Differential expression of neuroD in primary cultures of cerebral cortical neurons.

We have investigated the expression patterns of a basic helix-loop-helix regulatory gene, neuroD, in primary cultures of murine cerebral cortical neurons. The differentiation states of neurons in primary cultures were determined by the sensitivity of neurons to glutamate toxicity and the expression of specific proteins such as the phosphorylated form of a 200-kDa neurofilament, HPC-1/syntaxin 1A, and cell adhesion molecule L1. The expression of neuroD was determined by RT-PCR analysis and in situ hybridization. The experimental results thus obtained revealed that neuronal maturation is initiated between Day 7 and Day 11 in the culture as already known, and that the expression of neuroD decreases with increasing days in culture. Based on these findings, it was concluded that neuroD is expressed in immature neurons but not in mature ones.