Deliagina T
Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institute, S-17177 Stockholm, Sweden.
J Exp Biol. 1997 Dec;200(Pt 23):2957-67. doi: 10.1242/jeb.200.23.2957.
The main motor disorder evoked by unilateral labyrinthectomy (UL) in the lamprey (Lampetra fluviatilis) is a complete loss of equilibrium and rolling (rotation about the longitudinal axis) during swimming. A previous study has shown that the recovery of equilibrium control in the lamprey takes, on average, 33 days. However, lampreys were able to maintain equilibrium if UL was combined with removal of the ipsilateral eye ('surgical compensation' of the vestibular deficit). It was suggested that tonic excitatory inflow, rather than specific information about the orientation of the animal in space delivered by the remaining eye, is important for the recovery of equilibrium control. In the present study, a number of experiments were designed to test this hypothesis. It was found that illumination of the eye contralateral to the UL or continuous electrical stimulation (10 Hz) of the corresponding optic nerve resulted in immediate restoration of equilibrium control. The same result was obtained when the vestibular nerve on the UL side was stimulated. Thus, the roll control system in the lamprey, driven by only one labyrinth, is able to maintain equilibrium provided that the lack of tonic inflow from the missing labyrinth is compensated for by tonic vestibular or visual input. The present study has also shown that the importance of visual input for maintaining equilibrium after UL decreases with time. In animals that achieved a high degree of compensation, removal of the eyes on day 23 after UL evoked decompensation, whereas removal on day 70 did not. A reduction of the significance of visual input was also observed in surgically compensated UL lampreys. In these animals, removal of the remaining eye on days 1-3 after the first surgery resulted in a complete loss of equilibrium, removal on day 7 resulted in a partial loss, whereas removal on days 48-55 did not affect the postural stability. Three lines of evidence suggest that asymmetrical visual input evokes plastic changes in the roll control system. (i) In one group of animals, initially one eye was removed, and then 50 days later the labyrinth ipsilateral to the missing eye and remaining eye were removed. These animals exhibited a mild impairment of equilibrium control, in contrast to the animals in which both surgeries were performed simultaneously. (ii) In another group of animals, initially one eye was removed, and then 50 days later the remaining eye and both labyrinths were removed. These animals exhibited rolling towards the eye that remained intact for longer. (iii) A short-term electrical stimulation (5-10 min daily for 3 days) of the optic nerve (contralateral to UL) in blinded animals considerably improved the equilibrium control compared with that of non-stimulated animals; the improvement was observed for 60 days after stimulation.
在七鳃鳗（Lampetra fluviatilis）中，单侧迷路切除（UL）引发的主要运动障碍是游泳时完全失去平衡并翻滚（绕纵轴旋转）。先前的一项研究表明，七鳃鳗平衡控制功能的恢复平均需要33天。然而，如果将UL与同侧眼睛摘除相结合（对前庭缺陷进行“手术补偿”），七鳃鳗能够维持平衡。有人提出，对于平衡控制功能的恢复而言，持续性兴奋性传入信号很重要，而不是由剩下的眼睛传递的关于动物在空间中方位的特定信息。在本研究中，设计了一系列实验来验证这一假设。结果发现，对UL对侧的眼睛进行光照或对相应的视神经进行持续电刺激（10赫兹）会立即恢复平衡控制。刺激UL侧的前庭神经也得到了相同的结果。因此，七鳃鳗中仅由一个迷路驱动的翻滚控制系统，只要缺失迷路的持续性传入信号缺失能够通过持续性前庭或视觉输入得到补偿，就能维持平衡。本研究还表明，UL后视觉输入对维持平衡的重要性会随着时间降低。在实现了高度补偿的动物中，UL后第23天摘除眼睛会引发失代偿，而第70天摘除则不会。在手术补偿的UL七鳃鳗中也观察到视觉输入重要性的降低。在这些动物中，第一次手术后第1 - 3天摘除剩下的眼睛会导致完全失去平衡，第7天摘除会导致部分失去平衡，而第48 - 55天摘除则不会影响姿势稳定性。三条证据表明不对称视觉输入会引发翻滚控制系统的可塑性变化。（i）在一组动物中，最初摘除一只眼睛，然后在50天后摘除与缺失眼睛同侧的迷路以及剩下的眼睛。与同时进行这两种手术的动物相比，这些动物表现出轻度的平衡控制受损。（ii）在另一组动物中，最初摘除一只眼睛，然后在50天后摘除剩下的眼睛以及两个迷路。这些动物表现出朝着保持完整时间更长的眼睛一侧翻滚。（iii）与未受刺激的动物相比，对失明动物的视神经（UL对侧）进行短期电刺激（每天5 - 10分钟，持续3天）能显著改善平衡控制；刺激后60天内都观察到了这种改善。
