Biomedical subjects

Sachiko Koyama

Publications and source records attributed to Sachiko Koyama.

12 recordsLinked to original sources

PubMed2006

Chemical identification of MHC-influenced volatile compounds in mouse urine. I: Quantitative Proportions of Major Chemosignals.

The genes of the major histocompatibility complex (MHC) are highly polymorphic loci that encode cell surface proteins, class I and II molecules. They present peptide antigens to T cells and thereby control immunological self/nonself recognition. Increasing evidence indicates that MHC genes also influence odor and mating preferences; however, it is unclear how. Here we report the results of chemical analyses of male mouse urinary odors collected from a variety of mouse strains, including MHC-congenics, recombinants, mutants, and transgenics (i.e., beta2 microglobulin "knockouts," which lack class I expression, and transporters associated with antigen processing (TAP) knock-outs). After the identification of volatile odor components by gas chromatography/mass spectrometry, the odor profiles of urine samples were analyzed quantitatively by using stir bar sorptive extraction and gas chromatography/atomic emission detection. Results showed that MHC genes influenced the amounts of testosterone-mediated pheromones, sulfur-containing compounds, and several carbonyl metabolites. This is the first report to quantitatively link known mouse pheromones to classical, antigen-binding MHC loci. Surprisingly, these compounds were not influenced by TAP genes, even though these loci are MHC-linked and play a role in peptide presentation. Whereas identification of MHC-determined odorants does not reveal their metabolic origin, some constituents were also present in blood serum, and their levels were not altered by antibiotics.

Animals↗

PubMed2006

Speech comprehension assessed by electroencephalography: a new method using m-sequence modulation.

Electroencephalograms (EEGs) were recorded from eight Japanese speakers while they listened to Japanese and Spanish sentences (approximately 51s each). The sentences were modulated in amplitude by a binary m-sequence and played forward or backward. A circular cross-correlation function was computed between the EEG signals and the m-sequence and averaged across subjects. Independent component analysis of the averaged function revealed a component source response which was obtained only for the comprehensible Japanese and not for the incomprehensible sentences. The present study has thus shown that a 1-min long EEG signal is sufficient for the assessment of speech comprehension.

Acoustic Stimulation↗

PubMed2006

Chemotaxis assays of mouse sperm on microfluidic devices.

Sperm chemotaxis is an area of significant interest to scientists involved in reproductive science. Understanding how and when sperm cells are attracted to the egg could have profound effects on reproduction and contraception. In an effort to systematically study this problem, we have fabricated and evaluated a microfluidic device to measure sperm chemotaxis. The device was designed with a flow-through configuration using a spatially and temporally stable chemical gradient. Mouse sperm cells were introduced into the chemotaxis chamber between confluent flows of mouse ovary extract and buffer. The sperm experiencing chemotaxis swam toward the extract and were counted relative to those that swam toward the buffer. The ovary extracts were diluted from 10(2) to 10(7) times, and each extract dilution was screened for chemotaxis. Four out of six ovaries showed a strong chemotactic response at extract dilutions of 10(-3) to 10(-5). This device provided a convenient, disposable platform on which to conduct chemotaxis assays, and the flow-through design overcomes difficulties associated with distinguishing chemotaxis from trapping.

Animals↗

PubMed2005

Time may be compressed in sound representation as replicated in sensory memory.

The flow of time in the real world may differ from the one in the neural representation of auditory scene stored in the sensory memory, because the encoded information is free from the rule of actual time. The sensory memory underlying the automatic discriminative system is reflected by the mismatch negativity (MMN). The time-wise image of preceding sounds is integrated into the sensory memory as a 160-170 ms epoch. We measured the mismatch field (MMNm) and the reaction time responding to the omitted segments incorporated into a complex sound. The main result was that the encoded period from early to late omitted segment was shorter than the actual one, suggesting that time may be compressed in the sound representation.

Acoustic Stimulation↗

PubMed2004

Sound perception affected by nonlinear variation of accuracy in memory trace.

The mismatch negativity (MMN) reflects the neural representation of the acoustic environment stored in sensory memory. The short phase of sensory memory corresponds to the temporal window of integration (TWI) which integrates the neighboring sounds into a unitary event. We measured the magnetic MMN (MMNm) and the discriminative reaction time (RT) responding to an omitted segment incorporated into a complex sound. Consequently, for the late omitted segments, the MMNm amplitudes were decreased, and those latencies and the RTs were prolonged. The percentages of the correct responses were also reduced for the late omitted segments. In sum, the discriminative sensitivity nonlinearly declined toward the end of the TWI, suggesting that the time-wise accuracy of the neural trace nonlinearly varies in sensory memory.

Acoustic Stimulation↗

PubMed2004

Primer effects by conspecific odors in house mice: a new perspective in the study of primer effects on reproductive activities.

Half a century has passed since the first report of the influence of odors on mice. Odors are known to influence behavior (signaling effect) and affect the physiology (primer effect) of mice. This review focuses on summarizing the primer effects found so far in female and male mice. Odors from conspecifics of the opposite sex had the tendency to enhance reproductive activities, whereas odors from conspecifics of the same sex diminish them. Only 2,5-dimethylpyrazine, one of the odor components identified in group-housed females, has been reported to have a suppressive influence on both males and females by lowering reproductive activities. Studies showed progress from the discovery of phenomena to the identification of odor components that cause such changes in reproductive organs and related neuroendocrinological changes. Compared to studies on the mechanisms of primer effects in females, the mechanisms in males are not yet clarified, and detailed studies on effects on the reproductive organs are still in primitive stages especially for males. Hypotheses on the influence of changes in the concentration of testosterone, estrogen, and prolactin on spermatogenesis and sperm maturation after exposure to odors are discussed.

Animals↗

PubMed2004

The effect of phonological repetition on cortical magnetic responses evoked by visually presented words.

Neuroimaging studies have reported that the left superior temporal cortical area is activated by visually presented words. In the present study, we recorded cortical magnetic responses evoked by visual words and examined the effect of phonological repetition (e.g., hair-hare) on left superior temporal cortical activity, using pairs of homophonic Japanese words as stimuli. Unlike English, Japanese has a large number of homophone pairs with a totally different orthography. By taking advantage of this feature of the Japanese writing system, the effect of phonological repetition can be solely examined without being confounded by the effect of orthographic similarity. Magnetic responses were recorded over the bilateral temporal sites of the brain while subjects silently read words. The words were presented one by one; a quarter of them was immediately followed by a homophonic word. Clear magnetic responses in the latency range of 300-600 msec were observed in the left hemisphere, and the responses to the homophones were smaller than those to the first presented words. In the right hemisphere, clear responses were not consistently recorded in the same latency range, and no effect of phonological repetition was observed. The sources of the responses recorded over the left hemisphere were estimated to be in the left superior temporal cortical area adjacent to the auditory cortex and the source strength as well as the magnetic responses showed a reduction by phonological repetition. This result suggests that the activity in the left superior temporal cortical area is associated with access to the phonological representation of words.

Adult↗

PubMed2003

Relief effect of vitamin A on the decreased motility of sperm and the increased incidence of malformed sperm in mice exposed neonatally to bisphenol A.

Administration of 50 microg of bisphenol A (BPA) for the first 5 days after birth resulted in a decrease in the percentage of moving sperm, and an increase in the incidence of malformed sperm, in the epididymides of mice at 10 weeks of age, although no marked changes were found in the testicular histology between BPA-treated and vehicle-treated control mice. The deteriorating effects of 50 microg of BPA were ameliorated by the concurrent administration of 100 IU of retinol acetate (RA). Neonatal treatment with 0.5 microg of BPA for 5 days resulted in an increase in the incidence of malformed sperm, whereas the BPA effect became more severe in mice nursed by mothers fed a vitamin A-deficient (VAD) diet only a few days before and after parturition. On the other hand, neonatal treatment with 20 microg of estrogen for the first 5 days after birth resulted in an increase in the number of estrogen receptor alpha (ERalpha)-positive cells in the epithelium of the vas deferens, whereas only a few epithelial cells showed weak ERalpha-positive signals in the vehicle-treated control mice at 18 days after birth. This increase, however, was suppressed by the concurrent administration of RA. Although five daily treatments with 50 microg BPA led to no significant increase in the number of ERalpha-positive cells, it may have been due to the weak estrogenic activity of BPA, as discussed. These findings clearly showed that in mice, neonatal exposure to a relatively large dose of BPA causes damage to the motility and morphology of sperm, but the BPA effect is, to some extent, inhibited by a supplement of VA, and enhanced under a VAD condition.

Animals↗

PubMed2003

Magnetoencephalographic study of the cortical activity elicited by human voice.

In an attempt to identify voice-specific neural activities in auditory cortex in humans, we recorded cortical magnetic responses. Volunteers were instructed to listen to vocal and instrumental sounds matched in fundamental-frequency, duration, temporal envelope and average root mean square power. The stimuli were sounds produced by four singers and four musical instruments at each of two fundamental frequencies: 220 Hz (musical note A3) and 261.9 Hz (C3). Two components of the evoked responses were analyzed, one at approximately 100 ms (N1m) and the other 400 ms after the stimulus onset (sustained field, SF). The source locations of equivalent current dipoles for both components were estimated around the Heschl's gyrus in both hemispheres. Compared with the instrumental sound, the source strength of the SF component for the voice was significantly larger.

Acoustic Stimulation↗

PubMed2003

Study on the development of sperm motility and social dominance of male mice.

It has been shown that sperm motility and other parameters related to the reproductive activity varied depending on the social status of male mice. In order to clarify whether such variation is derived from inborn difference or depends on any conditions during maturation, we investigated developmental change of sperm motility, reproductive organs, and body size of ddY male mice. We also investigated how the establishment of social dominance of male mice during maturation was correlated with sperm motility. It was found that sperm motility was significantly higher during puberty than in adulthood, although there already existed relatively large statistical variance. The correlation between sperm motility and the social status was revealed to start after 10 weeks of age. It was suggested that a certain inborn difference of sperm motility became enlarged due to environmental factors experienced by male mice during maturation.

Aggression↗

PubMed2003

Cortical evidence of the perceptual backward masking effect on /l/ and /r/ sounds from a following vowel in Japanese speakers.

We examined the influence of stimulus duration of foreign consonant vowel stimuli on the MMNm (magnetic counter part of mismatch negativity). In Experiment 1, /ra/ and /la/ stimuli were synthesized and subjects were native Japanese speakers who are known to have difficulty discriminating the stimuli. "Short" duration stimuli were terminated in the middle of the consonant-to-vowel transition (110 ms). They were nevertheless clearly identifiable by English speakers. A clear MMNm was observed only for short-duration stimuli but not for untruncated long-duration (150-ms) stimuli. We suggest that the diminished MMNm for longer duration stimuli result from more effective masking by the longer vowel part. In Experiment 2 we examined this hypothesis by presenting only the third formant (F3) component of the original stimuli, since the acoustic difference between /la/ and /ra/ is most evident in the third formant, whereas F1 and F2 play a major role in vowel perception. If the MMNm effect depends on the acoustic property of F3, a stimulus duration effect comparable to that found with the original /la/ and /ra/ stimuli might be expected. However, if the effect is attributable to the masking effect from the vowel, no influence of stimulus duration would be expected, since neither stimulus contains F1 and F2 components. In fact, the results showed that the "F3 only" stimuli did not show a duration effect; MMNm was always elicited independent of stimulus duration. The MMN stimulus duration effect is thus suggested to come from the backward masking of foreign consonants by subsequent vowels.

Acoustic Stimulation↗

PubMed2003

Effects of vomeronasal organ removal on the sperm motility in male mice.

Odors play important roles in the communication of house mice. They release behaviors and prime changes of the physiological conditions of other individuals. In our previous study, we showed that sperm motility was lowered in the subordinate mice comparing with dominant mice. Our hypothesis is that the lowered sperm motility was due to some primer effects by odor substances derived from dominant mice. To test the hypothesis, we destroyed the vomeronasal organ (VNO) of male mice (VNX male) at 5 weeks of age and paired them with intact male mice (Experimental Group). As control group males, intact male mice were kept in pairs (Control Group). At 15 weeks of age, the sperm motility and weights of reproductive organs, and social dominance was analyzed. The subordinate VNX males were found to have high sperm motility comparable to the dominant males. It was suggested that there is male-to-male primer effects, mediated by VNO, that suppress sperm motility of the subordinate mice.

Analysis of Variance↗