Using high-resolution imaging with two-photon phosphorescent lifetime microscopy (2PLM), researchers learned that even brief interruptions in blood flow to capillaries in the brain can cause rapid, localized drops in oxygen that probably extend into nearby brain tissue. These stalls in blood flow, in the smallest vessels in the brain, could play a role in brain diseases like stroke, Alzheimer’s disease, and traumatic brain injury, where such disruptions are common.
Using a two-photon phosphorescent probe, a team comprising researchers from Boston University and Massachusetts General Hospital monitored capillary flux and partial pressure of oxygen (pO2) in the mouse cortex. The researchers sought to quantify oxygen dynamics around capillary stalls as they occurred in vivo.
2PLM provided high-resolution measurement of the pO2 in the brain, enabling the researchers to investigate the distribution and consumption of oxygen. It offered the spatial and temporal resolution necessary to capture stalls using single point measurements.
The researchers excited phosphorescence at 950 nm with a pulse laser, and controlled excitation power with an electro-optic modulator. The excitation and emission light were split with a primary dichroic, and excess laser power was blocked by a filter in the detection path. Photons were detected by a photomultiplier tube after passing through a secondary dichroic and emission filter.
Imaging planes started at about 50 μm below the cortical surface and extended to an approximate depth of 250-300 μm. The researchers selected 10-20 points in each plane, based on capillaries with clear cross-sections parallel to the imaging plane.
At each point, the researchers performed 1000 cycles of 10 microsecond (10-μs) excitation, and 290 μs of collection and photon counting.
The researchers measured red blood cell passage and oxygen levels in more than 300 mice capillaries. Using 2PLM, they tracked the moments when red blood cells temporarily stopped moving through a blood vessel and monitored the resulting oxygen changes in real time.
To quantify the effect of stalling on oxygen, they monitored capillary oxygen, flux, and speed in 10 to 20 capillaries for about 10 minutes. They repeated these 10-minute recordings in several different regions of interest.
They found that every stall caused an immediate decline in oxygen within the capillary, which was likely to spread to surrounding tissue. About 40% of stalls dropped to levels considered hypoxic, and about 25% fell to levels where cells could not sustain normal energy production.
The severity of hypoxia differed depending on the animal’s state. Awake animals were far more vulnerable than mice under anesthesia, highlighting how dependent the brain is on uninterrupted microvascular flow under normal conditions.
The researchers also found that nearby capillaries sometimes showed small drops in oxygen when a neighboring vessel stopped flowing. This suggests that the impact of a stall may extend to the microvascular network surrounding the blocked vessel.
Because some capillaries tend to stall repeatedly, the tissue in their vicinity may experience repeated bouts of hypoxia over time, the team found. This could be one way that capillary dysfunction contributes to brain diseases where stalling is common. With the increased incidence of stalling that occurs with age or diseases such as Alzheimer’s and stroke, the potential for acute metabolic disruption is increased.
Future work could extend the measurements to deeper cortical layers and provide comparisons between healthy and diseased models. Flow and oxygen distributions are different across brain regions and could potentially be found to result in different dynamics around stalling events.
The brain depends on a constant supply of oxygen, and unlike other organs, it has minimal stores of energy. While it is known that blockages in larger vessels can have devastating consequences for the brain, less is understood about the effects of momentary stalls in the smallest vessels, the capillaries. These stalls have been observed more often in aging brains and in conditions such as Alzheimer’s disease, stroke, and traumatic brain injury.
The use of 2PLM to study when and where stalls in capillary flow occur, and result in pockets of low oxygen in the brain, could provide valuable information on a way that the conditions for various brain diseases may be exacerbated.
Bio Photonics Research Award
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Using a two-photon phosphorescent probe, a team comprising researchers from Boston University and Massachusetts General Hospital monitored capillary flux and partial pressure of oxygen (pO2) in the mouse cortex. The researchers sought to quantify oxygen dynamics around capillary stalls as they occurred in vivo.
2PLM provided high-resolution measurement of the pO2 in the brain, enabling the researchers to investigate the distribution and consumption of oxygen. It offered the spatial and temporal resolution necessary to capture stalls using single point measurements.
The researchers excited phosphorescence at 950 nm with a pulse laser, and controlled excitation power with an electro-optic modulator. The excitation and emission light were split with a primary dichroic, and excess laser power was blocked by a filter in the detection path. Photons were detected by a photomultiplier tube after passing through a secondary dichroic and emission filter.
Imaging planes started at about 50 μm below the cortical surface and extended to an approximate depth of 250-300 μm. The researchers selected 10-20 points in each plane, based on capillaries with clear cross-sections parallel to the imaging plane.
At each point, the researchers performed 1000 cycles of 10 microsecond (10-μs) excitation, and 290 μs of collection and photon counting.
The researchers measured red blood cell passage and oxygen levels in more than 300 mice capillaries. Using 2PLM, they tracked the moments when red blood cells temporarily stopped moving through a blood vessel and monitored the resulting oxygen changes in real time.
To quantify the effect of stalling on oxygen, they monitored capillary oxygen, flux, and speed in 10 to 20 capillaries for about 10 minutes. They repeated these 10-minute recordings in several different regions of interest.
They found that every stall caused an immediate decline in oxygen within the capillary, which was likely to spread to surrounding tissue. About 40% of stalls dropped to levels considered hypoxic, and about 25% fell to levels where cells could not sustain normal energy production.
The severity of hypoxia differed depending on the animal’s state. Awake animals were far more vulnerable than mice under anesthesia, highlighting how dependent the brain is on uninterrupted microvascular flow under normal conditions.
The researchers also found that nearby capillaries sometimes showed small drops in oxygen when a neighboring vessel stopped flowing. This suggests that the impact of a stall may extend to the microvascular network surrounding the blocked vessel.
Because some capillaries tend to stall repeatedly, the tissue in their vicinity may experience repeated bouts of hypoxia over time, the team found. This could be one way that capillary dysfunction contributes to brain diseases where stalling is common. With the increased incidence of stalling that occurs with age or diseases such as Alzheimer’s and stroke, the potential for acute metabolic disruption is increased.
Future work could extend the measurements to deeper cortical layers and provide comparisons between healthy and diseased models. Flow and oxygen distributions are different across brain regions and could potentially be found to result in different dynamics around stalling events.
The brain depends on a constant supply of oxygen, and unlike other organs, it has minimal stores of energy. While it is known that blockages in larger vessels can have devastating consequences for the brain, less is understood about the effects of momentary stalls in the smallest vessels, the capillaries. These stalls have been observed more often in aging brains and in conditions such as Alzheimer’s disease, stroke, and traumatic brain injury.
The use of 2PLM to study when and where stalls in capillary flow occur, and result in pockets of low oxygen in the brain, could provide valuable information on a way that the conditions for various brain diseases may be exacerbated.
Bio Photonics Research Award
Visit: biophotonicsresearch.com
Nominate Now: https://biophotonicsresearch.com/award-nomination/?ecategory=Awards&rcategory=Awardee
#MeatAnalysis #FluorescenceTech #FoodQuality #FoodSafety #SpectroscopyInFood #MeatAuthentication #RapidDetection #FoodScience #MeatFreshness #MolecularDetection #FoodIndustryInnovation #NonDestructiveTesting #FoodMonitoring #SpectroscopyApplications #QualityControl #AdvancedSpectroscopy #MeatSpoilageDetection #FoodIntegrity #SmartFoodTesting #RealTimeAnalysis #FoodAuthenticity #FoodSafetyInnovation #SpectroscopyResearch #NextGenFoodSafety #InnovativeFoodScience,
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