow survival of sufficient DNA to express the antigen, while concomitantly generating sufficient amounts of immunostimulatory DNA fragments to drive Th1 booster effects. For gene therapy, all nuclease effects would appear to be negative, since these enzymes destroy gene expression while also stimulating cellular immune responses against transgene-modified host cells.

NMDA and non-NMDA receptor-mediated excitotoxicity are potentiated in cultured striatal neurons by prior chronic depolarization

The excitatory input from cortex and/or thalamus to striatum appears to promote the maturation of glutamate receptors on striatal neurons, but the mechanisms by which it does so have been uncertain. To explore the possibility that the excitatory input to striatum might influence glutamate receptor maturation on striatal neurons, at least in part, by its depolarizing effect on striatal neurons, we examined the influence of chronic KCl depolarization on the development of glutamate receptor-mediated excitotoxic vulnerability and glutamate receptors in cultured striatal neurons. Dissociated striatal neurons from E17 rat embryos were cultured for 2 weeks in Barrett's medium containing either low (3 mM) or high (25 mM) KCl. The vulnerability of these neurons to NMDA receptor agonists (NMDA and quinolinic acid), non-NMDA receptor agonists (AMPA and KA), and a metabotropic glutamate receptor agonist (trans-ACPD) was examined by monitoring cell loss 24 h after a 1-h agonist exposure. We found that high-KCl rearing potentiated the cell loss observed with 500 microM NMDA or 250 microM KA and yielded cell loss with 250 microM AMPA that was not evident under low KCl rearing. In contrast, neither QA up to 5 mM nor trans-ACPD had a significant toxic effect in either KCl group. ELISA revealed that chronic high KCl doubled the abundance of NMDA NR2A/B, AMPA GluR2/3, and KA GluR5-7 receptor subunits on cultured striatal neurons and more than doubled AMPA GluR1 and GluR4 subunits, but had no effect on NMDA NR1 subunit levels. These receptor changes may contribute to the potentiation of NMDA and non-NMDA receptor-mediated excitotoxicity shown by these neurons following chronic high-KCl rearing. Our studies suggest that membrane depolarization produced by corticostriatal and/or thalamostriatal innervation may be required for maturation of glutamate receptors on striatal neurons, and such maturation may be important for expression of NMDA and non-NMDA receptor-mediated excitotoxicity by striatal neurons. Striatal cultures raised under chronically depolarized conditions may, thus, provide a more appropriate culture model to study the role of NMDA or non-NMDA receptor subtypes in excitotoxicity in striatum.

Alterations in AMPA receptor subunit expression after experimental spinal cord contusion injury

The AMPA-preferring subtype of ionotropic glutamate receptors (GluRs) is a hetero-oligomeric ion channel assembled from various combinations of four subunits: GluR1, GluR2, GluR3, and GluR4. Antagonists of these receptors can mitigate the effects of experimental spinal cord injury (SCI), indicating that these receptors play a significant role in pathophysiology after spinal trauma. We tested the hypothesis that SCI alters expression of AMPA receptors using a standardized thoracic weight-drop model of rat contusive spinal cord injury. AMPA receptor subunit expression was measured at 24 hr and at 1 month after SCI with quantitative Western blot analysis and in situ hybridization. GluR2 protein levels were preferentially reduced near the injury site 24 hr after SCI. This reduction persisted at 1 month. At a cellular level, a significant decrease in both GluR2 and GluR4 mRNA was found in spared ventral motor neurons adjacent to the injury site and distal to it, with other AMPA subunit mRNAs maintained at control levels. In contrast, only GluR1 mRNA was decreased in the sympathetic preganglionic neurons of the intermediolateral horn. These results suggest population-specific and long-lasting changes in neuronal AMPA receptor composition, which may alter response to glutamate after SCI. These alterations may contribute not only to acute neuropathological consequences of injury, but they may also be partially responsible for the altered functional state of preserved tissue seen chronically after SCI.

Alterations in AMPA receptor subunit expression after experimental spinal cord contusion injury

The AMPA-preferring subtype of ionotropic glutamate receptors (GluRs) is a hetero-oligomeric ion channel assembled from various combinations of four subunits: GluR1, GluR2, GluR3, and GluR4. Antagonists of these receptors can mitigate the effects of experimental spinal cord injury (SCI), indicating that these receptors play a significant role in pathophysiology after spinal trauma. We tested the hypothesis that SCI alters expression of AMPA receptors using a standardized thoracic weight-drop model of rat contusive spinal cord injury. AMPA receptor subunit expression was measured at 24 hr and at 1 month after SCI with quantitative Western blot analysis and in situ hybridization. GluR2 protein levels were preferentially reduced near the injury site 24 hr after SCI. This reduction persisted at 1 month. At a cellular level, a significant decrease in both GluR2 and GluR4 mRNA was found in spared ventral motor neurons adjacent to the injury site and distal to it, with other AMPA subunit mRNAs maintained at control levels. In contrast, only GluR1 mRNA was decreased in the sympathetic preganglionic neurons of the intermediolateral horn. These results suggest population-specific and long-lasting changes in neuronal AMPA receptor composition, which may alter response to glutamate after SCI. These alterations may contribute not only to acute neuropathological consequences of injury, but they may also be partially responsible for the altered functional state of preserved tissue seen chronically after SCI.