71 7%Objective:To observe whether the primary afferent Aδ-fiber is involved in the signal transmission of the peripheral terminals distributing in the adjacent dermatomes and to investigate the mechanism of sensory transmission along meridian.Methods:SD rats anesthetized with 20% urethane (1 g/kg) were used in this study. The dorsal cutaneous nerve branches of spinal nerves from T 9 to T 12 segments innervating the Bladder Meridian of Foot-Taiyang (BL) area 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 Aδ-fibers and their changes of electrical activity

while another one for antidromically electrical stimulation.Results:Ninety Aδ-units were recorded on 67 intact rats. There were 31.1% rapid adaptation (RA) units and 65.9% slow adaptation (SA) units

with the mean adaptation duration being 20.82±2.51 sec (n=90)

the receptive field 17.76±3.40 mm 2 and the mechanoreceptive threshold 0.21±0.03 mN.There were 1 to 3 sensitive points (1.79±0.11) in each receptive field and 77.3% (n=88) of them distributed along BL. After an electrical stimulation(0.45 mA

0.1 ms

20 Hz

for 10 sec) was delivered to the stimulated nerve

the size of the receptive field of 71.9% (n=64) of Aδ-fibers extended. The mean area of receptive fields of all the examined units enlarged from 17.76±3.40 mm 2 to 71.98±13.07 mm 2 (P<0.001) and the receptive field of 74.6% (n=60) units changed from a dot

round or ellipse shape

with its long axis being in parallel with the longitudinal axis of the body. The number of sensitive point in each receptive field increased to 3.08±0.25 from 1.79±0.11

(P<0.01). The mechanoceptive threshold of 71.7% (n=60) units decreased to 0.12±0.04 mN (P<0.001). The changes of mechanoceptive properties appeared simultaneously with discharge changes but lasted longer than that of discharge change (P<0.01).Conclusion:These results suggest that low-threshold mechanoreceptive Aδ-fibers can be activated by antidromically electrical stimulation of cutaneous nerve of the adjacent spinal segment

indicating that the signal transmission occurs between two endings of peripheral afferent nerves from the adjacent spinal segments without any involvement of central nervous system

and Aδ-fibers are involved in the process of signal transmission. This may be an important mechanism of sensory transmission along meridian in traditional Chinese medicine.