Walker D W, Harding R
J Dev Physiol. 1984 Oct;6(5):387-99.
In fetal sheep acute hypoxia causes a decreased incidence of breathing movements and motor activity, and the excitability of polysynaptic reflexes in the hindlimbs is depressed. To determine whether this inhibitory effect extends to other areas in the fetal CNS, we have studied the effect of hypoxia on two reflexes with cranial pathways. The digastric (jaw opening) reflex was elicited by stimulation of the dental nerve through a pair of stainless steel electrodes implanted into the mandible (4 fetuses). The thyroarytenoid muscle of the larynx was reflexly activated by stimulation of the superior laryngeal nerve by a cuff electrode (4 fetuses). Low level stimulation at 1.5-2 X threshold was repeated at approximately 2 min intervals for 3-4 h; the stimulation did not alter the pattern of electrocortical activity, breathing movements, or cause arousal. The amplitude of the digastric reflex was greatest during low voltage electrocortical activity; conversely, the amplitude of the thyroarytenoid reflex was greatest during high voltage electrocortical activity. Isocapnic hypoxia lasting 30-60 min (16 trials), in which the PaO2 was reduced to 12-14 mmHg, did not reduce the amplitude of either reflex. The reduction of thyroarytenoid reflex amplitude which normally occurred during low voltage electrocortical activity was not present during hypoxia. These experiments show that the inhibitory effects of hypoxia on spinal reflexes, breathing movements and motor activity do not include these cranial pathways.
在胎羊中，急性缺氧会导致呼吸运动和运动活动的发生率降低，并且后肢多突触反射的兴奋性也会受到抑制。为了确定这种抑制作用是否会扩展到胎儿中枢神经系统的其他区域，我们研究了缺氧对两条具有颅神经通路的反射的影响。通过植入下颌骨的一对不锈钢电极刺激齿神经来引发二腹肌（张口）反射（4只胎儿）。通过袖带电极刺激喉上神经，反射性激活喉部的甲杓肌（4只胎儿）。以1.5 - 2倍阈值进行低强度刺激，每隔约2分钟重复一次，持续3 - 4小时；这种刺激不会改变皮层电活动模式、呼吸运动，也不会引起觉醒。二腹肌反射的幅度在低电压皮层电活动期间最大；相反，甲杓肌反射的幅度在高电压皮层电活动期间最大。持续30 - 60分钟的等碳酸血症性缺氧（16次试验），其中动脉血氧分压降至12 - 14 mmHg，并未降低任何一种反射的幅度。在缺氧期间，通常在低电压皮层电活动期间出现的甲杓肌反射幅度降低并未出现。这些实验表明，缺氧对脊髓反射、呼吸运动和运动活动的抑制作用并不包括这些颅神经通路。
