Hippocampal vascular supply and its mediating role in systemic physiological influences on hippocampal volume

Area of Science:

• Neuroimaging
• Cardiovascular Science
• Gerontology

Background:

• Aging-related cardiovascular changes can negatively affect brain circulation, leading to hippocampal atrophy and cognitive decline.
• The precise mechanisms linking systemic health alterations to hippocampal atrophy via its vasculature are not fully understood.

Purpose of the Study:

• To investigate the mediating role of hippocampal vascular features in the relationship between systemic factors and hippocampal volume.
• To explore how metabolic, autonomic, inflammatory, and vascular parameters influence hippocampal structure.

Main Methods:

• Utilized 7T MRI to measure hippocampal volume and segment hippocampal supply vessels in 191 participants (aged 30-59).
• Assessed 23 systemic parameters including metabolic syndrome markers, autonomic function, inflammation, and vascular stiffness.
• Employed mediation analysis to determine if hippocampal vessel velocity and size mediate the link between systemic factors and hippocampal volume.

Main Results:

• Hippocampal volume strongly correlated with hippocampal supply vessel velocity, particularly on the right side.
• Vessel velocity mediated the association between hippocampal volume and markers of vascular inflammation, autonomic function (heart rate variability, spontaneous baroreflex sensitivity), and metabolic disturbances (fasting insulin).
• No mediation was observed for parameters like blood pressure, adiposity, glucose, lipids, or certain inflammatory markers.

Conclusions:

• Vascular inflammation, autonomic dysfunction, and metabolic issues contribute to hippocampal atrophy.
• Hippocampal vessel velocity is a critical mediator in this process, impacting hippocampal structural integrity.
• Findings enhance understanding of cerebrovascular mechanisms underlying cognitive health and aging.