Abstract. In culture, hippocampal neurons develop a polarized form, with a single axon and several dendrites. Transecting the axons of hippocampal neurons early in development can cause an alteration of polarity; a process that would have become a dendrite instead becomes the axon (Dotti, C. G., and G. A. Banker. 1987. Nature (Lond.). 330:254-256). To investigate this phenomenon more systematically, we transected axons at varying lengths. The greater the distance of the transection from the soma, the greater the probability for regrowth of the original axon. However, it was not the absolute length of the axonal stump that determined the response to transection, but rather its length relative to the lengths of the cell's other processes. If one process was >10 #m longer than the others, it invariably became the axon regardless of its identity before transection. Conversely, when a cell's processes were nearly equal in length, it was impossible to predict which would become the axon. In these cases, axonal outgrowth began only after a long latency. During this interval, the processes appeared to be in dynamic equilibrium, some growing for short distances while others retracted. When one process exceeded the others by a critical length, it rapidly elongated to become the axon.The establishment of neuronal polarity during normal development may similarly involve an interaction among processes whose identities have not yet been determined. When, by chance, one exceeds the others by a critical length, it becomes specified as the axon.

Outgrowth of distinct axonal and dendritic processes is essential for the development of the functional polarity of nerve cells. In cultures of neurons from the hippocampus, where the differential outgrowth of axons and dendrites is readily discernible, we have sought molecules that might underlie the distinct modes of elongation of these two types of processes. One particularly interesting protein is GAP-43 (also termed B-50, F1 or P-57), a neuron-specific, membrane-associated phosphoprotein whose expression is dramatically elevated during neuronal development and regeneration. GAP-43 is among the most abundant proteins in neuronal growth cones, the motile structures that form the tips of advancing neurites, but its function in neuronal growth remains unknown. Using immunofluorescence staining, we show that GAP-43 is present in axons and concentrated in axonal growth cones of hippocampal neurons in culture. Surprisingly, we could not detect GAP-43 in growing dendrites and dendritic growth cones. These results show that GAP-43 is compartmentalized in developing nerve cells and provide the first direct evidence of important molecular differences between axonal and dendritic growth cones. The sorting and selective transport of GAP-43 may give axons and axonal growth cones certain of their distinctive properties, such as the ability to grow rapidly over long distances or the manner in which they recognize and respond to cues in their environment.

The ability to grow neurons in culture has made possible great strides in the field of neuroscience. Advances in optical microscopy, together with techniques involving the retroviral transformation of neuronal precursors and cell fusion, will pave the way for further developments.

GAP-43, a neuron specific growth-associated protein, is selectively distributed to the axonal domain in developing neurons; it is absent from dendrites and their growth cones. Using immunofluorescence microscopy, we have further examined the distribution of GAP-43 during the development of hippocampal neurons in culture, in order to determine when this polarized distribution arises. Cultured hippocampal neurons initially extend several short processes which have the potential to become either axons or dendrites. At this stage, before the morphological expression of polarity, GAP-43 is concentrated in the growth cones of these processes but is distributed more or less equally among them. Polarity becomes established when one of these processes elongates to become the axon. At the earliest stage when the emerging axon can be identified, GAP-43 is preferentially concentrated in its growth cone. During the next few days, as the remaining processes take on dendritic properties, they lose their residual GAP-43 immunoreactivity. Throughout development, GAP-43 remains highly concentrated in the axonal growth cone, but the concentration of GAP-43 in the axon shaft increases, beginning near the growth cone and progressing proximally until GAP-43 is uniformly distributed along the entire axon. At all stages of development, GAP-43 is also concentrated in the region of the Golgi apparatus. These results suggest that the selective sorting of at least one membrane protein into the axon coincides with the morphological expression of polarity. These results also raise the possibility that GAP-43 may play an important role in the early phases of axonal outgrowth, by which the functional polarity of neurons is established.

Abstract. We are interested in the relationship between the cytoskeleton and the organization of polarized cell morphology. We show here that the growth cones of hippocampal neurons in culture are specifically stained by a monoclonal antibody called 13H9. In other systems, the antigen recognized by 13H9 is associated with marginal bands of chicken erythrocytes and shows properties of both microtubuleand microfilament-associated proteins (Birgbauer, E., and F. Solomon. 1989. J. Cell Biol. 109:1609-1620. This dual nature is manifest in hippocampal neurons as well. At early stages after plating, the antibody stains the circumferential lamellipodia that mediate initial cell spreading. As processes emerge, 13H9 staining is heavily concentrated in the distal regions of growth cones, particularly in lamellipodial fans. In these cells, the 13H9 staining is complementary to the localization of assembled microtubules. It colocalizes partially, but not entirely, with phalloidin staining of assembled actin. Incubation with nocodazole rapidly induces microtubule depolymerization, which proceeds in the distal-to-proximal direction in the processes. At the same time, a rapid and dramatic redistribution of the 13H9 staining occurs; it delocalizes along the axon shaft, becoming clearly distinct from the phalloidin staining and always remaining distal to the receding front of assembled microtubules. After longer times without assembled microtubules, no staining of 13H9 can be detected. Removal of the nocodazole allows the microtubules to reform, in an ordered proximal-todistal fashion. The 13H9 immunoreactivity also reappears, but only in the growth cones, not in any intermediate positions along the axon, and only after the reformation of microtubules is complete. The results indicate that the antigen recognized by 13H9 is highly concentrated in growth cones, closely associated with polymerized actin, and that its proper localization depends upon intact microtubules.T HE ability of neurons to develop stereotyped morphologies, suitable for the functions of each individual cell, depends upon the activities of their growth cones. All of the motility of nerve cells is confined to these structures at the tips of growing axons and dendrites. Although in migratory cells the position of the leading edge can change frequently, the position of the growth cones persists once they are specified. There have been many analyses of the behavior and properties of growth cones, and of the cues that guide growth cones to their appropriate destinations (for reviews, see Landis, 1983;Lockerbie, 1987;Bray and Hollenbeck, 1988). However, rather less is known about the endogenous determinants of growth cone formation and organization. How does the cell specify the number and position of growth cones? How is growth cone motility coupled to the function of cytoskeletal elements within the growing fiber?Arguably, the unique properties of growth cones might arise not only from the presence of unique constituents but Dr. Goslin's and Dr. Banker's present add...

The goal of this randomized, blinded, crossover clinical trial was to determine whether Nuedexta (dextromethorphan and quinidine) enhanced speech, swallowing, and salivation in patients with ALS. Sixty patients with amyotrophic lateral sclerosis (ALS) received either Nuedexta or placebo for 28 to 30 days, followed by a 10 to 15-day washout period. Subsequently, patients were switched to the opposite treatment arm for the remaining days of the trial. The primary endpoint was a reduction in the self-report Center for Neurologic Study Bulbar Function Scale (CNS-BFS) score. The rater-administered ALS Functional Rating Scale Revised was the principal secondary endpoint. The CNS-BFS score improved with active treatment, decreasing from a mean of 59.3 in the placebo arm of the trial to 53.5 during the drug-treatment arm (p < 0.001). Each of the individual domains of bulbar function interrogated by the CNS-BFS responded to treatment with Nuedexta as follows: salivation: 15.8 versus 14.3 (p = 0.004); speech: 24.6 versus 22.2 (p = 0.003); swallowing: 18.9 versus 17.1 (p = 0.009). Similarly, the bulbar component of the ALS Functional Rating Scale Revised improved with active treatment (p = 0.003), although the drug did not affect the motor and respiratory components of this scale. This study is unique for several reasons. Firstly, it was driven by patient reports of improved speech and swallowing while taking Nuedexta for control of emotional lability. Secondly, the study was conducted over a short duration (70 days), and thirdly, a self-report scale was selected as the principle outcome measure. Considering the importance of bulbar functions, these results, if confirmed, point to an additional use of Nuedexta as an adjunct to the management of ALS.Electronic supplementary materialThe online version of this article (doi:10.1007/s13311-016-0508-5) contains supplementary material, which is available to authorized users.

Abstract. Hippocampal neurons growing in culture initially extend several, short minor processes that have the potential to become either axons or dendrites. The first expression of polarity occurs when one of these minor processes begins to elongate rapidly, becoming the axon. Before axonal outgrowth, the growth-associated protein GAP-43 is distributed equally among the growth cones of the minor processes; it is preferentially concentrated in the axonal growth cone once polarity has been established (Goslin, K., D. Schreyer, J. Skene, and G. Banker. 1990. J. Neurosci. 10:588-602). To determine when the selective segregation of GAP-43 begins, we followed individual cells by video microscopy, fixed them as soon as the axon could be distinguished, and localized GAP-43 by immunofluorescence microscopy. Individual minor processes acquired axonal growth characteristics within a period of 30-60 min, and GAP-43 became selectively concentrated to the growth cones of these processes with an equally rapid time course. We also examined changes in the distribution of GAP-43 after transection of the axon. After an axonal transection that is distant from the soma, neuronal polarity is maintained, and the original axon begins to regrow almost immediately. In such cases, GAP-43 became selectively concentrated in the new axonal growth cone within 12-30 min. In contrast, when the axon is transected close to the soma, polarity is lost; the original axon rarely regrows, and there is a significant delay before a new axon emerges. Under these circumstances, GAP-43 accumulated in the new growth cone much more slowly, suggesting that its ongoing selective routing to the axon had been disrupted by the transection. These results demonstrate that the selective segregation of GAP-43 to the growth cone of a single process is closely correlated with the acquisition of axonal growth characteristics and, hence, with the expression of polarity.

Objective: To use a historical placebo control design to determine whether lithium carbonate slows progression of amyotrophic lateral sclerosis (ALS).Methods: A phase II trial was conducted at 10 sites in the Western ALS Study Group using similar dosages (300-450 mg/day), target blood levels (0.3-0.8 mEq/L), outcome measures, and trial duration (13 months) as the positive trial. However, taking riluzole was not a requirement for study entry. Placebo outcomes in patients matched for baseline features from a large database of recent clinical trials, showing stable rates of decline over the past 9 years, were used as historical controls. Results:The mean rate of decline of the ALS Functional Rating Scale-Revised was greater in 107 patients taking lithium carbonate (Ϫ1.20/month, 95% confidence interval [CI] Ϫ1.41 to Ϫ0.98) than that in 249 control patients (Ϫ1.01/month, 95% CI Ϫ1.11 to Ϫ0.92, p ϭ 0.04). There were no differences in secondary outcome measures (forced vital capacity, time to failure, and quality of life), but there were more adverse events in the treated group. Conclusions:The lack of therapeutic benefit and safety concerns, taken together with similar results from 2 other recent trials, weighs against the use of lithium carbonate in patients with ALS. The absence of drift over time and the availability of a large database of patients for selecting a matched historical control group suggest that use of historical controls may result in more efficient phase II trials for screening putative ALS therapeutic agents. Classification of evidence:This study provided Class IV evidence that lithium carbonate does not slow the rate of decline of function in patients with ALS over 13 months. Neurology ® 2011;77:973-979 GLOSSARY ALS ϭ amyotrophic lateral sclerosis; ALSFRS-R ϭ ALS Functional Rating Scale-Revised; CI ϭ confidence interval; FVC ϭ forced vital capacity; MINO ϭ minocycline in ALS trial; NSAE ϭ nonserious adverse event; QOL ϭ quality of life; SAE ϭ serious adverse event; WALS ϭ Western ALS Study Group.