Pieces of intact or degenerated sciatic nerves autografted into contact with transected neurosecretory axons within the hypothalamus were invaded by neurophysin-positive axons. With increasing time after grafting, increasing numbers of axons were present in both types of grafts, but grafts of degenerated sciatic nerves always contained more axons. At the fine-structural level typical neurosecretory as well as nonneurosecretory axons were usually associated with basal lamina-enclosed neurolemmocyte processes; occasional axons occurred among collagen fibrils or within basal lamina scaffolds. Profiles with the fine structural characteristics of axon terminals were present by 20 days after transplantation.

No abstract

The hypothalamic supraoptic (SON) and paraventricular nuclei (PVN), median eminences (ME) and neural lobes (NL) of normally hydrated control rats (group 1), and of rats drinking 2% NaCl for 7 (group 2), 30 (group 3) or 90 days (group 4) were investigated using immunohistochemistry for neurophysins (NP), arginine vasopressin (AVP) or oxytocin (OXY). Animals from the 3 experimental groups showed equivalent decreased levels of immunoreactive NP in the SON and PVN, but the greatest decrease was in the SON. Dendrites of SON and PVN neurons became loaded progressively with immunoreactive NP, AVP and OXY as salt loading proceeded. In rats of group 2, axons leaving the SON and PVN showed a marked depletion of immunoreactive material. The latter was found mainly at the periphery of widely spaced axonal swellings, clearly contrasting with the small and narrowly spaced beads of the neurosecretory axons of control rats. In rats of groups 3 and 4, axons leaving the SON and PVN resembled those of control rats. In the ME of the animals in all experimental groups, the same degree of decrease of immunoreactive NP was observed. In rats of group 3, bundles of axons containing immunoreactive AVP and OXY frequently projected through the ependymal lining of the ME into the third ventricle. In the NL of all experimental animals, a marked decrease occurred in the amount of immunoreactive NP, AVP and OXY. The decrease of immunoreactive AVP, however, was more pronounced in rats of group 2 than in those of groups 3 and 4. The NL of rats in group 4 were approximately 80% larger than those of control rats. Particularly striking in these hypertrophied NL were networks of expanded perivascular basal lamina and large intra-axonal vacuoles. The survival of rats to the long-term salt loading and the changes observed in the hypothalamo-neurohypophysial system indicate that these animals have developed adaptive mechanisms to the salt load.

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...

No abstract