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-sarcosine, isoleucine angiotensin II to brain homogenates and slide-mounted sections of brainstem was determined. Treatment with 3-acetylpyridine significantly decreased specific 125I-sarcosine, isoleucine 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-sarcosine, isoleucine 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-sarcosine, isoleucine 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.