Fig. 1. Properties of cortical neurons in a glia-free culture for 3 days. (A-C) Neurons were stained with antibodies to GABA, to phosphorylated neurofilaments (P-Nf) and to class III ß-tubulin (TUJ1), respectively. A GABA-positive neuron is indicated by the arrow in (A). GABA-negative neurons, as indicated by the arrowheads in (A), extended phosphorylated neurofilament-positive axons, as indicated by the arrowheads in (B). All neurons were reactive with the TUJ1 antibody. Bar, 100 µm. (D) Distribution of standardized values for GABA immunoreactivity of the cultured cells after 3 DIV. Striped bars represent neurons bearing a phosphorylated neurofilament-positive axon, open bars represent neurons without axons and solid bars represent nonneuronal cells. Most excitatory neurons (standardized GABA intensity <0.4) bore an axon, whereas most inhibitory neurons (standardized GABA intensity 0.4; shaded area) did not.