Novel synapses compensate for a neuron ablated in embryos

Area of Science:

• Neuroscience
• Developmental Biology
• Neurobiology

Background:

• Neuronal death in adult leeches and mammals causes permanent deficits.
• The embryonic nervous system exhibits greater plasticity compared to adults.
• Interruption of the S cell chain in adult leeches leads to lasting deficits.

Purpose of the Study:

• To investigate the regenerative capacity and plasticity of leech S interneurons during embryogenesis.
• To determine if embryonic S interneurons can compensate for ablated cells by extending axons and forming new synapses.

Main Methods:

• S cell ablation in leech embryos (days 8-11) using a fine pin.
• Confirmation of cell deletion using cell-specific monoclonal antibodies.
• Tracing axon projections and synaptic connections via intracellular injection of horseradish peroxidase and 6-carboxyfluorescein dye.

Main Results:

• Embryonic S interneurons successfully regenerated axons, projecting twice their usual length into the lesioned ganglion.
• These regenerated axons formed functional electrical synapses with targets homologous to those of the deleted S cell.
• Neural conduction was often restored through these compensatory synaptic connections, replacing those lost due to ablation.

Conclusions:

• Growing S interneurons in both adult and embryonic leeches exhibit enhanced growth in response to target loss.
• However, only during embryogenesis is this growth extensive enough to successfully reach and innately replace lost synaptic targets.
• Embryonic neural plasticity allows for functional recovery following neuronal ablation, highlighting developmental resilience.