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-deg rees-C, stimulation of a single dorsal root has been shown to evoke do rsal root reflexes in ipsilateral roots throughout the lumbar and thor acic cord. The dorsal root reflex was evoked by activity in low thresh old dorsal root fibres, and left the cord through dorsal root fibres c onducting at 5.9 m/s. The ipsilateral dorsal root reflex travelled equ ally well in both directions along the cord at a calculated velocity o f 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 re flex within the cord was calculated to be 4.7 +/- 0.2 ms at 27-degrees -C, corresponding to approximately 2 ms at body temperature, suggestin g that a trisynaptic pathway is involved in the generation of the dors al root reflex at the segmental level.