Localization of 20alpha-hydroxysteroid dehydrogenase mRNA in mouse brain by in situ hybridization.
The enzyme 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) catalyzes the conversion of progesterone into its inactive form, 20alpha-hydroxyprogesterone. We studied the expression of 20alpha-HSD mRNA in mouse brain by in situ hybridization. 20alpha-HSD mRNA was exclusively found in neurons in cortex and hippocampus. In the cortex, the labelled cells were concentrated in the external granular layer, the external pyramidal layer and the inner granular layer. In the hippocampus, the labelling was mostly located over pyramidal cells of the CA1 layer. These results suggest that progesterone can be inactivated by 20alpha-HSD in some specific brain areas.