Engineers have combined light and sound imaging methods to observe how blood vessels supply oxygen to active brain neurons in awake animal models.
RT’s Three Key Takeaways:
- Single-Cell Oxygen Monitoring: Researchers integrated two imaging modalities to simultaneously record single-neuron calcium activity alongside oxygen release from individual red blood cells in awake mice.
- Mechanisms of Neurovascular Disease: The platform allows investigators to analyze how disruptions in neurovascular coupling and microvascular blood flow contribute to stroke and neurodegenerative diseases.
- Refining Clinical Imaging: A clearer cellular-level understanding of oxygen delivery dynamics could assist researchers and clinicians in interpreting indirect signals gathered during functional magnetic resonance imaging.
Researchers at Washington University in St. Louis have developed a microscopy platform that integrates two imaging modalities to display in real time how cerebral vasculature delivers oxygen to neurons, according to a study published in Nature Communications and a news release from the institution.
The platform merges two-photon microscopy and photoacoustic microscopy (TPM-PAM) to monitor cellular interactions in the brain. The engineering team, led by Song Hu, a professor of biomedical engineering at Washington University’s McKelvey School of Engineering, successfully documented single-neuron calcium activity concurrently with oxygen release from individual red blood cells in awake mice.
“Using this technology gives us a better understanding of these disease mechanisms,” said Song Hu, a professor of biomedical engineering at Washington University in St. Louis.
Bridging Neuronal Energy and Vasculature
While two-photon microscopy utilizes fluorescent probes to visualize neuronal activity, photoacoustic microscopy relies on light-generated sound waves to measure blood flow and blood oxygenation levels. Although neural activity consumes substantial energy, evaluating how the vascular system supplies fuel in direct response to brain function has historically presented technical hurdles.
“That’s why it’s important to image both of them, to understand how neuron activity consumes oxygen and how the vasculature changes its dynamics to meet the demand in real time,” said Hu.
“Combining the two for simultaneous imaging of neuronal activity and oxygen delivery, at single-cell level, has never been demonstrated before,” added Hu.
To evaluate the system, investigators stimulated the whiskers of awake mice while tracking neuronal calcium responses and corresponding oxygenation changes in the bloodstream. The researchers also deployed focused laser pulses to either occlude an individual capillary or excite a specific neuron, observing subsequent physiological shifts in neighboring cells and microvessels.
Overcoming Hardware Limitations
Integrating light and acoustic signals within the same field of view required engineering collaboration with colleagues at Northwestern University. Standard photoacoustic setups rely on opaque ultrasound detectors that obstruct light paths or demand optical lenses that compromise resolution.
“If you want to integrate the two, you have to make the two forms of energy share the same space, and this is not easy,” said Hu.
To resolve the barrier, the team designed an optically transparent acoustic sensor fabricated from a polymer micro-ring resonator positioned on glass. Incoming acoustic waves alter the physical shape of the ring and modify its optical resonance, converting ultrasound into optical measurements while letting excitation and fluorescence light pass through freely.
“It’s not compromising any of the two imaging technologies,” said Hu, a professor of biomedical engineering at Washington University in St. Louis.
Implications for Clinical Diagnostics and Respiratory Healthcare
Although research has been limited to preclinical animal models so far, understanding how blood vessels coordinate oxygen delivery could advance healthcare research into stroke, neurodegenerative disease, and other pathologies characterized by impaired neurovascular coupling.
The authors noted that the findings could also benefit noninvasive diagnostic methods such as functional magnetic resonance imaging (fMRI), which gauges neural activity indirectly via hemodynamic changes.
“If you can better understand neurovascular coupling, you will make this inference process more accurate,” said Hu.
