电刺激大鼠皮神经外周端对相邻脊髓节段皮神经内Aβ纤维的机械感受特性的影响

Changes in mechano-receptive properties of Aβ-fiber induced by antidromical electrical stimulation of the cutaneous nerve from adjacent spinal segment

为观察Aβ类初级传入纤维是否参与相邻脊髓节段外周末梢之间的信息传递及其相关机制 ,实验自近中端切断一侧T8～T12 脊髓节段背侧皮神经 ,将一支被切断的皮神经的外周端分离成数支细束 ,以单个Aβ纤维放电为指征 ,检测单位的传导速度、适应特性、机械感受阈值、感受野的形状和面积 ;在相邻脊髓节段、也与中枢断离的皮神经干上施加逆向电刺激 ( 0 45mA ,0 1ms,2 0Hz,10s) ,以观察该刺激对Aβ纤维的上述机械感受特性的影响。在 42只大鼠上共记录了 5 0个Aβ类单位。逆向电刺激相邻节段皮神经后 ,60 6% (n =3 3 )的单位感受野增大 ,全部单位的感受野平均面积从 8 94± 6 5 1mm2 显著增加到 2 0 3 4± 16 17mm2 (P <0 0 1)。 81 8% (n =2 0 )的单位感受野形状从点状、圆或与身体长轴垂直的椭圆变成与身体长轴斜行或平行的椭圆。 68 0 % (n =5 0 )的单位机械感受阈值下降 ,全部单位的平均阈值从 2 3 7± 1 2 4mN降至 2 2 9± 1 2 4mN (P <0 0 5 )。上述机械感受特性的改变可持续 5 2 2 3± 9 2 7至 5 6 93± 15 76min。跨节段电刺激后 ,有 5 0 0 % (n =5 0 )的单位同时出现放电的增加 ,但该增加仅持续 1 5 2± 0 46min ,显著短于机械感受特性改变的时程 (P <0 0 1)。

The purpose of the present study was to observe whether primary afferent Aβ-fiber is involved in the information transmission between peripheral terminals of adjacent dermatomes. The dorsal cutaneous nerve branches of spinal nerves from T 8 to T 12 segments were cut proximally. One peripheral stump end of the cut nerves was dissected into a few filaments for the examination of mechanoceptive properties of single Aβ-fibers and their discharges were observed while the other end was stimulated antidromically. Fifty Aβ-units were recorded in forty-two intact rats. After an electrical stimulation (0.45mA, 0.1 ms, 20 Hz, for 10 s) was delivered to the stimulated nerve, the size of the receptive field of 60.6% (n=33) Aβ-fibers extended. The mean area of receptive fields of all examined units enlarged from 8.94±6.51 mm 2 to 20.34±16.17 mm 2 (P<0.01) and the shapes of the receptive fields of 81.8% (n=20) units changed from a dot, round or ellipse with its long axis in parallel with the longitudinal axis of the body to an oblique ellipse with the longitudinal axis of the body. The mechanoceptive threshold of 68.0% (n=50) units decreased with a reduction in mean threshold from 2.37±1.24 to 2.29±1.24 mN (P<0.05). The duration of these changes in mechano-receptive properties increased from 52.23±9.27 to 56.93±15.76 min. Meanwhile, increasing discharge was found in 50.0% (n=50) units but lasted only for 1.52±0.46 min. The changes in mechanoceptive properties appeared simultaneously with discharge changes but had longer duration than that of discharge change (P<0.01). Discharges changes usually appeared in those units with the changes in mechanoceptive properties following an antidromical electrical stimulation of adjacent spinal segment. These results suggest that low-threshold mechanoreceptive Aβ-fibers are affected by antidromical electrical stimulation of the cutaneous nerve from an adjacent spinal segment, indicating that information transmission occurs between the two endings of peripheral afferent nerves from adjacent spinal segments without any involvement of the central nervous system, and that Aβ-fibers are involved in the process of information transmission between peripheral terminals from adjacent spinal segments.