Yeomans J S
Department of Psychology, University of Toronto, Ontario, Canada.
Behav Neurosci. 1990 Dec;104(6):991-9. doi: 10.1037//0735-7044.104.6.991.
Rats were trained to bar press for trains of conditioning (C) and test (T) pulses delivered via lateral hypothalamic electrodes. As intrapair (C-T) intervals increased from 10 ms to 100 ms, the frequency of pulses required for self-stimulation increased, similar to results of Smith and Coons (1970). This effect was observed only for electrode placements where self-stimulation was obtained at frequencies below 16 Hz and currents of 600 microA and higher. The effect was larger when the train duration was increased from 0.5 s to 2.0 s. The threshold increase was abolished when the T pulses were greater in current than the C pulses but not when C pulses were larger than T pulses. The larger T pulses also removed relative refractory period effects at a C-T interval of 1.0 ms. Therefore, the increase in required current or frequency at long C-T intervals appears to be due to a decline in axonal excitability (i.e., the subnormal period) rather than a decay in synaptic temporal summation. Possible flaws in other reports of paired-pulse "temporal summation decay" at long C-T intervals using 2 electrodes are discussed.
训练大鼠通过按压杠杆来获取经由下丘脑外侧电极传递的一连串条件（C）脉冲和测试（T）脉冲。随着配对内（C-T）间隔从10毫秒增加到100毫秒，自我刺激所需的脉冲频率增加，这与史密斯和库恩斯（1970年）的结果相似。仅在以低于16赫兹的频率、600微安及更高的电流获得自我刺激的电极放置位置观察到这种效应。当串刺激持续时间从0.5秒增加到2.0秒时，这种效应更大。当T脉冲的电流大于C脉冲时，阈值增加被消除，但当C脉冲大于T脉冲时则不然。更大的T脉冲也消除了在1.0毫秒的C-T间隔时的相对不应期效应。因此，在长C-T间隔时所需电流或频率的增加似乎是由于轴突兴奋性下降（即超常期），而不是突触时间总和的衰减。讨论了其他使用两个电极在长C-T间隔时成对脉冲“时间总和衰减”报告中可能存在的缺陷。
