【作者】 吴伟；

【导师】 杨昱鹏；

【作者基本信息】 中国科学技术大学 ， 神经生物学， 2022， 博士

【摘要】 神经可塑性是神经系统随着外界经验而发生改变的能力,对动物在多变的环境中生存至关重要。在出生后的一段时间窗口,即所谓的关键期,动物有很强的眼优势可塑性。随着发育的进行,眼优势可塑性在成年动物中逐渐降低,甚至消失。在成年动物中提高或恢复眼优势可塑性对治疗弱视以及损伤恢复有很重要的意义,但目前成年后眼优势可塑性的时程与机制仍不清楚。本研究首先利用在体内源信号光学成像、在体胞外电生理记录结合药理学方法研究了小鼠的成年眼优势可塑性的发生时程。内源信号光学成像使用红光(630±10 nm)和近红外光(720±10 nm)作为入射光,发现近红外光检测到的皮层反应要显著低于红光检测到的皮层反应,但在成年对照鼠中两种入射光检测到的眼优势分布并没有差异。在经历长时间单眼剥夺(7-8天)后,两种成像方法都在成年小鼠上检测到相同的眼优势偏移。然而在经历短期剥夺(4天)的成年小鼠上,红光未检测到眼优势的偏移,但近红外光检测到眼优势出现偏移。这种偏移主要由非缝合眼反应的增强所引起,说明是成年样的眼优势可塑性。我们进一步使用在体胞外电生理记录探索这种短期剥夺引起的可塑性的来源。长时间单眼剥夺使成年小鼠眼优势偏向未缝合眼,并由较强的未剥夺眼反应上升和微弱的剥夺眼反应下降介导,这与前人结果类似。短时间单眼剥夺不能引起全体细胞的显著的眼优势偏移。但如果将记录的细胞分为浅层(皮层下150μm-480 μm,主要为Ⅱ/Ⅲ层和Ⅳ层细胞)和深层(皮层下520 μm-800 μm,主要为V层细胞和少量Ⅵ层细胞),短期剥夺成年小鼠的浅层细胞没有眼优势可塑性,但深层细胞的眼优势则偏向未剥夺眼,表明深层神经元具有眼优势可塑性。这种深层和浅层细胞可塑性的差异在未剥夺对照小鼠和长时间剥夺小鼠中都没有检测到。成年眼优势可塑性依赖于NMDA受体。腹腔注射NMDA受体拮抗剂CPP可以阻断短期剥夺引起的在体电生理检测到的皮层深层眼优势偏移,也阻断了近红外光检测到的眼优势的偏移。这些结果表明短期剥夺已经可以引起依赖于NMDA受体的成年眼优势的偏移,而且发生在皮层深层。近红外光的内源信号光学成像可以检测到这种眼优势的偏移。胼胝体是大脑中连接左右皮层的白质结构。视皮层有大量的兴奋性神经元通过跨胼胝体的纤维参与到对侧视皮层的视觉信号处理和眼优势可塑性的发生。之前的研究认为在发育早期有一定比例的抑制性神经元的纤维跨过胼胝体,投射到对侧皮层,之后这些跨胼胝体的抑制性神经元迅速消失。但一侧的抑制性神经元是否对另一侧皮层产生影响目前仍不清楚。我们使用光遗传调控结合在体内源信号光学成像来探究一侧抑制性神经元对对侧视皮层的影响。光遗传激活一侧视皮层的抑制性神经元可以减弱对侧视皮层双眼区的自发放水平,同时还可以降低对侧皮层的视觉诱发的内源信号反应。这种抑制效应主要作用于双眼区,其中对同侧眼的抑制最强,对侧眼反应的抑制次之,而单眼区对侧眼反应的抑制最弱。抑制性神经元包含不同的亚群,激活PV神经元(parvalbumin-positive neurons)和SST神经元(somatostatin-expressing neurons)可以观察到类似的对对侧视皮层抑制现象。这些结果表明存在由抑制性神经元介导的跨脑半球的对侧抑制通路。综上所述,我们发现近红外光内源信号光学成像可以检测到成年小鼠中短期单眼剥夺诱发的深层神经元的眼优势可塑性,这一结果更新了前人认为的成年小鼠短期视剥夺无法诱发眼优势可塑性的结论,暗示成年个体深层神经元仍保存较强的可塑性。大脑半球间存在的相互抑制作用会影响视皮层的眼优势分布,为将来研究脑半球间的相互作用打下基础。更多还原

【Abstract】 The nervous system can adjust its connection with external experience(termed plasticity),which is essential for the survival of animals in complex environment.During a special time window(the critical period)after birth,animals show strong ocular dominance plasticity.This plasticity reduces and even disappears in adult animals.It is well known that restoration of plasticity in adulthood would be of benefit to amblyopia treatment and injury recovery.However,the mechanisms underlying adult plasticity are largely unknown.In this study,optical imaging of intrinsic signals,in vivo extracellular single-unit recording and pharmacological method were used to reveal the time-course of adult ocular dominance plasticity.Red light(630± 10 nm)and near-infrared light(720 ± 10 nm)were used as incident light in optical imaging of intrinsic signals recording.The detected response by near-infrared light was significantly lower than that by red light,and the ocular dominance index obtained with two illuminations was similar in adult non-deprived mice.Following long-term monocular deprivation(7-8 days),the ocular dominance shift was observed similarly by both incident wavelengths.Following shortterm deprivation,however,the ocular dominance shift was detected by near-infrared light rather than red light.This plasticity was mediated by the potentiation of non-suture eye response,suggesting this is adult ocular dominance plasticity.Then we used in vivo extracellular single-unit recording to find out the origin of short-term deprivation induced plasticity.Consistent with previous reports,long-term monocular deprivation biased the ocular dominance to the nondeprived eye,which was mediated by potentiation of nondeprived eye response and relatively weak depression of deprived eye response.Ocular dominance shifts for the total cell population were not observed after short-term deprivation(4 days).Then the cell population was divided into superficial(150 μm-480 μm under the pia,mainly L2/3 and L4 cells)and deep(520μm-800 μm under the pia mainly L5 cells and a few L6 cells)groups.In short-term deprived mice,ocular dominance shift was not observed in superficial neurons but the ocular dominance distribution of deep neurons was biased toward open eye.The difference between ocular dominance plasticity in the deep and superficial layers was not observed in neither the nondeprived mice nor the mice with long-term visual deprivation.The adult ocular dominance plasticity depends on NMDA receptor.We intraperitoneally administered CPP to mice with short term deprivation.This treatment blocked the ocular dominance shift in deep layers measured by electrophysiological recording,as well as the optical imaging with near-infrared light.These results suggested that short-term deprivation in adulthood is enough to induce NMDA receptor-dependent ocular dominance shift,which occurs in the deep layers and can be detected by optical imaging of intrinsic signals of near-infrared light.Excitatory neurons in visual cortex in both hemispheres connect each other through the corpus callosum and be involved in visual signal processing and ocular dominance plasticity.Previous studies have suggested that a certain proportion of callosal inhibitory neurons occurred in the early developmental stage and rapidly disappeared.We combined optogenetics and intrinsic signals optical imaging to investigate the potential role of inhibitory interneurons to contralateral visual cortex.When the inhibitory neurons were activated on one side of the hemisphere,it would reduce the basal spikes in the binocular region of another side of the hemisphere.Furthermore,it also inhibited the visually evoked response in the contralateral cortex.In the binocular region,we observed a stronger effect on the response to the ipsilateral eye than the contralateral eye.The effect was relatively weak in the monocular region.Similar phenomena were observed when two subpopulations of interneurons(parvalbumin-positive neurons and somatostatin-positive neurons)were activated.These results suggest that there may be a pathway between the two visual cortexes mediating the inhibition of interneurons to contralateral side.In summary,we found near-infrared intrinsic signal optical imaging can detecet the ocular dominane plasticity in deep layers after brief deprivation,which overthrow the conclusion that the ocular dominance plasticity can not be induced by short-term deprivation in adult mice.The inhibition between the binocular regions of two hemispheres effects the ocular dominace distribution,paving the way for future reaserch about interaction between hemispheres.更多还原