Development of miniature implantable electrode and telemeter for long-term recording of sympathetic efferent nerve activity

为了更好地理解交感神经对心血管系统的控制，测量各种血管床的交感神经流出量并分析给定干预后交感神经流出量的长期变化是很重要的。本研究的目的是开发一种新的可植入微电极和微型遥测装置，用于稳定和长期记录自由运动小动物的交感神经放电。我们用导电橡胶和吸水聚合物制备了两种新型双极袖带电极，可应用于大鼠肾神经。当微电极嵌入生理盐水时，电极的电阻抗为2.8 ~ 9.4 kΩ，频率范围为0.05 ~ 3 kHz，与交感放电带相对应。两个电极在几个星期内都显示出稳定的电阻抗，这表明阻抗足够低，只要电极与神经束有良好的接触，就可以在低背景噪音下记录交感神经活动。由于电极体积小（体积约为2mm^3），操作方便，因此每个电极植入神经所需的时间较短，不会因干燥或机械损伤而损伤神经，并且电极在急性型实验中使用时间长。因此，这种新型电极可用于记录有意识动物的交感神经放电。此外，我们还尝试开发一种微型遥测发射器，可以植入小动物体内。特别注意尽量减少背景噪音，传递交感神经信号而不失真。该遥测系统的噪声水平为几微伏，信号频带为0.05 ~ 3 kHz，表明该遥测系统能够记录有意识动物的交感神经放电。然而，发射器太大了，无法植入比猫或兔子更小的动物体内，因为它的尺寸是4 x 5 x 0.5厘米。有必要采用单端集成电路来减小发射机的尺寸。少

It is important for better understanding of sympathetic control of the cardiovascular system to measure sympathetic outflows to various vascular beds and analyze the long-term changes in sympathetic outflow following a given intervention. The aim of this study was to develop a new implantable microelectrode and a miniature telemetry device for stable and long-term recording of sympathetic neural discharges in freely moving small animals. We have made two types of the novel bipolar cuff electrodes with electro-conductive rubber or water-absorbent polymer, which can be applied to the renal nerve in the rat. When the microelectrodes were embedded in saline, electrical impedance of the electrodes was 2.8-9.4 kΩ in a frequency range of 0.05-3 kHz, which corresponded to the band of sympathetic discharge. Either electrode showed stable electrical impedance over several weeks, suggesting that the impedance was low enough to record sympathetic nerve activity with low background noise as long as … More the electrode had good contact with a nerve bundle. Because the present electrodes were of small size (volume, 2mm^3) and handled easily, it took a shorter time to implant each electrode on the nerve without any nerve injury due to drying or mechanical damage and the electrodes worked well as long as being used in the acute type of experiments. Therefore the novel electrodes may be useful for recording of sympathetic nerve discharge in conscious animals. Furthermore, we have attempted to develop a miniature telemetry transmitter, which can be implanted in small animals. Special care was taken to reduce the background noise as much as possible and transmit sympathetic nerve signal without any distortion. The noise level of the novel telemetry system was several microvolts and its signal frequency band was 0.05-3 kHz, indicating that the present novel telemetry system is able to record sympathetic nerve discharge in conscious animals. However, the transmitter was too large to be implanted in smaller animals than the cat or rabbit, because its size was 4 x 5 x 0.5cm. It will be necessary to reduce the size of the transmitter by using one-tip integrated circuit. Less