Longitudinal Multimodal fMRI to Investigate Neurovascular Changes in Spontaneously Hypertensive Rats.

Area of Science:

• Neuroscience
• Cardiovascular Science
• Medical Imaging

Background:

• Hypertension is a key risk factor for cognitive decline and brain pathologies.
• Existing research links hypertension to impaired neurovascular coupling and cerebral autoregulation, but mechanisms remain unclear.
• Studying neurovascular coupling during hypertension progression is crucial for understanding its effects.

Purpose of the Study:

• To longitudinally assess the impact of progressive hypertension on neurovascular coupling using functional MRI (fMRI) in spontaneously hypertensive rats (SHRs).
• To investigate changes in cerebral blood flow (CBF) and blood oxygenation-level-dependent (BOLD) responses over time in relation to hypertension.
• To evaluate neuronal viability and activity through MR spectroscopy during hypertension progression.

Main Methods:

• A longitudinal fMRI protocol was applied to eight female SHRs at 2, 4, and 6 months of age.
• Functional MRI, functional MR spectroscopy, and CBF quantification were performed under propofol anesthesia.
• Blood pressure, CBF, BOLD response, and metabolite signals (glutamate, NAA) were measured to assess neurovascular coupling.

Main Results:

• Blood pressure significantly increased at 4 and 6 months.
• Cerebral blood flow (CBF) increased acutely at 4 months, while the active region size decreased at 6 months.
• N-acetyl-aspartate (NAA) and glutamate signals remained constant, indicating preserved neuronal viability and activity.

Conclusions:

• Cerebral autoregulation is impaired in acute hypertension, but the BOLD response is maintained until later stages.
• Preserved NAA and glutamate signals suggest no neuronal death or activity loss in the observed stages.
• Observed BOLD signal changes are primarily attributed to vascular effects, not neuronal dysfunction, in early to mid-stage hypertension.