T cell repertoire in the liver of patients with autoimmune hepatitis

Despite a large number of T cells infiltrating into the liver of patients with autoimmune hepatitis (AIH), little is known about their roles or target antigens. To investigate the roles of these T cells in the pathogenesis of AIH, we have studied the clonality of alphabeta T cell populations in liver tissue by size spectratyping the complementarity-determining region (CDR)3 size lengths of T cell receptor (TCR) Vbeta-chain transcripts. Analysis of nine AIH patients who had the HLA DR4 haplotype showed clonal expansion in all samples. More than two T cell clones expanded in most patients. Although the expression of the TCR Vbeta genes was different among the nine patients, clonal expansion of T cells expressing either TCR Vbeta2, 3, 4, 16, or 22 was observed in two patients or more. TCR Vbeta4 clones expanded in 5 cases. Cloning and sequencing of TCR Vbeta CDR3 from PCR products revealed no whole CDR3-shared clones among different patients. In conclusion, several T cell clonotypes first recognize target antigens, then expand and accumulate in the liver of AIH patients. These suggest heterogeneity of autoantigens and the complexity of AIH immunopathogenesis in individual patients.

Relationship of 31P MR spectroscopy to the histopathological grading of chronic hepatitis and response to therapy

PURPOSE

In vivo phosphorus-31 MR spectroscopy (31P MRS) was performed in the human liver in order to investigate the relation between: the ratios of phosphorus metabolites in the liver; the histopathological grading of chronic hepatitis; and the response to therapy.

MATERIAL AND METHODS

Hepatic 31P MRS using the DRESS method (depth-resolved surface-coil spectroscopy) was carried out in 45 patients with chronic viral hepatitis or autoimmune hepatitis, and in 16 control subjects. We measured the ratios of the peak areas of phosphomonoesters (PME), inorganic phosphate (Pi), or phosphodiesters (PDE) to the peak area of beta-adenosine triphosphate (ATP).

RESULTS

The PDE/ATP ratio of patients with chronic hepatitis or liver cirrhosis was lower than that of control subjects (liver cirrhosis = 0.74; chronic active hepatitis = 1.13-1.21; normal = 1.43); only a small difference was found in the PME/ATP and Pi/ATP ratios. There was no correlation between the spectra and histopathological grading or response to therapy, but the response to therapy was poor when a reduced PDE/ATP ratio was present.

CONCLUSION

The PDE/ATP ratio measured by 31P MRS makes it possible to identify the transition of chronic active hepatitis into liver cirrhosis with a poor response to therapy.

Sequential relationship between actions of CRF and PGE2 in the brain on splenic sympathetic nerve activity in rats

An infusion of corticotropin-releasing factor (CRF, 0.1-5.0 micrograms/10 microliters/rat) into the third cerebral ventricle (i.c.v.) for 10 min increased the splenic sympathetic nerve activity in a dose-dependent manner in urethane + alpha-chloralose anesthetized rats. No changes in the arterial blood pressure and body temperature were observed. The CRF (1.0 micrograms/10 microliters)-induced enhancement of the splenic sympathetic nerve activity was completely blocked by an i.c.v. pretreatment with a CRF antagonist, alpha-helical CRF9-41 (alpha-hCRF, 10 micrograms/10 microliters). The increase in the splenic sympathetic nerve activity induced by CRF was not blocked by pretreatment with a cyclooxygenase inhibitor, sodium salicylate (100 micrograms/10 microliters). In contrast, the splenic sympathetic nerve activity also increased after an i.c.v. injection of prostaglandin E2 (PGE2, 1 ng/10 microliters) and the increase was completely blocked by i.c.v. pretreatment with alpha-hCRF. These findings suggested a sequential relationship between actions of CRF and PGE2, with an activation of PGE2 system followed by that of CRF system in the brain resulting in an increase in the splenic sympathetic nerve activity.

Quantitative measurement of HCV RNA in the serum: a comparison of three assays based on different principles

Quantitative measurement of hepatitis C virus (HCV) RNA is useful in patients with chronic hepatitis C, especially with interferon treatment. We examined the clinical usefulness of the AMPLICOR monitor assay, a newly developed assay for quantitative measurement, by comparing it with two other assays with different principles. A total of 48 patients with chronic hepatitis C who were treated with interferon-alpha (IFN-alpha) were studied: 19 were complete responders and 29 were non-responders. Hepatitis C virus RNA was measured quantitatively by AMPLICOR, branched DNA (bDNA) probe, and competitive polymerase chain reaction (C-PCR) assays. An internal quantification standard was used in the AMPLICOR assay. A cDNA competitor with a deletion of 15 base pairs in the middle portion was used in the C-PCR method. The concentration of HCV RNA was significantly correlated between the three assays adopted in this study. Sensitivity of assays was 100% by C-PCR, 90% by AMPLICOR and 69% by bDNA assays. The active quantitative range was best with the C-PCR assay and worst with the bDNA assay. The bDNA assay had a tendency to exhibit lower values for patients with serotype 2 than did the other two assays. The predictive rate of the long-term response to IFN-alpha therapy, before its initiation, was over 75% in all three assays. The predictive rate just after completing IFN-alpha therapy was as high as 80% by C-PCR and the AMPLICOR assays, but was low (58%) with the bDNA assay. The handling of the bDNA and AMPLICOR assays was much easier than the C-PCR assay, which required time and skill. These results indicate that the AMPLICOR assay is a simple and reliable method for measuring the serum concentrations of HCV RNA, and thus is suitable for clinical application.

Antibody response to E2/NS1 hepatitis C virus protein in patients with acute hepatitis C

Antibody response to the E2/NS1 protein of the hepatitis C virus (HCV) was studied in 26 patients with post-transfusion acute hepatitis C. Second-generation HCV (HCV-2) antibody, E2/NS1 antibody and HCV-RNA were measured in serial serum samples taken within 1 month and 3, 6 and 12 months after the onset of acute hepatitis C. The HCV genotype was also tested to study its clinical significance. Of 26 patients, eight showed normalization of alanine aminotransferase (ALT) and clearance of HCV-RNA (resolved group). In the remaining 18 patients, HCV viraemia and ALT abnormality (except one patient) continued for more than 3 years (unresolved group). Both HCV-2 and E2/NS1 antibodies were positive at least once in all patients. The prevalence of E2/NS1 antibody was significantly (P < 0.05) higher in the resolved group (88%) than in the unresolved group (39%) in the period within 1 month of onset; the prevalence was similar between the two groups thereafter. The prevalence of HCV-2 antibody did not differ between the two groups at any point. The HCV genotype was not related to the chronicity of acute hepatitis C. In conclusion, the E2/NS1 antibody appeared in all patients with acute hepatitis C and was associated with the clearance of HCV.

Acute hepatitis C transmitted by needlestick accident despite short duration interferon treatment

Hepatitis C virus (HCV) transmission by needlestick accidents involving hospital employees has become an important problem. The present report is of a case of acute hepatitis C that developed after a needlestick injury, despite short duration interferon treatment performed just after the accident in a trial effort to prevent HCV transmission. Nosocomial infection of HCV in medical employees is reviewed, and the current prospects for protecting them from HCV transmission after needlestick accident are discussed.

Intracerebroventricular injection of prostaglandin E2 increases splenic sympathetic nerve activity in rats

The effects of central administration of prostaglandin E2 (PGE2) and its selective agonists on splenic sympathetic nerve activity (SNA) were investigated in urethan- and alpha-chloralose-anesthetized rats. An intra-third-cerebroventricular (13V) injection of PGE2 (0.1-10 nmol/kg) increased splenic SNA in a dose-dependent manner. An I3V injection of an EP1 agonist, 17-phenyl-omega-trinor PGE2 (1-30 nmol/kg), also resulted in a dose-dependent increase in splenic SNA, with a time course similar to that of PGE2-induced responses. In contrast, EP2 agonists, butaprost (10-100 nmol/kg I3V) and 11-deoxy-PGE1 (10-100 nmol/kg I3V), had no effect on splenic SNA. An I3V injection of M & B-28767 (an EP3/EP1 agonist, EP3 >> EP1) increased splenic SNA only at high doses (10-100 nmol/kg). Pretreatment with an EP1 antagonist, SC-19220 (200 and 500 nmol/kg), completely blocked the responses of splenic SNA to PGE2 (0.1 nmol/kg) and M & B-28767 (10 nmol/kg), respectively. These findings indicate that brain PGE2 increases splenic SNA through its action on EP1 receptors.

The effect of interleukin-1 beta on the efferent activity of the vagus nerve to the thymus

The effects of intravenous (i.v.) administration of recombinant human interleukin-1 beta (rhIL-1 beta) and human interleukin-1 beta-fraction (hfrIL-1 beta) on the activity of vagal efferent fibers innervating the thymus were observed in urethane-anesthetized rats. An i.v. injection of 10 ng rhIL-1 beta or hfrIL-1 beta caused a similar degree of increase in the efferent activity, which lasted longer than 2 h. The least effective dose was 1 ng and dose-dependent responses were observed after i.v. injection of rhIL-1 beta at doses of 1 ng, 10 ng and 100 ng. The IL-1 beta-induced activation of efferent activity of the vagal branch to the thymus implicates their involvement in the neural modulation of the thymic function.

Observations on structural features and characteristics of biological apatite crystals. 9. Observation on dissolution of carious enamel crystals

In a series of studies to investigate the basic structural features and characteristics of the biological apatite crystals using a transmission electron microscope, we examined the ultrastructure of the human enamel, dentin, and bone crystals through the cross and longitudinal sections at near atomic resolution. Subsequently, using the same approach, we have been able to directly examine the images of the lattice imperfections in the crystal lattices of the human tooth and bone crystals, and the images of the fusion of the crystals. In this research, furthermore, using transmission and scanning electron microscopes, we examined the dissolution of the enamel crystals caused by the carious enamel from the same viewpoint. The material used for the observation of the dissolution of the enamel crystals was obtained from the region which corresponds to the middle layer of the enamel at the portion near the wall of a carious cavity caused by the fissure caries on the occlusal surface of the lower first molars. Small cubes of the materials used for the observation by transmission electron electron microscope were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut with a diamond knife without decalcification. The sections were examined with the HITACHI H-800H type transmission electron microscope operated at 200 kV. Each crystal was observed at an initial magnification of 300,000 times and at a final magnification of 10,000,000 times and over. The material used for the observation by the scanning electron microscope was the fractured surface obtained from the carious enamel. The fractured carious enamel surfaces were coated with carbon and gold and observed with the HITACHI HHS-2R type scanning electron microscope operated at 25 kV. The crystals were observed at a final magnification of 50,000 times. As a result, we have confirmed that the dissolution of the enamel crystals caused by a caries occurs in the units of "hexagonal cell". We sincerely believe that the electron micrographs shown in this report are the first to show the images of the dissolution of the enamel crystals caused by a caries at near atomic resolution.

Central interleukin-1 beta enhances splenic sympathetic nerve activity in rats

The central administration of immune cytokines such as interleukin-1 (IL-1) and interferon-alpha (IFN-alpha) results in the suppression of peripheral cellular immunity, which depends, at least partly, on the sympathetic nervous activity. An intrathird cerebroventricular (I3V) infusion of recombinant human IL-1 beta (rhIL-1 beta) (1-5 ng/rat) elicited a dose-dependent increase in the electrical activity of the splenic sympathetic nerve in urethane and alpha-chloralose anesthetized rats. The effect of rhIL-1 beta (1 ng/rat) was completely blocked by pretreatment with an IL-1 receptor antagonist (1 microgram/rat, I3V 10 min before rhIL-1 beta), sodium salicylate (1 microgram/rat), or alpha-melanocyte stimulating hormone (alpha-MSH) (400 ng/rat). Furthermore, an antagonist of corticotropin-releasing factor (CRF), alpha-helical CRF9-41 (2 micrograms/rat), completely abolished the rhIL-1 beta-induced increase in the splenic nerve activity, although an I3V infusion of CRF (1 microgram/rat) excited it. These results suggest that IL-1 beta in the brain activates splenic sympathetic activity by its receptor-mediated and prostaglandin-dependent action that is sensitive to alpha-MSH, depending on CRF system. Our findings, together with the previous results, suggest that the splenic sympathetic nerve represents one of the communication channels from the brain to the immune system.

Observations on structural features and characteristics of biological apatite crystals. 8. Observation on fusion of human enamel crystals

In a series of studies to investigate the basic structural features and characteristics of the biological apatite crystals, using a transmission electron microscope, we examined the ultrastructure of the human enamel, dentin, and bone crystals at near atomic resolution and showed the configuration of the hydroxyapatite structure through the cross and longitudinal sections of the crystals. Subsequently, based on the results of the observations by the authors of the ultrastructure of the tooth and bone, using the same approach, we have been able to directly examine the images of the lattice imperfections in the human tooth and bone crystals, such as the point defect structure, line defect, and face defect, in the crystals. In this report, we describe the images of the crystal fusion obtained by using the same approach from the sections of the human enamel crystals. The materials used for this study were the noncarious enamel from the freshly extracted human erupted lower first molars. The small cubes of the material were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut with a diamond knife without decalcification. The sections were examined with the HITACHI H-800 H and H-9000 type transmission electron microscopes operated at 200 kV and 300 kV. Each crystal was observed at an initial magnification of 300,000 times and at a final magnification of 10,000,000 times and over. We are, therefore, able to confirm that the fusion between the adjacent crystals can occur at some time during the life history of the human enamel. We sincerely believe that the electron micrographs shown in this report are the first to show the ultrastructures of the crystal fusion in the human enamel crystals at near atomic resolution.

Observations on structural features and characteristics of biological apatite crystals. 7. Observation on lattice imperfection of human tooth and bone crystals II

In a series of studies to investigate the structural features of the biological crystal, such as the tooth and bone, using an electron microscope, we examined the ultrastructure of the human enamel, dentin, and bone crystals at near atomic resolution and showed the configuration of the hydroxyapatite structure through the cross and longitudinal sections of the enamel, dentin, and bone crystals. Subsequently, based on the results of our observations of the ultrastructure of the tooth and bone crystals, we attempted to clarify the essential structural features and characteristics of the lattice imperfections in the hydroxyapatite structure composing of the human enamel, dentin, and bone crystals from the morphological viewpoint. Therefore, using the same approach, we examined the images of the lattice imperfection of the normal human enamel, dentin, and bone crystals. In this report, following the previous observation of the lattice imperfection on the point defect structure and the dislocations appearing in the inner structure of the crystal, we describe the image of the face defect structure obtained by using the same approach from the sections of the human enamel, dentin, and bone crystals, such as the stacking fault, grain boundary, and others. The materials used for this study were the human enamel, dentin, and bone crystals. The small cubes of the material were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut with a diamond knife without decalcification. The sections were examined with the HITACHI H-800 H and H-9000 type transmission electron microscopes operated at 200 kV and 300 kV respectively. Each crystal was observed at an initial magnification of 300,000 times and at a final magnification of 10,000,000 times and over. We sincerely believe that the electron micrographs shown in this report are the first to show the images of the lattice imperfections from the sections obtained from the hydroxyapatite crystal composing of the human enamel, dentin, and bone tissue, such as the grain boundary, stacking fault, and others, at near atomic resolution.

Hypothalamic modulation of splenic natural killer cell activity in rats

1. The cytotoxic activity of splenic natural killer cells measured by a standard chromium release assay in urethane and alpha-chloralose-anaesthetized rats was significantly suppressed 20 min after bilateral ablation of the medial part of the preoptic hypothalamus (MPO). The suppression was completely blocked by prior splenic denervation. The splenic natural killer cell activity of MPO sham-lesioned rats or thalamus-lesioned rats, both having an intact splenic innervation, were not different from that of a non-treated control group. 2. Electrical stimulation of the bilateral MPO (0.1 ms, 0.1-0.3 mA, 5-100 Hz) suppressed the efferent activity of the splenic nerve in all six rats examined. The reduction of the nerve activity was accompanied by a transient fall in blood pressure. An I.V. injection of phenylephrine (3 micrograms/0.3 ml) also evoked a suppression of the nerve activity, which was accompanied by transient hypertension, suggesting that the suppressive effect of the MPO stimulation was independent of changes in blood pressure. On the other hand, a bilateral lesion of the MPO resulted in a sustained increase in the electrical activity of the splenic sympathetic nerve filaments which lasted for more than 2 h. 3. Microinjection of monosodium-L-glutamate (0.1 and 0.01 M in 0.1 microliters saline) unilaterally into the MPO evoked a transient suppression of the efferent discharge rate of the splenic nerve activity within 1 min, which was also accompanied by a decrease in blood pressure. The injection of saline (0.1 microliter) into the MPO had no effect. The microinjection of recombinant human interferon-alpha (200 and 2000 U in 0.1 microliter saline) into the MPO dose dependently increased the splenic nerve activity without any change in blood pressure. 4. In contrast, microinjection of interferon-alpha into the paraventricular nucleus of the hypothalamus (PVN) had no effect on splenic nerve activity, although an injection of glutamate increased the nerve activity. 5. The present results, taken together with previous reports, suggest that the neuronal networks between the MPO and the splenic sympathetic nerve, which may be activated by centrally administered interferon-alpha, are important in the suppression of the splenic cellular immunity.

A comparative ultrastructural study of the mitotic chondrogenic cells in the mandibular condyle and tibial growth plate of the rat

Mitotic cells in the rat mandibular condyle (proliferative mandibular cells) were compared with mitotic cells in the rat tibial growth plate (proliferative tibial cells). In the tibial proliferative cells, the rough endoplasmic reticulum mostly became vacuolated during the latter stage of mitosis, whereas the rough endoplasmic reticulum of the proliferative mandibular cells rarely underwent disorganization. Further, a wide area remained outside of the mitotic spindle in the proliferative tibial cells at the metaphase, while only a narrow area remained in the proliferative mandibular cells. This finding might account for the difference of disorganization of the rough endoplasmic reticulum.

Observations on structural features and characteristics of biological apatite crystals. 6. Observation on lattice imperfection of human tooth and bone crystals. I

In a series of studies to investigate the basic structural features and characteristics of the biological apatite crystals, using an electron microscope, we examined the ultrastructure of the human enamel, dentin, and bone crystals at near atomic resolution and showed the configuration of the hydroxyapatite structure through the cross and longitudinal sections of the crystals. Subsequently, based on the results of the observations by the authors of the ultrastructure of the tooth and bone, using the same approach, we have been able to directly examine the images of the lattice imperfections in the human enamel, dentin, and bone crystals, such as the point defect structures and dislocations in the crystals. In this report, we describe the image of the point defect structures and line defect structures obtained, using the same approach from the sections of the human enamel, dentin, and bone crystals. The materials used for this study were the noncarious enamel and dentin from the freshly extracted human erupted lower first molars, and bone tissue obtained from the alveolar compact bone. The small cubes of the material were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut with a diamond knife without decalcification. The sections were examined with the HITACHI H-800 H and H-9000 types of transmission electron microscopes operated at 200 kV and 300 kV. Each crystal was observed at the initial magnification of 300,000-500,000 times and at the final magnification of 10,000,000 times and over. We sincerely believe that the electron micrographs shown in this report are the first to show the images of the lattice imperfections in the human enamel, dentin, and bone crystals, such as the point defect and line defect structures, at near atomic resolution.

Observations on structural features and characteristics of biological apatite crystals. 5. Three-dimensional observation on ultrastructure of human enamel crystals

In a series of studies to investigate the structural features of the biological crystals, such as the tooth and bone, using an electron microscope, we examined the ultrastructure of the enamel, dentin, and bone crystals at near atomic resolution and showed the configuration of the hydroxyapatite structure through the cross and longitudinal sections of the crystals. Thereafter, based on the results of the observations by the authors of the ultrastructure of the tooth and bone crystals, thinking that it might be possible to conduct direct three-dimensional observation of the configuration composing the unit cell of the hydroxyapatite crystals, we conducted a study on this. These results indicated that it was possible to sterically observe the configuration of the hydroxyapatite structure composing the enamel crystal. The materials used for this study were the middle layer of the noncarious enamel from the freshly extracted human erupted permanent molars. The small cubes of the enamel were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut with a diamond knife without decalcification and were examined with the HITACHI H-9000 H type transmission electron microscope operated at 300 kV. Each crystal was observed at an initial magnification of 500,000 times and at the final magnification of 10,000,000 times and over. We sincerely believe that the electron micrographs shown in this report are the first to show three-dimensionally the configuration of the hydroxyapatite structure composing the crystal in the cross and longitudinal sections of an enamel crystal.

Observations on structural features and characteristics of biological apatite crystals. 4. Observation on ultrastructure of human bone crystals

In a series of studies to investigate the structural features of the biological crystals such as the tooth and bone, following the previous observations of the tooth crystal using an electron microscope, we examined the ultrastructure of the human bone crystals at near atomic resolution through the cross and longitudinal sections of the crystals. The materials used for this study were the normal bone tissue obtained from the buccal alveolar compact bone of the human mandible in the portion of the lower first molar. The small cubes of the bone tissue were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut with a diamond knife without decalcification. The sections were examined with the HITACHI H-800 type transmission electron microscope operated at 200 kV. Each crystal was observed at the initial magnification of 300,000 times and at the final magnification of 10,000,000 times and over. Using this approach, we showed the configuration of the hydroxyapatite structure in the cross and longitudinal sections of the bone crystals deposited within and between the collagen fibrils (intrafibrillar and interfibrillar crystals) in the bone tissue. Furthermore, using the same approach, we observed the crystal lattices of the hydroxyapatite structure appearing in the cross and longitudinal sections. We sincerely believe that the electron micrographs shown in this report are the first atomic images from the section obtained from the hydroxyapatite crystal from the human alveolar bone.

An ultrastructural study of mitotic chondrocytes in the Swarm rat chondrosarcoma

The Swarm rat chondrosarcoma is a well established model system for the biochemical studies of cartilage proteoglycans. In this study, we observed the ultrastructure of mitotic chondrocytes in this tumor to confirm whether it is also useful as a morphological model system to examine the mitosis of chondrocytes. As a result, the mitotic chondrocytes in this tumor contained fairly prominent cell organelles, and the endoplasmic reticulum was mainly vacuolized and the Golgi stacks were replaced by the cluster of small vesicles during the later stage of the mitotic cycle. Although the cytoplasmic division began at the telophase, the cytoplasmic cleavage furrow was so narrow that dividing chondrocytes looked as if they were partitioned by a slit. These findings are almost consistent with the changes that occurred in the mitotic chondrocytes of the tibial growth plate, although the degree of disorganization in the Golgi apparatus is slightly different. Therefore, this tumor is useful as a convenient morphological model system to examine the mitosis of chondrocytes because of the facility for taking specimens.

Observations of structural features and characteristics of biological apatite crystals. 3. Observation on ultrastructure of human dentin crystals

In a series of studies to investigate the structural features of the biological crystals, using electron microscope, we examined the ultrastructure of the human dentin crystals at near atomic resolution through the cross and longitudinal sections of the crystals. The materials used for this study were the deep layer of the non-carious coronal dentin from freshly extracted human erupted permanent molars. The small cubes of the dentin were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut with a diamond knife without decalcification. The sections were examined with the HITACH H-700 type of transmission electron microscope operated at 200kV. Each crystal was observed at the initial magnification of 300,000 times and at the final magnification of 10,000,000 times and over. Using this approach, the authors have been able to show the configuration of the hydroxyapatite structure in the cross and longitudinal sections of the dentin crystals deposited within and between the collagen fibrils (intrafibrillar and interfibrillar crystal) in the intertubular dentin and observe the basic hexagonal pattern of the unit cell viewed down the c-axis. The authors sincerely believe that the electron micrograph shown in this report is the first atomic image to be obtained from a hydroxyapatite crystal from the human dentin, using the sections.

An ultrastructural study of mitotic chondrocytes in the proliferative zone of the rat tibial growth plate

Mitotic chondrocytes containing fairly prominent cell organelles were observed in the proliferative zone of the rat tibial growth plate by electron microscopy. During the later stage of mitosis, the endoplasmic reticulum was mostly vacuolated, and the Golgi stacks were replaced by spherical and cylindrical vacuoles and small vesicles. The cytoplasmic division began at early telophase. However, the cytoplasmic cleavage furrow was so narrow that dividing chondrocytes looked as if they were partitioned by a slit. This is probably one reason for the appearance of the binuclear cells that are occasionally observed in the tibial growth plate.

An ultrastructural study of the mitotic preosteoblasts in the primary spongiosa of the rat mandibular condyle

In this study, we observed mitotic preosteoblasts that have the structural features of osteoblasts in the primary spongiosa of the rat mandibular condyle. The rough endoplasmic reticulum and the Golgi apparatus showed remarkable disorganization during mitosis. The Golgi saccules were replaced by groups of large vacuoles and small vesicles. The cisternae of the rough endoplasmic reticulum also were vacuolized. Since this disorganization occurred in conjunction with the formation of the mitotic spindle, it is probably related to the changes of the microtubular cytoskeleton. Further, secretory granules were arrayed along the mitotic spindle microtubules at the metaphase, and concentrated around the midbody at the telophase. These findings indicate a close relationship exists between secretory granules and microtubules.

Observations on the structural features and characteristics of biological apatite crystals. 2. Observation on the ultrastructure of human enamel crystals

In a series of studies to investigate the structural features of biological crystals, using an electron microscope, we examined the ultrastructure of human enamel crystals at near atomic resolution through the cross and longitudinal sections of the crystals. The materials used for this study were the middle layer of the noncarious enamel from freshly extracted human erupted permanent molars. The small cubes of the enamel were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut with a diamond knife without decalcification. The sections were examined with HITACHI H-500 and H-700 types of transmission electron microscopes operated at 125-200 kV. Each crystal was observed at the initial magnification of 300,000 times and at the final magnification of 10,000,000 times and over. Using this approach, the authors have been able to show the configuration of the hydroxyapatite in the cross and longitudinal sections of the enamel crystals and observe the basic hexagonal pattern of the unit cell viewed down the c-axis. The authors sincerely believe that the electron micrograph shown in this report is the first atomic image to be obtained from a hydroxyapatite crystal from the human enamel, using the sections.