Akio Kikuta

Myelin localization of a central nervous system ligand for L-selectin

L-selectin is a lectin-like receptor involved in lymphocyte attachment to lymph node high endothelial venules (HEV). Previously, we showed that L-selectin also participates in the in vitro attachment of lymphocytes to central nervous system (CNS) white matter. Use of an L-selectin chimera demonstrated ligand sites within CNS white matter but not the peripheral nervous system (PNS). Now employing higher resolution mapping, including EM cytochemistry, we localize the ligands to the actual myelin sheaths of CNS neurons. In the shiverer mouse, which lacks compact myelin, ligands are greatly diminished. Comparison of the myelin-associated ligand with the previously characterized HEV-ligands demonstrates a number of differences.

Microvasculature of the Ovary

Oocyte development and hormone secretion are mutually related functions of the ovary. Oocytes develop and mature within developing follicles. Ovarian hormones are secreted from the stromal intersitial tissue, follicle, and corpora lutea, which are transformed from postovulatory follicles. The follicles, corpora lutea, and stroma compose the cortex of the ovary, and appear during the estrous cycle as successively transforming structures accompanied by very dynamic and continuous changes of their microvascular systems, including active angiogenesis, reconstruction, and degeneration of vessels.

Microvascularization of endocrine glands as studied by injection-replica SEM method

Endocrine cells or glands secrete their products, hormones, into the blood capillaries through the surrounding connective tissue space. These hormones are transported by blood flow to their target cells or tissues. Routes of hormone transport to the targets are, generally, by way of the heart. However, since the discovery of the hypophyseal portal vascular system (1,2), short-range vascular routes of hormone transport have received a great interest among endocrinologists. Most of the studies on microvascular architecture or microcirculation have been performed by light microscope methods mainly using injected sections. However, the limited depth of field with a light microscope does not provide sufficient visualization of blood vessels of tissues and organs.

Effects of formaldehyde on cardiovascular system in in situ rat hearts.

The aim of the present study was to examine the effects of formaldehyde solution on rat left ventricular function and compare it with those in hypertrophic hearts treated with isoproterenol by pressure-volume measurements with the catheter method. After 20-30 min. of intravenous infusion of 3.7% formaldehyde solution (FA) at 10 μl (3.7 mg)/kg/min, normal and hypertrophic hearts showed significant decreases in left ventricle end-systolic pressure (ESP), heart rate and cardiac output per minute, indicating an acute pumping failure. Hypertrophic hearts showed significantly smaller ESP, stroke volumes and cardiac output than those in normal hearts. Systolic pressure-volume area at midrange left ventricular volume (PVA(mLVV) : a mechanical work capability index) was significantly smaller than that in normal hearts and per cent of mean PVA(mLVV) versus pre-infusion mean value in hypertrophic hearts was significantly decreased compared to normal hearts 30 min. after FA infusion. The marked decrease in pH, base excess and no changes in PaO₂ and PaCO₂ suggest metabolic acidosis. The correction of metabolic acidosis with 9% NaHCO₃ did not influence on the acute pumping failure, indicating that metabolic acidosis did not cause it. Ultrastructural observations revealed marked dilation of the sarcoplasmic reticulum with intact sarcolemmal membranes and no disintegration of muscle myofibrils. Ryanodine receptors and calcium (Ca²⁺) pumps (SERCA2A) located in the sarcoplasmic reticulum have major roles in the cytosolic Ca²⁺ handling. Taken together, acute pumping failure by FA may derive from the impairment of Ca²⁺ handling in the cardiac excitation-contraction coupling.

The Ovary: Three-Dimensional Morphodynamics of the Luteo-Follicular Complex by SEM of Vascular Corrosion Casts and Other EM Techniques

The main ovarian activities are morphofunctionally related to the dynamic structure called the luteo-follicular complex (LFC). The LFC, in fact, is the morphodynamic expression of the continuous and cyclical modifications of the parenchymal ovarian components: the developing follicles and corpora lutea.

Ruthenium red antagonism of the effects of capsaicin mediated by extrinsic sensory nerves on myenteric plexus neurons of the isolated guinea-pig ileum

The effects of Ruthenium red and its antagonism of capsaicin-induced action on the electrophysiological behavior of myenteric neurons were investigated with intracellular recording techniques in the isolated guinea-pig ileum. Ruthenium red antagonized dose-dependently (1-10 microM) a capsaicin-induced marked long-lasting slow depolarizing action associated with increased input resistance, during which the cells spiked repeatedly or displayed anodal break excitation. This action of capsaicin has been found to be mediated via a release of substance P from sensory nerve endings. The slow depolarizing response to exogenous substance P applied by pressure microejection, which mimicked the capsaicin-induced action, was not affected by Ruthenium red. Therefore, present results indicate that Ruthenium red antagonizes the specific effect of capsaicin on myenteric neurons by acting on the presynaptically located peripheral nerve terminals of sensory neurons and inhibiting the release of substance P. Electron-microscopic examination showed that the neurotoxic action of capsaicin towards extrinsic sensory nerve fibers was also dose-dependently (1-10 microM) protected by pretreatment of ruthenium red. Present results suggest that Ruthenium red inhibits a capsaicin-induced activation of cation channels at the cell membrane of sensory nerves.

Evaluation of left ventricular mechanical work and energetics of normal hearts in SERCA2a transgenic rats

Cardiac sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a) is responsible for most of the Ca2+ removal during diastole and a larger Ca2+ handling energy consumer in excitation–contraction (E–C) coupling. To understand the cardiac performance under long-term SERCA2a overexpression conditions, we established SERCA2a transgenic (TG) Wistar rats to analyze cardiac mechanical work and energetics in normal hearts during pacing at 300 beats/min. SERCA2a protein expression was increased in TGI and TGII rats (F2 and F3 of the same father and different mothers). Mean left ventricular (LV) end-systolic pressure (ESP) and systolic pressure–volume area (PVA; a total mechanical energy per beat) at midrange LV volume (mLVV) were significantly larger in TGI rats and were unchanged in TGII rats, compared to those in non-TG [wildtype (WT)] littermates. Mean myocardial oxygen consumption per minute for E–C coupling was significantly increased, and the mean slope of myocardial oxygen consumption per beat (VO2)–PVA (systolic PVA) linear relation was smaller, but the overall O2 cost of LV contractility for Ca2+ is unchanged in all TG rats. Mean Ca2+ concentration exerting maximal ESPmLVV in TGII rats was significantly higher than that in WT rats. The Ca2+ overloading protocol did not elicit mitochondrial swelling in TGII rats. Tolerance to higher Ca2+ concentrations may support the possibility for enhanced SERCA2a activity in TGII rats. In conclusion, long-term SERCA2a overexpression enhanced or maintained LV mechanics, improved contractile efficiency under higher energy expenditure for Ca2+ handling, and improved Ca2+ tolerance, but it did not change the overall O2 cost of LV contractility for Ca2+ in normal hearts of TG rats.

Visualization of Human Vestibular Aqueduct with Computeraided Serial Section Reconstruction System

The computer-aided serial section reconstruction system (SERSERS) was employed to elucidate the entire configuration of the vestibular aqueduct in the human temporal bone. The advantages and the disadvantages of this system are discussed in comparison with several conventional methods such as X-ray visualization, plastic casting and graphic reconstruction. In spite of some limitations encountered, such as difficulty in placing a marker on each section or time consumption in data input, SERSERS can be useful in the study of the vestibular aqueduct, since a three-dimensional structure which can be observed from multidirectional aspects is reconstructed.

Three-Dimensional Microvascular Architecture of the Testis and Excurrent Duct System Studied by Corrosion Casting-Scanning Electron Microscopy

The mammalian testis and the excurrent duct system are composed of an extraordinarily long duct system, seminiferous tubules, epididymal ductules, and vas deferens, in which spermatogenesis, hormone secretion, and protein secretion and absorption continuously occur. In particular, the seminiferous tubules are compactly packed within the oval space by the tunica albuginea. In humans and many mammals, such as the rat and mouse, in which spermatogenesis is labile to high temperature, the testes are localized within the scrotum and spermatogenesis proceeds safely at a temperature 2–3° lower than that of the intraperitoneal cavity [1–3]. The vascular system that supplies and drains the scrotal testis has been considered to be organized in special vascular arrangements for cooling arterial blood before entering the testis, as well as enabling continuous and homogeneous blood flow throughout the testis.

Renal vasculature as observed by SEM of vascular casts. Basic architecture, development and aging of glomerular capillary beds

Scanning electron microscopy (SEM) of sample casts allows clear three-dimensional and long range viewing of fine blood vascular beds and other vascular systems, previously poorly visualized by conventional light or transmission electron microscopy of sectioned samples [1, 2, 3, 4, 5, 6, 7]. Spatial relations between the vessels and surrounding tissue elements cannot be examined in the cast as it is observed in isolation. Despite this limitation, displaying vascular patterns as independent structures already has proven useful and valuable in the study of microvascular architecture and microcirculation in various organs and tissues, including the kidney [8, 9, 10, 11, 12, 13, 14].