Biomedical subjects

C Chiang

Publications and source records attributed to C Chiang.

At least 19 recordsLinked to original sources

PubMed2002

Limited effect of recombinant porcine interleukin-12 on porcine lymphocytes due to a low level of IL-12 beta2 receptor.

The cytokine interleukin-12 (IL-12) is a key molecule in the regulation of CD4 + T cell development and specifically potentiates T helper 1 responses in mouse and man. However, biological effects mediated by IL-12 have not been well defined in pigs. Herein, recombinant porcine IL-12 (rPoIL-12) was expressed in a swine poxvirus system as a biologically active heterodimer and used to stimulate bovine or swine lymphoblast cells. After 3 days of incubation, only bovine blasts were responsive to the rPoIL-12 treatment as monitored by cell proliferation in several independent trials. Similarly, i.m. administration of rPoIL-12 in the hind leg of 3-week-old pigs indicated a reduction in the number of interferon-gamma (IFN-gamma) producing lymphocytes isolated from inguinal lymph nodes. The porcine IL-12R beta2 (IL-12Rbeta2) sequence was cloned and results generated by reverse transcriptase polymerase chain reaction (RT-PCR) demonstrated that the expression of IL-12R on porcine blasts as measured by the relative levels of IL-12Rbeta2 mRNA was less than that in bovine blasts and are in agreement with the reduced proliferation response of swine blast cells to rPoIL-12 treatment. Real time PCR analysis demonstrated that after PBMC stimulation, bovine blasts had an 11-fold increase in IL-12Rbeta2 mRNA levels while porcine blasts had almost no change. These data support a mechanism for IL-12 stimulation in swine inconsistent with that observed in conventional models.

Amino Acid Sequence↗

PubMed2002

Formulation factors in preparing BTM-chitosan microspheres by spray drying method.

Chitosan (CTS) microspheres were prepared by a spray drying method using type-A gelatin and ethylene oxide-propylene oxide block copolymer as modifiers. Surface morphological characteristics and surface charges of prepared microspheres were investigated by using scanning electron microscopy (SEM) and microelectrophoresis. The particle shape, size and surface morphology of microspheres were significantly affected by the concentration of gelatin. Betamethasone disodium phosphate (BTM)-loaded microspheres demonstrated good drug stability (less 1% hydrolysis product), high entrapped efficiency (95%) and positive surface charge (37.5 mV). The in vitro drug release from the microspheres was related to gelatin content. Microspheres containing gelatin/CTS 0.4 approximately 0.6(w/w) had a prolong release pattern for 12 h. These formulation factors were correlated to particulate characteristics for optimizing BTM microspheres in pulmonary delivery.

Anti-Inflammatory Agents↗

PubMed2002

Sonic hedgehog regulates otic capsule chondrogenesis and inner ear development in the mouse embryo.

Development of the cartilaginous capsule of the inner ear is dependent on interactions between otic epithelium and its surrounding periotic mesenchyme. During these tissue interactions, factors endogenous to the otic epithelium influence the differentiation of the underlying periotic mesenchyme to form a chondrified otic capsule. We report the localization of Sonic hedgehog (Shh) protein and expression of the Shh gene in the tissues of the developing mouse inner ear. We demonstrate in cultures of periotic mesenchyme that Shh alone cannot initiate otic capsule chondrogenesis. However, when Shh is added to cultured periotic mesenchyme either in combination with otic epithelium or otic epithelial-derived fibroblast growth factor (FGF2), a significant enhancement of chondrogenesis occurs. Addition of Shh antisense oligonucleotide (AS) to cultured periotic mesenchyme with added otic epithelium decreases levels of endogenous Shh and suppresses the chondrogenic response of the mesenchyme cells, while supplementation of Shh AS-treated cultures with Shh rescues cultures from chondrogenic inhibition. We demonstrate that inactivation of Shh by targeted mutation produces anomalies in the developing inner ear and its surrounding capsule. Our results support a role for Shh as a regulator of otic capsule formation and inner ear development during mammalian embryogenesis.

Animals↗

PubMed2002

Coordinate regulation and synergistic actions of BMP4, SHH and FGF8 in the rostral prosencephalon regulate morphogenesis of the telencephalic and optic vesicles.

We investigated the roles of bare morphogenetic protein (BMP), sonic hedgehog (SHH) and fibroblast growth factor (FGF)-expressing signaling centers in regulating the patterned outgrowth of the telencephalic and optic vesicles. Implantation of BMP4 beads in the anterior neuropore of stage 10 chicken embryos repressed FGF8 and SHH expression. Similarly, loss of SHH expression in Shh mutant mice leads to increased BMP signaling and loss of Fgf8 expression in the prosencephalon. Increased BMP signaling and loss of FGF and SHH expression was correlated with decreased proliferation, increased cell death, and hypoplasia of the telencephalic and optic vesicles. However, decreased BMP signaling, through ectopic expression of Noggin, a BMP-binding protein, also caused decreased proliferation and hypoplasia of the telencephalic and optic vesicles, but with maintenance of Fgf8 and Shh expression, and no detectable increase in cell death. These results suggest that optimal growth requires a balance of BMP, FGF8 and SHH signaling. We suggest that the juxtaposition of Fgf8, Bmp4 and Shh expression domains generate patterning centers that coordinate the growth of the telencephalic and optic vesicles, similar to how Fgf8, Bmp4 and Shh regulate growth of the limb bud. Furthermore, these patterning centers regulate regional specification within the forebrain and eye, as exemplified by the regulation of Emx2 expression by different levels of BMP signaling. In summary, we present evidence that there is cross-regulation between BMP-, FGF- and SHH-expressing signaling centers in the prosencephalon which regulate morphogenesis of, and regional specification within, the telencephalic and optic vesicles.

Abnormalities, Drug-Induced↗

PubMed2001

Manifestation of the limb prepattern: limb development in the absence of sonic hedgehog function.

The secreted protein encoded by the Sonic hedgehog (Shh) gene is localized to the posterior margin of vertebrate limb buds and is thought to be a key signal in establishing anterior-posterior limb polarity. In the Shh(-/-) mutant mouse, the development of many embryonic structures, including the limb, is severely compromised. In this study, we report the analysis of Shh(-/-) mutant limbs in detail. Each mutant embryo has four limbs with recognizable humerus/femur bones that have anterior-posterior polarity. Distal to the elbow/knee joints, skeletal elements representing the zeugopod form but lack identifiable anterior-posterior polarity. Therefore, Shh specifically becomes necessary for normal limb development at or just distal to the stylopod/zeugopod junction (elbow/knee joints) during mouse limb development. The forelimb autopod is represented by a single distal cartilage element, while the hindlimb autopod is invariably composed of a single digit with well-formed interphalangeal joints and a dorsal nail bed at the terminal phalanx. Analysis of GDF5 and Hoxd11-13 expression in the hindlimb autopod suggests that the forming digit has a digit-one identity. This finding is corroborated by the formation of only two phalangeal elements which are unique to digit one on the foot. The apical ectodermal ridge (AER) is induced in the Shh(-/-) mutant buds with relatively normal morphology. We report that the architecture of the Shh(-/-) AER is gradually disrupted over developmental time in parallel with a reduction of Fgf8 expression in the ridge. Concomitantly, abnormal cell death in the Shh(-/-) limb bud occurs in the anterior mesenchyme of both fore- and hindlimb. It is notable that the AER changes and mesodermal cell death occur earlier in the Shh(-/-) forelimb than the hindlimb bud. This provides an explanation for the hindlimb-specific competence to form autopodial structures in the mutant. Finally, unlike the wild-type mouse limb bud, the Shh(-/-) mutant posterior limb bud mesoderm does not cause digit duplications when grafted to the anterior border of chick limb buds, and therefore lacks polarizing activity. We propose that a prepattern exists in the limb field for the three axes of the emerging limb bud as well as specific limb skeletal elements. According to this model, the limb bud signaling centers, including the zone of polarizing activity (ZPA) acting through Shh, are required to elaborate upon the axial information provided by the native limb field prepattern.

Animals↗

PubMed2001

Anorectal malformations caused by defects in sonic hedgehog signaling.

Anorectal malformations are a common clinical problem affecting the development of the distal hindgut in infants. The spectrum of anorectal malformations ranges from the mildly stenotic anus to imperforate anus with a fistula between the urinary and intestinal tracts to the most severe form, persistent cloaca. The etiology, embryology, and pathogenesis of anorectal malformations are poorly understood and controversial. Sonic hedgehog (Shh) is an endoderm-derived signaling molecule that induces mesodermal gene expression in the chick hindgut. However, the role of Shh signaling in mammalian hindgut development is unknown. Here, we show that mutant mice with various defects in the Shh signaling pathway exhibit a spectrum of distal hindgut defects mimicking human anorectal malformations. Shh null-mutant mice display persistent cloaca. Mutant mice lacking Gli2 or Gli3, two zinc finger transcription factors involved in Shh signaling, respectively, exhibit imperforate anus with recto-urethral fistula and anal stenosis. Furthermore, persistent cloaca is also observed in Gli2(-/-);Gli3(+/-), Gli2(+/-);Gli3(-/-), and Gli2(-/-);Gli3(-/-) mice demonstrating a gene dose-dependent effect. Therefore, Shh signaling is essential for normal development of the distal hindgut in mice and mutations affecting Shh signaling produce a spectrum of anorectal malformations that may reveal new insights into their human disease equivalents.

Anal Canal↗

PubMed2001

Cytomegalovirus infection as a cause of pseudomembrane colitis: a report of four cases.

Pseudomembranous colitis is very commonly encountered in patients with acquired immune deficiency syndrome (AIDS), and has been characteristically associated with Clostridium difficile infection. We present four cases of AIDS-related diarrhea and pseudomembrane formation on endoscopy with pathologic features consistent with cytomegalovirus (CMV) colitis. Our findings indicate that CMV colitis should be considered in the differential diagnosis of pseudomembranous colitis in immunocompromised patients.

AIDS-Related Opportunistic Infections↗

PubMed2000

Top-down processing mediated by interareal synchronization.

Perception and cortical responses are not only driven "bottom-up" by the external stimulus but are altered by internal constraints such as expectancy or the current behavioral goal. To investigate neurophysiological mechanisms of such top-down effects, we analyzed the temporal interactions of neurons on different levels of the cortical hierarchy during perception of stimuli with varying behavioral significance. We found that interareal interactions in a middle-frequency range (theta and alpha; 4-12 Hz) strongly depend on the associated behavior, with a phase relationship and a layer specificity indicating a top-down-directed interaction. For novel unexpected stimuli, presumably processed in a feed-forward fashion, no such interactions occurred but high-frequency interactions (gamma; 20-100 Hz) were observed. Thus corticocortical synchronization reflects the internal state of the animal and may mediate top-down processes.

Animals↗

PubMed2000

Involvement of neurogranin in the modulation of calcium/calmodulin-dependent protein kinase II, synaptic plasticity, and spatial learning: a study with knockout mice.

Neurogranin/RC3 is a neural-specific Ca(2+)-sensitive calmodulin (CaM)-binding protein whose CaM-binding affinity is modulated by phosphorylation and oxidation. Here we show that deletion of the Ng gene in mice did not result in obvious developmental or neuroanatomical abnormalities but caused an impairment of spatial learning and changes in hippocampal short- and long-term plasticity (paired-pulse depression, synaptic fatigue, long-term potentiation induction). These deficits were accompanied by a decreased basal level of the activated Ca(2+)/CaM-dependent kinase II (CaMKII) ( approximately 60% of wild type). Furthermore, hippocampal slices of the mutant mice displayed a reduced ability to generate activated CaMKII after stimulation of protein phosphorylation and oxidation by treatments with okadaic acid and sodium nitroprusside, respectively. These results indicate a central role of Ng in the regulation of CaMKII activity with decisive influences on synaptic plasticity and spatial learning.

Animals↗

PubMed2000

Bi-directional interactions between visual areas in the awake behaving cat.

The study of the cooperativity among cortical areas is essential to our understanding of brain functioning. Here we investigated the relative contributions of top-down and bottom-up directed interactions between area 17 and area 7 of the cat visual system. Bipolar local field potentials were recorded while the animals performed a go/no-go task or were in a quiet resting state. The data were analyzed by applying measures of interaction based on the Wiener-Granger causality concept. We found that during the visual task top-down directed interactions were of a similar magnitude as the bottom-up component. Second, interareal couplings tended to increase in conditions requiring a discriminative effort. Third, during behaviors not dominated by visual processing non-directed interactions increased.

Animals↗

PubMed2000

Control of Shh activity and signaling in the neural tube.

The generation of diverse cell types in the neural tube requires inductive signals that are generally derived from tissues adjacent to the neural tube and capable of patterning cell fates at a distance. Shh, a signaling molecule secreted from the notochord and the floor plate, has been shown to induce motor neurons (MN) as well as interneurons, dorsal to the MN, in a concentration-dependent manner. The cellular response to the Shh signal is mediated by receptors, cytoplasmic factors as well as transcription factors, which act both positively and negatively to modulate Shh activity in the patterning of diverse cell types in the ventral neural tube. Additionally, Shh also cooperates with Bmp and Fgf molecules in the control of diverse neuronal cell fates in the brain.

Animals↗

PubMed2000

Specification of ventral neuron types is mediated by an antagonistic interaction between Shh and Gli3.

Specification of distinct neuron types in the ventral spinal cord is thought to be mediated by a graded concentration of Sonic hedgehog (Shh), a secreted signaling protein. Shh is made in the notochord, the most ventral part of the spinal cord, and in mice lacking Shh, ventral cell types are reduced or absent. The response to Shh depends on transcription factors of the Gli family, but the detailed mechanism is not understood. Here we show that Gli3 represses ventral fates in a dose-dependent manner. Whereas Shh -/- mutant mice show reductions in several classes of ventral interneurons and a complete absence of motor neurons, these cell types were rescued in Shh-/-;Gli3 -/- double mutants. This rescue of the Shh null phenotype depended on the level of Gli3 function; a partial rescue was observed in Shh-/-;Gli3 +/- embryos. We propose that Shh is required to antagonize Gli3, which would otherwise repress ventral fates. Differences between rostral and caudal regions suggest that other signaling molecules-in addition to Shh-may be involved in specifying ventral fates, particularly in the caudal region of the spinal cord.

Animals↗

PubMed1999

A sonic hedgehog-independent, retinoid-activated pathway of neurogenesis in the ventral spinal cord.

Sonic hedgehog (Shh) is thought to control the generation of motor neurons and interneurons in the ventral CNS. We show here that a Shh-independent pathway of interneuron generation also operates in the ventral spinal cord. Evidence for this parallel pathway emerged from an analysis of the induction of ventral progenitors that express the Dbx homeodomain proteins and of Evx1/2 (V0) and En1 (V1) neurons. Shh signaling is sufficient to induce Dbx cells and V0 and V1 neurons but is not required for their generation in vitro or in vivo. Retinoids appear to mediate this parallel pathway. These findings reveal an unanticipated Shh-independent signaling pathway that controls progenitor cell identity and interneuron diversity in the ventral spinal cord.

Animals↗

PubMed1999

Essential role for Sonic hedgehog during hair follicle morphogenesis.

The hair follicle is a source of epithelial stem cells and site of origin for several types of skin tumors. Although it is clear that follicles arise by way of a series of inductive tissue interactions, identification of the signaling molecules driving this process remains a major challenge in skin biology. In this study we report an obligatory role for the secreted morphogen Sonic hedgehog (Shh) during hair follicle development. Hair germs comprising epidermal placodes and associated dermal condensates were detected in both control and Shh -/- embryos, but progression through subsequent stages of follicle development was blocked in mutant skin. The expression of Gli1 and Ptc1 was reduced in Shh -/- dermal condensates and they failed to evolve into hair follicle papillae, suggesting that the adjacent mesenchyme is a critical target for placode-derived Shh. Despite the profound inhibition of hair follicle morphogenesis, late-stage follicle differentiation markers were detected in Shh -/- skin grafts, as well as cultured vibrissa explants treated with cyclopamine to block Shh signaling. Our findings reveal an essential role for Shh during hair follicle morphogenesis, where it is required for normal advancement beyond the hair germ stage of development.

Adipose Tissue↗

PubMed1999

Effect of trilinolein on strophanthidin-induced ventricular tachycardia in guinea pigs.

Trilinolein, a triacylglycerol with linoleic acid, was found to inhibit Ca2+ influx in cardiomyocytes. The purpose of this study was to evaluate the effects of trilinolein on ventricular arrhythmia induced by intravenous strophanthidin in guinea pigs anesthetized with intraperitoneal urethane. After strophanthidin- induced ventricular tachycardia, treatment with trilinolein (0.1, 1, 10 and 100 microg/kg) or control (0.04% propylene glycol) did not terminate ventricular tachycardia. However, 1, 10 and 100 microg/kg trilinolein could narrow the width of the QRS complex during ventricular tachycardia. Pretreatment with trilinolein before strophanthidin administration did not prevent the occurrence of ventricular tachycardia; the doses of strophanthidin required to induce arrhythmias (ventricular extrasystole and ventricular tachycardia) were similar in guinea pigs pretreated with trilinolein or control. However, there were fewer ventricular extrasystoles in guinea pigs pretreated with trilinolein than in the control group (ANOVA, p < 0.01). Moreover, the ventricular extrasystoles were fewer in guinea pigs pretreated with higher doses of trilinolein (100 microg/kg, 103 +/- 60; 10 microg/kg, 188 +/- 86) than lower doses of trilinolein (1 microg/kg, 366 +/- 102; 0.1 microg/kg, 436 +/- 145). This study demonstrated that trilinolein was not effective in terminating or preventing strophanthidin-induced ventricular tachycardia. However, trilinolein could improve ventricular depolarization and suppress ventricular extrasystoles.

Analysis of Variance↗

PubMed1999

Sonic hedgehog controls epaxial muscle determination through Myf5 activation.

Sonic hedgehog (Shh), produced by the notochord and floor plate, is proposed to function as an inductive and trophic signal that controls somite and neural tube patterning and differentiation. To investigate Shh functions during somite myogenesis in the mouse embryo, we have analyzed the expression of the myogenic determination genes, Myf5 and MyoD, and other regulatory genes in somites of Shh null embryos and in explants of presomitic mesoderm from wild-type and Myf5 null embryos. Our findings establish that Shh has an essential inductive function in the early activation of the myogenic determination genes, Myf5 and MyoD, in the epaxial somite cells that give rise to the progenitors of the deep back muscles. Shh is not required for the activation of Myf5 and MyoD at any of the other sites of myogenesis in the mouse embryo, including the hypaxial dermomyotomal cells that give rise to the abdominal and body wall muscles, or the myogenic progenitor cells that form the limb and head muscles. Shh also functions in somites to establish and maintain the medio-lateral boundaries of epaxial and hypaxial gene expression. Myf5, and not MyoD, is the target of Shh signaling in the epaxial dermomyotome, as MyoD activation by recombinant Shh protein in presomitic mesoderm explants is defective in Myf5 null embryos. In further support of the inductive function of Shh in epaxial myogenesis, we show that Shh is not essential for the survival or the proliferation of epaxial myogenic progenitors. However, Shh is required specifically for the survival of sclerotomal cells in the ventral somite as well as for the survival of ventral and dorsal neural tube cells. We conclude, therefore, that Shh has multiple functions in the somite, including inductive functions in the activation of Myf5, leading to the determination of epaxial dermomyotomal cells to myogenesis, as well as trophic functions in the maintenance of cell survival in the sclerotome and adjacent neural tube.

Animals↗

PubMed1998

Potent excitatory influence of prefrontal cortex activity on noradrenergic locus coeruleus neurons.

An influence of the prefrontal cortex on noradrenergic locus coeruleus neurons would have profound implications for the function of the locus coeruleus system. Although the medial prefrontal cortex does not substantially innervate the core of the nucleus locus coeruleus, evidence indicates that the medial prefrontal cortex projects to regions containing locus coeruleus dendrites; indirect medial prefrontal cortex-locus coeruleus projections are also possible. Here, we examined influences of prefrontal cortex activity on locus coeruleus firing rates by activating or inactivating the medial prefrontal cortex while recording impulse activity of locus coeruleus neurons extracellularly in anaesthetized rats. Most of our electrical stimulation experiments were conducted in rats which underwent lesions of the ascending dorsal bundle of noradrenergic fibres from the locus coeruleus to eliminate locus coeruleus projections to the prefrontal cortex, because antidromic activation of locus coeruleus from the prefrontal cortex affects even non-driven locus coeruleus neurons through collaterals. Single pulse stimulation (1 mA, 0.3-0.5 ms) of the dorsomedial (frontal region 2) or prelimbic region of the medial prefrontal cortex synaptically activated 13/16 (81%) or 16/56 (29%) locus coeruleus neurons, respectively. Train stimulation (20 Hz for 0.5 s) synaptically activated greater percentages of locus coeruleus cells, 11/12 cells (92%) for the dorsomedial prefrontal cortex, and 41/50 cells (82%) for the prelimbic cortex. No inhibitory responses in the locus coeruleus were obtained with dorsomedial prefrontal stimulation, and weak inhibition was found in 16% of locus coeruleus cells with prelimbic stimulation. Electrical stimulation of more lateral frontal cortex (Fr1 area) had no effects on locus coeruleus activity. Chemical stimulation of the dorsomedial prefrontal cortex with L-glutamate (10 or 100 mM) or D,L-homocysteic acid (10 mM) phasically activated 15/26 (55%) locus coeruleus cells, and 15/68 cells (22%) with prelimbic stimulation; such activation was sometimes followed by long-lasting oscillatory activity. No locus coeruleus cells exhibited purely inhibitory responses with chemical stimulation of any prefrontal cortex site. Inactivation of the dorsomedial or prelimbic region of the prefrontal cortex with lidocaine microinjection (2%, 180 or 300 nl) reduced locus coeruleus firing rates in 6/10 (60%) or 7/19 (37%) locus coeruleus cells, respectively. In no case did lidocaine in any prefrontal cortex site activate a locus coeruleus neuron. These results indicate that the medial prefrontal cortex provides a potent excitatory influence on locus coeruleus neurons. The fact that inactivation of the medial prefrontal cortex suppressed locus coeruleus firing indicates that the medial prefrontal cortex also provides a resting tonic excitatory influence on locus coeruleus activity.

Anesthesia↗

PubMed1998

Mediolateral patterning of somites: multiple axial signals, including Sonic hedgehog, regulate Nkx-3.1 expression.

The axial structures, the notochord and the neural tube, play an essential role in the dorsoventral patterning of somites and in the differentiation of their many cell lineages. Here, we investigated the role of the axial structures in the mediolateral patterning of the somite by using a newly identified murine homeobox gene, Nkx-3.1, as a medial somitic marker in explant in vitro assays. Nkx-3.1 is dynamically expressed during somitogenesis only in the youngest, most newly-formed somites at the caudal end of the embryo. We found that the expression of Nkx-3.1 in pre-somitic tissue explants is induced by the notochord and maintained in newly-differentiated somites by the notochord and both ventral and dorsal parts of the neural tube. We showed that Sonic hedgehog (Shh) is one of the signaling molecules that can reproduce the effect of the axial structures by exposing explants to either COS cells transfected with a Shh expression construct or to recombinant SHH. Shh could induce and maintain Nkx-3.1 expression in pre-somitic mesoderm and young somites but not in more mature, differentiated ones. The effects of Shh on Nkr-3.1 expression were antagonized by a forskolin-induced increase in the activity of cyclic AMP-dependent protein kinase A. Additionally, we confirmed that the expression of the earliest expressed murine myogenic marker, myf 5, is also regulated by the axial structures but that Shh by itself is not capable of inducing or maintaining it. We suggest that the establishment of somitic medial and lateral compartments and the early events in myogenesis are governed by a combination of positive and inhibitory signals derived from the neighboring structures, as has previously been proposed for the dorsoventral patterning of somites.

Animals↗