General Conclusions

Abstract

Our light and electron microscopic investigations reveal the presence of infundibular CSF contacting neuronal elements not only in fishes, amphibians and reptiles, but also in birds and mammals. By these findings one is induced to suppose that it is a general feature of the infundibular nucleus to be composed partly of CSF contacting neurons. Though the localization and organization of the infundibular nuclei is not uniform in the different animal classes we found CSF contacting neuronal elements in all the cell groups investigated: in fishes in the whole periventricular hypothalamic nucleus, in the medial part of the nucleus lateralis tuberis, in the vascular sac among the coronet cells; in amphibians in the infundibular lobe including the paraventricular organ, the periventricular posterior nucleus and the dorsal and ventral infundibular nuclei; and in the infundibular/arcuate nuclei of higher amniote vertebrates. Though the number of CSF contacting endings decreases in birds and mammals, yet it is obvious from our investigations that the infundibular nucleus of these animal classes is an important component of the CSF contacting neuronal system.