EMSA (50) was performed with an excess of cold competitors to define specificity of protein binding in nuclear extracts derived from primary neocortical neurons and fibroblasts (FIBs) kept in culture. As shown in Figures 4-6 , out of six predicted binding sites found upstream of the (a, b, g and d) subunit genes, four (GABRA4, GABRB1, GABRB3 and GABRD) displayed specific binding. In addition to specific binding of neuronal extracts to novel GABRA4 motifs, we have evidence for specific binding using FIB extracts ( Figure 5A and B) , of especial interest given that the expression of GABRs is restricted to the nervous system and repressors such as the RE1-silencing transcription factor (REST) (51, 52) expressed in non-neuronal cells have been implicated in the neural specificity of gene expression.