Johan Zelano

Dorsal root ganglion neurons up-regulate the expression of laminin-associated integrins after peripheral but not central axotomy.

The favorable prognosis of regeneration in the peripheral nervous system after axonal lesions is generally regarded as dependent on the Schwann cell basal lamina. Laminins, a heterotrimeric group of basal lamina molecules, have been suggested to be among the factors playing this supportive role. For neurons to utilize laminin as a substrate for growth, an expression of laminin binding receptors, integrins, is necessary. In this study, we have examined the expression of laminin binding integrin subunits in dorsal root ganglion (DRG) neurons after transection to either their peripherally projecting axons, as in the sciatic nerve, followed by regeneration, or the centrally projecting axons in dorsal roots, followed by no or weak regenerative activity. In uninjured DRG, immunohistochemical staining revealed a few neurons expressing integrin subunit α6, whereas integrin subunits α7 and foremost β1 were expressed in a majority of neurons. After an injury to the sciatic nerve, mRNAs encoding all three integrins were up‐regulated in DRG neurons. By anterograde tracing, immunoreactivity for all studied integrins was also found in association with growing axons after a sciatic nerve crush lesion in vivo. In contrast, mRNA levels remained constant in DRG neurons after a dorsal root injury. Together with previous findings, this suggests that integrin subunits α6, α7, and β1 have an important role in the regenerative response following nerve injury and that the lack of regenerative capacity following dorsal root injury could in part be explained by the absence of response in integrin regulation. J. Comp. Neurol. 480:162–169, 2004.

Levetiracetam as alternative stage two antiepileptic drug in status epilepticus : A systematic review

BACKGROUND The role of new antiepileptic drugs (AED) in the treatment of status epilepticus (SE) is of interest, especially in benzodiazepine-resistant status epilepticus where phenytoin is deemed inappropriate due to allergy or comorbidity. Levetiracetam (LEV) is a new AED with few side effects. It is easy to administer. Reports exist of its use in SE in adults. AIMS To clarify the evidence for use of LEV as an alternative stage two AED in treatment of SE by a systematic review of the literature. METHOD An online MEDLINE search identified 118 articles. The abstracts were screened for studies written in English, in which (1) at least two adults had been treated, and (2) LEV had been administered intravenously as the first AED, on its own or together with benzodiazepines. Ten studies were included. RESULTS Out of the ten studies, seven were retrospective observational, two prospective observational, and one prospective randomized. The studies described a total of 334 patients. The most common reason for administrating LEV was that standard treatment was deemed inappropriate. The efficacy ranged from 44% to 94%, with higher efficacy reported in the retrospective studies. CONCLUSIONS The evidence for use of LEV as an alternative stage two AED in SE is limited. The higher efficacy reported in retrospective studies indicates possible publication bias, and caution is advised when the results of these retrospective studies are considered in clinical decision-making.

Reduced removal of synaptic terminals from axotomized spinal motoneurons in the absence of complement C3

Complement proteins C1q and C3 play a critical role in synaptic elimination during development. Axotomy of spinal motoneurons triggers removal of synaptic terminals from the cell surface of motoneurons by largely unknown mechanisms. We therefore hypothesized that the complement system is involved also in synaptic stripping of injured motoneurons. In the sciatic motor pool of wild type (WT) mice, the immunoreactivity (IR) for both C1q and C3 was increased after sciatic nerve transection (SNT). Mice deficient in C3 (C3(-/-)) showed a reduced loss of synaptic terminals from injured motoneurons at one week after SNT, as assessed by immunoreactivity for synaptic markers and electron microscopy. In particular, the removal of putative inhibitory terminals, immunopositive for vesicular inhibitory amino acid transporter (VIAAT) and ultrastructurally identified as type F synapses, was reduced in C3(-/-) mice. In contrast, lesion-induced removal of nerve terminals in C1q(-/-) mice appeared similar to WT mice. Growth associated protein (GAP)-43 mRNA expression in lesioned motoneurons increased much more in C3(-/-) compared to WT mice after SNT. After sciatic nerve crush (SNC), the C3(-/-) mice showed a faster functional recovery, assessed as grip strength, compared to WT mice. No differences were detected regarding nerve inflammation at the site of injury or pattern of muscle reinnervation. These data indicate that a non-classical pathway of complement activation is involved in axotomy-induced adult synapse removal, and that its inhibition promotes functional recovery.

SynCAM1 expression correlates with restoration of central synapses on spinal motoneurons after two different models of peripheral nerve injury

SynCAM1 and neuroligins (NLGs) are adhesion molecules that govern synapse formation in vitro. In vivo, the molecules are expressed during synaptogenesis, and altered NLG function is linked to synapse dysfunction in autism. Less is known about SynCAM1 and NLGs in adult synapse remodeling. CNS synapse elimination occurs after peripheral nerve injury, which causes a transient decrease in synapse number on spinal motoneurons. Here we have studied the expression of SynCAM1 and NLGs in relation to changes in synaptic covering on spinal motoneurons. We performed sciatic nerve transection (SNT) or crush (SNC), axotomy models that result in poor or good conditions for axon regeneration, respectively. The two lesions resulted in similar synapse elimination and in poor (SNT) and good (SNC) return of synapses after 70 days. Functional recovery was good after SNC but absent after SNT. SynCAM1 mRNA decreased after 14 days in both models and was restored 70 days after SNC, but not after SNT. NLG2 and ‐3 mRNAs decreased to a smaller degree after SNC than after SNT. Synaptophysin immunoreactivity correlated with SynCAM1 mRNA 70 days after SNT and NLG2 mRNA 70 days after SNC. Surprisingly, an inverse correlation was seen between NLG3 mRNA and Vglut2, a marker for excitatory synapses, 70 days after SNT. We conclude that 1) SynCAM1 mRNA levels seem to reflect the loss and restoration of synapses on motoneurons, 2) down‐regulation of NLGs is not a prerequisite for synapse elimination, and 3) expression of SynCAM1 and NLGs is regulated by different mechanisms during regeneration. J. Comp. Neurol. 517:670–682, 2009.

Axonal regeneration after sciatic nerve lesion is delayed but complete in GFAP- and vimentin-deficient mice.

Peripheral axotomy of motoneurons triggers Wallerian degeneration of injured axons distal to the lesion, followed by axon regeneration. Centrally, axotomy induces loss of synapses (synaptic stripping) from the surface of lesioned motoneurons in the spinal cord. At the lesion site, reactive Schwann cells provide trophic support and guidance for outgrowing axons. The mechanisms of synaptic stripping remain elusive, but reactive astrocytes and microglia appear to be important in this process. We studied axonal regeneration and synaptic stripping of motoneurons after a sciatic nerve lesion in mice lacking the intermediate filament (nanofilament) proteins glial fibrillary acidic protein (GFAP) and vimentin, which are upregulated in reactive astrocytes and Schwann cells. Seven days after sciatic nerve transection, ultrastructural analysis of synaptic density on the somata of injured motoneurons revealed more remaining boutons covering injured somata in GFAP–/–Vim–/– mice. After sciatic nerve crush in GFAP–/–Vim–/– mice, the fraction of reinnervated motor endplates on muscle fibers of the gastrocnemius muscle was reduced 13 days after the injury, and axonal regeneration and functional recovery were delayed but complete. Thus, the absence of GFAP and vimentin in glial cells does not seem to affect the outcome after peripheral motoneuron injury but may have an important effect on the response dynamics.

Down-regulation of mRNAs for synaptic adhesion molecules neuroligin-2 and -3 and synCAM1 in spinal motoneurons after axotomy

After peripheral axotomy, synapses are eliminated from the somata of spinal motoneurons. Recent evidence indicates that synaptic adhesion molecules play a role in maintenance of synaptic contacts, but so far such molecules have not been investigated in the context of synapse elimination after injury. In vitro, the neuroligins (NLGs) and SynCAM1 drive formation of synapses, and RNAi of NLGs results in decreased synaptic input, indicating an important role for these molecules in synaptic biology. To address potential involvement of NLGs and SynCAMs in postinjury synapse elimination, we investigated the mRNA expression of NLG1, ‐2, and ‐3; SynCAM1 and ‐3; and PSD‐95—an intracellular NLG‐binding scaffolding protein—in rat spinal motoneurons in control animals and after sciatic nerve transection (SNT). mRNA signals for NLG2, NLG3, SynCAM1, and SynCAM3, but not NLG1, were seen in uninjured motoneurons. Immunoreactivity for SynCAM was seen in close relation to synaptophysin immunoreactivity on the surface of motoneurons and in close relation to neurofilament immunoreactivity in the sciatic nerve. After axotomy, the signals for NLG2, NLG3, and SynCAM1 mRNAs decreased, whereas the signal for NLG1 mRNA remained undetectable and that for SynCAM3 remained at control levels. The signal for PSD‐95 mRNA decreased gradually and reached approximately 50% of control values 2 weeks after axotomy. Thus the retrograde response to axotomy of spinal motoneurons involves a rapid down‐regulation of NLG2, NLG3, and SynCAM1 mRNAs and a gradual decrease in PSD‐95 mRNA. This indicates that down‐regulation of synaptic adhesion molecules plays a role in postinjury synapse elimination. J. Comp. Neurol. 503:308–318, 2007.

Expression of nectin-1, nectin-3, N-cadherin, and NCAM in spinal motoneurons after sciatic nerve transection.

We here study the expression patterns of the cell adhesion molecules nectin-1, nectin-3, N-cadherin, and neural cell adhesion molecule (NCAM) in motoneurons after sciatic nerve transection (SNT). Nectins are a newly discovered family of adhesion molecules that colocalize with N-cadherin in synapses and are expressed in axons during development. By in situ hybridization (ISH), we found nectin-3, N-cadherin, and NCAM mRNA in uninjured motoneurons. In uninjured animals, nectin-3 mRNA was present in a few vesicular acetylcholine transporter (VAChT)-positive cells of small motoneuron size in lamina IX of the spinal cord. SNT induced a significant increase of nectin-1, nectin-3, and NCAM mRNA, but the signal for N-cadherin mRNA was not affected. After SNT, signal for nectin-3 mRNA appeared over most motoneurons. We next investigated the presence of N-cadherin and nectin protein in synapses on spinal motoneurons by immunohistochemistry. Only N-cadherin immunoreactivity was seen in close relation to synaptophysin staining, while nectin-1 and nectin-3 immunoreactivity did not display such proximity. SNT resulted in decreased immunoreactivity for N-cadherin around the motoneuron soma, while nectin-1 and nectin-3 immunoreactivity remained unchanged. In the peripheral sciatic nerve, nectin-3 immunoreactivity was observed both in controls and following injury and nectin-3 colocalized with both neurofilament and the Schwann cell marker S100. In addition, an increased ISH signal for nectin-3 mRNA could be seen over the proximal stump of the sciatic nerve after SNT. We conclude that motoneuron injury induces complex changes in the spatiotemporal expression pattern of the investigated cell adhesion molecules.

Clinical course of poststroke epilepsy: a retrospective nested case–control study

Recently, several epidemiological studies have demonstrated that epilepsy develops after approximately 10% of all cerebrovascular lesions. With an aging population, poststroke epilepsy is likely to be of increasing relevance to neurologists and more knowledge on the condition is needed. Patients with poststroke epilepsy are likely to differ from other epilepsy patient populations regarding age, side‐effect tolerability, comorbidities, and life expectancy, all of which are important aspects when counselling newly diagnosed patients to make informed treatment decisions.

The synaptic protein encoded by the gene Slc10A4 suppresses epileptiform activity and regulates sensitivity to cholinergic chemoconvulsants

The expanding number of disease-causing dysfunctions of synaptic proteins illustrates the importance of investigating newly discovered proteins involved in neuronal transmission. The gene Slc10A4 encodes a recently described carrier protein present in pre-synaptic terminals of cholinergic and monoaminergic neurons. The biological significance of this recently described transporter protein is currently unknown. We here investigated whether absence of the Slc10a4 protein has any impact on function of the cholinergic system. We first investigated the sensitivity of Slc10a4 null mice to cholinergic stimulus in vitro. In contrast to wild type mice, gamma oscillations occurred spontaneously in hippocampal slices from Slc10a4 null mice. Furthermore, moderate treatment of Slc10a4 null slices with the cholinergic agonist carbachol induced epileptiform activity. In vivo, 3-channel EEG measurements in freely behaving mice revealed that Slc10a4 null mice had frequent epileptiform spike-activity before treatment, and developed epileptic seizures, detected by EEG and accompanied by observable behavioral components, more rapidly after injection of the cholinergic agonist pilocarpine. Similar results were obtained on non-operated mice, as evaluated by behavioral seizures and post mortem c-Fos immunohistochemistry. Importantly, Slc10a4 null mice and wild type control mice were equally sensitive to the glutamatergic chemoconvulsant kainic acid, demonstrating that absence of Slc10a4 led to a selective cholinergic hypersensitivity. In summary, we report that absence of the recently discovered synaptic vesicle protein Slc10a4 results in increased sensitivity to cholinergic stimulation.

The Extent of Synaptic Stripping of Motoneurons after Axotomy Is Not Correlated to Activation of Surrounding Glia or Downregulation of Postsynaptic Adhesion Molecules

Synapse elimination in the adult central nervous system can be modelled by axotomy of spinal motoneurons which triggers removal of synapses from the cell surface of lesioned motoneurons by processes that remain elusive. Proposed candidate mechanisms are removal of synapses by reactive microglia and astrocytes, based on the remarkable activation of these cell types in the vicinity of motoneurons following axon lesion, and/or decreased expression of synaptic adhesion molecules in lesioned motoneurons. In the present study, we investigated glia activation and adhesion molecule expression in motoneurons in two mouse strains with deviant patterns of synapse elimination following axotomy. Mice deficient in complement protein C3 display a markedly reduced loss of synapses from axotomized motoneurons, whereas mice with impaired function of major histocompatibility complex (MHC) class Ia display an augmented degree of stripping after axotomy. Activation of microglia and astrocytes was assessed by semiquantative immunohistochemistry for Iba 1 (microglia) and GFAP (astrocytes), while expression of synaptic adhesion molecules was determined by in situ hybridization. In spite of the fact that the two mouse strains display very different degrees of synapse elimination, no differences in terms of glial activation or in the downregulation of the studied adhesion molecules (SynCAM1, neuroligin-2,-3 and netrin G-2 ligand) could be detected. We conclude that neither glia activation nor downregulation of synaptic adhesion molecules are correlated to the different extent of the synaptic stripping in the two studied strains. Instead the magnitude of the stripping event is most likely a consequence of a precise molecular signaling, which at least in part is mediated by immune molecules.