Gerbil angiotensin II AT1 receptors are highly expressed in the hippocampus and cerebral cortex during postnatal development

Increasing evidence suggests that Angiotensin II, classically known from its many effects regulating salt and water homeostasis, is also involved in brain development and cognitive functions through activation of AT1 Angiotensin II receptors. The recently cloned gerbil AT1 receptor is expressed in brain areas controlling hydro-mineral homeostasis, and particularly highly expressed in limbic areas such as the hippocampal formation. We quantified the gerbil AT1 receptor messenger RNA expression and receptor binding by quantitative in situ hybridization and receptor autoradiography, respectively, in the hippocampal formation and cerebral cortex of gerbils during postnatal development. The receptor messenger RNA and binding were present from birth and showed a gradual and sustained increase through postnatal maturation in the CA1 and CA2 regions of the hippocampus and in the dentate gyrus. Conversely, in the CA3 region, no binding was detected while receptor messenger RNA peaked at 15 days after birth and disappeared in the adult. The highest receptor messenger RNA expression and binding were found in the septomedial portions of the CA1 region and at septal levels of the CA2 region. We detected the highest receptor messenger RNA expression at postnatal day one in the frontolateral pole of the cerebral hemispheres. In these areas, and in the frontoparietal and insular cortex, receptor messenger RNA dramatically decreased during postnatal life. Similarly, we found receptor messenger RNA expression in the cingulate, retrosplenial, perirhinal and infralimbic cortex with higher values during the first two weeks of development and decreased expression in the adult. However, receptor binding in the cerebral cortex, did not decrease during postnatal life. The differential profile of receptor messenger RNA expression and binding in the gerbil cortex and hippocampus during postnatal maturation suggest a role for AT1 receptors in the development and function of the corticohippocampal system.