Svirskis Gytis, Baranauskas Gytis, Svirskiene Natasa, Tkatch Tatiana
Neurophysiology laboratory, Neuroscience Institute, Lithuanian University of Health Sciences, Kaunas, Lithuania.
PLoS One. 2015 Sep 28;10(9):e0139472. doi: 10.1371/journal.pone.0139472. eCollection 2015.
The superior colliculus in mammals or the optic tectum in amphibians is a major visual information processing center responsible for generation of orientating responses such as saccades in monkeys or prey catching avoidance behavior in frogs. The conserved structure function of the superior colliculus the optic tectum across distant species such as frogs, birds monkeys permits to draw rather general conclusions after studying a single species. We chose the frog optic tectum because we are able to perform whole-cell voltage-clamp recordings fluorescence imaging of tectal neurons while they respond to a visual stimulus. In the optic tectum of amphibians most visual information is processed by pear-shaped neurons possessing long dendritic branches, which receive the majority of synapses originating from the retinal ganglion cells. Since the first step of the retinal input integration is performed on these dendrites, it is important to know whether this integration is enhanced by active dendritic properties. We demonstrate that rapid calcium transients coinciding with the visual stimulus evoked action potentials in the somatic recordings can be readily detected up to the fine branches of these dendrites. These transients were blocked by calcium channel blockers nifedipine CdCl2 indicating that calcium entered dendrites via voltage-activated L-type calcium channels. The high speed of calcium transient propagation, >300 μm in <10 ms, is consistent with the notion that action potentials, actively propagating along dendrites, open voltage-gated L-type calcium channels causing rapid calcium concentration transients in the dendrites. We conclude that such activation by somatic action potentials of the dendritic voltage gated calcium channels in the close vicinity to the synapses formed by axons of the retinal ganglion cells may facilitate visual information processing in the principal neurons of the frog optic tectum.
哺乳动物的上丘或两栖动物的视顶盖是主要的视觉信息处理中心，负责产生定向反应，如猴子的扫视或青蛙的捕食躲避行为。上丘和视顶盖在青蛙、鸟类、猴子等远缘物种中具有保守的结构功能，这使得在研究单个物种后能够得出较为普遍的结论。我们选择青蛙视顶盖是因为我们能够在顶盖神经元对视觉刺激做出反应时进行全细胞电压钳记录和荧光成像。在两栖动物的视顶盖中，大多数视觉信息由具有长树突分支的梨形神经元处理，这些神经元接收来自视网膜神经节细胞的大部分突触。由于视网膜输入整合的第一步是在这些树突上进行的，因此了解这种整合是否通过活跃的树突特性得到增强很重要。我们证明，在体细胞记录中，与视觉刺激诱发的动作电位同时出现的快速钙瞬变可以很容易地在这些树突的细分支中检测到。这些瞬变被钙通道阻滞剂硝苯地平和氯化镉阻断，表明钙通过电压激活的L型钙通道进入树突。钙瞬变传播速度极快，在不到10毫秒的时间内传播超过300微米，这与动作电位沿树突主动传播、打开电压门控L型钙通道导致树突中钙浓度快速瞬变的观点一致。我们得出结论，视网膜神经节细胞轴突形成的突触附近的树突电压门控钙通道被体细胞动作电位激活，可能有助于青蛙视顶盖主要神经元的视觉信息处理。
