Morphology of neuroglia in the hypothalamus of the opossum (Didelphis virginiana), armadillo (Dasypus novemcinctus mexicanus) and cat (Felis domestica)

Abstract

The hypothalamus of the opossum (Didelphis virginiana), the armadillo (Dasypus novemcinctus mexicanus), and the cat (Felis domestica) was studied using Del Rio Hortega's silver carbonate technique, as modified by Scharenberg ('60). This technique demonstrates astrocytes, oligodendroglia, and neuronal perikarya, but does not impregnate microglia. The morphology of macroglia was observed in ten comparable nuclei in each of the three species. The subpial and subependymal areas were also examined.Astrocytes display more cell body angularity and have more processes in most hypothalamic regions of the cat when compared to similar regions of the opossum and armadillo.In the anterior hypothalamic nucleus, the ventromedial and the dorsomedial hypothalamic nuclei, and the medial mammillary nucleus of all three species, astrocytes send processes to neurons, but neuronal and astrocytic perikarya are usually not directly contiguous. However, oligodendrocytes in a perisomatic position on neurons are a consistent feature in these nuclei.A closer relationship appears to exist between astrocytes and neurons in the neurosecretory nuclei. In the supraoptic nucleus and paraventricular nucleus of all three species a basket-like structure, designated a "pericellular envelope" was observed surrounding neuronal perikarya. This structure is composed of astrocytic and oligodendroglial cell bodies and processes, and is most highly developed in the cat.A dense astrocytic plexus was observed in the suprachiasmatic nucleus of the cat, and in the comparable nuclei of the armadillo and opossum. The most prominent macroglial cell type of the lateral hypothalamic and lateral mammillary nuclei of all three species is the interfascicular oligodendrocyte. The posterior hypothalamic nucleus of each species has many perisomatic oligodendrocytes, and in the armadillo and cat astrocytes are closely related to the larger neurons.A subpial plexus, consisting of a palisade of small glial cells with many processes, is present in the hypothalamus of the three species. Ependymal cells have long projecting processes throughout the length of the third ventricle in the armadillo hypothalamus, but such processes are only apparent in the region of the infundibular nucleus and median eminence in the opossum and cat.In recent years there has been a resurgence of interest in the morphology of neuroglia. The focus of this interest has been primarily upon the identification of the classical types of neuroglia with electron microscopy. General agreement has developed upon the structural features of astrocytes and oligodendrocytes, as seen with this technique, but the characteristics of microglia, and indeed their very existence, has been the subject of controversy (Duncan, '65; Maxwell and Kruger, '65, '66; Kruger and Maxwell, '66;1 A portion of this investigation consisted of a dissertation submitted to the Department of Anatomy, The Ohio State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy.