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Biomedical subjects

A Chiba

Publications and source records attributed to A Chiba.

At least 145 records · Page 8Linked to original sources
PubMed1989

Immunocytochemical localization of S-100 protein in the hypophysis and saccus vasculosus of the elasmobranchs Mustelus manazo and Scyliorhinus torazame.

S-100 protein-immunoreactive cells were demonstrated by immunocytochemical procedures in the hypophysis and saccus vasculosus of two species of elasmobranchs (Mustelus manazo and Scyliorhinus torazame). In the saccus vasculosus of M. manazo, immunoreactivity was detectable exclusively in the fibrous portions interposed between the epithelial layer and the blood vessels. In the neurohypophysis, tanycytes and astrocytes of the median eminence were immunostained, but only a few labeled cells were found in the neurointermediate lobe. In S. torazame, the neurohypophysis displayed a similar distribution of immunoreactivity, but there were no labeled cells in the saccus vasculosus. In both species, none of the glandular cells of the hypophysis displayed immunoreactivity. Electron-microscopic examination showed that the immunostained cells in the saccus vasculosus correspond to astrocytes.

Animals↗
PubMed1988

Synaptic rearrangement during postembryonic development in the cricket.

Synaptic rearrangement during development is a characteristic of the vertebrate nervous system and was thought to distinguish vertebrates from the invertebrates. However, examination of the wind-sensitive cercal sensory system of the cricket demonstrates that some identified synaptic connections systematically decrease in strength as an animal matures, while others increase in strength over the same period. Moreover, a single sensory neuron could increase the strength of its synaptic connection with one interneuron while decreasing the strength of its connection with another interneuron. Thus, rather than being a hallmark of the vertebrate nervous system, synaptic rearrangement is probably characteristic of the development of many if not all nervous systems.

Action Potentials↗
PubMed1988

Occurrence of lymphohaemopoietic tissue in the meninges of the stingray Dasyatis akajei (Elasmobranchii, chondricthyes).

The cytoarchitecture of the lymphohaemopoietic masses occurring in the "meninx primitiva" of the stingray Dasyatis akajei (Elasmobranchii, Chondricthyes) has been analyzed by light and scanning and transmission electron microscopy. Lymphohaemopoietic aggregates showing similar morphologies occurred along all the central nervous system, but they were more frequent in the telencephalon, diencephalon, and mesencephalon. In each aggregate, the granulopoietic tissue appeared in a fibroblastic stroma surrounding the large blood vessels, and the lymphoid components were present in a reticular network. Developing and mature eosinophils and heterophils--as well as lymphocytes, monocytes, macrophages, and plasma cells--are the main free cells present in these meningeal aggregates. The remarkable intimate association between macrophages and lymphoid cells to form close cell clusters suggests some immunological capacity for the meningeal lymphohaemopoietic tissue. According to their capacities, presence of lymphoid tissue, and histological organization, the meningeal lymphohemopoietic aggregates of Dasyatis akajei resemble other lymphomyeloid aggregates associated with cranium and choroid plexuses in Holocephali and Ganoidei. The phylogenetical relationships of these aggregates with mammalian bone marrow are discussed.

Animals↗
PubMed1987

Vascularization of the hypothalamo-hypophysial complex in Japanese elasmobranchs: a scanning electron microscope study of blood vascular casts.

To study in detail vascularization in the hypothalamo-hypophysial complex in some Japanese elasmobranchs, injection casts of blood vessels were observed by scanning electron microscopy. Materials used were a gummy shark (Mustelus manazo), a cloudy dogfish (Scyliorhinus torazame) and a skate (Raja porosa). The vascular supply to the hypothalamo-hypophysial region of the elasmobranchs is carried out by the inferior hypothalamic arteries and their branches that originate from the internal carotid artery. In the gummy shark, a pair of inferior hypothalamic arteries send several branches to the median eminence running along the anterolateral sides of the distal adenohypophysis. These branches form the capillary plexus, displaying anastomosis and convolution at the ventral surface of the median eminence. The plexus assumes capillary glomeruli at the lateral region of the posterior median eminence. Numerous branches derived from the plexus are directed backward through the pars distalis, join with the capillary net work (which develop in the neuro-intermediate lobe) and are finally gathered together to form a thick hypophysial vein. The ventral lobe receives several arterial branches from the internal carotid arteries and carotid artery to form a unique vascular bed. Therefore, it is assumed that in elasmobranchs the hypothalamic control of the ventral lobe is weaker than that of adenohypophysial components.

Animals↗
PubMed1986

Aggregation of the smooth muscle cells found in certain hemopoietic organs and tissues of the stingray, Dasyatis akajei (Elasmobranchii, Chondrichthyes).

A combined light and electron microscopic study revealed that there are conspicuous aggregations of smooth muscle cells in several hemopoietic organs and tissues such as in the Leydig (esophageal) and epigonal organs, diencephalic choroid plexus and perihypophyseal connective tissue sheath of the stingray, Dasyatis akajei. These cells were gathered in bundles of varying caliber or arranged concentrically around a central focus, but neither innervation nor gap junction was found. In some of the concentrically arranged cells, signs of degeneration were noticed. The possible origin of these structures is discussed in relation to the vascularity of the loose connective tissue.

Animals↗
PubMed1981

Scanning and transmission electron microscope studies of the supraependymal neurons in the third ventricular wall of the Arctic lamprey, Lampetra japonica.

Scanning electron microscopy of the third ventricular wall of the arctic lamprey, Lampetra japonica, revealed the occurrence of supraependymal neurons in several regions of the ventricular surface. These neurons--as varicose fibers of various calibers--traversed among the cilia, microvilli, and bulbous protrusions of the ependymal surface. Occasionally synapse-like contact were found between these nerve fibers and the intraventricular processes of the cerebrospinal fluid (CSF)-contacting subependymal neurons in the hypothalamus. A possible function of the supraependymal neurons is discussed in relation to the hypothalamic neuroendocrine system.

Animals↗
PubMed1981

Ectopic presence of saccus vasculosus tissue in the neurohypophysis of three species of plectognath fishes (Tetraodontiformes, Teleostei).

The extraregional occurrence of saccus vasculosus tissue was observed in the neurohypophysis of several specimens of three species of plectognath fishes, Fugu niphobles. Fugu poecilonotus and Canthidermis rotundatus. The ectopic tissue occurred as a compact multitubular structure in the posterior portion of the pars nervosa, either being buried in it or attaching to its dorsal margin. Scanning electron microscopy revealed that ectopic crown cells of F. niphobles were distributed further in the ependymal layer of the infundibulum. A possible route of these crown cells to the neurohypophysis was discussed with special reference to the close anatomical relationship between the neurohypophysis and the saccus vasculosus in the embryonic stage.

Animals↗
PubMed1980

Refractoriness of the cyclic AMP response to catecholamines in rat parotid slices in vitro.

Parotid slices respond to norepinephrine with a rapid but transient accumulation of cyclic AMP. Continued exposure of the slices to norepinephrine results in a loss of responsiveness to subsequent application of norepinephrine (refractoriness or desensitization). Refractoriness could not be overcome by exposing the slices to a supra-maximum concentration of norepinephrine. The suppressed response was clearly seen at 15 min after the first exposure to norepinephrine, but about 60 min were required for reaching complete suppression. The refractoriness also depended on the concentration of agonists, and their order of potency correlated well with their agonistic activity. The induction of desensitization was beta- agonist specific, and was blocked by beta-adrenergic blocking agents such as atenolol and alprenolol. The recovery from desensitization was observed by removing norepinephrine from the medium. The recovery was not evident until 15 min after washing the slices, but was nearly complete after 1 hr. Although parallel changes were observed between the initial increase in cyclic AMP level and the degree of desensitization by norepinephrine, the induction of desensitization does not seem to be mediated by cyclic AMP. The mechanism underlying this phenomenon does not appear to involve the activation of phosphodiesterase, the formation of an inhibitory substance in the medium or an increase in the rate of excretion of cyclic AMP. Changes in the ATP level by norepinephrine did not always correlate with the degree of refractoriness. No significant changes in the amount of [3H]-dihydroalprenolol binding were found in the membrane fraction prepared from the slices incubated with norepinephrine. These results suggest that the induction of desensitization may be mediated by modulating the coupling process between the receptor and adenylate cyclase.

Adenosine Triphosphate↗