Alireza Jamshidi Fard, J. Bagust ,
Volume 1, Issue 3 (Summer 1997)
Abstract
Wall and Shortland (1991) have shown that afferent fibres entering the cord in thoracic and lumbar roots of adult rats have branches that may penetrate up to 11 segments caudally from the root entry zone. We have investigated the extent of branching and conduction velocities of ascending and descending branches of lumbar and thoracic primary afferent in isolated spinal cords of adults hamsters (60-100g) and juvenile rats (30-46 g). Hemisected spinal cords were maintained at cold artificial cerebrospinal fluid (25-27 C) in which the Ca2+ had been replaced by Mn2+ (2mm) to block synaptic activity. Hamsters, antidromic conducted responses were obtained up to 10 segments caudal to dorsal roots T6-T7 and 17 segments rostral to L3. The mean conduction velocity was 3.7 m/s (s.e.m.& 0.4) for descending primary afferents(n=21) and 9.9 a 1.2 m/s for ascending afferents (n=26). In the rat , antidromic responses were measured over 4 segments caudal and 17 segments rostral to the L3 dorsal root. Conclusion velocities were 4.4 & 0.5 m/s and 7.7 & 0.7 m/s for descending and ascending branches respectively (n=4). The result were similar to those reported by Wall & Shortland , although the temperature. Difference between the in vitro and in vivo preparations would have resulted in approximately halving of the velocity in isolated cord preparation. The conduction velocity of descending fibres was about half fibres which may be related to size differences within the branches.
