Effects of space flight on the histological characteristics of the aortic depressor nerve in the adult rat: electron microscopic analysis.
The effects of microgravity on the histological characteristics of the aortic depressor nerve, which is the afferent of the aortic baroreflex arc, were determined in 10 female adult rats. The rats were assigned for nursing neonates in the Space Shuttle Columbia or in the animal facility on the ground (NASA Neurolab, STS-90), and were housed for 16 days under microgravity in space (microg, n=5) or under one force of gravity on Earth (one-g, n=5). In the Schwann cell unit in which the axons of unmyelinated fibers are surrounded by one Schwann cell, the average number of axons per unit in the microg group was 2.1 +/- 1.6 (mean +/- SD, n=312) and significantly less than that in the one-g group (3.0 +/- 2.9, n=397, p<0.05). The proportion of unmyelinated fibers in the aortic depressor nerve in the microg group was 64.5 +/- 4.4% and significantly less than that in the one-g group (74.0 +/- 7.3%, p<0.05). These results show that there is a decrease in the number of high-threshold unmyelinated fibers in the aortic depressor nerve in adult rats flown on the Shuttle Orbiter, suggesting that the aortic baroreflex is depressed under microgravity during space flight.
Department of Physiology, Fukushima Medical University School of Medicine, Fukushima, Japan. yamasaki@fmu.ac.jp
Masao
M
Yamasaki
Tsuyoshi
T
Shimizu
Masao
M
Miyake
Yukako
Y
Miyamoto
Shin-Ichiro
S
Katsuda
Hirotaka
H
O-Ishi
Tadanori
T
Nagayama
Hidefumi
H
Waki
Kiyoaki
K
Katahira
Haruyuki
H
Wago
Toshiyasu
T
Okouchi
Shunji
S
Nagaoka
Chiaki
C
Mukai
D000818:Animals; D001011:Aorta / Q000033:anatomy & histology* / Q000294:innervation*; D001369:Axons / Q000502:physiology; D017704:Baroreflex / Q000502:physiology*; D005260:Female; D008854:Microscopy, Electron; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012583:Schwann Cells / Q000502:physiology; D013026:Space Flight; D014893:Weightlessness