|Budget Amount *help
¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2003: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 2002: ¥600,000 (Direct Cost: ¥600,000)
1.The digastric muscle acts for both feeding (including mastication and swallowing) and respiration. In this study, we examined whether or not the muscle activity is detectable during anoxia in developing rats. Rats at four different ages : day 5,10,16 and 24 were exposed to 100% N_2 under pentobarbital or ketamine/xylazine anesthesia, and the electromyograms of digastric muscles (dEMG) and diaphragm (diaEMG) were examined simultaneously.
2.Prior to the anoxic exposure, at all ages, the dEMG was similar to or less apparent than the diaEMG, which was detected at each inspiratory movement.
3.In anoxia, we first observed the dEMG activity, mostly sporadic (days 5 and 10) or mostly tonic (days 16 and 24), when diaEMG activity was temporarily suppressed (we termed it, Phase 1). Secondly, synchronous phasic or tonic dEMG and phasic diaEMG were recorded temporarily before terminal apnea (we termed it, Phase 2). These phenomena were also obtained in vagotomized rats (all ages) or in N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801, injected rats (days 16 and 24).
4.In conclusion, our results suggest that in anoxia dEMG activity is detectable during diaEMG suppression in early anoxia, irrespective of the developmental age, the anesthetic (pentobarbital, ketamine/xylazine), vagotomy, or MK-801 injections.
5.To the best of our knowledge, this is the first recording of dEMG activity during severe hypoxia in newborn animals, and on the dEMG activity during diaEMG suppression in early anoxia, we cannot exclude a possibility that the activity is related not to respiration but to swallowing. Based on the results we obtained in this study, it seems necessary to investigate the effect of hypoxia (include anoxia) on swallowing reflex and ventilation in anesthetized rats.