Development of Ca2+ hotspots between Lymnaea neurons during synaptogenesis

Area of Science:

• Neuroscience
• Cell Biology
• Synaptic Plasticity

Background:

• Calcium (Ca2+) channel clustering is crucial for mature synapses.
• Spatial distribution of Ca2+ channels in newly formed synapses is not well understood.
• The target cell specificity of presynaptic Ca2+ 'hotspots' remains unclear.

Purpose of the Study:

• To investigate the development and target cell specificity of Ca2+ gradients at newly formed synapses.
• To test if Ca2+ hotspots are specialized mechanisms for targeting channels to synaptic sites.
• To understand the role of Ca2+ channel distribution in early synaptogenesis.

Main Methods:

• Utilized soma-soma paired and single neurons from the mollusk Lymnaea.
• Employed Fura-2 imaging and two-photon laser scanning microscopy (Calcium Green).
• Coupled optical imaging with electrophysiological techniques (voltage clamp, differential perfusion).

Main Results:

• Voltage-induced Ca2+ gradients (hotspots) developed at presynaptic contact points with postsynaptic neurons, but not in single cells.
• Ca2+ hotspots coincided with the onset of synaptic transmission and were target cell contact specific.
• Whole-cell Ca2+ current density was similar, but Ba2+ current amplitude was higher at the presynaptic contact site.

Conclusions:

• Voltage-induced Ca2+ hotspots form in presynaptic cells during synaptogenesis.
• These Ca2+ gradients are target cell contact specific, suggesting channel redistribution.
• This spatial redistribution of existing channels likely facilitates synaptic transmission at new connections.