Link Brain-wide Projectome to Neuronal Dynamics in the Mouse Brain

Medicine Basic Medical Sciences Biophysics Medical Imaging Life Sciences
brain-wide projectome neuronal dynamics mouse somatosensory cortex dopaminergic neurons

Background Introduction

The brain is composed of different subtypes of neurons, which form complex neural networks through local and long-range synaptic connections. Understanding the functions of these neural networks requires knowledge of their connection patterns (projectome) and neuronal dynamics. Although advancements in mesoscale connectomics and cell-resolution functional imaging technologies have made it possible to reveal the structural organization or function of neurons in different brain regions, obtaining both neuronal activity and whole-brain connectomes of the same neurons remains a challenge, especially for neurons in subcortical brain regions.

Source Introduction

This paper was jointly authored by members of multiple research teams, including Xiang Li, Yun Du, Jiang-Feng Huang, and others from institutions such as Huazhong University of Science and Technology and the Chinese Academy of Sciences. The paper was published in January 2024 in the journal Neuroscience Bulletin.

Research Objectives and Methods

Research Objectives

The main aim of this study is to link whole-brain connectomes with neuronal dynamics, addressing the challenge of simultaneously obtaining the activity and projection patterns of the same neurons from previous studies. The research focuses on the mouse brain, including multiple cortical and subcortical areas such as the somatosensory cortex, dorsal hippocampus, and substantia nigra pars compacta.

Research Methods

The study employs various techniques, including in vivo microscopy imaging and high-resolution fluorescent micro-optical sectioning tomography (fMOST) to map the whole-brain projection patterns of functionally relevant neurons in the somatosensory cortex, dorsal hippocampus, and substantia nigra pars compacta. Strategies were also developed to identify molecularly defined neuronal subtypes, addressing the issue of linking whole-brain connectomes with neuronal dynamics.

Detailed Steps

  1. Animal Experiment Preparation: Male C57BL/6J and DAT-Cre mice aged 6-13 weeks were used for the experiments. Following viral injections, viruses were allowed to express for 6-7 weeks.
  2. Virus and Surgical Operations: Multiple AAV viruses were used for infection, including AAV2/8-CamKII-Cre and AAV2/9-hEF1a-DIO-eYFP-WPRE-PA. Brain injections were performed using a standard stereotaxic system.
  3. Somatosensory Cortex (S1BF) Experiments: Viruses were injected into layer 2⁄3 of the somatosensory cortex, followed by labeling and imaging. Tactile stimuli in the form of airflow and moving walls were used, and neuronal calcium dynamics were recorded.
  4. Dorsal Hippocampus (dCA1) Experiments: Mixed viruses were injected into the dCA1 region, and in vivo imaging was conducted with implanted GRIN lenses to record neuronal responses to foot shocks.
  5. Substantia Nigra Pars Compacta (SNC) Experiments: Viruses were injected into the SNC region, and GRIN lenses were implanted to record calcium dynamics of specifically labeled dopamine neurons.

Main Results

Summary of Results

  1. Somatosensory Cortex (S1BF):

    • Using two-photon imaging and fMOST, the research team analyzed the responses of 61 layer 2⁄3 neurons in the S1BF to tactile stimuli, with 8.2% of the neurons showing responses.
    • Whole-brain imaging was conducted using fMOST for these neurons, and projections of 43 neurons were successfully registered, revealing differences in projection patterns across the brain.

  2. Dorsal Hippocampus (dCA1):

    • Recordings from 30 dCA1 neurons showed varied response patterns to foot shock, with some neurons being excited, others inhibited, and some non-responsive.
    • Detailed morphological analysis and registration of neurons in the dCA1 region were performed using fMOST and adaptive optics microscopy.

  3. Substantia Nigra Pars Compacta (SNC):

    • Specific labeling and imaging of dopamine neurons in the SNC were performed, recording calcium dynamics in 7 neurons and finding that response patterns correlated with projection patterns to the target brain areas.
    • Whole-brain imaging and projection analysis of these neurons were conducted using fMOST technology.

Data Analysis

  • Multiple algorithms were employed for image processing and cell registration, including image registration based on vascular distribution and GRIN lens trajectory, and tear adaptive optics microscopy calibration methods based on Zernike modes.
  • By analyzing neuronal response patterns and projection target areas, the whole-brain projection patterns of functionally defined neurons were elucidated.

Conclusions and Significance

Conclusions

The methods developed in this study successfully linked whole-brain connectomes with neuronal dynamics, achieving this for the first time in both cortical and subcortical regions. Findings indicate that even with similar projection patterns, neurons can exhibit functional heterogeneity, providing new insights into the functional organization of the brain.

Significance and Value

  1. Scientific Value: The study’s findings significantly contribute to understanding the working principles of neural networks, providing new methods to understand how the brain functions through complex connection patterns.
  2. Application Value: The imaging and analysis techniques developed in this study can be applied not only in basic scientific research but also in clinical neuroscience research, offering new tools and methods for uncovering neuropathological mechanisms.

Research Highlights

  1. Novelty: Successfully linked whole-brain connectomes with neuronal dynamics for the first time, particularly for neurons in subcortical regions.
  2. Methodological Innovation: Employed a variety of cutting-edge techniques, including in vivo imaging, adaptive optics microscopy, and high-resolution fMOST imaging, achieving comprehensive analysis of functionally and molecularly defined neurons.
  3. Wide Applicability: The methods and strategies developed can be widely applied to different types of neurons and functional studies, opening new directions for neuroscience research.

Other Valuable Information

The research was supported by multiple projects, including the National Natural Science Foundation of China and the National Key R&D Program of China, involving collaborations among various research institutions. The research team acknowledges the support and contributions of numerous researchers and technicians. This study not only advances neuroscience research but also provides open data and code for other researchers to further explore and validate.

By meticulously designing experiments and analyzing data, this paper demonstrates the feasibility and methodology of linking whole-brain connectomes with neuronal dynamics, offering important references and insights for future neuroscience research.