Parvalbumin expression affects synaptic development and physiology at the Drosophila larval NMJ

Area of Science:

• Neuroscience
• Cell Biology
• Synaptic Physiology

Background:

• Presynaptic calcium (Ca2+) is crucial for synaptic development and function.
• Parvalbumin (PV) is a calcium-binding protein that can buffer intracellular Ca2+.
• Drosophila neurons normally do not express PV, making them a suitable model to study PV's effects.

Purpose of the Study:

• To investigate the role of presynaptic Ca2+ buffering by expressing PV in Drosophila neurons.
• To determine the impact of PV on Ca2+ dynamics, synaptic transmission, and motor terminal structure.
• To explore the relationship between presynaptic Ca2+ levels and synaptic growth.

Main Methods:

• Expressing parvalbumin (PV) in identified Drosophila Ib motor neuron terminals innervating muscle fiber 5.
• Measuring intracellular Ca2+ transients using the fluorescent indicator OGB-1 following single action potentials (APs) and AP trains.
• Performing electrophysiological recordings from muscle fiber 5 to assess synaptic facilitation and transmitter release.
• Utilizing confocal microscopy to analyze the structural changes in motor terminals.

Main Results:

• PV expression reduced the amplitude and decay time constant of Ca2+ transients evoked by single APs.
• For AP trains, PV decreased the rate of rise and decay of intracellular Ca2+ ([Ca2+]i) without affecting the plateau level.
• Paired-pulse facilitation and synaptic enhancement during AP trains were reduced in PV-expressing terminals.
• Transmitter release for single APs increased, potentially as a homeostatic response.
• PV expression led to smaller motor terminals with fewer synaptic boutons and active zones.

Conclusions:

• Buffering presynaptic Ca2+ with PV alters Ca2+ dynamics and reduces synaptic facilitation.
• Reduced Ca2+ transients and facilitation may trigger a homeostatic increase in transmitter release.
• Presynaptic Ca2+ levels appear to play a role in regulating motor terminal growth, with reduced Ca2+ leading to smaller terminals.