Location of renin-angiotensin system components in the hypoglossal nucleusof the rat

The renin-angiotensin system (RAS) in the hypoglossal nuclei of the rat was studied by immunohistochemistry. Antibodies to angiotensin AT(1) receptor (AT1), angiotensinogen (ANG), renin (REN). angiotensin converting enzyme (A CE) and angiotensin II (AII) were used. All the components of the RAS with the exception of renin were detected. Light and electron microscopy reveale d the following results: ANG was predominantly found in astrocytes, with sm all amounts in neuronal dendrites; ACE was found in the cytoplasm of neuron s, dendrites and astrocyte processes; AT1 was found in the cytoplasm of neu rons and dendrites, but not on the membrane; and AII was found mainly in as trocytes with some located in the dendrites and cytoplasm. Right hypoglossa l nerve lesion caused an increase in expression of AT1 in neurons as early as 2 days post-lesion. An increase in expression of ANG in astrocytes was a lso seen, but at a much later time of 3 weeks post-lesion. For AII, stainin g occurred in both the neurons and astrocytes in the undamaged hypoglossal nucleus. Nerve lesion caused a disappearance of neuronal stains and an incr ease in astrocyte stains. There were no changes in ACE staining after nerve lesion. We speculate that ANG and AII are made within the astrocytes, wher eas ACE could either be uptaken from blood or de novo synthesized. AT1 may potentially be internal soluble receptors. As to the function of AII in the hypoglossal nucleus, the data do not support AII as a neurotransmitter in the hypoglossal nucleus. It may function as a neuromodulator and also be in volved in basic cellular activities, e.g. regulation of transcription facto rs. (C) 2001 Elsevier Science B.V. All rights reserved.