Afferent connections to cardiovascular sites in the amygdala: a horseradish peroxidase study in the cat.

To investigate afferent connections to nuclei of the amygdala that have been shown electrophysiologically to receive inputs from baro- and chemoreceptors, small discrete deposits of horseradish peroxidase (HRP) were placed in the region of the central and lateral nuclei of the amygdala in cats. HRP deposits localized to the medial central nucleus of the amygdala labeled neurons in the ipsilateral hypothalamus, primarily in the paraventricular and ventromedial nuclei. In addition, the parabrachial nuclei and the locus coeruleus were observed to project to the region of the central nucleus. After HRP deposits in the medial portion of the lateral nucleus of the amygdala only a few labeled neurons were found scattered throughout the ipsilateral hypothalamus. In addition thalamic and cortical projections shown by previous investigators were confirmed. This study has demonstrated that in the cat several areas in the hypothalamus and brain stem project to the medial portions of the central and lateral nuclei of the amygdala suggesting that these areas may be relay stations for baro- and chemoreceptor information projecting to the amygdala.