Temperature-dependence of reflex transmission in the neonatal rat spinal cord, in vitro: influence on strychnine- and bicuculline-sensitive inhibition.

The amplitude, latency and rise time of the monosynaptic reflex, recorded from the spinal cord of the neonatal rat in vitro, was temperature-dependent with optimal conditions occurring at 25 degrees C. The reflex was inhibited when conditioning stimuli were applied to an adjacent dorsal root at 1-150 msec before the monosynaptic reflex was evoked; the inhibition had both an early and a late phase. The early phase of inhibition occurred at conditioning-test intervals of 1-20 msec with peak inhibition occurring at 7 msec. Raising the temperature of the bath to 31 degrees C or exposing the cord to strychnine blocked the early phase of inhibition. The late phase of inhibition occurred at conditioning-test intervals greater than 20 msec, was unaffected by temperature and was blocked by bicuculline. The early phase of inhibition therefore appears to be postsynaptic in origin and mediated by glycine while the late component of inhibition may be presynaptic in origin and mediated by gamma-aminobutyric acid (GABA).