Spatiotemporal Dynamics of Tissue Oxygenation in Awake, Behaving Mice

Brain arterioles respond to local neural activity by altering regional blood flow patterns in a manner which optimizes oxygen supply to respiring cells (‘functional hyperemia’). Recent studies of functional hyperemia in awake rodents shows a bimodal arteriole diameter increase when neural activity is prolonged, indicating at least two primary control mechanisms for an early and late phase. However, it is unclear if the early and late components of the hemodynamic response are differentially regulated across space and time. Here, I test the hypothesis that behavioral state differentially affects the early and late components of functional hyperemia – both spatially and temporally. Using widefield intrinsic optical signal imaging and two-photon imaging of hemodynamics in awake, head-fixed mice that were free to ambulate on an air-supported ball treadmill, I observed robust biphasic changes in oxyhemoglobin, deoxyhemoglobin and vascular cell intracellular [Ca2+] in response to prolonged whisker stimulation. The magnitude and kinetics of these changes were related to the cerebrovascular segment within the cranial window. Unlike the early component (1-5sec), the magnitude of the late hemodynamic component (20-30sec) was strongly influenced by animal locomotion. In situations where the animal ran, oxy- and deoxyhemoglobin changes were more pronounced where whisker stimulation coincided with locomotion. In comparing the region of highest response to whisker stimulation (‘centre’) to surrounding regions, I observed that the magnitude of blood flow increase was proportionally greater for the late component only. Furthermore, optical flow analysis within the 3x3 mm cranial window revealed that the spatial profile of the hemodynamic response to extended stimulation was stereotyped. When I increased vascular tone directly using mural cell Gq-chemogenetics, this dramatically limited both the magnitude and spatial properties of the evoked hemodynamic response and instead intensified vasomotion. My data suggest that the late component of sustained functional hyperemia in awake mice exhibits spatially and temporally distinct control mechanisms compared to the early component, and that driving vasomotion directly decouples neural activity-evoked oxygenation changes in the brain. These findings have important implications for interpreting data acquired by clinical neuroimaging modalities like functional magnetic resonance imaging. Understanding the relationship between neuronal activity and brain blood flow is also vital for preventing and treating brain lesions of vascular origin.

Name thesis:degree_name

Master of Science (MSc)

Discipline thesis:degree_discipline

Medicine – Neuroscience

Grantor dc:publisher.institution

Cumming School of Medicine

Year dc:date.issued

2020

Author dc:creator

• Peringod, Govind

Advisor dc:contributor.advisor

• Gordon, Grant R

Committee members dc:contributor.committeemember

• Bains, Jaideep S
• Murari, Kartikeya

• Neurovascular coupling
• brain blood flow
• functional hyperemia
• vasomotion
• brain arteriole
• behavior
• whisker stimulation
• mural cell
• calcium signaling
• chemogenetics
• awake-animal
• widefield
• two-photon
• intrinsic optical imaging
• optical flow

Statement dc:rights

• University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.

Language dc:language.iso

eng, en

DOI

http://dx.doi.org/10.11575/PRISM/38705

OAI identifier oai:identifier

oai:ucalgary.scholaris.ca:1880/113196