Cardiac Arrest during Gamete Release in Chum Salmon Regulated by the Parasympathetic Nerve System

Cardiac arrest caused by startling stimuli, such as visual and vibration stimuli, has been reported in some animals and could be considered as an extraordinary case of bradycardia and defined as reversible missed heart beats. Variability of the heart rate is established as a balance between an autonomic system, namely cholinergic vagus inhibition, and excitatory adrenergic stimulation of neural and hormonal action in teleost. However, the cardiac arrest and its regulating nervous mechanism remain poorly understood. We show, by using electrocardiogram (ECG) data loggers, that cardiac arrest occurs in chum salmon (Oncorhynchus keta) at the moment of gamete release for 7.39±1.61 s in females and for 5.20±0.97 s in males. The increase in heart rate during spawning behavior relative to the background rate during the resting period suggests that cardiac arrest is a characteristic physiological phenomenon of the extraordinarily high heart rate during spawning behavior. The ECG morphological analysis showed a peaked and tall T-wave adjacent to the cardiac arrest, indicating an increase in potassium permeability in cardiac muscle cells, which would function to retard the cardiac action potential. Pharmacological studies showed that the cardiac arrest was abolished by injection of atropine, a muscarinic receptor antagonist, revealing that the cardiac arrest is a reflex response of the parasympathetic nerve system, although injection of sotalol, a β-adrenergic antagonist, did not affect the cardiac arrest. We conclude that cardiac arrest during gamete release in spawning release in spawning chum salmon is a physiological reflex response controlled by the parasympathetic nervous system. This cardiac arrest represents a response to the gaping behavior that occurs at the moment of gamete release.

由惊吓刺激（如视觉刺激、振动刺激）引发的心搏骤停已在部分动物中被报道，可被视为心动过缓的特殊病例，并定义为可逆性漏搏。
心率变异性被证实为自主神经系统（具体为胆碱能迷走神经抑制）与真骨鱼类（teleost）神经、激素作用的兴奋性肾上腺素能刺激之间的平衡状态。
然而，心搏骤停及其调控的神经机制仍未得到充分阐释。
本研究借助心电图（electrocardiogram, ECG）数据记录仪，发现大麻哈鱼（Oncorhynchus keta）在配子释放时会发生心搏骤停，雌性个体的持续时长为7.39±1.61秒，雄性个体为5.20±0.97秒。
相较于静息期基础心率，产卵行为期间的心率显著升高，这表明心搏骤停是产卵行为期间异常高心率状态下出现的特征性生理现象。
心电图形态学分析显示，心搏骤停紧邻着尖高T波（T-wave），这提示心肌细胞的钾离子通透性升高，该变化可延缓心肌动作电位的传导。
药理学实验表明，注射毒蕈碱受体拮抗剂阿托品（atropine）可阻断心搏骤停，这揭示心搏骤停是副交感神经系统（parasympathetic nervous system）的反射性反应；而注射β肾上腺素能受体拮抗剂索他洛尔（sotalol）则对心搏骤停无显著影响。
本研究得出结论：产卵期大麻哈鱼配子释放过程中的心搏骤停是由副交感神经系统调控的生理性反射反应。
该心搏骤停对应于配子释放瞬间出现的张口行为（gaping behavior）。