Highly active neurons emerging in vitro.

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Systems Neuroscience

Background:

• Neuronal networks exhibit variable firing rates, with a small fraction of neurons showing exceptionally high activity.
• The emergence and long-term stability of these highly active outlier neurons remain poorly understood.
• Understanding these neuronal outliers is crucial for comprehending information processing in the brain.

Purpose of the Study:

• To investigate the developmental emergence and temporal maintenance of highly active neurons in vitro.
• To characterize the properties and population dynamics of these outlier neurons.
• To determine if highly active neurons represent a distinct functional subpopulation.

Main Methods:

• Primary cultures of mouse hippocampal neurons were used.
• High-activity neurons were identified and traced over 7 weeks using optical monitoring of Arc-dVenus expression.
• Arc promoter activity, indicative of neuronal activity, was tracked over time.

Main Results:

• 0.3%-0.4% of neurons spontaneously expressed Arc-dVenus, indicating high firing rates under baseline conditions.
• These highly active neurons were spatially clustered and showed intermittent, repeated expression over weeks.
• A significant portion of these neurons maintained Arc-dVenus expression for approximately 2 weeks.

Conclusions:

• Highly active neurons constitute a stable, distinct functional subpopulation within the neuronal network.
• These outlier neurons are not transient but are maintained over time, suggesting specific developmental selection or stabilization mechanisms.
• The findings differentiate these high-activity neurons from typical neurons with normal firing rates.