Neonatal expression of progesterone receptor isoforms in the cerebellar Purkinje cell in rats.

The cerebellar Purkinje cell (PC) is a typical site for neurosteroid formation. Progesterone synthesized de novo in developing PCs participates in the promotion of dendritic growth, spinogenesis and synaptogenesis in this neuron and such organizing actions may contribute to the formation of the cerebellar neuronal circuit during rat neonatal life. Progesterone receptors (PR) occur as two isoforms (PR-A and PR-B) derived from a single gene. To clarify the mode of organizing actions of progesterone, therefore, we examined the expression of these PR isoforms in the rat cerebellum during development. Western immunoblot analysis revealed that both PR isoforms were expressed highly in the cerebellum during neonatal life and the expression decreased thereafter. PR-like immunoreactivity was localized primarily in PCs in the neonatal cerebellum. Thus, progesterone may act directly on PCs via PR isoforms to promote its dendritic growth, spinogenesis and synaptogenesis.