Stimulation-induced changes in [Ca2+] in lizard motor nerve terminals

Area of Science:

• Neuroscience
• Cellular Biology
• Biophysics

Background:

• Motor neuron terminals are crucial for muscle contraction.
• Calcium influx into presynaptic terminals triggers neurotransmitter release.
• Understanding calcium dynamics is key to understanding synaptic function and dysfunction.

Purpose of the Study:

• To investigate calcium (Ca2+) dynamics within motor terminal boutons during neuronal activity.
• To determine the relationship between Ca2+ entry and synaptic depression.
• To explore spatial gradients of Ca2+ within boutons.

Main Methods:

• Ionophoretic injection of five Ca2+-sensitive dyes into motor axons.
• High-temporal-resolution confocal microscopy to monitor fluorescence changes (delta F/Frest).
• Recording of endplate potentials (EPPs) and simultaneous measurement of Ca2+ fluorescence.

Main Results:

• Stimulation-induced Ca2+ increases were localized to boutons and correlated with extracellular Ca2+ concentration.
• omega-conotoxin GVIA reduced both Ca2+ influx and EPPs.
• In the presence of 3,4-diaminopyridine (3,4-DAP), synaptic depression occurred without a significant reduction in Ca2+ entry, indicating Ca2+ entry is not the cause of depression.
• Calculated peak [Ca2+] increases ranged from 150 nM to 940 nM.
• Spatial Ca2+ gradients were observed within boutons, with faster decay near the membrane.

Conclusions:

• Synaptic depression at motor terminals is not mediated by a reduction in presynaptic Ca2+ entry.
• Significant spatial gradients of Ca2+ exist within motor boutons following stimulation.
• Ca2+ dynamics are complex and influenced by dye affinity and experimental conditions.