Altered impulse activity modifies synaptic physiology and mitochondria in crayfish phasic motor neurons

Area of Science:

• Neuroscience
• Cell Biology
• Physiology

Background:

• Crayfish phasic motor synapses exhibit rapid fatigue during high-frequency stimulation.
• Long-term adaptation (LTA) can reduce synaptic depression and enhance synaptic stamina.

Purpose of the Study:

• To investigate if activity-induced synaptic fatigue-resistance during LTA is dependent on mitochondrial oxidative competence.
• To explore the correlation between mitochondrial function and enhanced synaptic stamina.

Main Methods:

• In vivo conditioning stimulation of crayfish abdominal extensor motor neurons (axon 3).
• Pharmacological inhibition of mitochondrial ATP synthesis using dinitrophenol and sodium azide.
• Confocal microscopy to assess mitochondrial rhodamine-123 (Rh123) fluorescence.
• Axotomy to investigate the role of axonal transport.

Main Results:

• Periodic stimulation induced LTA, reducing synaptic depression and increasing synaptic stamina.
• Inhibition of mitochondrial ATP synthesis exacerbated synaptic depression in conditioned axons.
• Conditioned axons showed significantly higher mitochondrial Rh123 fluorescence, indicating increased oxidative competence.
• Axotomy prevented the induction of both increased synaptic stamina and enhanced mitochondrial fluorescence.

Conclusions:

• Activity-induced LTA enhances synaptic stamina in crayfish motor neurons.
• Increased mitochondrial oxidative competence is correlated with and dependent upon enhanced synaptic stamina.
• Axonal transport is essential for the induction of both synaptic adaptation and mitochondrial changes.