Thompson S W, Gerber G, Sivilotti L G, Woolf C J
Department of Anatomy and Developmental Biology, University College London, UK.
Brain Res. 1992 Nov 6;595(1):87-97. doi: 10.1016/0006-8993(92)91456-o.
Long duration, primary afferent evoked ventral root potentials (VRP's) have been recorded in vitro from hemisected spinal cords prepared from 8-12-day-old rat pups. Single shock stimulation of a dorsal root at stimulus strengths sufficient to recruit C/group IV afferent fibres evoked a long duration (11.9 +/- 1.2 s) ipsilateral VRP in all preparations. This long duration VRP consisted of two components, (i) a slow wave, time to peak 137.0 +/- 5.1 ms, the amplitude of which was reduced to 8.7% of mean control value in the presence of the N-methyl-D-aspartate (NMDA) antagonist D-AP5 (40 microM), (ii) a prolonged wave with a time to peak of 2.0 +/- 0.2 s which was partially resistant to D-AP5 (40 microM). Both the slow and the prolonged waves were unaffected following superfusion with the metabotropic excitatory amino acid (EAA) receptor antagonist L-AP3 (100-200 microM). Low frequency (1-10 Hz) repetitive stimulation (20 s duration) of high threshold dorsal root afferents evoked a temporal summation of synaptic activity which generated a progressively depolarizing VRP. This cumulative VRP was graded with frequency of stimulation (0.89 +/- 0.13 to 1.25 +/- 0.19 mV). The cumulative VRP was followed by a post-stimulus depolarization which outlasted the period of repetitive stimulation by tens of seconds (47.6 +/- 8.4 to 91.2 +/- 19.9 s). In the presence of AP5 the amplitude of the cumulative VRP was depressed to 54.5 +/- 11.5% of control values when low frequency (1.0 Hz) stimulation was used. The proportion of the cumulative VRP resistant to D-AP5 increased as the frequency of stimulation was increased to 10 Hz. The decay time of the post-stimulus depolarization was unaffected by AP5. Neither the amplitude nor the post-stimulus depolarization of the cumulative VRP was affected by 200 microM L-AP3. It is suggested that both an AP5 sensitive and AP5 insensitive potential contribute to the long duration VRP evoked in the neonatal rat spinal cord following single shock high threshold afferent stimulation. Moreover, the AP5 insensitive prolonged depolarization is manifest following sustained low frequency stimuli and higher frequency inputs.
在体外记录了从8至12日龄大鼠幼崽制备的半切脊髓中长时程的初级传入诱发性腹根电位（VRP）。以足以募集C/IV组传入纤维的刺激强度对背根进行单次电击刺激，在所有标本中均诱发了长时程（11.9±1.2秒）的同侧VRP。这种长时程VRP由两个成分组成：（i）一个慢波，峰值时间为137.0±5.1毫秒，在存在N-甲基-D-天冬氨酸（NMDA）拮抗剂D-AP5（40微摩尔）时，其幅度降低至平均对照值的8.7%；（ii）一个峰值时间为2.0±0.2秒的延长波，对D-AP5（40微摩尔）有部分抗性。在用代谢型兴奋性氨基酸（EAA）受体拮抗剂L-AP3（100 - 200微摩尔）灌流后，慢波和延长波均未受影响。对高阈值背根传入纤维进行低频（1 - 10赫兹）重复刺激（持续20秒）诱发了突触活动的时间总和，产生了逐渐去极化的VRP。这种累积VRP随刺激频率分级（0.89±0.13至1.25±0.19毫伏）。累积VRP之后是刺激后去极化，其持续时间比重复刺激期长数十秒（47.6±8.4至91.2±19.9秒）。在存在AP5的情况下，当使用低频（1.0赫兹）刺激时，累积VRP的幅度降低至对照值的54.5±11.5%。随着刺激频率增加到10赫兹，累积VRP中对D-AP5有抗性的比例增加。刺激后去极化的衰减时间不受AP5影响。累积VRP的幅度和刺激后去极化均不受200微摩尔L-AP3影响。提示AP5敏感和AP5不敏感电位均对单次电击高阈值传入刺激后新生大鼠脊髓中诱发的长时程VRP有贡献。此外，在持续低频刺激和更高频率输入后，AP5不敏感的延长去极化表现明显。
