Fine Structural Changes in Explants of the Neural Lobe of the Rat Hypophysis

Abstract

To obtain a purified population of pituicytes, pieces of rat neural lobes were dissected free of the pars intermedia, incubated in a variety of media, and fixed at regular intervals between 7 and 56 days of incubation. Many neurosecretory axons survived for up to 21 days without any apparent signs of degeneration. Most axons, however, degenerated and were progressively phagocytosed and subsequently eliminated by pituicytes and microglial cells. Lysed axons that were not eliminated, persisted as dense bodies or paracrystalline inclusions. After 30 days of culture, cluster-forming pituicytes predominated the explants. Pituicytes underwent morphologic changes such as medium-dependent decrease or increase of lipid inclusions, Golgi activation, process extension and interdigitation, formation of gap junctions and bundles of intermediate filaments. At the explant surface in contact with the culture medium, pituicytes differentiated into an epithelial layer of ciliated and microvilli-bearing cells linked by junctional complexes. Long-term neural lobe explants are a relatively pure source of viable pituicytes and should be useful for further studies on the functional significance of these cells.In a series of recent experimental investigations on the regenerative capabilities of neurosecretory axons originating from the hypothalamic magnocellular paraventricular and supraoptic nuclei and transected at the level of the hypothalamus, we have explored the influence of a variety of microenvironments on the initiation and sustenance of regeneration (1 -6). The results obtained led t o the conclusion that the microenvironment of perivascular connective tissue is conducive to the initiation of neurosecretory axon regeneration while sustained growth and establishment of functional axon terminals are apparently dependent on the additional presence of a variety of glial or glia-like cells. The highest number of regenerated neurosecretory axons was observed within the pituicyte-predominated microenvironment of syngeneic grafts of neural lobes. Only in the presence of pituicytes, i.e. the characteristic astrocyte-like cells of the neural lobe, but not of any other glia cell type did neurosecretory axon terminals align in a palisade fashion at perivascular basal laminae. These observations led us to hypothesize that pituicytes are capable of conveying unique messages, most likely in the form of diffusible factors, that elicit specific responses from neurosecretory neurons. In order to substantiate this hypothesis, it became necessary to obtain a sizeable population of live pituicytes that remain viable for a period of time. Repeated trials to obtain dispersed primary cultures of pituicytes were unsuccessful.Organotypic cultures of neural lobes likewise had not yielded completely satisfactory results, either in our laboratory (7) or apparently in other laboratories (8). More recently, however, more encouraging results were obtained with short-term cultures of neural lobes of newborn rats (9-11). Bicknell et af. (personal com...

Requirement of polysialic acid for the migration of the O-2A glial progenitor cell from neurohypophyseal explants

“…earlv nostnatal (PN 1. PN3 and PN7), and ad& rats'as described previously ('Dellmann et al;. Briefly, the hypophyses were removed with the usual aseptic procedures and then placed in a small volume of Dulbecco's Modified Eagle's Medium (DMEM; GIBCO) containing 100 U/ml penicillin and 0.15 mg/ml streptomycin or in Gey's Balanced Salt Solutions.…”

Ependymal and choroidal cells in culture: Characterization and functional differentiation

“…Frequently, more or less short incubations of CVOs (4-8 days in vitro) were made in SSM (Olivieri-Sangiacomo and Correr, 1973). In more recent studies, cultures of explants from neural lobe were used to obtain long-term cultures (until 56 days) of pituicytes in SSM and in SFM conditions (Dellmann et al, 1991). Neurosecretory axons of the explants degenerated and were phagocytosed by pituicytes and microglial cells during the first 21 days in culture.…”

“…Organotypic cultures of slices or pieces containing ventricular walls or CVOs were also developed to study the role of ependymal cells, e.g., in neuronependyma interactions (Dellmann et al, 1991;Goldman et al, 1993;Tominaga et al, 1994) or in diseases such as hydrocephalus linked to ''immotile cilia syndrome'' (Nakamura and Sato, 1993).…”

Changes in Distribution of Cystatin C, Apolipoprotein E and Ferritin in Rat Hypothalamus after Hypophysectomy

“…The intensity of stainings were also reduced. In addition, the accumulation of cell debris-like dots positive for vasopressin (15)(16)(17)(18). Thereafter, the stalk is reorganized into a neural lobe like tissue, but the cellular mechanism(s) responsible for such was seen in the median eminence and the ventral portions of the SON.…”