- 學位論文
烏龜心臟迷走神經功能與形態之研究
Functional and Histological Studies of Turtle Cardiac Vagal Nerve
摘要
摘要 本研究確認了烏龜迷走神經之心臟迷走分支並研究其神經纖維組成及各組群對心跳速率和心肌收縮力的功能控制的可能關聯性。實驗以班龜(Ocadia sinensis)為實驗動物，以巴比妥鈉(Sodium pentobarbital, 25mg/kg)進行靜脈注射麻醉，從頸動脈插管紀錄血壓(BP)，心跳(HR)。解剖上發現從胸部迷走神經分出一分支至心臟。利用切斷或局部麻醉藥可待因(Lidocaine)阻斷此分支，發現迷走神經使心跳速率和心肌收縮力下降的作用完全消失。以穿透式電子顯微切片分析此心臟迷走神經分支的纖維組成。心臟迷走神經分支之神經纖維總在500至1800之間，其中平均有14%為有髓鞘神經纖維，86%為無髓鞘神經纖維。有髓鞘神經纖維直徑為1.8-6 慆，無髓鞘神經纖維直徑為0.3-2.3 慆。利用電刺激頸部迷走神經激起心臟迷走神經分支之複合動作電位，發現其中包含三個主要成分，分別為A、B及C群。電刺激頸部迷走神經，直到刺激強度激發起B群反應時，心跳速率或心肌收縮力皆產生下降現象，持續增加刺激強度至引發C群反應時，抑制心跳速率或心肌收縮力的作用達到最強。電刺激頸部迷走神經，刺激頻率低於5Hz時，右側頸部迷走神經抑制心跳速率的作用顯著大於左側頸部迷走神經。刺激頻率10Hz時，右側與左側頸部迷走神經抑制心跳速率或心肌收縮力的作用並無顯著差異。可能烏龜迷走神經右側心臟迷走神經分支中有較多控制心跳速率的神經纖維。
並列摘要
Abstract The objectives of the present study were to identify the cardiac vagal nerve of the turtle, to characterize its fiber composition and to correlate its composition with cardiac inhibitory functions. Turtles (Ocadia sinensis) were anesthetized with sodium pentobarbital (25mg/kg). Blood pressure and heart rate were measured from a cannula placed in the right carotid artery. Cardiac vagal nerve was identified as a thoracic vagal branch going into the heart. Transection or local anesthetic blocking of this branch abolished completely the negative chronotropic and inotropic effects produced by cervical vagal stimulation. Electron microscopic analysis of the cardiac vagal nerve revealed that the cardiac vagal nerve is comprised of from 500 to 1800 axon fibers. Among these, 86% were unmyelinated fiber, 0.3-2.3 慆 in diameter; and 14% were myelinated fiber, 1.8-6 慆 in diameter. Compound action potentials evoked in the cardiac vagal nerve by electrical stimulation of the cervical vagal nerve consisted of three major components, namely, A, B, and C groups. A decrease in heart rate or an inhibition of cardiac contractility were observed on repetitive stimulation of the cervical vagus nerve with an intensity which gave rise to the B potential group. When the stimulus intensity was increased to recruit the C potential group, cardioinhibitions reached maximum. A comparison of the chronotropic effect produced by the right and left cervical vagal stimulation showed that at stimulation frequency of 0.5, 1 and 5 Hz, the right vagus produced significantly stronger heart rate inhibition. Right and left cervical vagal stimulation at a constant frequency of 10Hz are approximately equipotent on heart rate and ventricular contraction. We conclude that turtle heart is innervated by a pair of cardiac vagal nerve from the right and left thoracic vagal nerve, respectively. The cardioinhibitory functions are subserved by small myelinated fibers and large unmyelinated fibers. Chronotropic and inotropic fibers may be distributed unevenly in the brain, such that the right cardiac vagal nerve may contain more chronotropic motor fibers.