[Interaction between pelvic and pudendal afferent inputs in lumbar-sacral spinal cord in rats]

Time-dependent inhibition is one of the means to study the interactions between peripheral inputs. The present study was performed on anesthetized and paralyzed Wistar rats using the technique of conditioning-testing stimulation. Electric stimulation (1.5 3 folds of the threshold intensity) was given to pelvic and pudendal nerves. Extracellular recordings were made from convergent neurons at L(6)-S(1) segments of the spinal dorsal horn. Stimulus intervals between conditioning and testing stimulation were measured when a half of the testing responses were inhibited by conditioning responses or the inhibition just began to occur. The time-dependent inhibition was seen in neurons situated deeper than 300 m beneath the dorsal surface of the spinal cord, and not in more superficial neurons. The inhibition intervals were in the range of 1 360 ms and became longer when conditioning stimulation was given to the pelvic nerve. The inhibition intervals were 1 3 ms in superficial neurons (<300 micrometer) and no apparent time-dependent inhibition occurred. The inhibition in deeper neurons was partially reduced by cold block conducted at segments C(5-6) and the blockage was more significant when conditioning stimulation was applied to the pelvic nerve. These findings suggest that the inputs from the pelvic and pudendal nerves may converge on single neurons at deeper lumbosacral dorsal horn and the pudendal nerve induced responses are more likely to be inhibited in these neurons, which may be further strengthened by superspinal structures.