High voltage electron microscopy of the optic neuropile of the housefly, Musca domestica

Area of Science:

• Neuroscience
• Insect Vision
• Electron Microscopy

Background:

• The lamina ganglionaris is the first synaptic region in the fly visual system.
• Understanding its neural circuitry is crucial for insect vision research.

Purpose of the Study:

• To visualize the 3D structure of synaptic cartridges in the housefly lamina ganglionaris.
• To investigate the connections and potential interactions of neurons within these cartridges.

Main Methods:

• High voltage electron microscopy (HVEM) was used on thick (0.25 µm) sections.
• Stereo pairs at 1,000 kV provided 3D reconstructions of neuronal structures.
• Detailed modifications in EM techniques for HVEM were described.

Main Results:

• 3D representations clearly showed the lateral spread and bifurcation of Type I monopolar interneurons.
• Retinular axons were observed making contact with each other near the cartridge neck.
• No junctional modifications were found between adjacent retinular axon terminals.

Conclusions:

• The study demonstrates the utility of HVEM for 3D reconstruction of neuropile.
• Speculation on potential functional coupling between neighboring retinular axons prior to synapsing with interneurons.
• This proposed coupling could explain previously observed electrophysiological data.