Imaging hypothalamic activity using diffusion weighted magnetic resonance imaging in the mouse and human brain

Area of Science:

• Neuroscience
• Medical Imaging
• Physiology

Background:

• Hypothalamic appetite regulation is crucial for energy balance, but its objective evaluation is challenging.
• Disturbances in appetite regulation lead to severe feeding disorders.
• Current methods for assessing appetite are often indirect, relying on food intake and body weight.

Purpose of the Study:

• To develop a direct, non-invasive method for visualizing hypothalamic activation during fasting.
• To investigate the use of diffusion-weighted magnetic resonance imaging (dMRI) for this purpose.
• To explore potential applications in diagnosing appetite disorders.

Main Methods:

• Utilized diffusion-weighted magnetic resonance imaging (dMRI) on fed and fasted mouse and human brains.
• Employed a range of b values (10-2000 s.mm⁻²) for detailed imaging.
• Analyzed dMRI data using biexponential diffusion modeling and Linear Discriminant Analysis (LDA).

Main Results:

• Observed significant increases in slow diffusion parameters in the fasted hypothalamus, indicative of neurocellular swelling.
• Detected these diffusion changes within specific hypothalamic nuclei (Arcuate, Ventromedial, Dorsomedial).
• LDA successfully classified fed versus fasted states in both mice and humans based on dMRI data.

Conclusions:

• Fasting induces a detectable neurocellular swelling response in the hypothalamus, likely due to increased glutamatergic neurotransmission and ionic accumulation.
• This swelling propagates through astrocytic networks, becoming detectable via MRI.
• dMRI offers a novel, non-invasive approach for evaluating appetite regulation and hypothalamic pathologies.