A relation between synaptic specificity and the acquisition of presynaptic properties

Area of Science:

• Neuroscience
• Cell Biology
• Developmental Biology

Background:

• Synaptogenesis, the formation of synapses, is crucial for neural circuit development.
• The role of intrinsic neuronal programs versus target-derived cues in presynaptic development is not fully understood.
• Helisoma neurons provide a model system to study neuronal development and synaptogenesis.

Purpose of the Study:

• To investigate the specificity of synaptogenesis in identified adult Helisoma neurons.
• To determine the acquisition of presynaptic properties independent of target contact.
• To explore the role of calcium currents in presynaptic development and secretory capacity.

Main Methods:

• Cell culture of identified adult Helisoma neurons (B5 and B19).
• Functional connection assays to assess synaptogenesis specificity.
• Development of a giant synaptic terminal model using isolated neuron somata.
• Electrophysiological recordings to study calcium currents (LVA and HVA) in different neuronal compartments.

Main Results:

• Cholinergic neuron B5 forms indiscriminate chemical connections, while neuron B19 shows target selectivity.
• Neuron B5 acquires presynaptic properties before target contact, unlike neuron B19.
• Isolated B5 somata gain neurotransmitter release capacity and exhibit changes in calcium currents (loss of LVA, retention of HVA).
• Neurite extension in B5 maintains LVA/HVA currents in the soma but only HVA in growth cones, indicating differential regulation.

Conclusions:

• Neuron B5 possesses an intrinsic program for developing presynaptic components independent of target cues.
• This intrinsic developmental program may explain B5's lack of target cell discrimination during synaptogenesis.
• Differential regulation of calcium currents is linked to local secretory capacity in developing neurons.