Biology subjects

Mitani, H.

Publications and source records attributed to Mitani, H..

3 recordsLinked to original sources

bioRxiv2022

Acquirement of the autonomic nervous system modulation evaluated by heart rate variability in medaka (Oryzias latipes)

Small teleosts have recently been established as models of human diseases. However, measuring heart rate by electrocardiography is highly invasive for small fish. The physiological nature and function of vertebrate autonomic nervous system (ANS) modulation of the heart has traditionally been investigated in larvae with an incompletely developed ANS or in anesthetized adults, whose ANS activity may possibly be disturbed under anesthesia. Here, we defined the frequency characteristics of heart rate variability (HRV) modulated by the ANS from observations of heart movement in high-speed movie images and changes in ANS regulation under environmental stimulation in unanesthetized adult medaka (Oryzias latipes), a small teleost. The HRV was significantly reduced by atropine (1 mM) in the 0.25 - 0.65 Hz and by propranolol (100 M) at 0.65-1.25 Hz range, suggesting that HRV in adult medaka is modulated by both the parasympathetic and sympathetic nervous systems within these frequency ranges. Such modulations of HRV by the ANS were remarkably suppressed in anesthetized adult medaka. Continuous exposure to light suppressed HRV only in the 0.25 - 0.65 Hz range, indicating parasympathetic withdrawal. The power of HRV increased along developmental processes. These results suggest that ANS modulation of the heart in adult medaka is frequency-dependent phenomenon, and that the impact of long-term environmental stimuli on ANS activities can be precisely evaluated in unanesthetized adult fish using this method.

physiology↗

bioRxiv2022

Intraspecific diversity based on low temperature induced arrhythmia in embryonic heart of medaka (Oryzias latipes)

BackgroundCold tolerance during embryonic development, especially blood circulation is important for growth in poikilothermic animals. Medaka (Oryzias latipes), has cold tolerance and is distributed in the highest latitudes occupied by the genus Oryzias. Regarding cold tolerance in embryogenesis, Hd-rR strain belonging to the southern Japanese (S.JPN) group showed arrhythmia when the embryo was exposed to 15 {degrees}C in the heartbeat initiation period (st. 24), whereas the embryo of Odate medaka, which belongs to the northern Japanese (N.JPN) group, showed stable heartbeats. ResultsIn this study, to verify the sensitivity to low temperature in the medaka wild populations, heartbeat intervals of st. 24 embryos derived from three N.JPN, eight S.JPN, and two western Korean/Chinese (W.KOR) populations were investigated at an arbitrary temperature range of 12-15 {degrees}C. There was no significant difference in the mean values of the heart rates and the coefficient of variation (CV) of interbeat intervals in the N.JPN, S.JPN, and W.KOR groups. A temperature dependency of the CV within 12-15 {degrees}C was observed only in five S.JPN specimens, whereas three S.JPN, the N.JPN and the W.KOR specimens showed no alteration in CV with temperature. Temperature dependency of the heart rate was also varied in the S.JPN specimens. ConclusionsThese results suggest that the temperature dependency of the CV under 12-15 {degrees}C during the heartbeat initiation period is a variation within the S.JPN after the divergence from the N.JPN.

developmental biology↗

bioRxiv2017

Medaka population genome structure and demographic history unveiled via Genotyping-by-Sequencing

Medaka is a model organism in medicine, genetics, developmental biology and population genetics. Lab stocks composed of more than 100 local wild populations are available for research in these fields. Thus, medaka represents a potentially excellent bioresource for screening disease-risk- and adaptation-related genes in genome-wide association studies. Although the genetic population structure should be known before performing such an analysis, a comprehensive study on the genome-wide diversity of wild medaka populations has not been performed. Here, we performed genotyping-by-sequencing (GBS) for 81 and 12 medakas captured from a bioresource and the wild, respectively. Based on the GBS data, we evaluated the genetic population structure and estimated the demographic parameters using an approximate Bayesian computation (ABC) framework. The autosomal data confirmed that there were substantial differences between local populations and supported our previously proposed hypothesis on medaka dispersal based on mitochondrial genome (mtDNA) data. A new finding was that a local group that was thought to be a hybrid between the northern and the southern Japanese groups was actually a sister group of the northern Japanese group. Thus, this paper presents the first population-genomic study of medaka and reveals its population structure and history based on autosomal diversity.

evolutionary biology↗