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Biomedical subjects

S Choi

Publications and source records attributed to S Choi.

At least 163 records · Page 9Linked to original sources
PubMed1997

Translocation of autophosphorylated calcium/calmodulin-dependent protein kinase II to the postsynaptic density.

Calcium/calmodulin-dependent protein kinase II (CaMKII) undergoes calcium-dependent autophosphorylation, generating a calcium-independent form that may serve as a molecular substrate for memory. Here we show that calcium-independent CaMKII specifically binds to isolated postsynaptic densities (PSDs), leading to enhanced phosphorylation of many PSD proteins including the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA)-type glutamate receptor. Furthermore, binding to PSDs changes CaMKII from a substrate for protein phosphatase 2A to a protein phosphatase 1 substrate. Translocation of CaMKII to PSDs occurs in hippocampal slices following treatments that induce CaMKII autophosphorylation and a form of long term potentiation. Thus, synaptic activation leads to accumulation of autophosphorylated, activated CaMKII in the PSD. This increases substrate phosphorylation and affects regulation of the kinase by protein phosphatases, which may contribute to enhancement of synaptic strength.

Animals↗
PubMed1997

Decreased probability of neurotransmitter release underlies striatal long-term depression and postnatal development of corticostriatal synapses.

Changes in synaptic efficacy are crucial for the development of appropriate neural circuits and brain information storage. We have investigated mechanisms underlying long-term depression (LTD) at glutamatergic synapses in the striatum, a brain region important in motor performance and cognition, and a target for Huntington and Parkinson diseases. Induction of striatal LTD is dependent on postsynaptic depolarization and calcium influx through L-type channels. Surprisingly, LTD maintenance appears to involve a decrease in the probability of neurotransmitter release from presynaptic terminals as evidenced by increases in paired-pulse facilitation and the coefficient of variation of synaptic responses that are tightly associated with LTD expression. Furthermore, both the apparent probability of neurotransmitter release and the magnitude of LTD decrease concomitantly during postnatal development, consistent with the idea that striatal LTD is involved in a developmental decrease in the probability of neurotransmitter release at corticostriatal synapses. The presynaptic changes that underlie striatal LTD may also be important for motor performance and certain forms of learning and memory.

Aging↗
PubMed1997

Control of endogenous norepinephrine release in the hypothalamus of male rats changes over adolescent development.

In order to evaluate mechanisms that could contribute to the effect of adolescent development on the in vivo utilization of norepinephrine (NE) in the hypothalamus, the depolarized release of endogenous norepinephrine (using 50 mM potassium) was measured in vitro in hypothalamic explants from male rats over late juvenile (28 days) to young adult (70 days) ages. Depolarized release, expressed as a percent of the total endogenous pool, was significantly greater in juveniles than in either adolescents (42 days) or young adults. Incubation in the presence of idazoxan, an alpha 2-adrenoceptor antagonists, increased the depolarized fractional NE release in adolescent and young adult rats; however, the same drug decreased depolarized release in juveniles. Inhibition of norepinephrine reuptake by incubation in the presence of nisoxetine (1 microM) significantly increased depolarized release (fractional and absolute) in young adults only. A higher concentration of nisoxetine (5 microM) significantly increased depolarized release in juveniles, but significantly reduced release in adults. Nisoxetine did not influence release in adolescents at either concentration. The possibilities that adolescents development brings about a change in alpha 2-adrenoceptor subtype and that juveniles may have a greater NE reuptake capacity than adults are discussed. Hypothalamic NE projections are important to several regulatory functions, and changes that take place in this system over adolescence may be important for the emergence of adult-typical responses as well as render adolescents vulnerable to specific dysfunctions.

Adrenergic alpha-Antagonists↗
PubMed1997

A large-insert (130 kbp) bacterial artificial chromosome library of the rice blast fungus Magnaporthe grisea: genome analysis, contig assembly, and gene cloning.

Magnaporthe grisea (Hebert) Barr causes rice blast, one of the most devastating diseases of rice (Oryza sativa) worldwide. This fungus is an ideal organism for studying a number of aspects of plant-pathogen interactions, including infection-related morphogenesis, avirulence, and pathogen evolution. To facilitate M. grisea genome analysis, physical mapping, and positional cloning, we have constructed a bacterial artificial chromosome (BAC) library from the rice infecting strain 70-15. A new method was developed for separation of partially digested large-molecular-weight DNA fragments that facilitated library construction with large inserts. The library contains 9216 clones, with an average insert size of 130 kbp (> 25 genome equivalents) stored in 384-well microtiter plates that can be double spotted robotically on to a single nylon membrane. Several unlinked single-copy DNA probes were used to screen 4608 clones in the library and an average of 13 (minimum of 6) overlapping BAC clones was found in each case. Hybridization of total genomic DNA to the library and analysis of individual clones indicated that approximately 26% of the clones contain single-copy DNA. Approximately 35% of BAC clones contained the retrotransposon MAGGY. The library was used to identify BAC clones containing a adenylate cyclase gene (mac1). In addition, a 550-kbp contig composed of 6 BAC clones was constructed that encompassed two adjacent RFLP markers on chromosome 2. These data show that the BAC library is suitable for genome analysis of M. grisea. Copies of colony hybridization membranes are available upon request.

Ascomycota↗
PubMed1997

Scheduling processes in working memory: instructions control the order of memory search and mental arithmetic.

Humans must often use working memory to execute processes one at a time because of its limited capacity. Two experiments tested where limits in access to working memory occur. Subjects searched a short-term memory set for one stimulus digit and performed mental arithmetic with another stimulus digit. In one experiment, they were told to carry out the mental arithmetic before the memory search and to make the arithmetic response first. In the other, they were instructed to perform the tasks in the opposite order. The overt responses were executed in the prescribed order. Moreover, the covert working memory processes were executed in the prescribed order, as revealed by a critical path network analysis of reaction times. Results are explained in terms of a double-bottleneck model in which central processes and responses are constrained to be carried out for one task at a time.

Adult↗
PubMed1997

Spinal extradural leiomyoma in a pediatric patient with acquired immunodeficiency syndrome: case report.

OBJECTIVE AND IMPORTANCE: We report a case of two separate cervicothoracic, extradural leiomyomas occurring in a male pediatric patient with acquired immunodeficiency syndrome (AIDS). To our knowledge, such a case has never been reported in the literature. CLINICAL PRESENTATION: A 9-year-old male patient with AIDS presented with progressive leg weakness. At examination, he was myelopathic with paraparesis and a T4 sensory level to pinprick. A magnetic resonance image revealed two separate cervicothoracic lesions causing cord compression. INTERVENTION: The patient underwent resection of both lesions. Postoperatively, he regained normal strength in his legs and was discharged home after 2 weeks. CONCLUSION: With the ever-growing number of pediatric patients with AIDS, the entity will likely be encountered with increasing frequency in the future. Because of the potential for neurological recovery and cure, the neurosurgeon should be cognizant of this entity.

Acquired Immunodeficiency Syndrome↗
PubMed1996

The hypothalamic ventromedial nuclei couple activity in the hypothalamo-pituitary-adrenal axis to the morning fed or fasted state.

Function in the adrenocortical system is markedly altered by availability of food. Basal activity is lowest and stress responsivity highest in the morning when nocturnal rats eat approximately 90% of their daily calories during the dark. After an overnight fast, basal corticotrophin and corticosteroid levels are elevated, and responsivity to stressors is decreased. Central neural sites that control these changes are unidentified. The hypothalamic ventromedial nuclei (VMN) appear to signal satiety; lesions result in increased food intake, obesity, and elevated basal insulin and corticosteroids. Thus, the VMN are good candidates for calorically mediated control of adrenocortical system function in satiated rats. We injected colchicine into the VMN to cause reversible inhibition of activity (Avrith and Mogenson, 1978) and tested the effects on basal and stimulated function in the adrenocortical system. Colchicine-injected rats that fed ad libitum exhibited increased basal but reduced corticotrophin and corticosterone responses to restraint in the morning compared with controls. By contrast, after an overnight fast, control rats had increased basal adrenocortical hormones and decreased stress responses that did not differ from colchicine-injected rats. Colchicine was visualized within cells in the VMN for up to 5 d using fluorescein/colchicine, and the treatment did not cause increased gliosis; moreover, the functional effects of the injections were reversed within 15 d. We conclude that (1) the VMN serve to couple activity in the adrenocortical system to energy intake and (2) discrete colchicine injections provide a behaviorally and neuroendocrinologically useful period of inhibition without causing permanent functional damage.

Animals↗
PubMed1996

Adolescent development influences functional responsiveness of noradrenergic projections to the hypothalamus in male rats.

Hypothalamic noradrenergic utilization in vivo and the in vitro depolarized release of norepinephrine (NE) were measured at 28, 42, and 70 days of age in male rats to determine the impact of adolescent development on the functional responsiveness of this transmitter system. At each age, function was determined in control rats and rats challenged by restraint. NE utilization in vivo was estimated by measuring the decrease in NE levels following administration of a synthesis inhibitor, alpha-methyl-p-tyrosine methyl ester (alpha-MT, 250 mg/kg). The half-life of approach to a new steady-state was determined. To measure depolarized release of NE, the hypothalamus was incubated in vitro in a high potassium (50 mM) medium and the percent of endogenous NE released into the medium was determined. The in vivo results indicated that hypothalamic NE utilization in control animals decreases as animals mature. Additionally, the in vitro results indicated that the percent NE released upon depolarization also decreased with maturation in control animals. Restraint shifted the NE decay curve measured in vivo to the right at all ages. Overall, however, restraint tended to increase NE utilization at 70 days, have little effect at 42 days, and retard utilization at 28 days. Furthermore, restraint markedly reduced the depolarized release of NE at 28 days, had no effect at 42 days and slightly, but significantly, increased release at 70 days. Restraint significantly increased plasma corticosterone at all ages. Hypothalamic NE projections are important to an organism's regulatory responses, and changes that take place over adolescence in this system may be important for the emergence of adult-typical responses as well as render adolescents vulnerable to specific dysfunctions.

Analysis of Variance↗
PubMed1996

Comparative intravitreal antibiotic therapy for experimental Enterococcus faecalis endophthalmitis.

OBJECTIVE: To evaluate the most effective intravitreal antibiotic treatment of vancomycin-sensitive and -resistant Enterococcus faecalis endophthalmitis. DESIGN: Animal experiment. SETTING: Seventy-eight New Zealand white rabbits received an intravitreal injection of 10(5) vancomycin-sensitive or -resistant E faecalis organisms in one eye. Infections were allowed to proceed 3 hours before dividing animals randomly into the following treatment groups (n = 6, each): the vancomycin-sensitive E faecalis model--(1) vancomycin (1 mg/0.1 mL), (2) combined vancomycin (1 mg/0.1 mL) and amikacin (0.4 mg/0.1 mL), (3) combined vancomycin (1 mg/0.1 mL) and gentamicin (0.1 mg/0.1 mL), (4) combined vancomycin (1 mg/0.1 mL) and ceftazidime (2 mg/0.1 mL), (5) combined ampicillin (5 mg/0.1 mL) and gentamicin (0.1 mg/0.1 mL), and (6) pristinamycin (1 mg/0.1 mL); and the vancomycin-resistant E faecalis model--(1)same as above, excluding group 4. Control groups received sterile balanced salt solution. Twenty-four hours following intravitreal treatment, vitreous humor was collected for quantitative bacteriological studies. RESULTS: Intravitreal therapy with combined vancomycin and amikacin provided the most effective reduction of vancomycin-sensitive E faecalis organisms compared with combined vancomycin and gentamicin therapy (P =.10, Wilcoxon's rank sum test) or any other treatment group (P < .01, Wilcoxon's rank sum test). For vancomycin-resistant E faecalis endophthalmitis model, the combined ampicillin and gentamicin therapy was the most effective, followed by the combined vancomycin and amikacin therapy (P < .01, Wilcoxon's rank sum test). CONCLUSIONS: Treatment with intravitreal vancomycin plus amikacin and with intravitreal ampicillin plus gentamicin provide an effective bactericidal therapy for severe experimental vancomycin-sensitive and -resistant E faecalis endophthalmitis, respectively.

Animals↗
PubMed1996

Low-grade pure and mixed cerebral astrocytomas treated in the CT scan era.

From 1974 to 1992, 63 patients diagnosed with low-grade pure or mixed oligo-astrocytoma were seen and treated at our institution. All patients underwent CT scan pre-operatively. There were 20 female and 43 males ranging in age from 12 to 73 years (median age of 33 years). 15 patients had a stereotactic biopsy as the only surgical procedure. 34 had a partial tumor resection and 14 a gross total tumor resection. 43 patients were treated with post-operative radiotherapy whereas 20 patients underwent surgery only as part of the initial management. 50 to 60 Gy (median 59.4 Gy) were given with daily fractions of 1.8 to 2 GY. Tumor volume ranged from 3.4 to 441 cm3. Median tumor volume was larger for radiotherapy treated patients. Median follow-up was 54 months (range of 4 to 240 months). The overall 10 and 15 actuarial survival rates were 37% and 25% respectively. The 5 years survival rate for patients treated at initial diagnosis with surgery alone was 66% and it was 67.3% for patients treated with radiation therapy (P = NS). Prognostic factors having independent significant impact on survival were: extent of surgery, age gender and tumor volume. As well, survival for patients with low-grade astrocytoma in the CT scan era appears to be improved compared to historical controls in the literature.

Adolescent↗
PubMed1996

Epidermal denervation and its effects on keratinocytes and Langerhans cells.

Skin innervation has been considered to subserve sensory perception only, but several lines of evidence suggest that there are "effector' influences of skin innervation on the immune system and keratotinocytes. In this study, we transected the sciatic nerves of rats and examined the effects of denervation on the epidermis. In normal skin, the epidermis was densely innervated by fine axons that were immunostained with several axonal markers, including neuronal ubiquitin carboxyl terminal hydrolase (protein gene product 9.5). All of the epidermal axons in the regions innervated by sciatic nerve disappeared within 24-48 h after transection of sciatic nerve, and remained absent as long as subsequent reinnervation by regenerating axonal sprouts was prevented. Denervation produced changes in both the keratinocytes and the Langerhans cells, the bone marrow-derived antigen-presenting cells of the epidermis. The thickness of epidermis decreased within 7 days. By 48 h after transection, the Langerhans cells and their dendritic processes became intensely immunoreactive for protein gene product. Protein gene product 9.5 expression on Langerhans cells remained prominent as long as skin was denervated, but disappeared with reinnervation. By reverse transcription-polymerase chain reaction, we demonstrated the presence of the transcripts for protein gene product 9.5 in epidermis, consistent with the synthesis of the protein by the Langerhans cells. We conclude that epidermal sensory fibres have novel influences on both keratinocytes and Langerhans cells of the epidermis.

Animals↗
PubMed1996

Production and role of cytokines in the CNS of mice with acute viral encephalomyelitis.

Semliki Forest Virus (SFV) causes a more severe acute encephalomyelitis in B6 than in SJL mice despite similar T cell proliferation and antibody responses in these two strains. To determine the immunological mechanisms that may contribute to this difference, CNS tissues from SFV-infected B6 and SJL mice were analyzed for viral replication, inflammatory responses and cytokine production, by semiquantitative reverse transcriptase-PCR and immunohistochemistry. Although initially similar on day 2 p.i., SFV replicated to higher viral titers in B6 than SJL mice on days 4 and 7 p.i. Infectious virus was cleared from both strains by day 10 p.i. There were no differences in numbers of CD4+, CD8+ or MHC class I and II+ inflammatory cells at any time point. Higher levels of IL-4 mRNA, lower levels of TNF-alpha, IL-6, IL-1 beta and IL-2 mRNAs and lower IL-2+ and IFN-gamma+ cells were found in B6. These findings suggest that despite comparable immune responses, different patterns of cytokine production correlated with higher levels of virus in the brains and more severe clinical disease in B6, and more efficient clearance of virus and less severe disease in SJL mice.

Acute Disease↗
PubMed1996

Overexpression and simple purification of a truncated, immunologically reactive GST-HCV core (1-123) fusion protein.

A full-length and a truncated gene for the core protein of hepatitis C virus (HCV) were linked to the gene for glutathione S-transferase (GST), and the expression of each GST-HCV core fusion protein was analyzed. The truncated GST-HCV core (1-123) fusion protein was expressed as a mostly soluble and partly insoluble form comprising more than 50% of the total protein in Escherichia coli after induction by isopropylthio-beta-D-galactoside (IPTG), while the full length GST-HCV core (1-191) fusion protein was not expressed, suggesting that the hydrophobic carboxy terminal region in the core protein affects its expression. In addition, the GST-HCV core (1-123) fusion protein purified by GST-agarose chromatography reacted specifically with an anti-HCV serum from a patient.

Amino Acid Sequence↗