Functional Organization of Vestibulo-Ocular Responses in Abducens Motoneurons
Functional Organization of Vestibulo-Ocular Responses in Abducens Motoneurons
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DOI：
10.1523/jneurosci.2626-16.2017
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发表时间：
2017-04-12
影响因子：
5.3
通讯作者：
Straka, Hans
中科院分区：
文献类型：
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作者：
Dietrich, Haike;Glasauer, Stefan;Straka, Hans
前庭-眼反射(VORs)是所有脊椎动物凝视稳定的主要贡献者。在头部水平运动中，外展运动神经元形成反射弧线的最后一个元素，将视觉前庭输入整合到眼外直肌的临时精确运动指令中。在这里，我们通过对非洲爪哇幼虫半完整体外标本的形态、放电特性和突触药理学的评估，研究了外展运动神经元分化为亚型的可能性。头部正弦运动时的细胞外神经记录显示，在前庭刺激期间，静息率和激活阈值是连续的。由于对刺激频率和速度变化的敏感性不同，外展运动神经元可以细分为两个亚群，一个编码头部运动的频率和速度(组I)，另一个精确编码与刺激频率无关的角速度(组II)。计算模型表明，在测试的刺激范围内，第二类运动神经元是实际眼球运动的主要贡献者。分离成两个功能亚群与谷氨酸受体亚型的不同激活相一致。前庭兴奋性传入在I组运动神经元主要由NMDA受体介导，其次由AMPA受体介导，而在II组运动神经元以AMPA受体介导的兴奋为主。此外，甘氨酸能同侧前庭抑制输入在水平VOR时被激活，而紧张性GABA能抑制可能起源于前庭外。这些发现支持眼外运动神经元在生理和药理学上的不同功能亚群的存在，这些亚群在凝视稳定期间协调协调大动态范围的眼外运动指令。
Vestibulo-ocular reflexes (VORs) are the dominating contributors to gaze stabilization in all vertebrates. During horizontal head movements, abducens motoneurons form the final element of the reflex arc that integrates visuovestibular inputs into temporally precise motor commands for the lateral rectus eye muscle. Here, we studied a possible differentiation of abducens motoneurons into subtypes by evaluating their morphology, discharge properties, and synaptic pharmacology in semi-intact in vitro preparations of larval Xenopus laevis. Extracellular nerve recordings during sinusoidal head motion revealed a continuum of resting rates and activation thresholds during vestibular stimulation. Differences in the sensitivity to changing stimulus frequencies and velocities allowed subdividing abducens motoneurons into two subgroups, one encoding the frequency and velocity of head motion (Group I), and the other precisely encoding angular velocity independent of stimulus frequency (Group II). Computational modeling indicated that Group II motoneurons are the major contributor to actual eye movements over the tested stimulus range. The segregation into two functional subgroups coincides with a differential activation of glutamate receptor subtypes. Vestibular excitatory inputs in Group I motoneurons are mediated predominantly by NMDA receptors and to a lesser extent by AMPA receptors, whereas an AMPA receptor-mediated excitation prevails in Group II motoneurons. Furthermore, glycinergic ipsilateral vestibular inhibitory inputs are activated during the horizontal VOR, whereas the tonic GABAergic inhibition is presumably of extravestibular origin. These findings support the presence of physiologically and pharmacologically distinct functional subgroups of extraocular motoneurons that act in concert to mediate the large dynamic range of extraocular motor commands during gaze stabilization.