Axoglial synaptoid contacts in the neural lobe of the human fetus

Pituicyte Cues Regulate the Development of Permeable Neuro-Vascular Interfaces

The hypothalamo-neurohypophyseal system (HNS) regulates homeostasis through the passage of neurohormones and blood-borne proteins via permeable blood capillaries that lack the blood-brain barrier (BBB). Why neurohypophyseal capillaries become permeable while the neighboring vasculature of the brain forms BBB remains unclear. We show that pituicytes, the resident astroglial cells of the neurohypophysis, express genes that are associated with BBB breakdown during neuroinflammation. Pituicyte-enriched factors provide a local microenvironment that instructs a permeable neurovascular conduit. Thus, genetic and pharmacological perturbations of Vegfa and Tgfβ3 affected HNS vascular morphogenesis and permeability and impaired the expression of the fenestral marker plvap. The anti-inflammatory agent dexamethasone decreased HNS permeability and downregulated the pituicyte-specific cyp26b gene, encoding a retinoic acid catabolic enzyme. Inhibition of Cyp26b activity led to upregulation of tight junction protein Claudin-5 and decreased permeability. We conclude that pituicyte-derived factors regulate the "decision" of endothelial cells to adopt a permeable endothelial fate instead of forming a BBB.

Co-localization of TFF3 peptide and oxytocin in the human hypothalamus

TFF-peptides (formerly P domain peptides, trefoil factors) are typical secretory products of many mucous epithelial cells. TFF3 is also synthesized in the hypothalamus and has anxiolytic or anxiogenic activities when injected into the rat amygdala. Here we show by immunohistochemistry that TFF3 is localized to a distinct population of neurons of the human hypothalamic paraventricular and supraoptic nuclei. Generally, TFF3-positive cells are co-localized in oxytocin-producing cells and not in vasopressin-producing cells. Relatively large amounts of TFF3-but not TFF1 and TFF2-are present in the posterior lobe of the human pituitary, where it is probably released into the bloodstream. Furthermore, TFF3 was also detectable in human postmortem cerebrospinal fluid.

Ultrastructure of the neurohypophysis

This review summarizes our current knowledge of the ultrastructure of the human neurohypophysis and includes comments on its anatomy, physiology, and embryology. The neurohypophysis represents a unique tissue having neural and endocrine characteristics and possessing ultrastructural features distinct from those of conventional endocrine organs such as the anterior pituitary, thyroid, pancreatic islets, etc. In contrast to these glands, the neurohypophysis is composed of the processes of mature neurons. As such, it is not capable of synthesizing hormones but only of their storage and release. Neurosecretion is one of the most exciting areas of neuroendocrinology and, although spectacular progress has been achieved in elucidating the process, a number of aspects are incompletely understood. Recent evidence indicates that the magnocellular nuclei of the hypothalamus, the anatomic origin and functional basis of the neurohypophysis, produce not only vasopressin and oxytocin, the so-called "neurohypophyseal hormones," but a number of other biologically active peptides as well. The physiologic function of these substances is largely unknown but they may be of profound importance in endocrine homeostasis. Based on these novel findings, the role of the neurohypophysis in endocrine regulation has to be re-evaluated.

Phagocytosis of myelin sheath fragments by dendrites

In serial ultrathin sections of the frog spinal cord, profiles of dendritic appearance were identified that contained myelin fragment inclusions and received synaptic contacts. In a number of cases it could be established that the inclusions were derived from adjacent myelin sheaths. It is suggested that the phenomenon may refer to a turnover of the myelin sheath in which the detached myelin fragments are eliminated by dendrites.

Axoglial contacts in the area postrema of the cat: an ultrastructural study

Axoglial contacts were observed in an ultrastructural study of the area postrema of the cat. According to the disposition of the electron-dense projections attached to the adjoining membranes these contacts were classified as symmetrical or asymmetrical. The axon profiles contained aggregations of clear vesicles randomly distributed or grouped in cluster adjacent to the electron-dense projections. Dense core vesicles were occasionally seen. The neuroglial profiles were either astrocytic or ependymoglial in nature. The astrocytes showed a clear cytoplasm, polymorphous vesicles, mitochondria, glycogen granules, and bundles of filaments. The ependymal cells, in contrast, had a more electron-dense and granular appearance, tubular structures, irregular vesicular formations, profiles of smooth reticuloendoplasm, and filaments grouped in bundles or isolated in the cytoplasm. The possibility that these contacts might play a role in the chemical transfer from neurons to glial cells is discussed on the basis of existing biochemical data.

The developmental expression of neurofilament and glial filament proteins in the human pituitary gland: an immunohistochemical study with monoclonal antibodies

Monoclonal antibodies (MA) specific for neurofilaments (NF) and glial filaments (GF) were used to study the development of the normal human pituitary gland in fetuses, premature infants and adults. A total of 16 serially sectioned pituitary glands was examined. The expression of both NF and GF proteins correlated with maturation of the pituitary gland. Axons, but not cell bodies, were observed to contain immunoreactive NF proteins and these labeled axons were restricted almost exclusively to the pars nervosa. However, in early stages of development, intra-axonal NF proteins were not detectable. Aggregates of NF material in ' blobs ' were also observed in the pars nervosa of adults and a premature infant who survived 6 months following birth. They were never observed in more immature pituitary glands. Cells containing immunoreactive GF proteins were present in all subdivisions of the pituitary gland and they were more common in later stages of development. However, such cells represented only a minority of those present in the pituitary gland and cells in the pars distalis did not express GF protein until after birth. ' Blobs ' comprised of immunoreactive GF proteins were also seen. They were restricted to the pars nervosa and appeared later in development.