利用CaMPARI对 果蝇 幼虫中枢神经系统中突触前和突触后伴侣的功能性特征
June 16th, 2026
该方案利用遗传编码工具评估 果蝇黑胃蝇 幼虫中枢神经系统中特定神经伴侣之间的活体功能突触活动。CsChrimson介导的前突触cIVda感觉神经元的光遗传刺激，诱导突触后盆地4中间神经元中CaMPARI的钙依赖性光转换。
我们的研究重点是评估活体和解剖果蝇幼虫中特定神经节点伙伴之间的功能突触连接。传统方法需要解剖或物理刺激。该协议在完整幼虫中使用光遗传学，减少了伪影。
首先，在微波炉中将玉米粉琼脂培养基加热8-10秒而不煮沸，然后在室温下冷却而不使其固化。在完全冷却之前，将全反视黄醇或ATR加入到0.5毫摩尔的浓度，以补充需要csChrimson激活的果蝇的培养基。用铝箔完全覆盖试管以防止光照。
将携带CaMPARI和csChrimson基因的处女雌性与携带GAL4和LexA驱动基因的雄性交叉，放在含有准备好的培养基的塑料试管中。准备不含ATR的平行试管作为对照。将试管在25摄氏度下孵育，直到幼虫达到第三龄幼虫阶段。
使用画笔收集第三龄幼虫。将幼虫在含有0.1摩尔PBS的三孔微斑板中冲洗，以去除任何附着的食物。在干净的18 x 18毫米盖玻片的每个角落放置少量粘土。
将幼虫放在盖玻片上的PBS滴液中，让它以腹侧朝下定向。在含有幼虫的盖玻片上方放置干净的显微镜载玻片。通过在角落上涂抹粘土来固定盖玻片，施加足够的压力以固定幼虫而不将其压碎或打破玻璃。
将含有幼虫的载玻片放在配备40x/1.2物镜的共聚焦显微镜的舞台上。在显微镜软件界面中，点击Live。然后在Z Stack面板下，点击Set First然后Set Last，最后点击Stop以获取表达CaMPARI的突触后神经元的基线Z Stack。
在Channels菜单下，将488纳米的绿色通道设置为0.8%的激光功率。接下来，将561纳米的红色通道设置为0.8%的激光功率。在Z Stack菜单下，将Interval值设置为1微米。
在采集菜单中，选择Presets以设置256 x 256像素的分辨率。线平均值设置为2，双向扫描，扫描速度为9，允许自动更新像素时间。在整个实验中，在黑暗环境中进行所有成像，保持相同的采集参数。
将405纳米的光转换光设置为0.5%的激光功率。将561纳米的光遗传学刺激光设置为0.8%的激光功率。点击Live，然后在直方图面板下选择Best Fit。
让两个激光同时刺激幼虫30秒，然后停止刺激。在使用与基线相同参数的后刺激ZStack采集过程中，观察ATR喂养的幼虫的激光刺激神经元中的红色CaMPARI荧光，并且在控制组中，光转换最小。在Fiji ImageJ软件中，点击File，然后选择Open。
在具有默认设置的BioFormats导入选项窗口中，点击OK以打开获得的ZStack图像。在Image菜单下，选择Color，然后选择Split Channels以查看获得的图像的红色和绿色通道。对于背景减除，点击Process，然后选择Subtract Background。
在弹出窗口中，将滚动球半径设置为50像素，然后点击OK并在Process Stack窗口中选择Yes。接下来，在分析菜单下，选择Tools，然后选择ROI Manager以打开ROI窗口。使用自由选择工具在单个细胞周围划定感兴趣的区域。
在ROI窗口中，选择Add以保存所选轮廓。然后点击Measure以生成面积、平均值、标准差和集成密度结果。重复该过程以分别在绿色和红色通道中对同一幼虫的多个细胞进行处理。
将结果导出到电子表格后，测量每个细胞的红色与绿色或R by G集成密度比，并将这些值平均以计算每个幼虫的基线和后刺激图像的平均R by G比。最后，通过从后刺激的R by G比中减去基线R by G比来计算荧光的变化或delta R by G，以量化突触后钙活动。在第三龄幼虫中，对IV类树突分支或cIVda神经元与basin-4中间神经元之间的功能连接研究显示，在光转换和光遗传学光刺激之前，basin-4中间神经元显示出绿色荧光，这是由于胞质CaMPARI表达。
在基线条件下未检测到红色荧光，这证实了在刺激前不存在光转换。同时进行光转换光暴露和光遗传学刺激导致CaMPARI从绿色荧光转换为红色荧光。对照组中红色荧光的缺失表明，光转换是由csChrimson介导的神经元活动特异性驱动的。
实验动物的绿色与红色荧光的delta显著高于无ATR对照。该协议可用于确认突触伙伴关系，通过在活体发育中的动物中跟踪突触前刺激，并随后立即观察突触后反应。最具挑战性的步骤是适当的动物固定，这将需要足够的压力以防止移动而不伤害动物。
未来的研究可以实现跟踪特定神经元群体之间的突触连接的形成、加强，甚至消除，在发育中的动物中进行。
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Overview
This article presents a method to functionally validate synaptic connectivity in the Drosophila larval nervous system by combining optogenetic activation with CaMPARI-based calcium imaging. The approach enables researchers to assess activity-dependent synaptic signaling between identified sensory neurons and interneurons in intact, undissected third-instar larvae.
Key Study Components
Area of Science
- Neurobiology
- Functional connectomics
- Optogenetics
- Calcium imaging
Background
- Connectome studies have mapped synaptic connectivity in various species, including Drosophila.
- Electron microscopy provides detailed anatomical data but lacks functional information.
- Recent Drosophila research has identified key neuronal networks underlying specific behaviors, such as nociception.
- Class IV dendritic arborization (cIVda) sensory neurons form major synaptic contacts with Basin-4 interneurons by the third instar larval stage.
Purpose of Study
- To functionally assess synaptic connectivity between cIVda nociceptors and Basin-4 interneurons in Drosophila larvae.
- To demonstrate the utility of CaMPARI as an activity-dependent reporter in live, undissected larvae.
- To establish a proof-of-principle protocol combining optogenetic stimulation and CaMPARI photoconversion.
Methods Used
- Immobilization of third-instar Drosophila larvae on microscope slides.
- Optogenetic activation of cIVda nociceptors using the red-shifted channelrhodopsin CsChrimson.
- Simultaneous CaMPARI photoconversion in Basin-4 interneurons to detect calcium influx.
- Fluorescence imaging to monitor CaMPARI color change as a readout of synaptic activity.
Main Results
- Calcium-dependent photoconversion of CaMPARI was observed in Basin-4 interneurons following optogenetic stimulation of cIVda neurons.
- The method provided functional evidence of synaptic connectivity despite internal larval movements and focal plane changes.
- The approach validated the anatomical connections identified by connectome studies with functional data.
Conclusions
- CaMPARI-based photoconversion is a reliable indicator of synaptic activation in intact Drosophila larvae.
- The protocol enables functional validation of connectomic data in vivo.
- This method can be broadly applied to study neuronal network function in genetically tractable organisms.
Frequently Asked Questions
Executive Industry Relevance
Functional validation of synaptic connectivity is critical for de-risking target selection and advancing mechanistic understanding in neurobiology-driven drug discovery. This CaMPARI-based approach enables direct assessment of activity-dependent signaling between defined neuronal partners in intact systems, bridging the gap between anatomical connectomics and actionable functional data. Such methods enhance predictive confidence at the target validation and early discovery inflection points, supporting portfolio decisions in CNS and neurodevelopmental pipelines.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables interrogation of functional synaptic connectivity beyond anatomical mapping.
- Supports mechanistic de-risking by confirming physiologically relevant neuronal interactions.
- Improves predictive confidence for target engagement and pathway modulation.
Screening & Assay Development
- Facilitates development of validated, activity-dependent readouts for neuronal assays.
- Provides quantitative, ratiometric outputs suitable for reproducible screening workflows.
- Enables robust assay standardization by integrating optogenetic stimulation with functional imaging.
Translational & Preclinical Research
- Aligns functional synaptic data with disease-relevant neural circuits in preclinical models.
- Supports continuity from discovery through preclinical validation by linking connectomic and functional endpoints.
- De-risks translational biomarker strategies by confirming in vivo neuronal activity patterns.
Pipeline & Workflow Integration
This method integrates into the discovery continuum from target validation through assay development and preclinical research, providing a reusable platform for functional connectomics in genetically tractable systems.
- Discovery Biology: Validates synaptic function and pathway engagement in intact neural circuits.
- Screening: Delivers quantitative, reproducible readouts for compound or genetic perturbation studies.
- Analytics: Enables ratiometric measurement of calcium-dependent activity for comparative analysis.
- Translational Research: Bridges anatomical and functional data to inform disease-relevant model selection.
- Enterprise Reuse: Establishes a scalable workflow adaptable to diverse neuronal targets and circuits.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence and reduces mechanistic ambiguity in neural target validation.
- Operational Value: Standardizes functional readouts and supports reproducibility across experiments.
- Strategic Value: Informs go/no-go decisions and prioritizes targets with validated functional relevance.
- Portfolio Impact: Enables risk-adjusted advancement of CNS and neurodevelopmental programs.
Implementation Considerations
- Requires expertise in optogenetics, calcium imaging, and genetic model systems.
- Needs fluorescence microscopy infrastructure and precise light delivery systems.
- Demands cross-team standardization for assay reproducibility and data interpretation.
- Adaptation to other model systems depends on genetic tractability and optical accessibility.
- Internal movement and focal plane changes in live imaging must be managed for reliable outputs.