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It seems we have a small problem on Dutch Wikipedia which also regards this article: do pioneer neurons only get produced in the cortex as a derivative of the preplate, or are they also created at other places inside the embryo? Solejheyen (talk) 13:55, 16 November 2009 (UTC)[reply]
Please allow me to shed some light on this issue. The link given above concerns an article specifically discussing development in thalamus and cortex, so any description of pioneer neurons in that article would surely be limited to pioneer neurons produced in thalamus and cortex, and not elsewhere in the body. Looking at other sources, e.g. [1] and [2], leads one to the conclusion that pioneer neurons are not just present in the cortex, but are also present outside the cortex. To stay with the above examples, [1] indicates that, in the embryonic nervous system of locusts, pioneer neurons are formed in the developing sense organs in the epidermis (skin), and from there have pioneer axons grow towards the central nervous system (CNS), i.e. the ventral nerve cord (VNC) of the insect. The other example [2] indicates that in Drosophilae, four types of pioneer neurons are involved in shaping the VNC itself, and also describes a mechanism (Slit/Robo) that explains how pioneer neurons from outside the VNC are guided to either cross the VNC or connect to various upward and downward nerve paths inside the VNC. For the above reasons, one can surmise that the definition as given in the current version of this lemma is too limited, as it defines a pioneer neuron to be a specific type of neuron that behaves in a specific way inside the cortex. Surely such pioneer neurons do exist, but that is just one instance of a pioneer neuron. In my humble/honest opinion, a pioneer neuron should be defined in a much broader sense, for instance by defining it as any type of neuron that acts as a pathfinder for subsequent neurons by being the first neuron to find the proper route towards its destination, wherever that may be in the developing body or brain. The mechanisms by which the axon of a pioneer neuron (i.e a pioneer axon is guided is still being researched, but is presumably different depending on the type of nearon and type of pathway that is being established. With this as main definition, one could use (parts of) the current definition in the lemma as an example of pioneer occurrance, and also mention some other examples, like the ones described above in [1] and [2]. As pioneer neurons occur throughout the developing embryo to lay the pathways that finally comprise the whole nervous system, one should be careful in (re)writing the article as not to state specific features or mechanisms for one specific type of pioneer neuron, as general statements about pioneer neurons in general. Hoping the above is helpful in improving this article both here and on the Dutch Wikipedia. Best regards, Trewal (talk) 23:34, 18 November 2009 (UTC)[reply]
