SPREAD OF THE DORSAL-ROOT REFLEX IN AN ISOLATED PREPARATION OF HAMSTER SPINAL-CORD

In an isolated preparation of hamster spinal cord maintained at 27-degrees-C, stimulation of a single dorsal root has been shown to evoke dorsal root reflexes in ipsilateral roots throughout the lumbar and thoracic cord. The dorsal root reflex was evoked by activity in low threshold dorsal root fibres, and left the cord through dorsal root fibres conducting at 5.9 m/s. The ipsilateral dorsal root reflex travelled equally well in both directions along the cord at a calculated velocity of 0.5 m/s at 27-degrees-C. Comparison of the stimuli required to evoke dorsal root reflexes in adjacent and distant ipsilateral dorsal roots suggests that once this system is activated it operates largely in an all-or-none manner. The delay in the generation of the dorsal root reflex within the cord was calculated to be 4.7 +/- 0.2 ms at 27-degrees-C, corresponding to approximately 2 ms at body temperature, suggesting that a trisynaptic pathway is involved in the generation of the dorsal root reflex at the segmental level.