Effect of prolonged riluzole exposure on cultured motoneurons in a mouse model of ALS

Riluzole is the only FDA-approved drug to treat amyotrophic lateral sclerosis, but its long-term effects on motoneurons are unknown. Therefore, we treated primary mouse spinal cord cultures with 2 μM riluzole for 4-9 days and then used whole cell patch clamp to record the passive and active properties of both wild-type and SOD1(G93A) motoneurons. At this concentration, riluzole blocks >50% of the sodium component of a persistent inward current that plays a major role in determining motoneuron excitability. Prolonged riluzole treatment significantly decreased the amplitude of the persistent inward current. This effect was specific for SOD1(G93A) motoneurons, where the amplitude decreased by 55.4%. In addition, prolonged treatment hyperpolarized the resting membrane potential as well as the voltage onset and voltage maximum of the persistent inward current (∼2-3 mV in each case). These effects appeared to offset one another and resulted in no change in the firing properties. In a subset of cells, acute reapplication of 2 μM riluzole during the recording decreased repetitive firing and the persistent inward current, which is consistent with the normal effects of riluzole. The downregulation of the persistent inward current in response to prolonged riluzole administration is in contrast to the strong upregulation of this same current after descending neuromodulatory drive to the cord is lost following spinal injury. This dichotomy suggests that decreased activation of G protein-coupled pathways can induce upregulation in the persistent inward current but that direct channel block is ineffective.

Altered postnatal maturation of electrical properties in spinal motoneurons in a mouse model of amyotrophic lateral sclerosis

Spinal motoneurons are highly vulnerable in amyotrophic lateral sclerosis (ALS).Previous research using a standard animal model, the mutant superoxide dismutase-1 (SOD1)mouse, has revealed deficits in many cellular properties throughout its lifespan. The electrical properties underlying motoneuron excitability are some of the earliest to change; starting at 1 week postnatal, persistent inward currents (PICs) mediated by Na+ are upregulated and electrical conductance, a measure of cell size, increases. However, during this period these properties and many others undergo large developmental changes which have not been fully analysed.Therefore, we undertook a systematic analysis of electrical properties in more than 100 normal and mutant SOD1 motoneurons from 0 to 12 days postnatal, the neonatal to juvenile period.We compared normal mice with the most severe SOD1 model, the G93A high-expressor line. We found that the Na+ PIC and the conductance increased during development. However, mutant SOD1 motoneurons showed much greater increases than normal motoneurons; the mean Na+PIC in SOD1 motoneurons was double that of wild-type motoneurons. Additionally, in mutant SOD1 motoneurons the PIC mediated by Ca2+ increased, spike width decreased and the time course of the after-spike after-hyperpolarization shortened. These changes were advances of the normal effects of maturation. Thus, our results show that the development of normal and mutant SOD1 motoneurons follows generally similar patterns, but that the rate of development is accelerated in the mutant SOD1 motoneurons. Statistical analysis of all measured properties indicates that approximately 55% of changes attributed to the G93A SOD1 mutation can be attributed to an increased rate of maturation.

Persistent inward currents in spinal motoneurons: important for normal function but potentially harmful after spinal cord injury and in amyotrophic lateral sclerosis

Meaningful body movements depend on the interplay between synaptic inputs to motoneurons and their intrinsic properties. Injury and disease often alter either or both of these factors and cause motoneuron and movement dysfunction. The ability of the motoneuronal membrane to generate persistent inward currents (PICs) is especially potent in setting the intrinsic excitability of motoneurons and can drastically change the motoneuron output to a given input. In this article, we review the role of PICs in modulating the excitability of spinal motoneurons during health, and their contribution to motoneuron excitability after spinal cord injury (SCI) and in amyotrophic lateral sclerosis (ALS) leading to exaggerated long-lasting reflexes and muscle spasms, and contributing to neuronal degeneration, respectively.

Correlation of thrombosis with increased platelet turnover in thrombocytosis

There are no readily applicable methods to routinely assess thrombosis risk and treatment response in thrombocytosis. Reticulated platelets (RP) define the most recently released platelets in the circulation, and the RP% has been shown to estimate platelet turnover in thrombocytopenic states. We examined whether increased RP values were associated with thrombotic complications in thrombocytosis. Platelet count, RP%, and absolute RP count were measured at presentation in 83 patients with chronic or transient thrombocytosis, 46 patients with deep vein (DVT) or arterial (ART) thrombosis and normal platelet counts, and 83 healthy controls with normal platelet counts. Chronic thrombocytosis patients presenting with thrombosis (n = 14) had significantly higher RP% (14.7% +/- 10. 1%, mean +/- SD) than asymptomatic chronic thrombocytosis patients (n = 23, RP% = 3.4% +/- 1.8%), healthy controls (3.4% +/- 1.3%), DVT patients (n = 21, 3.8% +/- 2.1%), or ART patients (n = 25, 4.5% +/- 4.1%, P < .05 for all comparisons). Chronic thrombocytosis patients with thrombosis also had significantly higher absolute RP counts than asymptomatic chronic thrombocytosis patients (98 +/- 64 x 10(9)/L [range, 54 to 249 x 10(9)/L] v 30 +/- 13 x 10(9)/L [range, 11 to 51 x 10(9)/L]; P = .0004), whereas healthy controls, DVT, and ART patients had similarly low absolute RP counts (6 +/- 6 x 10(9)/L, 9 +/- 7 x 10(9)/L, and 11 +/- 7 x 10(9)/L, respectively; P > .49). The RP% and absolute RP counts remained significantly higher in chronic thrombocytosis patients with thrombosis when patients were further subdivided into primary myeloproliferative disorders versus secondary thrombocytosis. Similarly elevated RP percentages and absolute counts were also noted in transient thrombocytosis patients with thrombosis (n = 6, 11.5% +/- 4.4% and 90 +/- 46 x 10(9)/L, respectively) when compared with asymptomatic transient thrombocytosis patients (n = 40, 4.5% +/- 2.7% and 35 +/- 16 x 10(9)/L, respectively) and to all control groups (P < .05 for all comparisons). In addition, 7 of 8 thrombocytosis patients who were studied before developing symptoms of thrombosis had elevated absolute RP counts compared with only 1 of 63 thrombocytosis patients who remained asymptomatic. Follow-up studies in seven chronic thrombocytosis patients showed that successful aspirin treatment of symptomatic recurrent thrombosis significantly reduced the RP% from 17.1% +/- 10.9% before therapy to 4.8% +/- 2.0% after therapy; absolute RP counts decreased from 102 +/- 67 x 10(9)/L to 26 +/- 10 x 10(9)/L (P < .01 for both). We conclude that thrombosis in the setting of an elevated platelet count is associated with increased platelet turnover, which is reversed by aspirin therapy. Measurement of reticulated platelets to assess platelet turnover may be useful in evaluating both treatment response and thrombotic risk in thrombocytosis.

Human neutrophil elastase releases cell surface mucins from primary cultures of hamster tracheal epithelial cells

Primary hamster tracheal epithelial cells growing on a collagen gel matrix produce high molecular weight mucins indistinguishable from mucins produced in vivo. Using a modified version of these confluent cultures, we have demonstrated here that (i) release of mucins can be stimulated by human neutrophil elastase (HNE; EC 3.4.21.37); (ii) HNE can degrade mucins, and both mucin release and degradation by HNE require an active catalytic site; and (iii) there are at least two pools of mucins in these cells: one is a rapidly turning-over spontaneously releasable constitutive pool, the other is a slowly turning-over HNE-releasable pool. We provide evidence that the HNE-releasable mucins are membrane bound and associated with the secretory cell apical surface.