Fig. 3. Time-lapse video microscopic analysis of neuronal behavior in glia-free culture. Neurons were monitored every 6 minutes for 6 days and then stained with antibodies to identify neuronal type. (A) An excitatory neuron extended several minor processes, one of which (arrow) began to elongate rapidly and to form an axon. (B) Two processes of an inhibitory neuron exhibited alternate growth and retraction without giving rise to an axon during the 6 days of recording. Note the movement of the cell body towards the growing process. (C) Two processes of an inhibitory neuron exhibited alternate growth and retraction without axon formation, but movement of the cell body was not detected. (D) An inhibitory neuron for which extensive movement of the cell body was apparent. The long process indicated by the arrows was revealed to be an axon by staining with antiphosphorylated neurofilaments (not shown). Time is shown in hours:minutes. Bar, 50 µm.