This transgene expresses a fusion protein consisting of Cre recombinase and a modified ligand binding domain of the human progesterone receptor under the control of a mouse calcium-calmodulin-dependent kinase IIa promoter. The ligand binding domain was modified such that it binds and can be activated by the synthetic steroid, RU486, but not the endogenous ligand, progesterone. Upon induction of transgene expression with RU486, activity was noted in the hippocampus and cortex.