The hypothalamo-hypophysial system in Acipenseridae

Summary The proximal neurosecretory contact region (PCR) of Acipenseridae, a homologue of the tetrapod median eminence, has been studied by light, fluorescence and electron microscopy. It occupies the rostral and chiefly the ventral surfaces of the hypothalamic tuber cinereum. PAF-positive fibres occur in the zone of the preoptico-hypophysial tract but their terminal enlargements are concentrated mainly in the external zone. They make contact with the primary portal capillaries situated in the pia mater. Monoaminergic fibres and terminals with an intense green fluorescence are localized in the same regions. The fibres of some bipolar monoaminergic neurons of the PCR make contact both with the third ventricle and the primary portal capillaries.Three types of granule-containing neurosecretory fibres and terminals have been recognized in the PCR. Fibres of types A₁ (d=120–300 nm) and A₂ (d=100–170 nm) are peptidergic PAF-positive, although some fibres, including some of type A₁; belong possibly to PAF-negative type. Monoaminergic type B fibres have granules 80–100 nm in diameter. Neurosecretory terminals and vascular endfeet of tanycytes make contact with the 70 nm thick outer basement membrane of the primary portal capillaries. Several laminae of thin horizontally oriented tanycyte processes form a boundary between the external zone and the preoptico-hypophysial tract. Few neuroglial cells with pale cytoplasm, numerous lysosomes and lipofuscin granules are seen in this region. It is hypothesized that, as in other vertebrates, both peptide hypophysiotropic neurohormones and monoamines are discharged from the PCR into the portal circulation and affect the activity of the glandular cells of the pars distalis.Dedicated to Prof. Dr. Drs. h.c. W. Bargmann on the occasion of his 70th birthday     

Morphofunctional basis of neurosecretory cell plasticity

Mass accumulation and storage of neurosecretory products are typical only for nonapeptidergic elements, as it has been shown by our study of the structure and function in neurosecretory cells of different nature. All liberinergic, statinergic and monoaminergic neurosecretory cells keep constancy in the state of high functional activity of extrusive processes at normal conditions. Morpho-functional features of these elements principally differ from those of nonapeptidergic neurosecretory cells, which are characterized by remarkable secretory cycles. The extremely large size of elementary secretory granules, maximum development of the Herring bodies, various modes of secretion, secretory and extrusive cycles in neurosecretory function, and massive accumulation of neurosecretory granules occurring in neurosecretory terminals finally, all these characters are considered to be the primary features of a high plasticity of the nonapeptidergic neurosecretory cell. A high reactivity of nonapeptidergic neurosecretory cells has been demonstrated here by the quantitative ultrastructural research of the dynamics of functional activity of neurosecretory terminals at both experimental and physiological stressful states. The highest plasticity of nonapeptidergic neurosecretory cells compared to all other neurosecretory cell types may be provided by their ability to restore the initial law level of functional activity, referred to as "functional reversion".     

Morpho-functional analysis of the steroid-producing cells in pink salmon fry gonads Oncorhynhus gorbuscha (Walbaum) in normal condition and after estradiol treatment

Localization and peculiarities of steroid-producing cells of gorbuscha fry gonads were studied in normal conditions and after experimental conditions. In females steroid-producing cells are found also in the follicle tunica and between interstitial cells, greatly differing in ultrastructure in these two localities. In males, these cells are located only in the testicular tunica, being homogeneous in ultrastructure. Chronical hormonal treatment of the fry with oestradiol-dipropionate induced in males, contrary to females, a considerable increase in the number and functional activity of steroid-producing cells and the appearance of these cells in the stroma of testis also. In females only a mass appearance of lipid-like droplets in the cytoplasm of steroid-producing cells is observed, which is also characteristic of males. The revealed morpho-functional peculiarities of steroid-producing cells are discussed in terms of their presumed important role in regulation of sex differentiation in fishes.     

The hypothalamo-hypophysial system in acipenseridae

Summary The neurohypophysis of sexually mature male and female Acipenser güldenstädti Brandt and Acipenser stellatus Pallas was studied light and electron microscopically. The recessus hypophysei lined with ependymal cells of two main types, narrow and wide, are in the center of the neurohypophysial roots. Processes from both cell types run radially to the basement membrane of the connective tissue layers abutting on the hypophysial intermediate lobe. Protrusions penetrating deep into the recessus hypophyseus are found in the apical parts of the wide cells. Pituicytes are rare in the neurohypophysis. The ultrastructure of both ependymal cell types and of the pituicytes is described. Nonmyelinated Gomori-positive (peptidergic) neurosecretory A₁ and A₂ type fibres and their terminals containing elementary neurosecretory granules (1400–1800 Å and 1000–1400 Å respectively) are the main structural elements of the neurohypophysis. Some dark and single myelinated neurosecretory fibres have been found. The adrenergic fibres (type B) were described earlier (Polenov et al., 1972a). The structural peculiarities of the neurohypophysis are discussed in functional and comparative-morphological terms.     

The hypothalamo-hypophysial system in acipenseridae

Summary The distribution of adrenergic and peptidergic (Gomori-positive) structures of the hypophysial neuro-intermediate complex in Acipenseridae has been studied by means of light, fluorescence, and electron microscopy. Adrenergic fibres (B-fibres) and their terminals have been detected in the neurohypophysis of these fishes. The terminal swellings of B-fibres as well as the terminals of the neurosecretory peptidergic fibres (A₁ and A₂) make contact with the basement membrane of the connective tissue layer separating the neurohypophysis from the intermediate lobe. Capillaries are situated within this layer and, therefore, the main part of the fibre terminals is in contact with the pericapillary space. The release of catecholamines from the adrenergic terminals into the capillaries connected with the general circulation is supposed. The diffusion of catecholamines through the connective tissue layer into the parenchyma of the intermediate lobe is also suggested. Hence, the glandular activity of the intermediate lobe seems to be under the dual control of adrenergic and peptidergic elements of the hypothalamus.The authors wish to express their deep appreciation to G. M. Persov, Dr. Sc. Biol., Head of the Laboratory of Experimental Ichthyology, Petershof Biological Institute of the University of Leningrad, for the material supplied for fluorescence microscopy, and to Mr. G. V. Sabinin for photographic services.     

The hypothalamo-hypophysial system in acipenseridae

Summary Neurohypophyses of sexually mature Acipenser güldenstädti Brandt and Acipenser stellatus Pallas maintained in hypertonic solutions were studied by means of light and electron microscopy. The fish were caught in the Ural and transferred into basins containing either freshwater (controls) or 32, 22 and 17 NaCl solutions respectively. The neurohypophyses of control animals kept in freshwater for two days contained a large amount of Gomori-positive neurosecretory material (4 arbitrary units). An abundance of neurosecretory granules of different kinds, predominantly elementary ones, was observed electron microscopically in neurosecretory fibres and terminals of these fish. A decrease in the amount of neurosecretory material was found in all experimental animals: up to 1–2 units in A. güldenstädti after 3.5–10 h in 32 NaCl, and up to 3.5 units in A. stellatus after 4.5–48 h in 22 or 17 NaCl. The number of neurosecretory granules decreased considerably in the fibres and terminals in all experimental series, but that of granulated, disintegrating granules and granule-shadows increased markedly, especially in preterminal parts of axons. An increased number of hypertrophied mitochondria, lamellar bodies, residual granules and especially synaptic vesicles was seen. These changes speak for an active discharge of neurohormones into the general circulation, a phenomenon well known to be characteristic of stress responses. Pathological ultrastructural changes (breakdown of terminals, extracellular wide cisternae) were visible in A. güldenstädti neurohypophyses at the end of the experiments. Also tanycytes — narrow ependymal cells — and pituicytes underwent noticeable changes.We wish to express our deep appreciation to the Director of the Guriev Branch of the Institute of Sturgeon Industry, N. E. Peseridi, M. Sc. Biol., for very valuable help in making this study possible.     

The hypothalamo-hypophysial system in acipenseridae

Summary The percentage of peptidergic (A₁ and A₂) and adrenergic (B) neurosecretory terminals was studied in the neurohypophysis of sexually mature female sturgeons. Neurosecretory terminals of the A₂ type prevail in the neurohypophysis, whereas A₁ and B terminals are rare. The activity of these types of terminals was established (1) during upstream migration, (2) shortly after spawning, and (3) three to six weeks after spawning. Terminals of B type are the most active elements during all the periods studied. These elements become strongly activated in sturgeons during upstream migration, i.e., earlier than the peptidergic neurosecretory terminals. Peptidergic terminals, especially elements of type A₂, become synchronously and strongly activated in fish shortly after spawning. In the late postspawning period neurosecretory terminals of all three types become synchronously inactive, persisting in a quiescent state in comparison to the two previous periods. The appearance of neurosecretory material discharged into the intercellular clefts by exocytosis correlates on the whole with the activity level of the A₁ and A₂ terminals in each individual studied. A functional correlation exists between the activity of the peptidergic and adrenergic neurosecretory terminals in the neurohypophysis. The data obtained are discussed with reference to a concept regarding spawning in some fish species as a physiological stress (Polenov et al., 1976). A possible dual control (peptide and monoamine neurohormones) over the function of visceral organs and glandular cells of the intermediate lobe of the hypophysis is also suggested (Polenov, 1970, 1975, 1978; Polenov and Belenky, 1973).Dedicated to the memory of Professor Wolfgang Bargmann, a great scientist and a generous friend