Angiotensin type 1 receptor immunoreactivity in the thoracic spinal cord

The angiotensin II type 1 receptor (AT1R) in the central nervous system (CNS) plays a pivotal role in determining blood pressure. However, the relationship of the receptor to neurones in the spinal cord which are the final CNS contribution to sympathetic outflow is unknown. Here we first use RT-PCR to show that AT1A, AT1B and AT2 receptors are expressed in thoracic spinal cord of the rat. Using light microscopic immunohistochemistry we find that the AT1 receptor in the thoracic spinal cord is located on neurones and ependymal cells. Neurones with extensive immunostaining of somata and dendrites were located in the intermediolateral cell column (IML) and lamina X (the central autonomic area), regions associated with autonomic outflow, as well as in lamina V. Retrograde labelling and dual immunolabelling with nNOS revealed that those AT1R-immunopositive cells in the IML were sympathetic preganglionic neurones, while those in lamina X were unlikely to be. Punctate labelling resembling that of axonal fibres and terminals was evident in lamina II of the dorsal horn and throughout the cord. Electron microscopy in the IML and lamina X revealed that these puncta were presynaptic terminals, but also astrocyte processes. Immunolabelling was also evident beneath the plasma membrane in neuronal somata. These data show that the AT1R in the spinal cord is ideally located to influence autonomic outflow and hence participate in the CNS determination of blood pressure.