How the primate fornix is affected by age

Area of Science:

• Neuroscience
• Aging Research
• Primate Neurobiology

Background:

• The fornix is crucial for memory and cognition.
• Age-related changes in the fornix may underlie cognitive impairment.

Purpose of the Study:

• To investigate age-related structural changes in nerve fibers and neuroglial cells within the fornix of rhesus monkeys.
• To correlate these structural changes with observed cognitive impairments.

Main Methods:

• Histological examination of fornix tissue from 25 rhesus monkeys aged 4-33 years.
• Quantification of myelinated nerve fibers, axonal degeneration, myelin alterations, and neuroglial cell types (astrocytes, microglia, oligodendrocytes).
• Correlation analysis between structural findings and cognitive performance data.

Main Results:

• No change in fornix cross-sectional area, but a significant loss of myelinated nerve fibers.
• Increased axonal degeneration and myelin sheath alterations observed with age.
• Increased frequency of paranodal profiles suggesting remyelination; a 20% increase in oligodendrocytes.
• Decreased nerve fiber density and increased axonal degeneration/myelin alterations correlate with cognitive impairment.

Conclusions:

• Age-related fornix changes, including nerve fiber loss and degeneration, are linked to cognitive decline in rhesus monkeys.
• Increased oligodendrocytes and paranodal profiles suggest ongoing, potentially inefficient, remyelination efforts.
• These structural changes may disrupt hippocampal connectivity and reduce nerve conduction velocity, contributing to cognitive impairment.