Distribution of angiotensin II type-2 receptor (AT2) mRNA expression in the adult rat brain

Radioactively labeled cRNA probes were used for in situ hybridization histochemistry to establish a detailed map of the sites of expression of the recently cloned angiotensin II, type 2 (AT2) receptor mRNA in the adult rat brain. The distribution of the AT2 receptor mRNA was consistent with that of the AT2 binding sites, which were previously established by autoradiographic binding studies. Thus, high AT2 receptor mRNA expression was observed in the lateral septum, in several thalamic nuclei, in the subthalamic nucleus, in the locus coeruleus, and in the inferior olive. Due to the superior resolution and sensitivity of in situ hybridization, AT2 receptor expression was localized at the cellular level, and some additional brain nuclei expressing AT2 receptor mRNA have been identified. These include the red nucleus, the pedunculopontine tegmental nucleus, the bed nucleus of the supraoptic decussation, the paragenual nucleus, and numerous brainstem nuclei. Several brain nuclei, such as the motor hypoglossal nucleus and the cerebellar nuclei, where AT2 receptor binding had previously been identified in young animals only, showed a high expression of the AT2 receptor mRNA in the adult rat. No correlation was found between the expression of the AT2 and the type 1 (AT1) receptor mRNAs. A combination of the in situ hybridization and glial fibrillary acidic protein (GFAP) immunohistochemistry shows that the AT2 receptor in the lateral septum showed that the AT2 receptor was not detected in GFAP immunoreactive astroglial cells, therefore indicating that AT2 is neuronal rather than glial in this brain region.