A. Porte

An unusual familial cardiomyopathy characterized by aberrant accumulations of desmin-type intermediate filaments

Immunofluorescence microscopy using antibodies specific for different intermediate filament types has been used to study a rare familial cardiomyopathy characterized electron microscopically by massive accumulations of unordered intermediate filaments. The results show that the inclusions in cardiac muscle cells are composed of the desmin type of intermediate filament characteristic of muscle tissues, and draw attention to the importance of these filaments in maintaining normal cardiac ultrastructure and function.

Fine structure and development of the pars tuberalis in mammals

The precise function of the tuberal lobe or pars tuberalis (PT) of the adenohypophysis identified anatomically by Tilney (1) and embryologically by Atwell (2) still poses an enigma (3). This lobe, consist-ing mainly of chromophobic cells in most species, was long considered an undifferentiated rostral extension of the pars distalis (PD). Electron microscopy, however, has revealed that the PT cells, except those lining the follicular cavities, clearly have the characteristics of peptide-producing glandular cells in mammals (4–13) as well as in other classes of vertebrates (3, 13, 17). The chromophobic cells of the rat PT containing small secretory vesicles were at first interpreted as corticotrophs (4, 6). Since typical gonadotrophs cells also proliferate in the PT after hypophysectomy, this lobe was thought to have mainly auxiliary or substitutional function in the case of high PD hormone demand (4, 8). This opinion has been corroborated by immunocytochemical data (18, 19). However, electron-microscope studies on the PT of various mammals under normal and experimental conditions (5, 10–13), and during its ontogenesis in the rat and the mouse (20, 21), and immunocytochemical data (22), indicate that PT glandular cells are in general peculiar to this lobe, i.e. are not found in the other adenohypophyseal lobes. So it seems highly probable that the PT has a specific but as yet undetermined function which should no longer be neglected in hypophyseal physiology.

The rostral zone of the intermediate lobe of the mouse hypophysis, a zone of particular concentration of corticotrophic cells. A light and electron microscopic study.

SummaryThe rostral zone of the intermediate lobe of the mouse hypophysis can clearly be distinguished from the other lobes of the adenohypophysis, especially from the pars tuberalis and the remainder of the intermediate lobe. It consists almost exclusively of corticotrophic cells which show reactive changes after adrenalectomy. The hypophysial stalk is entirely surrounded by this zone; laterally it forms large cell aggregations which extend dorsally as thin cell strands. The corticotrophs are also found within the hypophysial stalk which they invade along the blood vessels; frequently they are dispersed among the typical cells of the intermediate lobe, especially along the neural lobe and the hypophysial cleft.

Subcellular localization of calcium in the mouse hypophysis

SummaryApplication of the K-pyroantimonate technique combined with glutaraldehydeosmium fixation results in a reproducible intracellular distribution of mineral precipitates in the mouse hypophysis. Control experiments—with chelators and electron probe microanalysis— reveal that these precipitates consist mainly of calcium.Regularly present in the mitochondria, Ca also seems to be stored in the Golgi apparatus of the glandular cells and in the axoplasmic reticulum and the “synaptic” vesicles of the neurosecretory fibres. These structures thus appear able to control intracytoplasmic calcium movements. These observations agree with physiological data showing the existence of an intracellular Ca pool that can be mobilized by specific stimulation.The presence of diffuse precipitates in the pituicytes, together with the existence of gap junctions between them, suggest that these cells regulate the ionic environment of the neurosecretory nerve fibres; in this way, they too might participate in neurohypophysial hormonal release.

Nematosomes or nucleolus-like bodies in hypothalamic neurons, the subfornical organ and adenohypophysial cells of the rat

SummaryFibrillar intracytoplasmic bodies, generally referred to as nematosomes or nucleolar like bodies (NLBs), are not only observed in various types of neurons in the hypothalamus and subfornical organ but also in the glandular cells of the pars tuberalis and the pars intermedia hypophyses. According to their cytochemical properties the NLBs are probably of ribonucleoprotein nature. Within the neurons NLBs occur within perikarya and processes. Their presence within the neurosecretory nerve fibers of the neural lobe proves their ability to migrate within the axon. Morphologic modifications of NLBs are observed in stimulated neurons and after colchicine treatment. Colchicine causes a characteristic dense texture of NLBs and a peripheral agglomeration of mitochondria very similar to the rosette arrangement observed in oocytes. Our findings suggest a structural and functional similarity of NLBs in neurons and oocytes, in which their nucleolar origin appears obvious and where they seem to represent preribosomal material. It is very likely that the axonal migration of the NLBs reflects transport of ribosomal RNA for delayed utilization (as in oocytes).

A light and electron microscopic study of the pre- and postnatal development and secretory differentiation of the pars tuberalis of the rat hypophysis

SummaryThe development of the pars tuberalis was studied in the rat fetus from 13 days of gestation to 6 weeks after birth. After the closure of Rathkes pouch, the pars tuberalis anlage is clearly distinguishable from the anlagen of the partes intermedia and distalis. It comprises the entire basal portion of the adenohypophysial anlage; the limit between the anlagen of the pars tuberalis and the pars distalis is defined by Atwells recess, i.e. the pathway taken by the hypophysial vessels coming from the vascular plexus of the median eminence.At 14 days the pars tuberalis cells are characterized by the presence of glycogen which persists in the adult. Their secretory differentiation (elaboration of granules with a diameter of 100–120 nm) is obvious at 15 days of gestation. It therefore, clearly precedes that of the other hypophysial cell types. Its functional differentiation takes place well before its adhesion to the primary vascular plexus of the portal system. Cystic formations appear just before birth in the pars tuberalis, much later than those of the pars distalis.These observations on the development of the pars tuberalis, together with previous observations on the adult PT in various species, showing that the specific glandular cells of the pars tuberalis are cytologically different from all known adenohypophysial cell types, seem to indicate a specific endocrine function of this lobe.

Immunocytochemical evidence for intragranular processing of pro-opiomelanocortin in the melanotropic cells of the rabbit

SummaryThe immunogold technique, employing antisera with clear-cut specificities, was used to localise different processing stages of pro-opiomelanocortin (POMC) in rabbit melanotropic cells. While the antiserum against γ3-MSH labelled all the secretory granules including intrasaccular condensations in the Golgi apparatus, antisera against α-MSH only labelled extra-Golgi secretory vesicles (SV). All extra-Golgi SV were likewise labelled with the three antisera against α-MSH used, despite their different specificities for the desacetylated, N-acetylated or C-amidated forms of the peptide. The antibody against β-endorphin also labelled the extra-Golgi SV, while only some SV were labelled with the antibody against γ-endorphin. These results correlate with biochemical data in favour of mainly — if not exclusively — intragranular processing of POMC. Except for γ3-MSH, the cleavage of which could coincide with Golgi packaging of secretory material, other post-translational modifications of the precursor seem to occur when SV are discharged outside the Golgi area. The cleavage of γ-endorphin appears to be a later step in POMC processing, occurring in some mature SV.

Embryonic development and secretory differentiation in the pars tuberalis of the mouse hypophysis

SummaryThe pars tuberalis (PT) of the mouse, like that of other mammals, consists mainly of glandular cells rich in glycogen and peculiar to this lobe. In the mouse, the glandular cells are characterized by large, dense secretory vesicles (up to 300 nm in diameter), the abundance of which indicates a marked secretory activity. The PT develops from a distinct antero-ventral area of Rathkes pouch. The border between the anlagen of the PT and the pars distalis is formed by Atwells recessus which represents the access for the vessels afferent to the pars distalis. The pedicle of Rathkes pouch is incorporated into the PT anlage, thus contributing to its formation. The entire PT anlage is characterized by glycogen accumulation from the commencement of its formation and persisting in the adult tuberal lobe. Secretory differentiation of the glandular cells of the PT occurs at day 12 of gestation, preceding that of all other adenohypophysial cell types. The secretory features of these cells (development of ergastoplasm and Golgi apparatus, abundance of dense secretory vesicles) appear at an early stage of the embryonic life (14 days) comparable to those of mature cells. These results confirm earlier observations in the foetal rat where hypophysial secretion also begins in the PT. The existence of peculiar glandular cells speaks in favour of a specific but still unknown function of the PT during foetal and adult life.

Oxytocin-immunoreactive nerve fibers in the pars intermedia of the pituitary in the rabbit and hare

SummaryThe pars intermedia of the pituitary in the rabbit and hare is abundantly innervated by axons reacting selectively with antibodies against oxytocin. These axons contain dense secretory vesicles about 140 nm in diameter, i.e., smaller than those in the neurosecretory axons of the neural lobe. No fiber elements staining for other peptides (vasopressin, somatostatin, substance P) were observed in the pars intermedia, except rare leu-enkephalin axons restricted to the rostral zone of the gland. Dopaminergic innervation appears to be completely absent from the intermediate lobe. This was shown by the lack of reaction with an antibody against tyrosine-hydroxylase, which did reveal a well-developed tubero-infundibular system of nerve fibers. Axons reacting with an antibody against serotonin were irregularly distributed in the pars intermedia.In the absence of dopaminergic axons, the extensive oxytocin-like innervation may play a major role in regulating the melanotrophic cell activity in the Leporidae.

The fine structure of the conducting system of the monkey heart (Macaca mulatta)

SummaryIn the sino-atrial (S-A) node of the monkey heart two types of muscle cells occur: 1. typical nodal cells which are the predominant cells and form the nodal fibers. 2. “Intercalated clear cells” with various diameters (4 to 12 μm) and containing poorly developed myofibrils, rich in glycogen and demonstrating poor staining properties. These latter cells are dispersed, few in number, and never form discrete fibers of themselves, but are intercalated between the cell rows of the typical nodal fibers. Such intercalated clear cells become more numerous at the periphery of the node. Interconnection between the S-A node and the conventional atrial muscle is established by a progressive transformation of nodal fibers into atrial fibers producing an intermediate (or junctional) type of fiber at the nodal periphery. However, in addition, few nodal fibers make direct contact with the atrial cardiocytes. Our light and EM studies have failed to prove the existence of truly specialized internodal pathways. Nevertheless intercalated clear cells, nodal-like cells, junctional or intermediate type of cells are relatively frequent in valvular regions (Thebesian, Eustachian, A-V, fossa ovalis) and less frequent in other regions of the atrial wall.