Journal of Neurochemistry

Teng, Felicia Y. H.; Ling, Belinda M. T.; Tang, Bor Luen

doi: 10.1111/j.1471-4159.2004.02366.xpmid: 15140179

The molecule Nogo has captured the imagination of many as a possible key player, and therefore therapeutic target, in the pathological settings of central nervous system (CNS) injury and degenerative pathology. Found in both glial cells and neurons, the endogenous, physiological role of Nogo is as yet unknown. Recently reported targeted disruption of the Nogo gene did not result in any obvious neuro‐anatomical or neurological phenotype. Compared with wild‐type mice, Nogo‐deficient mice also did not exhibit a truly convincing enhancement in their ability to regenerate CNS neurons upon injury. Does the molecule have any important physiological function at all? Other recent discoveries of new interacting partners of Nogo at the mitochondria and the CNS paranode suggest intriguing links to the modulation of apoptosis and developmental organization or signalling at the axoglial junction.

Zlokovic, Berislav V.

doi: 10.1111/j.1471-4159.2004.02385.xpmid: 15140180

According to the amyloid hypothesis, accumulation of amyloid β‐peptide (Aβ) in the brain is the primary pathogenic event in Alzheimer's disease (AD). Recent evidence indicates that Aβ within the intravascular space is linked to Aβ deposited in the brain suggesting that transport of Aβ between the brain, blood and cerebrospinal fluid, and across the blood–brain barrier, regulates brain Aβ. Thus, understanding Aβ exchanges between brain and blood, and vice versa, and developing transport‐based systemic Aβ‐lowering strategies may provide new important insights into pathogenesis and therapeutic control of AD.

Yung, Hong Wa; Bal‐Price, Anna K.; Brown, Guy C.; Tolkovsky, Aviva M.

doi: 10.1111/j.1471-4159.2004.02395.xpmid: 15140181

We have investigated the mechanism by which nitric oxide (NO) induces the death of mouse astrocytes. We show that NO (from donor diethylenetriamine‐NO adduct) induces death with several features of apoptosis, including chromatin condensation, phosphatidylserine exposure on the outer leaflet of the plasma membrane, Bax translocation to the mitochondria and cytochrome c release, but no caspase activation or nuclear fragmentation is observed. Nitric oxide also elevates p53 expression, causing a concomitant increase in p53 serine 18 phosphorylation and p53 translocation from the cytoplasm to the nucleus. Activation of Bax and p53 is important for NO‐induced apoptosis‐like cell death because Bax‐ or p53‐deficient astrocytes are much more resistant than wild‐type cells to the same NO treatment. We further demonstrate that LY294002‐sensitive kinases are responsible for controlling serine 18 phosphorylation of p53, thereby regulating the pro‐apoptotic activity of p53 in astrocytes. While apoptosis is suppressed in the presence of LY294002, however, death by necrosis is increased, suggesting that LY294002‐sensitive kinases additionally suppress a latent necrotic response to NO. We conclude that NO‐induced death in astrocytes is mediated by p53‐ and Bax‐dependent mechanisms, although full manifestation of apoptosis is aborted by concomitant inhibition of caspase activation. More generally, our data suggest that apoptotic mediators should be evaluated as the cause of cell death even in cases where a full apoptotic phenotype is lacking.

Ferger, Boris; Leng, Andreas; Mura, Anna; Hengerer, Bastian; Feldon, Joram

doi: 10.1111/j.1471-4159.2004.02399.xpmid: 15140182

The impact of pro‐inflammatory cytokines such as tumor necrosis factor‐α (TNF‐α) in the pathology of Parkinson's disease (PD) and in MPTP neurotoxicity remains unclear. Here, male TNF‐α (–/–) deficient mice and C57bL/6 mice were treated with MPTP (4 × 15mg/kg, 24 h intervals) and in one series, thalidomide was administered to inhibit TNF‐α synthesis. Real‐time RT‐PCR revealed that the striatal mRNA levels of TNF‐α, of the astrocytic marker glial fibrillary acidic protein (GFAP) and of the marker for activated microglia, macrophage antigen complex‐1 (MAC‐1), were significantly enhanced after MPTP administration. Thalidomide (50 mg/kg, p.o.) partly protected against the MPTP‐induced dopamine (DA) depletion, and TNF‐α (–/–) mice showed a significant attenuation of striatal DA and DA metabolite loss as well as striatal tyrosine hydroxylase (TH) fiber density, but no difference in nigral TH and DA transporter immunoreactivity. TNF‐α deficient mice suffered a lower mortality (10%) compared to the high mortality (75%) seen in wild‐type mice after acute MPTP treatment (4 × 20mg/kg, 2 h interval). HPLC measurement of MPP+ levels revealed no differences in TNF‐α (–/–), wild‐type and thalidomide treated mice. This study demonstrates that TNF‐α is involved in MPTP toxicity and that inhibition of TNF‐α response may be a promising target for extending beyond symptomatic treatment and developing anti‐parkinsonian drugs for the treatment of the inflammatory processes in PD.

Clinckers, Ralph; Smolders, Ilse; Meurs, Alfred; Ebinger, Guy; Michotte, Yvette

doi: 10.1111/j.1471-4159.2004.02355.xpmid: 15140183

The present microdialysis study evaluated the anticonvulsant activity of extracellular hippocampal dopamine (DA) and serotonin (5‐HT) with concomitant assessment of the possible mutual interactions between these monoamines. The anticonvulsant effects of intrahippocampally applied DA and 5‐HT concentrations were evaluated against pilocarpine‐induced seizures in conscious rats. DA or 5‐HT perfusions protected the rats from limbic seizures as long as extracellular DA or 5‐HT concentrations ranged, respectively, between 70–400% and 80–350% increases compared with the baseline levels. Co‐perfusion with the selective D2 blocker remoxipride or the selective 5‐HT1A blocker WAY‐100635 clearly abolished all anticonvulsant effects. These anticonvulsant effects were mediated independently since no mutual 5‐HT and DA interactions were observed as long as extracellular DA and 5‐HT levels remained within these protective ranges. Simultaneous D2 and 5‐HT1A receptor blockade significantly aggravated pilocarpine‐induced seizures. High extracellular DA (> 1000% increases) or 5‐HT (> 900% increases) concentrations also worsened seizure outcome. The latter proconvulsive effects were associated with significant increases in extracellular glutamate (Glu) and mutual increases in extracellular monoamines. Our results suggest that, within a certain concentration range, DA and 5‐HT contribute independently to the prevention of hippocampal epileptogenesis via, respectively, D2 and 5‐HT1A receptor activation.

Zheng, Wen‐Hua; Quirion, Rémi

doi: 10.1111/j.1471-4159.2004.02350.xpmid: 15140184

Insulin‐like growth factor‐1 (IGF‐1) and brain‐derived neurotrophic factor (BDNF) are trophic factors required for the viability and normal functions of various neuronal cells. However, the detailed intracellular mechanism(s) involved in these effects in neuronal cells remains to be fully elucidated. In present study, the respective intracellular signaling pathway induced by IGF‐1 and BDNF and their possible role in neuronal survival were investigated. Both IGF‐1 and BDNF protected hippocampal neurons from serum deprivation‐induced death with IGF‐1 apparently being more potent. Western blot analyses showed that both IGF‐1 and BDNF induced the activation of the phosphatidylinositide 3 kinase (PI3)/Akt (protein kinase B) kinase and the mitogen‐activated protein kinase (MAPK) pathways. The phosphorylation of Akt and its downstream target, FKHRL1, induced by IGF‐1 was rapid and sustained while that of MAPK was transient. The reverse situation was observed for BDNF. Moreover, IGF‐1 potently induced the tyrosine phosphorylation of insulin receptor substrate‐1 (IRS‐1) and its association with PI3 kinase while BDNF was weak in these assays. In contrast, the tyrosine phosphorylation of Shc proteins was dramatically stimulated by BDNF, with IGF‐1 having only a minimal effect. Most interestingly, only the inhibitor of the PI3K/Akt pathway, LY294002, was able to block the survival effects of both IGF‐1 and BDNF; an inhibitor of the MAPK pathway inhibitor, PD98059, being ineffective. Taken together, these data reveal that the survival properties of both IGF‐1 and BDNF against serum deprivation are mediated by the activation of the PI3K/Akt, but not the MAPK, pathway in hippocampal neurons.

Chen, Nianhang; Zhen, Juan; Reith, Maarten E. A.

doi: 10.1111/j.1471-4159.2004.02386.xpmid: 15140185

The different psychomotor‐stimulant effects of cocaine, GBR12909, and benztropine may partially stem from their different molecular actions on the dopamine transporter (DAT). To explore this possibility, we examined binding of these inhibitors to mutated DATs with altered Na+ dependence of DAT activities and with enhanced binding of a cocaine analog, [3H]2β‐carbomethoxy‐3β‐(4‐fluorophenyl)tropane (CFT). In [3H]CFT competition assays with intact cells, the mutation‐induced change in the ability of Na+ to enhance the apparent affinity of CFT, cocaine, GBR12909, and benztropine was inhibitor‐independent. Thus, for the four inhibitors, the curve of [Na+] versus apparent ligand affinity was steeper at W84L compared with wild type, shallower at D313N, and flat at W84LD313N. At each mutant, the apparent affinity of CFT and cocaine was enhanced regardless of whether Na+ was present. However, the apparent affinity of GBR12909 and benztropine for W84L was reduced in the absence of Na+ but near normal in the presence of 130 mm Na+, and that for D313N and W84LD313N was barely changed. At the single mutants, the alterations in Na+ dependence and apparent affinity of the four inhibitors were comparable between [3H]CFT competition assays and [3H]dopamine uptake inhibition assays. These results demonstrate that DAT inhibitors producing different behavioral profiles can respond in an opposite way when residues of the DAT protein are mutated. For GBR12909 and benztropine, their cocaine‐like changes in Na+ dependence suggest that they prefer a DAT state similar to that for cocaine. However, their cocaine‐unlike changes in apparent affinity argue that they, likely via their diphenylmethoxy moiety, share DAT binding epitopes that are different from those for cocaine.

Jiménez, C. R.; Ter Maat, A.; Pieneman, A.; Burlingame, A. L.; Smit, A. B.; Li, K. W.

doi: 10.1111/j.1471-4159.2004.02353.xpmid: 15140186

The activity‐dependent release of peptides from the neuro‐endocrine caudodorsal cell (CDC) system of the freshwater snail Lymnaea stagnalis regulates egg laying and related behaviors. In this study, we optimized a mass spectrometry‐based approach to study the spatio‐temporal dynamics of peptides that are largely derived from the CDC hormone precursor during an egg‐laying cycle and a CDC discharge in vitro. Semi‐quantitative peptide mass profiling using matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) indicated a massive depletion of peptides from the neurohemal area in the cerebral commissure (COM) during egg laying and the existence of a reserve pool of peptides in the CDC somata that were transported to the COM to restore peptide levels. The depletion of CDC peptides from the COM was correlated to their release during an induced electrical discharge in vitro. Moreover, MALDI‐MS of the releasate revealed extensive truncation of the carboxyl terminal peptide. Finally, two novel peptides of 1788 and 5895 Da, not encoded by the CDC hormone precursor, also exhibited temporal quantitative changes similar to those of CDC peptides. Sequencing of the peptide of 1788 Da by tandem mass spectrometry yielded the novel sequence HF(FH)FYGPYDVFQRDVamide. Together, this implicates a more complex set of CDC peptides for the regulation of egg laying than previously anticipated.

Olszewski, Rafal T.; Bukhari, Noreen; Zhou, Jia; Kozikowski, Alan P.; Wroblewski, Jarda T.; Shamimi‐Noori, Susan; Wroblewska, Barbara; Bzdega, Tomasz; Vicini, Stefano; Barton, Franca B.; Neale, Joseph H.

doi: 10.1111/j.1471-4159.2004.02358.x

La Cour, Clotilde Mannoury; Hanoun, Naïma; Melfort, Maxette; Hen, René; Lesch, Klaus‐Peter; Hamon, Michel; Lanfumey, Laurence

doi: 10.1111/j.1471-4159.2004.02367.xpmid: 15140188

The functional properties of GABAB receptors were examined in the dorsal raphe nucleus (DRN) and the hippocampus of knock‐out mice devoid of the 5‐HT transporter (5‐HTT–/–) or the 5‐HT1A receptor (5‐HT1A–/–). Electrophysiological recordings in brain slices showed that the GABAB receptor agonist baclofen caused a lower hyperpolarization and neuronal firing inhibition of DRN 5‐HT cells in 5‐HTT–/– versus 5‐HTT+/+ mice. In addition, [35S]GTP‐γ‐S binding induced by GABAB receptor stimulation in the DRN was approximately 40% less in these mutants compared with wild‐type mice. In contrast, GABAB receptors appeared functionally intact in the hippocampus of 5‐HTT–/–, and in both this area and the DRN of 5‐HT1A‐knock‐out mice. The unique functional changes of DRN GABAB receptors closely resembled those of 5‐HT1A autoreceptors in 5‐HTT–/– mice, further supporting the idea that both receptor types are coupled to a common pool of G‐proteins in serotoninergic neurons.