Supplementation of CD4+CD25+ regulatory T cells suppresses experimental autoimmune uveoretinitis.

AIMS: To investigate whether supplementation of natural CD4+CD25+ regulatory T cells ameliorates mouse experimental autoimmune uveoretinitis (EAU) induced by CD4+ T cell-dependent interphotoreceptor retinoid-binding protein (IRBP). METHODS: C57BL/6 mice were immunised with human interphotoreceptor retinoid-binding protein peptide 1-20 (IRBP(1-20)), and IRBP(1-20)-sensitised T cells were obtained. CD4+CD25+ T cells derived from naive mice were cocultured with IRBP(1-20)-sensitised T cells, and their proliferation responses and cytokine production were measured. In addition, CD4+CD25+ T cells were transferred intravenously into mice 7 or 15 days after immunisation with IRBP(1-20), and the severity of EAU and T cell proliferation responses were evaluated. RESULTS: CD4+CD25+ regulatory T cells effectively inhibited both the proliferation of, and interleukin (IL)2, IL5 and interferon (IFN)gamma production by, IRBP(1-20)-sensitised T cells. Adoptive transfer of CD4+CD25+ regulatory T cells to IRBP(1-20)-immunised mice conferred considerable protection from EAU development and inhibition of T cell proliferation responses to IRBP(1-20). CONCLUSION: These findings show that natural CD4+CD25+ regulatory T cells possess the ability to inhibit activation of IRBP-reactive T cells that have been already sensitised in vivo, and adoptive transfer of these cells ameliorates EAU even in the effector phase. Supplementation of natural CD4+CD25+ regulatory T cells may have therapeutic potential for effective treatment of uveitis.

Sensory system-predominant distribution of leukotriene A4 hydrolase and its colocalization with calretinin in the mouse nervous system.

Leukotriene B4 is a potent lipid mediator, which has been identified as a potent proinflammatory and immunomodulatory compound. Although there has been robust evidence indicating that leukotriene B4 is synthesized in the normal brain, detailed distribution and its functions in the nervous system have been unclear. To obtain insight into the possible neural function of leukotriene B4, we examined the immunohistochemical distribution of leukotriene A4 hydrolase, an enzyme catalyzing the final and committed step in leukotriene B4 biosynthesis, in the mouse nervous system. Immunoreactivity for leukotriene A4 hydrolase showed widespread distribution with preference to the sensory-associated structures; i.e. neurons in the olfactory epithelium and vomeronasal organ, olfactory glomeruli, possibly amacrine cells, neurons in the ganglion cell layer and three bands in the inner plexiform layer of the retina, axons in the optic nerve and tract up to the superior colliculus, inner and outer hair cells and the spiral ganglion cells in the cochlea, vestibulocochlear nerve bundle, spinal trigeminal tract, and lamina II of the spinal cord. Double immunofluorescence staining demonstrated that most of the leukotriene A4-hydrolase-immunopositive neurons coexpressed calretinin, a calcium-binding protein in neurons. The ubiquitous distribution of leukotriene A4 hydrolase was in sharp contrast with the distribution of leukotriene C4 synthase [Shimada A, Satoh M, Chiba Y, Saitoh Y, Kawamura N, Keino H, Hosokawa M, Shimizu T (2005) Highly selective localization of leukotriene C4 synthase in hypothalamic and extrahypothalamic vasopressin systems of mouse brain. Neuroscience 131:683-689] which was confined to the hypothalamic and extrahypothalamic vasopressinergic neurons. These results suggest that leukotriene B4 may exert some neuromodulatory function mainly in the sensory nervous system, in concert with calretinin.

Apoptosis in the developing CNS.

In this review, apoptosis during normal development of the CNS and abnormal apoptosis inducing hydrocephaly and arhinencephaly will be discussed. As the prominent sites of apoptosis during normal development of the CNS, we focused on the area of fusion of the neural plate to form the neural tube, the developing rhombomeres, and neuronal loss in the CNS during embryogenesis and postnatal development. As examples of abnormal apoptosis inducing abnormal brain morphogenesis, we will discuss genetically induced arhinencephaly and hydrocephaly. It was suggested that apoptosis of the precursor mitral cells in the anlage of the olfactory bulb was induced by non-innervation of olfactory neurons, and apoptosis of the precursor neurons in the pyriform cortex was induced by the non-innervation caused by the death of mitral cells in the mutant arhinencephalic mouse brain (Pdn/Pdn). Thus, sequential apoptosis of the precursor neurons and sequential manifestation of the brain abnormalities were proposed in arhinencephalic mutant mouse embryos and also in the arhinencephalic brains induced experimentally by fetal laser surgery exo utero. Meanwhile, it was speculated that the Gli3 gene, mutation of which is responsible for the arhinencephaly in Pdn/Pdn mice, might play a role in mesenchymal programmed cell death during development.

Regulation of neuregulin expression in the injured rat brain and cultured astrocytes.

In this report, we investigated whether reactive astrocytes produce neuregulins (glial growth factor 2/heregulin/acetylcholine receptor-inducing activity or neu differentiation factor) and its putative receptors, ErbB2 and ErbB3 tyrosine kinases, in the injured CNS in vivo. Significant immunoreactivities with anti-neuregulin, anti-ErbB2, and anti-ErbB3 antibodies were detected on astrocytes at the injured site 4 d after injury to the adult rat cerebral cortex. To elucidate the mechanisms for the upregulation of neuregulin expression in astrocytes, primary cultured astrocytes were treated with certain reagents, including forskolin, that are known to elevate the intracellular level of cAMP and induce marked morphological changes in astrocytes. Western blot analysis showed that the expression of a 52 kDa membrane-spanning form of a neuregulin protein was enhanced in cultured astrocytes after administration of forskolin. The upregulation of glial fibrillary acidic protein was also observed in astrocytes treated with forskolin. In contrast, inactivation of protein kinase C because of chronic treatment with phorbol ester 12-O-tetradecanoyl phorbol 13-acetate downregulated the expression of the 52 kDa isoform, although other splice variants with apparent molecular sizes of 65 and 60 kDa were upregulated. These results suggest that the enhancement of neuregulin expression at injured sites is induced, at least in part, by elevation in intracellular cAMP levels and/or a protein kinase C signaling pathway. The neuregulin expressed on reactive astrocytes may stimulate their proliferation and support the survival of neurons surrounding cortical brain wounds in vivo.

Highly selective localization of leukotriene C4 synthase in hypothalamic and extrahypothalamic vasopressin systems of mouse brain.

While leukotriene C4 (LTC4) was originally identified as a potent bronchoconstrictor, the compound has versatile biological activities besides inflammatory reactions. Although the high content of LTC4 has been reported in the hypothalamus and median eminence, the precise localization of the compound remained obscure. To elucidate its possible functions in the neuroendocrine systems, we determined immunohistochemical localization of LTC4 synthase, a key enzyme to produce LTC4 using mouse brains. Light microscopy and confocal laser scanning microscopy showed that LTC4 synthase was selectively localized in the vasopressinergic magnocellular neurons of the hypothalamic paraventricular, supraoptic and suprachiasmatic nuclei and in the retrochiasmatic area, as well as in axons that emanated from these neurons to the pars nervosa of the pituitary gland. At subcellular level, however, LTC4 synthase and arginine vasopressin appeared to localize differently within individual neurons. LTC4 synthase immunoreactivity was also observed in the axons of the extrahypothalamic system including the bed nucleus of the stria terminalis, lateral habenular nucleus, midbrain central gray, medial amygdaloid nucleus and ventral septal area, although this immunoreactivity was relatively minor. The other brain regions did not contain LTC4 synthase immunoreactivity. The distribution of LTC4 synthase did not overlap with that of either oxytocin or luteinizing hormone releasing hormone. Therefore, LTC4 is considered to be involved in neural functions of the brain magnocellular vasopressinergic system such as water retention. LTC4 may also be involved in extrahypothalamic vasopressinergic neural functions including the regulation of learning and memory, social recognition memory, sexual and aggressive behavior, etc.

Surgical manipulation of mammalian embryos in vitro.

Whole-embryo culture systems are useful in the fields of not only embryology but also teratology, toxicology, pharmacology, and physiology. Of the many advantages of whole-embryo culture, we focus here on the surgical manipulation of mammalian embryos. Whole-embryo culture allows us to manipulate mammalian embryos, similarly to fish, amphibian and avian embryos. Many surgical experiments have been performed in mammalian embryos in vitro. Such surgical manipulation alters the destiny of morphogenesis of the embryos and can answer many questions concerning developmental issues. As an example of surgical manipulation using whole-embryo culture systems, one of our experiments is described. Microsurgical electrocauterization of the deep preaxial mesodermal programmed cell death zone (fpp) in the footplate prevented the manifestation of polydactyly in genetic polydactyly mouse embryos (Pdn/Pdn), in which fpp was abolished.

Transient expression of juvenile-type neurocan by reactive astrocytes in adult rat brains injured by kainate-induced seizures as well as surgical incision.

Neurocan is one of the major chondroitin sulfate proteoglycans expressed in nervous tissues. The expression of neurocan is developmentally regulated, and full-length neurocan is detected in juvenile brains but not in adult brains. In the present study, we demonstrated by western blot analysis that full-length neurocan transiently appeared in adult rat hippocampus when it was lesioned by kainate-induced seizures. Immunohistochemical studies showed that neurocan was detected mainly around the CA1 region although the seizure resulted in neuronal cell degeneration in both the CA1 and CA3 regions of the hippocampus. Double-labeling for neurocan mRNA and glial fibrillary acidic protein demonstrated that many reactive astrocytes expressed neurocan mRNA. The re-expression of full-length neurocan was also observed in the surgically injured adult rat brain. In contrast, the expression of other nervous tissue chondroitin sulfate proteoglycans, such as phosphacan and neuroglycan C, was not intensified but rather was either reduced in the kainate-lesioned hippocampus or in the surgically injured cerebral cortex. These observations indicate that induction of neurocan expression by reactive astrocytes is a common phenomenon in the repair process of adult brain injury, and therefore, it can be postulated that juvenile-type neurocan plays some roles in brain repair.

Acrolein as a fixative for enzyme cytochemistry.

Since acrolein can penetrate more quickly and deeply into tissue blocks than glutaraldehyde, the possibility of the use of this aldehyde as a prefixative in enzyme cytochemistry was reinvestigated. At low concentrations, acrolein preserves the activities of the enzymes investigated, including those of glucose-6-phosphatase, which is known as one of the most vulnerable to aldehyde fixation; thus, acrolein is usable in enzyme ultracytochemistry. Enzyme activities are also preserved in tissues fixed with acrolein and glutaraldehyde combined. The rapid penetration of acrolein enables fixation in larger tissue blocks and provides greater freedom in specimen selection, especially important advantages when encountering heterogeneous materials as in pathology.

High-molecular-weight cadmium-binding proteins in rat liver cytosol: isolation and partial characterization of an approximately 50-kDa protein.

The time-dependent changes in the chromatographic pattern of subcutaneously injected cadmium associated with non-metallothionein cadmium-binding proteins were studied in the rat liver cytosol. Prior to the induction of cadmium-thionein (less than 3 h), cadmium appeared in three major peaks (P-1 with the void volume, P-2 and P-3) on Sephacryl S-300 column chromatography. Accompanied with the emergence of apo-metallothionein (about 3 h after administration), the amount of P-3 decreased and instead a cadmium-thionein peak (P-4) increased. Ion-exchange chromatography of P-3 with a combination of CM and DEAE Bio-Gel columns showed the existence of three major cadmium-binding proteins with molecular sizes of 46 kDa (in the CM Bio-Gel column eluate), 50 kDa (in the DEAE Bio-Gel column eluate), and 41 kDa (in the non-adsorbed fraction). The cadmium-binding protein in the CM Bio-Gel column eluate was purified to apparent homogeneity. The purified protein (CM-CdP) was 47 or 53 kDa in molecular size as determined by SDS-polyacrylamide gel electrophoresis or gel filtration chromatography, respectively. The apparent dissociation constant and maximum binding for cadmium were about 1 microM and 1 mol of the metal/mol of protein, respectively. The isoelectric point was estimated to be 8.8. The amino acid composition showed that the protein was relatively rich in glutamyl (including its amide) and alanyl residues. The N-terminal amino acid sequence was determined as Ala-Pro-Ile-Ala-Gly-Lys-Lys-Ala-Lys-Ala-Gly-Ile-Leu-Leu-Gly-. In-vitro experiments revealed that cadmium bound to CM-CdP could be easily transferred to apo-metallothionein, confirming that the affinity for the metal of the former protein was lower than that of the latter.

Developmental profile of three enolase isozymes in rat brain determination from one-cell embryo to adult brain.

Levels of three enolase isozymes (??, ?? and ??) were determined in rat tissues from one-cell embryo to adult brain with a sensitive enzyme immunoassay system. Each embryo of the early stage (gestational age, 0-3 days) contained about 5 x 10(?17) mol of ?? enolase. The nervous system-specific ?? and ?? enolases would be detected in the embryos of 6-8 days, which contain no histologically recognizable neurones. The 8-day embryos contained 4.3 x 10(?17) and 3.4 x 10(?16) mol of ?? and ?? enolases. Amounts of all the three enolases were increased with growth of the embryo. The nervous system-specific enolases (?? and ??) in the brain kept increasing until 1-2 months of postnatal age, whereas the ?? enolase level in the brain was relatively constant after the 15-day embryo through the adult rat.

Critical period of bilirubin-induced cerebellar hypoplasia in a new Sprague-Dawley strain of jaundiced Gunn rats.

Homozygous (j/j) and heterozygous (j/+) newborn Gunn rats of the Sprague-Dawley strain were photoirradiated for 24 h at scheduled postnatal days and the effects of irradiation on the cerebellar development were examined at 30 days of life. Improvement of the survival rate was the most notable effect of photoirradiation. A single 24-h dose of photoirradiation during a period of postnatal days 4-11 effectively prevented hypoplasia in the j/j rat cerebellum. No prevention by light was observed at days 3 and 12. It was found that the most effective day of irradiation on the cerebellar development of j/j rats was centered on postnatal day 7. When plasma bilirubin was assessed during the period of postnatal days 7-10, a distinct diminution of the concentration was observed, restricted to only the period of the light treatment. Although there were some differences in the effective day as well as in the degree of efficacy of phototherapy among cerebellar lobules or sublobules, day 7 was the most critical for cerebellar hypoplasia due to bilirubin.

Postnatal changes of the number and lobular distribution of acid phosphatase positive and lipid granule-containing cells in the cerebellum of hyperbilirubinemic Gunn rats.

Developing homozygous (jj) and heterozygous (j+) Gunn rat cerebella were examined histologically from postnatal days 5 to 60. Sagittal sections of the cerebellar vermis of jj rats revealed that the anterior and medial lobes were significantly smaller in area than in j+ rats on and after postnatal day 10. However, the nodulus did not display significant differences in jj rats. Two classes of acid phosphatase (ACPase)-positive cells (L cells and S cells), and lipid granule-containing S cells were recognized exclusively in the jj rat cerebellum during the postnatal period studied. S cells, which are probably microglia, had an oval dark nucleus and contained many lysosomes, some of which contained lipid droplets. They appeared in all the lobules except the nodulus on day 5 and reached maximum in incidence by day 15. They were distributed all over the cerebellar layers including the white matter. Lipid granule-containing S cells appeared on postnatal day 10 and were most abundant in severely affected lobules, such as the declive and tuber, on day 30. Purkinje cells of jj rats showed vacuolation in their cytoplasm on and after postnatal day 5. After 20 days of life, the number of Purkinje cells in anterior- and medius-lobus were markedly decreased. Some severely damaged Purkinje cells became L cells with an extremely high ACPase activity. They appeared initially on postnatal day 15 and increased in number until day 30. No L cells were observed in the nodulus. These show that the severely damaged Purkinje cells and ACPase-positive and lipid granule-containing microglia cells are most abundant in the late- and intermediate-maturing regions of the vermis. Since they are either rare or absent in any earlier-maturing region, the nodulus, these data suggest toxic effects of bilirubin in the cerebellum are closely related to the ontogenic development of the individual cerebellar lobules.

Glycine-like immunoreactivity in the rat auditory pathway.

From neurophysiological and biochemical studies it has been suggested that glycine can function as a major inhibitory neurotransmitter in the central nervous system of mammals. In the present study, anti-glycine antiserum was obtained from rabbits immunized with glycine conjugated to rabbit serum albumin via glutaraldehyde and purified by affinity chromatography. The antibody thus obtained was found specific for glycine as determined by an enzyme immunoassay system. The immunocytochemical distribution of glycine in the auditory tract and internal ear was investigated with the antibody. In the central auditory pathway, glycine-like immunoreactivity was mainly located in the ventral and dorsal cochlear nuclei, trapezoid body, lateral lemniscus and inferior colliculus. In the labyrinth, immunoreactivity was detected in the vestibular ganglion and the supporting cells of the crista ampullaris and the organ of Corti, but not in the spiral ganglion. These findings suggest an important role of glycine in the auditory and vestibular pathways.

Induction of agenesis of the corpus callosum by the destruction of anlage of the olfactory bulb using fetal laser surgery exo utero in mice.

It has long been discussed why some congenital anomalies were often involved with abnormalities in other organs, for example, brain anomalies accompanied by limb anomalies or cleft palate. The mechanism of combined abnormalities has been mysterious, and usually explained as pleiotropism. A combination between agenesis of the olfactory bulb and agenesis of the corpus callosum has been reported. In the present experiments, it has been suggested that non-attachment of the olfactory nerve to the rostro-ventral tip of the telencephalon blocked the induction of the olfactory bulbs from the telencephalon in genetic arhinencephalic mouse embryos. It was shown that the destruction of the olfactory bulb anlage using fetal laser surgery exo utero becomes a trigger of agenesis of the corpus callosum and irregular connection of the anterior commissure in later morphogenesis of the mouse brain. We believe that a fetal surgical experiment like this will make clear the morphogenetic mechanism of the combined abnormalities that have been previously explained as pleiotropism.

The arrest of luteinizing hormone-releasing hormone neuronal migration in the genetic arhinencephalic mouse embryo (Pdn/Pdn).

From previous observations, it was suggested that non-attachment of the olfactory nerve to the telencephalon blocked the induction of the olfactory bulbs in genetic arhinencephalic mouse embryos (Pdn/Pdn). The olfactory nerve ends in a tangle beneath the forebrain in these embryos. From these observations, we speculated that the migration of luteinizing hormone-releasing hormone (LHRH) neurons might be disturbed in the olfactory nerve. A mass of LHRH neurons was observed in the end of the olfactory nerve fibers, but LHRH neurons were found in the hypothalamus in Pdn/Pdn embryos on day 16 of gestation. Narrow by-paths were found between the olfactory nerve and the forebrain, and the migration of LHRH neurons through these by-paths was observed in Pdn/Pdn embryos on day 13 of gestation. From the reports that a gene deleted in the arhinencephalic syndrome (Kallmann's syndrome) shares homology with neural cell adhesion molecules (N-CAM), it was speculated that non-attachment of the olfactory nerve in the Pdn/Pdn embryo might be associated with abnormalities of N-CAM. The axon fibers of the olfactory nerve reacted specifically with anti-N-CAM IgG both in +/- (+/+ and/or Pdn/+) and Pdn/Pdn on day 11.5 and 12, but not on day 13 and 16 of gestation. The axon fibers of the olfactory nerve were positive to anti-N-CAM IgG specifically just during the developmental period that the olfactory nerve fibers attached to the telencephalon. It is still not clear whether non-attachment of the olfactory nerve may be associated with N-CAM or not from the present observations.

Apoptotic degeneration in the arhinencephalic brain of the mouse mutant Pdn/Pdn.

The homozygotes of a mouse strain with genetic polydactyly (Polydactyly Nagoya, Pdn) exhibit arhinencephaly and various brain malformations. In the present experiment, abnormal apoptotic degeneration in the arhinencephalic brain of Pdn/Pdn embryos and newborns was investigated immunohistochemically and by molecular genetic techniques. Polyclonal antibody against single-stranded DNA detected the nuclei of programmed dying cells (apoptotic cells) specifically in the interdigital necrotic zone of the normal mouse limb plate on day 14 of gestation. We used this antibody against single-stranded DNA to investigate the apoptotic degeneration in Pdn/Pdn brain. Abnormal apoptosis was observed in the infralimbic cortical plate, hypothalamus and periventricular thalamus on day 0 after birth in Pdn/Pdn brains. The TRPM-2 gene, which has been considered to mediate apoptosis, was expressed in the developing normal and Pdn/Pdn brains. TRPM-2 gene expressions in the brain stem and cerebellum of arhinencephalic Pdn/Pdn fetuses and newborns were higher than those of +/+ littermates. From these facts, it was suggested that the abnormal apoptosis caused a large amount of cell loss in the arhinencephalic mouse brain, and this cell loss induced the expansion of the ventricle, followed by the hydrocephaly.

Clonally accumulating T cells in the anterior chamber of Behçet disease.

PURPOSE: To clarify the nature of infiltrating T cells into the anterior chamber of a patient with Behçet disease. METHODS: Aqueous humor was obtained from a patient with ocular Behçet disease by paracentesis. RNA isolated from the cells in aqueous humor was reverse transcribed into complementary DNA. Complementary DNA encoding the variable (V) diversity (D) joining (J) (junctional) region of T-cell receptor beta chain V domain (TCR BV) chain was amplified by T-cell receptor BV family polymerase chain reaction. RESULTS: Polymerase chain reaction Southern blot analysis showed that T-cell receptor BV3, BV5, and BV7 were dominantly expressed on ocular T cells of this patient. In addition, DNA sequencing revealed that monoclonal or oligoclonal T-cell accumulation was found in T-cell receptor BV3(+), BV5(+), and BV7(+) T cells. CONCLUSION: These findings suggest that some T cells infiltrating into the anterior chamber of a patient with ocular Behçet disease expand by antigen-driven stimulation, indicating the pivotal role of T cells in the pathogenesis of ocular Behçet disease.

Evaluation of particulate embolic materials with MR imaging, scanning electron microscopy, and phase-contrast microscopy.

PURPOSE: To analyze the properties and embolic effect of microfibrillar collagen (MFC), Gelfoam powder, and polyvinyl alcohol (PVA) materials that are used in embolization procedures in the head and neck. METHODS: The shape and surface of these embolic agents were examined with scanning electron microscopy and phase-contrast microscopy. The mean number of areas of T2-weighted high signal intensity was measured on MR images in a rat embolization model to estimate the embolic effect. RESULTS: By scanning electron microscopy and phase-contrast microscopy, MFC appears fibriform and has various sizes and an irregular surface. Gelfoam is of uniform size and has a smooth surface. PVA materials are granulated and have a rough surface. MFC is somewhat suspendable and its shape changes moderately after suspension. Gelfoam is very suspendable and its shape changes rapidly. PVA showed only mild swelling. The embolic effect of MFC was the lowest of the materials examined. Large PVA particles (250 to 500 microns) showed a lesser embolic effect than Gelfoam or small PVA particles (50 to 150 microns) or medium-sized PVA particles (150 to 250 microns). No significant differences were observed among the embolic effects of Gelfoam, small PVA particles (50 to 150 microns), and medium PVA particles (150 to 250 microns). CONCLUSIONS: MFC and large PVA particles (250 to 500 microns) should be used for embolization of vascular anatomy involving potentially dangerous anastomoses. Gelfoam, PVA particles of 150- to 250-micron diameter, and PVA particles of 50- to 150-micron diameter are adequate for embolization involving homogeneous and peripheral anatomy.

Experimental creation of fusiform carotid artery aneurysms using vein grafts in rats.

OBJECTIVE: We developed an in vivo model of growing fusiform aneurysms, using vein grafts to the rat carotid artery. This aneurysm model might demonstrate the pathological features of the development and growth of aneurysms to become giant aneurysms. METHODS: Placement of an interposed femoral vein graft to restore carotid artery flow was performed in Wistar rats. On Day 21, 75% of the grafts (mean diameter, 1.6 mm) were found to be dilated to resemble fusiform aneurysms (mean diameter, 5.82 mm), and 53% of these were giant. Quantitative analysis of the histological findings was performed using image-analyzing software. RESULTS: Histological findings were similar to those for human intracranial giant aneurysms. The average length of the initial grafts in the aneurysm group was 9.1+/-1.9 mm, and grafts were significantly longer and more tortuous than in the normal graft group (6.4+/-0.8 mm) (P = 0.01). Cross-sectional areas of the aneurysms (mean, 18.9 mm2) were significantly correlated with the following: 1) the area of intra-aneurysmal thrombosis (mean, 11.1 mm2) (P < 0.0001); 2) the number of intrathrombotic vascular channels (P = 0.005); and 3) the area of dissection, with hemorrhage, between the thrombus and the wall of the aneurysm (mean, 0.72 mm2) (P = 0.0013). Scanning electron microscopic examination showed evidence of endothelial damage associated with growth of the aneurysms. CONCLUSION: Recurrent hemorrhaging from intrathrombotic vascular channels caused dissection between the thrombus and the aneurysm wall, which led to growth of the experimental aneurysms to giant aneurysms. With this model, we demonstrated the growth mechanism of giant fusiform aneurysms.

Histopathological study of balloon embolization: silicone versus latex.

Bilateral, symmetrical, experimental aneurysms were produced with anastomosed vein flap in the carotid arteries of 24 mongrel dogs. Aneurysms were occluded with latex or silicone balloons on each side and observed angiographically from 2 weeks to 2 months. A histopathological study was performed subsequently using light and scanning electron microscopy. Rupture after balloon embolization occurred in five aneurysms; all of which were incompletely occluded by a silicone balloon. On subsequent angiograms, four silicone balloons and one latex balloon were found to have migrated into the aneurysm, resulting in aneurysmal expansion. Parent artery occlusion was more common with latex balloons than silicone balloons. Histopathologically, residual fresh thrombi, decreased proliferation of fibroblasts within the aneurysmal cavity, and poor endothelialization were present around the silicone balloon. These results suggest that the intra-aneurysmal organization, as seen in the aneurysm occluded by the silicone balloon, will be delayed because the balloon is not fixed within the aneurysm, and that this free-floating and rotating balloon causes repeated trauma to the aneurysm wall, contributing to subsequent enlargement and rupture of the aneurysm. The superior antithrombogenic nature of silicone may be responsible for the bias of such phenomena toward the silicone balloon.