Applying serotonergic (5-HT) agonists or grafting of fetal serotonergic cells into the spinal cord improves locomotion after spinal cord injury. Little is known about the role of 5-HT receptors in the control of voluntary locomotion, so we administered inverse agonists of 5-HT₂ (Cyproheptadine; Cypr), 5-HT_2A neutral antagonist (Volinanserin; Volin), 5-HT_2C neutral antagonist (SB 242084), and 5-HT_2B/2C inverse agonist (SB 206553) receptors intrathecally in intact rats and monitored their effects on unrestrained locomotion. An intrathecal cannula was introduced at the low thoracic level and pushed caudally until the tip reached the L2/L3 or L5/L6 spinal segments. Locomotor performance was evaluated using EMG activity of hindlimb muscles during locomotion on a 2 m long runway. Motoneuron excitability was estimated using EMG recordings during dorsi- and plantar flexion at the ankle. Locomotion was dramatically impaired after the blockage of 5-HT_2A receptors. The effect of Cypr was more pronounced than that of Volin since in the L5/L6 rats Cypr (but not Volin) induced significant alteration of the strength of interlimb coordination followed by total paralysis. These agents significantly decreased locomotor EMG amplitude and abolished or substantially decreased stretch reflexes. Blocking 5-HT_2B/2C receptors had no effect either on locomotion or reflexes. We suggest that in intact rats serotonin controls timing and amplitude of muscle activity by acting on 5-HT_2A receptors on both CPG interneurons and motoneurons, while 5-HT_2B/2C receptors are not involved in control of the locomotor pattern in lumbar spinal cord.

施加5-羟色胺能（5-HT）激动剂或将胎儿5-羟色胺能细胞移植到脊髓中可改善脊髓损伤后的运动能力。对5-HT受体在控制自主运动中的作用了解甚少，因此我们施用了5-HT ₂反向激动剂（赛庚啶； Cypr），5-HT _2A中性拮抗剂（Volinanserin； Volin），5-HT _2C中性拮抗剂（SB 242084）和5-HT _{2B / 2C}完整大鼠的鞘内逆激动剂（SB 206553）受体，并监测其对不受约束的运动的影响。在低胸水平引入鞘内插管并向尾推动，直到尖端到达L2 / L3或L5 / L6脊柱节段。在2 m长的跑道上进行运动时，使用后肢的肌电活动评估运动能力。在肌腱的脚背和足底屈曲期间，使用EMG记录估计了Motoneuron的兴奋性。5-HT _2A阻滞后运动受到显着损害受体。Cypr的作用比Volin的作用更明显，因为在L5 / L6大鼠中，Cypr（但不是Volin）诱导了肢体协调强度的显着改变，继而完全瘫痪。这些药物可显着降低运动肌电图振幅，并消除或显着降低拉伸反射。阻断5-HT _{2B / 2C}受体对运动或反射没有影响。我们建议在完整的大鼠中，5-羟色胺通过作用于CPG中间神经元和运动神经元上的5-HT _2A受体来控制肌肉活动的时间和振幅，而5-HT _{2B / 2C}受体不参与腰椎脊髓运动模式的控制。