Trajectories of impairment in amyotrophic lateral sclerosis: Insights from the Pooled Resource Open‐Access ALS Clinical Trials cohort

Introduction: Rate of decline of the Amyotrophic Lateral Sclerosis Functional Rating Scale‐Revised (ALSFRS‐R) score is a common outcome measure and a powerful predictor of mortality in ALS. Methods: Observed rate of decline (postslope) of ALSFRS‐R, its linearity, and its relationship to decline at first visit (preslope) were examined in the Pooled Resource Open‐Access ALS Clinical Trials cohort by using longitudinal mixed effects models. Results: Mean ALSFRS‐R postslope in 3,367 patients was ?0.99 points/month. Preslope and postslope were correlated and had powerful effects on survival. ALSFRS‐R trajectories were slightly accelerated overall, but slope and direction/degree of curvature varied. Subscore decline was sequential by site of onset. Respiratory subscore decline was the least steep. Discussion: Variable curvilinearity of ALSFRS‐R trajectories confounds interpretation in clinical studies that assume linear decline. Subscore trajectories recapitulate phenotypic diversity and topographical progression of ALS. ALSFRS‐R is better used as a multidimensional measure. Muscle Nerve 57 : 937–945, 2018     

Fragments of SLIT3 inhibit cellular migration

The repellent factor family of Slit molecules has been described as having a repulsive function in the developing nervous system on growing axons expressing the Roundabout (Robo) receptors. Recent studies determined the effects of Slit molecules on the migratory and invasive potential of several types of tumor cells but also on synovial fibroblasts (SFs) derived from rheumatoid arthritis (RA) patients. To optimize a potential therapeutic application we aimed at generatingfragments of Slit3 showing the same functional ability as the full-length molecule but having the advantage of a smaller size. Recombinant Slit3 proteins were expressed and analyzed by western blotting. Their activity was defined by functional assays such as migration assays with RASF and melanoma cells. Recombinant Slit3 containing only leucine rich repeat domain?2 (D2), the domain important for Robo binding and the minimal functional unit D2 dNC were both able to inhibit migration of RASFs as effectively as Slit3 with all 4?repeats. Collectively, our data showed that the ability of Slit3 to reduce the migratory activity of synovial cells from patients with RA and melanoma cells can be mimicked by small protein fragments derived from Slit3. Slit3 fragments may be helpful in therapeutic attempts; however, further studies are necessary in order to elucidate their activity in vivo.     

Spatiotemporally graded NMDA spike/plateau potentials in basal dendrites of neocortical pyramidal neurons

Glutamatergic inputs clustered over approximately 20-40 microm can elicit local N-methyl-D-aspartate (NMDA) spike/plateau potentials in terminal dendrites of cortical pyramidal neurons, inspiring the notion that a single terminal dendrite can function as a decision-making computational subunit. A typical terminal basal dendrite is approximately 100-200 microm long: could it function as multiple decision-making subunits? We test this by sequential focal stimulation of multiple sites along terminal basal dendrites of layer 5 pyramidal neurons in rat somatosensory cortical brain slices, using iontophoresis or uncaging of brief glutamate pulses. There was an approximately sevenfold spatial gradient in average spike/plateau amplitude measured at the soma, from approximately 3 mV for distal inputs to approximately 23 mV for proximal inputs. Spike/plateaus were NMDA receptor (NMDAR) conductance-dominated at all locations. Large Ca(2+) transients accompanied spike/plateaus over a approximately 10- to 40-microm zone around the input site; smaller Ca(2+) transients extended approximately uniformly to the dendritic tip. Spike/plateau duration grew with increasing glutamate and depolarization; high Ca(2+) zone size grew with spike/plateau duration. The minimum high Ca(2+) zone half-width (just above NMDA spike threshold) increased from distal (approximately 10 microm) to proximal locations (approximately 25 microm), as did the NMDA spike glutamate threshold. Depolarization reduced glutamate thresholds. Simulations exploring multi-site interactions based on this demonstrate that if appropriately timed and localized inputs occur in vivo, a single basal dendrite could correspond to a cascade of multiple co-operating dynamic decision-making subunits able to retain information for hundreds of milliseconds, with increasing influence on neural output from distal to proximal. Dendritic NMDA spike/plateaus are thus well-suited to support graded persistent firing.     

Spread of dendritic excitation in layer 2/3 pyramidal neurons in rat barrel cortex in vivo

In layer 2/3 pyramidal neurons of barrel cortex in vivo, calcium ion concentration ([Ca2+]) transients in apical dendrites evoked by sodium action potentials are limited to regions close to the soma. To study the mechanisms underlying this restricted pattern of calcium influx, we combined two-photon imaging of dendritic [Ca2+] dynamics with dendritic membrane potential measurements. We found that sodium action potentials attenuated and broadened rapidly with distance from the soma. However, dendrites of layer 2/3 cells were electrically excitable, and direct current injections could evoke large [Ca2+] transients. The restricted pattern of dendritic [Ca2+] transients is therefore due to a failure of sodium action-potential propagation into dendrites. Also, stimulating subcortical activating systems by tail pinch can enhance dendritic [Ca2+] influx induced by a sensory stimulus by increasing cellular excitability, consistent with the importance of these systems in plasticity and learning.