Analysis of calcium channels in single spines using optical fluctuation analysis

Area of Science:

• Neuroscience
• Cell Biology
• Biophysics

Background:

• Synapses, crucial for learning and memory, form on dendritic spines.
• Calcium ion (Ca2+) influx into spines triggers synaptic plasticity.
• Voltage-sensitive calcium channels (VSCCs) are key regulators of Ca2+ signaling.

Purpose of the Study:

• To quantify the number and properties of VSCCs in individual dendritic spines.
• To investigate the spatial distribution and modulation of VSCCs within CA1 pyramidal neurons.
• To understand the role of VSCCs in synaptic plasticity.

Main Methods:

• Two-photon laser scanning microscopy to image Ca2+ transients in spines and dendrites.
• Analysis of trial-to-trial fluctuations in Ca2+ signals to determine VSCC number and open probability.
• Experimental manipulation of GABA(B) receptors to assess their modulatory effects.

Main Results:

• Each dendritic spine contains 1-20 VSCCs, with the number correlating positively with spine volume.
• Single VSCC openings on spines were detectable.
• VSCCs in proximal dendritic spines exhibit high open probability (approx. 0.5) following action potentials.
• GABA(B) receptor activation reduced VSCC open probability in apical spines (to approx. 0.3) but not in basal spines or dendrites.

Conclusions:

• The number of VSCCs per spine is regulated by spine volume.
• VSCCs in different dendritic locations exhibit distinct functional properties.
• GABA(B) receptors provide precise submicrometre regulation of VSCC activity in specific dendritic spine populations.
• These findings offer insights into the fine-tuned control of synaptic plasticity.