Localization of AT(2) angiotensin II receptor gene expression in rat brain by in situ hybridization histochemistry

To localize the gene expression of AT(2) angiotensin II receptors in rat brain we performed in situ hybridization histochemistry using S-35-labeled antisense riboprobes. The AT(2) receptor mRNA expression pattern was compared in consecutive brain sections, from 2 week old rats, with the receptor expression by means of [I-125]Sar(1)-ANG II binding and displacement with AT(2) selective ligands followed by autoradiography. Expression of AT(2) receptor mRNA was found in several thalamic nuclei (ventral posterolateral, mediodorsal, central medial, paracentral, and paraventricular), the medial geniculate nuclei, the nucleus of the optic tract, the subthalamic nucleus, the interposed nucleus of the cerebellum, and in the inferior olive. In these areas the AT(2) receptor gene expression corresponds well with [I-125]Sar(1)-ANG II binding. In addition, AT(2) receptor mRNA expression was found in the red nucleus where no [I-125]Sar(1)-ANG II binding was present. No significant hybridization of the AT(2) receptor antisense probe was found in septal nuclei, the locus coeruleus, the dorsolateral geniculate nucleus, or the cerebellar cortex, areas rich in [I-125]Sar(1)-ANG II binding. Our results indicate that some brain regions may be involved in AT(2) receptor formation, transporting the receptor protein to other brain areas. However, in most structures, both the formation and expression of receptors occur, suggesting the existence of local AT(2) receptor circuits, or that of AT(2) autoreceptors. Other structures express only the receptor protein, indicating that these AT(2) receptors are produced elsewhere. Our present data are the basis for further studies on the clarification of AT(2) receptor pathways in the brain.