Manns Martina, Freund Nadja, Leske Oliver, Güntürkün Onur
Biopsychology, Faculty of Psychology, Institute of Cognitive Neuroscience, Ruhr-University Bochum, Bochum 44780, Federal Republic of Germany.
Dev Neurobiol. 2008 Jul;68(8):1123-34. doi: 10.1002/dneu.20647.
In pigeons, asymmetric photic stimulation around hatch induces functional visual asymmetries that are accompanied by left-right differences in tectal cell sizes. Different aspects of light-dependent neuronal differentiation are known to be mediated by the brain-derived neurotrophic factor (BDNF). Therefore, we investigated by means of single or triple BDNF- or saline-injections into the right eye of dark-incubated pigeon hatchlings if ocular BDNF enrichment mimics the effects of biased visual input. As adults, the birds were tested in a grit-grain discrimination task to estimate the degree and direction of visual lateralization followed by a morphometric analysis of retinal and tectal cells. The grit-grain discrimination task demonstrated that triple BDNF-injections enhanced visuoperceptual and visuomotor functioning of the left eye system. Morphometric analysis showed bilateral cell-type dependent effects within the optic tectum. While single-BDNF injections increased cell body sizes of calbindin-positive efferent neurons, triple-injections decreased cell sizes of parvalbumin-positive cells. Moreover, single BDNF-injections increased retinal cell sizes within the contralateral eye. Analysis of BDNF-induced intracellular signaling demonstrated enhanced downstream Ras activation for at least 24 h within both tectal halves whereas activity changes within the contralateral retina could not be detected. This points to primarily tectal effects of ocular BDNF. In sum, exogenous BDNF modulates the differentiation of retinotectal circuitries and dose-dependently shifts lateralized visuomotor processing towards the noninjected side. Since these effects are opposite to embryonic light stimulation, it is unlikely that the impact of light onto asymmetry formation is mediated by retinal BDNF.
在鸽子中，孵化前后不对称的光刺激会诱发功能性视觉不对称，同时伴随着视顶盖细胞大小的左右差异。已知脑源性神经营养因子（BDNF）介导了光依赖性神经元分化的不同方面。因此，我们通过向在黑暗中孵化的鸽子幼雏的右眼单次或三次注射BDNF或生理盐水，来研究眼内BDNF富集是否能模拟偏向性视觉输入的效果。成年后，对这些鸟进行沙粒辨别任务测试，以评估视觉偏向的程度和方向，随后对视网膜和视顶盖细胞进行形态计量分析。沙粒辨别任务表明，三次注射BDNF增强了左眼系统的视觉感知和视觉运动功能。形态计量分析显示，在视顶盖内存在双侧细胞类型依赖性效应。单次注射BDNF增加了钙结合蛋白阳性传出神经元的细胞体大小，而三次注射则减小了小白蛋白阳性细胞的大小。此外，单次注射BDNF增加了对侧眼内的视网膜细胞大小。对BDNF诱导的细胞内信号传导的分析表明，视顶盖两侧至少24小时内下游Ras激活增强，而对侧视网膜内的活性变化未被检测到。这表明眼内BDNF主要作用于视顶盖。总之，外源性BDNF调节视网膜-视顶盖回路的分化，并剂量依赖性地将偏向性视觉运动处理转向未注射侧。由于这些效应与胚胎期光刺激相反，因此光对不对称形成的影响不太可能由视网膜BDNF介导。
