Anatomy and discharge properties of pre-motor neurons in the goldfish medulla that have eye-position signals during fixations
Anatomy and discharge properties of pre-motor neurons in the goldfish medulla that have eye-position signals during fixations
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DOI：
10.1152/jn.2000.84.2.1035
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发表时间：
2000-08-01
影响因子：
2.5
通讯作者：
Tank, DW
中科院分区：
文献类型：
--
作者：
Aksay, E;Baker, R;Tank, DW
以前对金鱼的研究表明，水平眼球运动的动眼速度-位置神经积分器可能局限于显示眼睛位置信号的一组不同的延髓神经元。为了确定这一定位，用单细胞神经生物素标记和细胞外记录来表征这些位置神经元的解剖和放电特性，同时用巩膜搜索线圈法监测眼球运动。所有标记的胞体(n=9)均位于下网状结构的内侧柱内，长约350微米，深约250微米，宽约125毫米。定位神经元树突广泛分布于延髓腹侧半部，尤以胞体前500亩处分支较重(n=9)。轴突要么沿着明确的腹侧通路通向同侧外展神经(n=4)，要么穿过中线(n=2)投射到对侧位置神经元群和对侧外展神经。使用细胞外单一单位记录绘制的躯体区域图显示，位置神经元(n>；120)是该区域与眼动相关的主要细胞类型。位置神经元的放电没有低于同侧眼睛水平注视位置的阈值。在此阈值以上，放电频率随颞叶位置的增加而线性增加[平均位置敏感度=2.8(棘波/S)/度，n=44]。对于给定的注视位置，颞部扫视后的平均放电率高于鼻部扫视(n=19/19)；这种滞后的程度随着位置敏感度的增加而增加。伴随着短暂眼跳的射电率转变为超射(n=43/44)，平均开始于眼跳开始前17.2ms(n=17)。伴随短暂眼跳的峰值放电率变化与眼速相关(n=36/41)。解剖结果表明，金鱼延髓位置神经元的胞体与动眼神经系统的其他部分分离，树突区与有速度信号的神经元的轴突终末重叠，轴突能够将命令传递给外展神经。生理发现表明，位置神经元携带的信号可以被运动神经元用来确定眼睛的注视位置。这些结果与位置神经元作为水平眼球运动的速度-位置神经积分器元素的作用是一致的。
Previous work in goldfish has suggested that the oculomotor velocity-to-position neural integrator for horizontal eye movements may be confined bilaterally to a distinct group of medullary neurons that show an eye-position signal. To establish this localization, the anatomy and discharge properties of these position neurons were characterized with single-cell Neurobiotin labeling and extracellular recording in awake goldfish while monitoring eye movements with the scleral search-coil method. All labeled somata (n = 9) were identified within a region of a medially located column of the inferior reticular formation that was similar to 350 mu m in length, similar to 250 mu m in depth, and similar to 125 mm in width. The dendrites of position neurons arborized over a wide extent of the ventral half of the medulla with especially heavy ramification in the initial 500 mu m rostral of cell somata (n = 9). The axons either followed a well-defined ventral pathway toward the ipsilateral abducens (n = 4) or crossed the midline (n = 2) and projected toward the contralateral group of position neurons and the contralateral abducens. A mapping of the somatic region using extracellular single unit recording revealed that position neurons (n > 120) were the dominant eye-movement-related cell type in this area. Position neurons did not discharge below a threshold value of horizontal fixation position of the ipsilateral eye. Above this threshold, firing rates increased linearly with increasing temporal position [mean position sensitivity = 2.8 (spikes/s)/degrees, n = 44]. For a given fixation position, average rates of firing were higher after a temporal saccade than a nasal one (n = 19/19); the magnitude of this hysteresis increased with increasing position sensitivity. Transitions in firing rate accompanying temporal saccades were overshooting (n = 43/44), beginning, on average, 17.2 ms before saccade onset (n = 17). Peak firing rate change accompanying temporal saccades was correlated with eye velocity (n = 36/41). The anatomical findings demonstrate that goldfish medullary position neurons have somata that are isolated from other parts of the oculomotor system, have dendritic fields overlapping with axonal terminations of neurons with velocity signals, and have axons that are capable of relaying commands to the abducens. The physiological findings demonstrate that the signals carried by position neurons could be used by motoneurons to set the fixation position of the eye. These results are consistent with a role for position neurons as elements of the velocity-to-position neural integrator for horizontal eye movements.