Mordechai Abraham

Ultrastructure of the cell types and of the neurosecretory innervation in the pituitary of Mugil cephalus L. from freshwater, the sea, and a hypersaline lagoon II. The proximal pars distalis

The ultrastructure of the cells of the rostral pars distalis and their neurosecretory innervation were studied in the pituitaries of Mugil cephalus from fresh water (FW), the sea (SW), and a hypersaline lagoon (HL). The secretory granules of the eta cells have a median diameter of 2600 A in FW, 2300 A in SW, and 1800 A in HL. Large-sized nucleus and nucleolus, a well developed endoplasmic reticulum, and abundance in secretory granules in FW eta cells were interpreted as indicating high synthetic activity, while scarcity of granules, decrease of cellular size as well as reduction of the volume of the RPD in HL specimens were interpreted as indicating high release and inadequate synthesis. An intercellular channel system formed by specialized channel cells in the eta cell region is described. In the epsilon cell region, a channel system is formed by invaginating membranes of the epsilon cells. Neurosecretory granules in the rostral neurohypophysis are of two types: (1) presumably peptidergic, which accompany the capillaries and probably most of them empty into the capillaries before the latter penetrate the epithelial region; and (2) presumably aminergic granules which are close to the interface which separates the neurohypophysis from the rostral pars distalis. Neurosecretory elements in the adenohypophyseal region between the eta cells, are of the aminergic type. The possible roles of the different neurosecretory granules are discussed.

The blood-testis barrier in Aphanius dispar (Teleostei)

SummaryThin sections of normal testes from the cyprinodont Aphanius dispar were studied by electron microscopy after intravascular injection of live specimens with horseradish peroxidase. The intercellular space in the spermatogenic cysts is marked differently by the tracer according to the degree of differentiation of the germ cells. Spermatogonia and gonocytes undergoing meiosis are surrounded by a dark band of the marker. This band gradually disappears during spermiogenesis. In cysts containing ripe spermatozoa, the marker penetrates a short distance between the bases of adjoining Sertoli cells bordering the cysts, but is arrested by tight junctional complexes near the lumina of the cysts. The tight junctions between the Sertoli cells provide a permeability barrier between the vascular spaces of the stroma and the lumina of ripe cysts.

The influence of environmental salinity on the prolactin- and gonadotropin-secreting regions in the pituitary of Mugil (Teleostei) ☆

Specimens of two species of Mugil were collected from three environments differing in salinity (freshwater, seawater, and a hypersaline lagoon). Volumetric and histological changes in the proximal and rostral pars distalis of pituitaries from these fish are described. The most pronounced changes occur in the size of the rostral pars distalis of M. capito. This lobe (whose main component is the prolactin-secreting region) varies, occupying from 8% of the total hypophysis in fish from the hypersaline lagoon (7.8% salinity), to 42.6% in fish from freshwater. This increase in the size of the rostral pars distalis is accompanied by an increase in the size and granular content of individual eta cells. The volumetric changes of the proximal pars distalis are the inverse of those of the rostral pars distalis. Proximal pars distalis changes were most pronounced in M. cephalus, where this lobe occupies 35% of the hypophysis in specimens collected from the Mediterranean Sea during the spawning season, as compared with 7.3% of the hypophysis in specimens collected from freshwater. The prolactin content of the pituitary in M. cephalus as assayed by the water-drive test in Triturus vulgaris and T. alpestris is high in the freshwater specimens and low or almost nonexistent in specimens collected from the sea. Striking histological changes, possibly indicative of a degenerative process, are observed in the nucleus lateralis tuberis of M. cephalus specimens confined to freshwater for several years. These changes and their relationship to the volumetric variations of the rostral and proximal pars distalis of the pituitary are discussed. Data on the mucous and chloride cells of the gills as well as on the sodium plasma level are presented.

The cellular envelope of oocytes in teleosts

SummaryStructural and functional relationships between oocytes and their envelopes were studied by means of electron microscopy in several teleost species after injection of live fish with horseradish peroxidase. The marker first appeared in the capillaries and the pericapillary spaces of the ovarian stroma. It then entered the collagen-filled spaces between the granulosa and theca cells; these spaces are in direct connection with the pericapillary spaces. The marker penetrated between the follicle cells and into the channels of the zona radiata surrounding the microvilli which traverse these channels. The marker was never found inside the microvilli or in the follicle cells; finally, it reached the surface of the oocytes and was internalized via micropinocytosis. Six stages in the course of folliculogenesis were observed, determined by (1) the formation of follicular and thecal cellular layers and a collagen-filled space between them, (2) the development of microvilli of oocytal and follicular origin, (3) the differentiation of the vitelline envelope and the pore channels, (4) pinocytotic activity of the oocytes, and (5) rapid growth of the oocyte and its envelopes during vitellogenesis.

The ovarian cycle during the intermoult in ovigerous Macrobrachium rosenbergii

Abstract Adult female Macrobrachium rosenbergii held in captivity in optimal growing conditions spawned within a few hours after their pre-mating moult. If fertilized, the females carried the eggs with the developing embryos under their 1st–4th abdominal segments in a brood chamber. In about 90% of the animals investigated, while the developing embryos were being carried, a new batch of oocytes was maturing in the ovaries, increasing from 100 μm to 530 μm, the final size of ripe eggs. Ovarian cycle time sequences were established with reference to pre-mating moult, color changes of the developing embryos, zoea hatching and pre-mating moult of the next cycle. The relationship between growing oocytes and their follicular cell envelope was studied by light and electron microscopy.

Freeze-etch study of the teleostean pituitary

SummaryThe structure of membranes in the pituitary of several teleostean species was studied with the freeze-etching technique. Nuclear pore density is higher in hormone-secreting than in stellate cells, suggesting a higher rate of nucleo-cytoplasmic interactions in the secretory cells. The perinuclear endoplasmic reticulum (ER) in the MSH-secreting cells has a large number of fenestrae, whereas in the ER whorls of the prolactin-secreting cells the fenestration occurs only rarely. Three different types of membrane specializations are described, presumably related to exo-endocytotic events at the level of the plasmalemma.

Effects of metformin on plasma insulin, glucose metabolism and protein synthesis in the common carp (Cyprinus carpio L.)

Abstract A heterologous radioimmunoassay was developed to measure insulin levels in common carp plasma, using Bonito insulin components. The specificity of the antibodies was demonstrated by using an immunocytochemical technique and by dose-response curves of plasma dilutions from carp which were paralleled to the Bonito insulin standard curve. Plasma insulin levels of fasted carp were 5.4 ng/ml and nearly doubled in fed fish. The incorporation of 3 H leucine into white muscle proteins of fed fish doubled as compared to the fasting group. Treatment with metformin increased the disposal of glucose during glucose tolerance tests and the incorporation of 3 H leucine into white muscle proteins, inhibited gluconeogenesis from 14 C alanine, but had no effect on plasma insulin or basal glucose levels. The mode of action of metformin is probably similar in fish and mammals.

Response of club cells in the skin of the carp Cyprinus carpio to exogenous stressors

The ultrastructure of club cells and neighbouring filament cells and leucocytes in the epidermis of carp, was studied under normal conditions and after exposure to several stressors: acid water, heavy metals, organic manure, brackish water and wounding. The effects of the stressors were remarkably similar. The club cells increased in size and contained more endoplasmic reticulum and Golgi areas. In both control and stressed fish, most mitotic figures of the filament cells were found adjacent to club cells, as was demonstrated after colchicine injection. Whereas in the controls apoptosis of filament cells was scarce and limited to the upper layer of the epithelium, in the stressed fish it was commonly seen in close proximity to the club cells but not in other mid-epidermal parts of the epithelium. This indicates that club cells influence the cellular kinetics of the filament cells. Under stress conditions leucocytes infiltrated the epidermis. Some were seen inside club cells. Apparently these leucocytes were taken up in phagosomes and subsequently they showed signs of necrotic degeneration. Leucocyte incorporation and degeneration in club cells were not observed in control fish. Control of the cellular turnover of filament cells and the elimination of leucocytes may represent new functions for club cells, which have mainly been associated with the production of pheromones.

Effects of adrenosterone on gonadal and body growth in Tilapia nilotica (Teleostei, Cichlidae)

Fertilized eggs of the bony fish Tilapia nilotica were incubated in water containing adrenosterone (5 mg/liter). The treatment resulted in a significant enhancement of body growth accompanied by gonadal degradation. All the treated fish examined at the end of the treatment period (3 months) were devoid of any normal gonadal structures. At the age of 8 months, none of the treated fish possessed ovarian tissues, and 92% of the expected number of male fish had regenerated testicular tissue.

Effects of a dry diet on the antidiuretic hormone content of the neurohypophysis in spiny mice as compared to the albino rat and mouse

Abstract Changes in ADH content of the neurohypophysis of two xeric rodent species ( Acomys cahirinus and Acomys russatus ) and two mesic laboratory albino species ( Rattus norvegicus and Mus musculus ) were investigated by means of bioassay. When kept on a dry diet, the ADH content of the rat hypophysis decreased continuously, sinking lowest at 17 days of water deprivation, by which time all the rats succumbed. On the other hand, in both species of Acomys and in the albino mouse on a similar regime, initial depletion of ADH was followed by repletion of the hormone store. This recovery was more evident when ADH content was expressed in relation to body weight. As normal specimens of all four species did not show any striking inter-specific variation in neurohypophysial ADH content, it appears that the resistant species are characterized by an adaptive mechanism of replenishing hormone content when challenged.