Currie S N, Stein P S
Department of Biology, Washington University, St. Louis, MO 63130.
Brain Res. 1992 May 22;581(1):91-100. doi: 10.1016/0006-8993(92)90347-c.
Glutamate antagonists applied to the cutaneous-processing region of the rostral scratch circuit in turtles reduced the excitability of the rostral scratch reflex. Segments D3-D6 (D3 = 3rd postcervical) of the midbody spinal cord receive cutaneous afferents from the rostral scratch receptive field and perform the initial integration of this cutaneous sensory input. These cutaneous-processing segments are located anterior to the rostral scratch motor pattern generator that resides mainly in segments D7-D10 located in and near the hindlimb enlargement. We prepared 1 or 2 of the midbody segments for bath application of glutamate antagonists in preparations with a complete transection of the spinal cord anterior to segment D3. Each preparation was immobilized by neuromuscular blockade and fictive scratch motor output was recorded from hindlimb muscle nerves. Application of the NMDA N-methyl-D-aspartate) antagonist APV (D-2-amino-5-phosphonovaleric acid, 50 microM) to a midbody segment significantly reduced the motor burst frequency of rostral scratch responses evoked by 3-Hz electrical stimulation of a site in that segment's dermatome. These data suggest that NMDA receptors contribute to cutaneous processing in the rostral scratch circuit. Application of APV to a midbody segment also reduced the magnitude of temporal summation in the scratch circuit in response to electrical stimuli delivered to the shell at 4- to 5-s intervals. Temporal summation was monitored at the level of hindlimb motor output as well as at the level of unit activity from 'long-afterdischarge' neurons in the midbody segments. Our observations are consistent with the hypothesis that NMDA receptors contribute to the prolonged activation of 'long-afterdischarge' neurons and the multisecond storage of excitation in the scratch reflex pathway.
将谷氨酸拮抗剂应用于龟类吻侧搔抓回路的皮肤处理区域，可降低吻侧搔抓反射的兴奋性。中体脊髓的D3 - D6节段（D3 = 颈后第3节段）接收来自吻侧搔抓感受野的皮肤传入信息，并对这种皮肤感觉输入进行初始整合。这些皮肤处理节段位于吻侧搔抓运动模式发生器的前方，吻侧搔抓运动模式发生器主要位于后肢膨大处及附近的D7 - D10节段。我们在D3节段前方脊髓完全横断的标本中，对1个或2个中体节段进行谷氨酸拮抗剂的浴用处理。每个标本通过神经肌肉阻滞固定，并从后肢肌肉神经记录虚构的搔抓运动输出。将NMDA（N - 甲基 - D - 天冬氨酸）拮抗剂APV（D - 2 - 氨基 - 5 - 磷酸戊酸，50微摩尔）应用于一个中体节段，可显著降低通过对该节段皮节中的一个部位进行3赫兹电刺激所诱发的吻侧搔抓反应的运动爆发频率。这些数据表明，NMDA受体有助于吻侧搔抓回路中的皮肤处理。将APV应用于一个中体节段，也可降低搔抓回路中对以4至5秒间隔施加于龟壳的电刺激的时间总和幅度。在中体节段“长后放电”神经元的单位活动水平以及后肢运动输出水平监测时间总和。我们的观察结果与以下假设一致，即NMDA受体有助于“长后放电”神经元的延长激活以及搔抓反射通路中兴奋的多秒存储。
