Ultrastructure and quantification of synapses in the insect nervous system

Area of Science:

• Neuroscience
• Cell Biology
• Electron Microscopy

Background:

• Standard electron microscopy (EM) is effective for visualizing synaptic junction organelles in insect species.
• Synaptic profiles in single sections often represent a few morphological classes, necessitating serial section analysis for full understanding.
• Central synapses are frequently multiple-contact types, with variations in postsynaptic elements defining individual junctions.

Purpose of the Study:

• To elucidate the utility of standard EM methods in characterizing insect synaptic junctions.
• To establish protocols for identifying and classifying synaptic sites within neuropile.
• To provide methods for estimating synaptic contact numbers using EM data.

Main Methods:

• Utilizing standard electron microscopy (EM) for ultrastructural analysis of synaptic junctions.
• Employing serial sectioning techniques to reconstruct synaptic morphology and understand profile variations.
• Tracing neuronal processes (dendrite-axon continuity) to identify neuron of origin.

Main Results:

• Morphological stereotypy observed within synaptic classes, with variations explained by sectioning planes.
• Identification of multiple-contact synapses as a common feature in central nervous systems.
• Development of methods for estimating synaptic profiles and contacts from single and serial sections, accounting for section thickness and junction size.

Conclusions:

• Standard EM, particularly with serial sectioning, is crucial for comprehensive synaptic junction analysis in insects.
• Understanding profile variations from different sectioning planes aids in identifying synaptic sites and characterizing neuropile organization.
• Methods for quantifying synaptic contacts can be refined using EM data and correction formulae.