Characterization of postsynaptic potentials evoked by sural nerve stimulation in hindlimb motoneurons from acute and chronic spinal XXXX .

@entity7463 @entity468
The purpose of this study was to characterize the changes in postsynaptic potentials recorded in ankle extensor motoneurons resulting from activation of the sural nerve after spinal cord transection in the adult cat. Eight acute and nine chronic animals were spinalized at T12. Intracellular recordings from motoneurons innervating the triceps surae were performed. Sural nerve stimulation evoked complex synaptic potentials consisting of early and late components in all motoneurons. Early excitatory and inhibitory postsynaptic potentials (PSPs), as well as long latency excitatory postsynaptic potentials were recorded and averaged for assessment of @entity7463 amplitude and duration. Early PSPs, both excitatory and inhibitory, were significantly larger in the motoneurons of @entity468 spinalized 4-6 months earlier. Central latency of excitatory potentials were similar in the two samples of motoneurons, but the central latency associated with the initial inhibitory @entity7463 was significantly shorter in the recordings from motoneurons of chronic spinal @entity468 . In most recordings, an additional inhibitory @entity7463 followed the initial excitatory @entity7463 in motoneurons, and this secondary inhibitory @entity7463 was similar in peak amplitude and duration in both samples of motoneurons. Also, a long latency excitatory @entity7463 was recorded in a large percentage of motoneurons from both samples. This potential was typically of greater amplitude and longer duration in the motoneurons from chronic animals, when compared to recordings from acute animals. Although changes in amplitude and duration of @entity7463 activity could be documented, there was no marked alteration in the frequency of occurrence of each @entity7463 pattern recorded from the two preparations. This suggests that the synaptic pathways mediating the sural nerve reflexes have not qualitatively changed in the chronic spinal animal. The changes in amplitudes and durations of the PSPs in the chronic spinal cat indicate, however, that quantitative changes have occurred. The quantitative changes have probably occurred in the interneuronal networks activated by cutaneous nerve (sural) stimulation, since it was shown that only minor changes in motoneuron membrane properties could be recorded in these same chronic spinal animals.
