The regulation of gene expression in differentiated neurons is poorly understood. By studying the transcriptional regulation of particular "model genes", whose expression is neuron specific, we hope to gain insight into the mechanisms governing neuron specific gene expression as a whole. The rat hippocalcin gene encodes a small calcium binding protein. Northern blot analysis and an in-situ hybridization study demonstrated that rat hippocalcin gene expression is brain specific, with different neuronal populations transcribing the gene to varying extents. Particularly high hippocalcin mRNA levels are found in the hippocampus, caudate putamen and olfactory tubercle of the rat brain. RT-PCR analysis detected hippocalcin gene expression in neuronal x glial hybridoma (NG108) and rat pheochromocytoma (PC12) cell lines; however not in 3T3 fibroblast (3T3) or human embryonic kidney (HEK) cell lines. To investigate the regulation of this cell-specific expression, the rat hippocalcin gene was cloned and it's structure determined. Genomic regions were then tested for transcriptional activity in transgenic mice. 3.2 kb of the hippocalcin gene upstream region directs neuron-specific expression of a lacZ reporter gene, in a pattern partially corresponding with endogenous hippocalcin gene expression. Reporter gene expression was invariably observed in the hippocampus, suggesting the presence of a hippocampal-specific-cis-regulatory element. Transcriptional activity of the -3.2 to +1 kb hippocalcin upstream region was investigated in more detail using transient transfection of reporter constructs into neuronal (NG108 and PC12) and non-neuronal (3T3 and HEK) cell lines. This analysis identified three, cell-specific, positively activating, elements between -3.2 to 1.4 kb. One of these elements is a small 300 bp fragment, that independently directs high levels of neuronal-cell-line-specific reporter gene expression.