Afferent and efferent connections of small nuclei in the posterolateral hypothalamus of the cat.

Four separate neuronal groups, termed the anterior, dorsal, ventral, and posterior nuclei of the juxtamamillary complex, were labeled retrogradely from the thalamic lateral posterior nucleus with horseradish peroxidase. The retrograde labeling was predominantly ipsilateral in the anterior, dorsal, and ventral nuclei, while it was predominantly contralateral in the posterior nucleus. The anterior, dorsal, and posterior nuclei could be detected clearly in Nissl sections; the ventral nucleus was only identified by horseradish peroxidase transport. The distribution of afferents to the juxtamamillary nuclei was investigated with the Fink-Heimer technique. Following lesions of the olfactory tubercle and underlying structures, degenerating fibers in the medial forebrain bundle terminated discretely in the juxtamamillary nuclei. The dense terminal pattern conformed to the borders of the nuclei and was sometimes visible macroscopically. This pattern resembles that of medial forebrain bundle afferents to nuclei gemini in the rabbit and rat. Since the anatomical portions of these nuclei are also similar, it was concluded that the nuclei of the cat are comparable with the nuclei gemini in the rabbit and rat.