Developmental consequences of neuromuscular junctions with reduced presynaptic calcium channel function

Area of Science:

• Neuroscience
• Developmental Biology
• Synaptic Plasticity

Background:

• Neurotransmitter release at synapses is typically regulated by presynaptic calcium influx via voltage-gated calcium channels.
• Homeostatic mechanisms in developing neural circuits often compensate for deficits in synaptic transmission.

Purpose of the Study:

• To investigate homeostatic regulatory mechanisms at the Drosophila neuromuscular junction (NMJ) in response to reduced calcium influx during development.
• To determine if the developing NMJ can compensate for impaired calcium entry.

Main Methods:

• Utilized the temperature-sensitive Drosophila mutant, cac(TS2), which exhibits reduced calcium entry.
• Examined synaptic transmission by measuring excitatory postsynaptic potential (EPSP) amplitudes in third instar larvae.
• Performed morphological analysis of Ib and Is motor neuron terminals, assessing length and varicosity number.

Main Results:

• Larvae with the cac(TS2) mutation raised at elevated temperatures showed reduced EPSP amplitudes in both Ib and Is motor neurons.
• Synaptic efficacy remained reduced even when larvae were raised at permissive temperatures or exposed to high temperatures later in development.
• Morphological analysis revealed significantly reduced terminal length and varicosity numbers in cac(TS2) mutants, indicating impaired structural development.

Conclusions:

• The Drosophila NMJ demonstrates an inability to fully compensate physiologically or structurally for reduced evoked calcium entry during larval development.
• This finding contrasts with typical compensatory mechanisms observed in other synaptic transmission deficits.