Towards a New Neuromorphology

(6) By using appropriate molecular markers, all neuron types in the adult CNS can be traced back to a specific progenitor zone within a specific FMU, and the progeny of any FMU can be traced to their final positions with the help of selective labeling approaches. (7) Early outgrowing axons form bundles, which tend to pass close to the border zones of the radial units. By means of their molecularly diversely tuned growth cones, these extending axons decide how to behave at each boundary they encounter, sometimes even reorienting at right angles. Collectively these early axonal bundles form a checkerboard-like scaffold, which accentuates the molecular regionalization of the CNS and leads to the formation of topographically ordered synaptic fields.