Neuronal Localization of Specific Angiotensin II Binding Sites in the Rat Inferior Olivary Nucleus

Adult male Sprague‐Dawley rats were treated with 3‐acetylpyridine, a neurotoxin selective for the inferior olivary nucleus. Following treatment, the rats exhibited deficits in locomotor behavior indicative of destruction in the inferior olivary nucleus. The rats were sacrificed 3 weeks later, and the binding of 125I‐sarcosine1, isoleucine8 angiotensin II to brain homogenates and slide‐mounted sections of brainstem was determined. Treatment with 3‐acetylpyridine significantly decreased specific 125I‐sarco‐sine', isoleucine8 angiotensin II binding in homogenates of posteroventral brainstem (containing the inferior olivary nucleus) by approximately 50%. Homogenates of dorsal brainstem and hypothalamus‐thalamus‐midbrain showed no significant changes in specific binding. Treatment with 3‐acetylpyridine did not significantly alter the radioligand binding affinity which was determined in the hypothalamus‐thalamus‐midbrain. Autoradiographic analysis of 125I‐sarcosine1, isoleucine8 angiotensin II binding in the brainstem sections indicated that specific angiotensin II binding sites in the inferior olivary nucleus were virtually eliminated by the 3‐acetylpyridine treatment. In addition, a comparatively small, but significant, decrease in specific 125I‐sarcosine1, isoleucine8 angiotensin II binding occurred in the solitary tract nucleus/dorsal vagal motor nucleus complex. These results indicate that specific angiotensin II binding sites in the inferior olivary nucleus occur exclusively on neuronal perikarya and/or dendrites.