3D Imaging Technology Reveals Intricate Synaptic Interactions

Scientists have made a breakthrough in understanding the intricacies of the synapse, the junction where neurons communicate with one another. The findings, published in PNAS, unveil one of the most detailed 3D images of the synapse to date. Led by Dr. Steve Goldman, MD, Ph.D., from the University of Rochester and the University of Copenhagen, the research team has opened new avenues for studying neurodegenerative diseases such as Huntington’s disease and schizophrenia.

“It is one thing to understand the structure of the synapse from the literature, but it is another to see the precise geometry of interactions between individual cells with your own eyes,” explains study co-author Abdellatif Benraiss, Ph.D., a research associate professor in the Center for Translational Neuromedicine. “The ability to measure these extremely small environments is a young field, and holds the potential to advance our understanding of a number of neurodegenerative and neuropsychiatric diseases in which synaptic function is disturbed.”

The scientists focused their investigation on synapses involving medium spiny motor neurons, which are progressively lost in Huntington’s disease. To identify these synapses, the team utilized viruses to assign separate fluorescent markers to axons, motor neurons, and astrocytes. By employing multiphoton microscopy and infrared branding techniques, they successfully imaged and relocated the cells of interest.

To further analyze the synaptic structures, the team employed a serial block-face scanning electron microscope located at the University of Copenhagen. This innovative device enabled the creation of 3D, nanometer-scale models of the labeled cells and their interactions within the synapse. These models revealed the intricate geometry and structural relationships between astrocytes and synapses, highlighting their crucial role in maintaining the synaptic environment.

The researchers discovered surprising results by comparing the brains of healthy mice with those carrying the mutant gene responsible for Huntington’s disease. In healthy mice, astrocytes enveloped the synapse, creating a tight bond and ensuring the proper regulation of chemicals involved in cell communication. However, in mice with Huntington’s disease, astrocytes were less effective at investing in and sequestering the synapse, resulting in the leakage of essential chemicals that disrupt typical cell-cell communication.

The implications of this research extend beyond Huntington’s disease. Astrocyte dysfunction has been linked to other conditions such as schizophrenia, amyotrophic lateral sclerosis, and frontotemporal dementia. This technique offers a powerful tool for studying the structural basis of these diseases and may aid in evaluating the effectiveness of cell replacement strategies, which involve replacing diseased glial cells with healthy ones, to treat these debilitating disorders.