Biomedical subjects

Ayako Ishikawa

Publications and source records attributed to Ayako Ishikawa.

7 recordsLinked to original sources

PubMed2006

Metacontrast masking suggests interaction between visual pathways with different spatial and temporal properties.

We examined the spatiotemporal characteristics of metacontrast using sinusoidal grating stimuli as the target and mask for quantitative comparison with the functional properties of the visual cortex. The magnitude of metacontrast effects depended on the stimulus features such as the orientation and spatial frequency of the target and mask. The characteristics of metacontrast dynamically changed depending on the stimulus onset asynchrony (SOA). At short SOAs (0 to approximately 40 ms), metacontrast exhibited a high stimulus feature specificity and a low contrast sensitivity, whereas at long SOAs ( approximately 40 to 80 ms), metacontrast exhibited a low stimulus feature specificity and a high contrast sensitivity. We suggest that metacontrast is explained by the interaction between two parallel visual pathways: one with a low contrast sensitivity and a high feature specificity, and the other with a high contrast sensitivity and a low feature specificity.

Adult↗

PubMed2005

Factors affecting production of transgenic rats by ICSI-mediated DNA transfer: effects of sonication and freeze-thawing of spermatozoa, rat strains for sperm and oocyte donors, and different constructs of exogenous DNA.

Factors affecting the efficiency of producing transgenic rats by intracytoplasmic sperm injection (ICSI)-mediated DNA transfer were investigated. Epididymal spermatozoa from Sprague-Dawley (SD) rats were sonicated and/or frozen-thawed for cutting the tail and membrane disruption. The sperm heads were exposed for 1 min to different concentrations (0.02-2.5 microg/ml) of 3.0 kb enhanced green fluorescent protein (EGFP) DNA solution, and then microinjected into the denuded F1 hybrid (Donryu x LEW) rat oocytes. The optimal concentration of EGFP DNA solution was 0.1 microg/ml, as determined by the in vitro developmental competence into morulae/blastocysts of the ICSI oocytes and the EGFP expression of the resultant embryos. The efficiency of producing transgenic rat offspring (per transferred zygote) was 2.8%, 1.6%, and 3.3% in the oocytes injected with sonicated, frozen-thawed, and sonicated + frozen-thawed sperm heads, respectively. The founder transgenic rats carrying the EGFP gene transmitted their transgenes to their progeny according to the Mendelian fashion, suggesting the stable incorporation of the transgenes into the rat genomes. Four rat strains (F344, LEW, Donryu, and SD) were compared for their suitability as sperm/oocyte donors for the production of transgenic rats by ICSI with sonicated, frozen-thawed and solution of EGFP DNA-exposed sperm heads. The efficiency of producing transgenic rats in the SD strain (8.2%) was higher than that in the LEW strain (0.9%), while those in the F344 and Donryu strains (4.3%-4.4%) were intermediate. One plasmid DNA (Fyn, 5.0 kb) and two BAC DNA (BAC/Fyn, 208 kb; Svet1/IRES-Cre, 186 kb) were successfully introduced into the SD rat genomes via ICSI, with the producing efficiencies of 2.8%, 0.9%, and 2.4%, respectively.

Animals↗

PubMed2004

Production of transgenic rats by ooplasmic injection of spermatogenic cells exposed to exogenous DNA: a preliminary study.

The aim of the present study was to investigate the efficiencies of producing transgenic rats by the ooplasmic injection of sperm heads (intracytoplasmic sperm injection: ICSI) and elongating spermatids (elongating spermatid injection: ELSI) exposed to the EGFP DNA solution. A slightly lower proportion of ICSI oocytes using sperm heads exposed to a concentration of 0.5 microg/ml DNA solution for 1 min developed into offspring (13.3%, 48/361) when compared to that of oocytes injected with nontreated sperm heads (19.4%, 32/165). Eight ICSI offspring were found to be EGFP-carrying transgenic rats (16.7% per offspring; 2.2% per embryo). After a 1-min exposure of the elongating spermatids to 5 microg/ml of DNA solution, 8.8% (45/511) of the ELSI oocytes developed into offspring while 12.7% (22/173) of the ELSI oocytes using nontreated spermatids developed. Six ELSI offspring carried the EGFP DNA (13.3% per offspring; 1.2% per embryo). The conventional pronuclear microinjection of 5 microg/ml of DNA solution resulted in the higher production of offspring (29.7%, 104/350) and the birth of three transgenic rats (2.9% per offspring; 0.9% per embryo). Thus, sperm heads and elongating spermatids were practically useful as the vector of exogenous DNA if the DNA-exposed spermatogenic cells were microinseminated into rat oocytes.

Animals↗

PubMed2004

Donor and recipient rat strains affect full-term development of one-cell zygotes cultured to morulae/blastocysts.

The present study was conducted to examine the developmental potential to offspring of rat embryos cultured from 1-cell to morula/blastocyst stage. Pronuclear zygotes from Wistar x Wistar or (SD x DA) x Wistar strains were cultured in modified rat 1-cell embryo culture medium (mR1ECM) for 96 h in 5% CO(2) in air at 37 C. The proportion of the 3-way cross hybrid zygotes developing into morula/blastocyst stage (74%) was higher than that of the Wistar zygotes (66%). Day-5 morulae/blastocysts developed in vitro were transferred into Day-3 or -4 pseudopregnant recipients of Wistar or SD x DA strain. The transfer of cultured embryos resulted in the birth of offspring at 13-59%, while that of non-cultured control blastocysts showed birth rates of 35-65%. The best offspring rate of cultured embryos (59%) was obtained when the hybrid 1-cell zygotes were cultured in mR1ECM medium and transferred into the 2-days earlier uteri of SD x DA recipients. These results suggest that genetic background of recipients as well as donors is a possible factor affecting full-term development of rat morulae/blastocysts derived from 1-cell stage zygotes cultured in vitro.

Animals↗

PubMed2004

Effect of activation regimens for rat oocytes on full-term development after round spermatid injection.

The present study was designed to compare the effect of two activation regimens for rat oocytes on full-term development after round spermatid injection (ROSI). Oocytes were treated either with 1.25 mM SrCl2 for 20 min or with two direct-current (DC) pulses at 100 V/mm for 99 msec followed by exposure to 2 mM 6-dimethylaminopurine (6-DMAP) for 20 min. Single spermatids then were injected into the oocytes that were ready for polar body extrusion. The proportions of oocytes surviving injection and exhibiting pronuclear formation were comparable between the SrCl2 group (76.8% and 45.6%, respectively) and the DC+6-DMAP group (78.3% and 34.9%, respectively). More SrCl2-activated ROSI oocytes (44.2%) cleaved into the two-cell stage than did those activated with DC+6-DMAP (34.7%). However, the proportions of the two-cell embryos developing to morulae/blastocysts and live offspring were significantly (P = 0.0005 and 0.042) lower in the SrCl2 group (12.3 and 6.1%, respectively) than the DC+6-DMAP group (36.1 and 14.6%, respectively). Our results indicate DC+6-DMAP is better than SrCl2 for oocyte activation prior to successful ROSI of rats.

Adenine↗

PubMed2003

Factors influencing chromosome condensation and development of cloned rat embryos.

Factors influencing premature chromosome condensation (PCC) in transferred rat nuclei have been examined. Chromosome condensation of rat cumulus cell nuclei did not occur when the cell nuclei were injected into enucleated rat oocytes. By contrast, chromosome condensation did occur after transfer to enucleated mouse oocytes or intact rat oocytes. In the first serial NT experiment, rat somatic cell nuclei were injected into enucleated mouse oocytes, and the reconstructed oocytes were activated by strontium chloride. From these reconstructed embryos, karyoplasts containing pronucleus-like vesicles were transferred into pronuclear zygote-derived cytoplasts by a DC pulse. Transfer of a total of 340 serial NT zygotes into recipient females, including 206 two-cell embryos, resulted in only seven implantation sites. In the second serial NT experiment, rat somatic cell nuclei were injected into intact rat oocytes; the recipient metaphase-plate was then aspirated under UV light from the NT oocytes in which PCC of injected nuclei was observed. After activation of the NT oocytes, karyoplasts were introduced into zygote-derived cytoplasts. Transfer of a total of 115 serial NT zygotes, including 37 two-cell embryos, resulted in four implantation sites but no live offspring. These results establish a mean of inducing chromosome condensation in rat oocytes and demonstrate that reconstructed rat zygotes can be prepared by serial NT procedures. Developmental competence of these embryos remains to be clarified.

Animals↗

PubMed2003

Factors affecting premature chromosome condensation of cumulus cell nuclei injected into rat oocytes.

To date, production of cloned rats by somatic cell nuclear transfer (NT) has not yet been successful. Inducing premature chromosome condensation (PCC) of injected cell nuclei in recipient cytoplasm is considered essential for successful mouse cloning by the Honolulu method. In the present study, some factors affecting PCC of rat cumulus cell nuclei injected into rat oocytes were examined. Wistar female rats (young: 4 to 5-week-old, mature: > or =10-week-old) were superovulated by injections of eCG and hCG, and oocytes recovered 14 or 17 h after hCG injection were received with cumulus cell nuclei using piezo-driven micromanipulator. When the oocytes were recovered 14 h post-hCG injection from young rats and the nuclear injection into oocytes was completed within 45 min, PCC was observed in 44-49% of NT oocytes. In the case of oocytes from mature rats, PCC occurred in 11-19% of the NT oocytes. Oocytes recovered 17 h post-hCG injection did not support PCC of the injected nuclei (0-7%) regardless of the donor age. Treatment of oocytes with a neutral cysteine protease inhibitor, N-acetylleucylleucylnorleucinal, slightly increased the incidence of PCC (48 vs 37%). Comparison of rat strains for oocyte donors indicated that proportions of NT oocytes undergoing PCC in Wistar and LEW oocytes (41-46%) were higher than those in Donryu and F344 oocytes (17-25%). Thus, ability of rat oocytes to promote PCC of the injected nuclei is dependent on the characteristics of oocytes, such as age or strain of donor rats, and timing of oocyte recovery.

Animals↗